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vpt
08-30-2011, 05:37 PM
I have a couple extra weed eater motors laying around and I am always trying to think of a use for them but never come up with much. The one I have used for a couple of my own experiments like oxygen injection and testing my leaf blower before putting big power to it. But I just know there has to be some good use for them. What have you done with small motors? Ideas on stuff they can be used for?

Pictures are always great too! ;)

Scottike
08-30-2011, 05:48 PM
I have a similar problem - I have a back pack blower engine I can't decide what to do with.
I've seen them adapted for use on model airplanes, and the one I've got could work on a small pit scooter. (as in race track pit)
A friend of mine suggested converting it into a gas powered drill motor - not a bad idea, but I don't have a need for one of those.
It may just have to be yard sale fodder or trading stock.

edit: You did mean gas powered rather than electric, didn't you ?

MrSleepy
08-30-2011, 05:49 PM
Have you tried cooling your brakes with them..seems to work well in F1 :).

Willy
08-30-2011, 06:10 PM
My first thought would be to use it for a powered bicycle.
There's tons of info out there for converting a weed eater engine for bike use.
The most popular design theme seems to be using it on a custom made rear rack with the engine driving the rear tire via a machined and knurled drive wheel. You could design it so that it could pivot the entire assembly out of engagement with the rear wheel when not needed.

Black_Moons
08-30-2011, 07:06 PM
Friction drives eat your tire pertty quick.

I got one too, was planing on turning it into a motorbike motor.. but never got around to it, the real kits work so much better.

Racerx
08-30-2011, 07:15 PM
Use one to make a gas powered blender, for those margaritas at the track!:)

davidwdyer
08-30-2011, 08:00 PM
I used one one time to make a small motor for a duck hunting canoe, the kind which has a straight shaft.

There was also one I gave one to a neighbor kid who wanted to motorize a skateboard. I haven't heard if be broke something trying to use it.

PTSideshow
08-30-2011, 09:10 PM
Large scale RC boats and buggies, I have a 25cc 1/6 buggy 40 pounds does about 35 Miles an hour. They call em ankle busters. I have a couple engines that I would like to make a large scale air boat RC out of
rcairboats (http://www.rcairboats.net/phpBB/index.php) they had some great videos on it a while ago.
Tower Hobbies (http://www.towerhobbies.com/index.html)

They had a 1/4 scale NASCAR and World of Outlaws type sprint cars with the weed wacker engines.
They have all kinds of speed stuff and fancy mufflers for the engines too.

Dawai
08-30-2011, 09:14 PM
Skateboard power..

Robot power..

Portable car booster...

Bicycle power plant.. (wide open and slide)

J. Randall
08-30-2011, 09:28 PM
I have been thinking about grafting one on to a medium sized angle grinder that has a bad armature. Also have thought about linking 2 motors together, and running one and taking compressed air from the other.
James

brian Rupnow
08-30-2011, 09:31 PM
Good power pack for an ultra light---basically a motorized glider.

vpt
08-30-2011, 09:40 PM
Great ideas so far! I thought about the 1/5th RC car but I don't think I would get enough enjoyment from it. I have all the full size toys to play with when I have time.

The emergency jumper for the car/truck idea is interesting. I have a generator that I carry with me now but something cheap and smaller would be cool. What kind of AC amps can be extracted from a car alternator?

Two of them together for a compressor is a neat idea too, as well is the angle grinder idea! I got the feeling after a week of this thread I will be out of motors and looking for more. :D

Yes I am talking gas motors Scott.

Lester Burch
08-30-2011, 09:47 PM
I used them to make RC Airboats i have used 18cc to 50 cc engines on them.
http://i11.photobucket.com/albums/a175/mudmasher/DSC_2335.jpg
http://i11.photobucket.com/albums/a175/mudmasher/Picture022.jpg

flylo
08-30-2011, 09:48 PM
Have a fiend that put a prop on one, moved the tank,put a twist throttle put it on a bike. He had to pedal start but after getting going could break 40MPH without pedeling & had under $20+ the bike in the project. Way cool!:D

Rustybolt
08-30-2011, 09:53 PM
I used one one time to make a small motor for a duck hunting canoe, the kind which has a straight shaft.


What size motor?
I want to that for my canoe.

Iraiam
08-30-2011, 10:03 PM
Many of them can make a quite descent model airplane engines, I have converted several "weed eater" engines over to model airplane use. I usually remove all the flywheel and magneto stuff and make a prop hub and use an electronic ignition module. Also many of them require changing out the carburetor to a different model.

My latest incomplete project is a 98cc Tecumseh 2 stroke engine I removed from an old snow thrower. I think it's going to be a good one.

Willy
08-30-2011, 10:15 PM
What kind of AC amps can be extracted from a car alternator?

An alternator of course rectifies AC voltage and current to DC. But as a very rough rule of thumb 12-14 V automotive alternators require about 1 HP for every 20-25 amps of output. The more voltage applied to the field circuit the the more energy the alternator will put out. For example under full load a 100 amp unit will require at least 4-5 HP.

Lots of variables here, but you definitely won't have enough HP to burn out an automotive alternator.

sasquatch
08-30-2011, 10:24 PM
Another source for ideas may come up if you post your'e question here:


http://kramerville.net/ubb

(This is the old "Machine Builders " site.)

flutedchamber
08-31-2011, 01:26 AM
One makes a dandy heavy duty drill motor. Make sure you use a T handle..if you value your wrists.

A.K. Boomer
08-31-2011, 08:48 AM
Iv always wanted to build an opposed twin out of them and link two together by means of having them share the same crankcase, and gear to gear the cranks together so they rotate in opposite directions but reach TDC at the same time,
This engine would be an example in perfect mechanical balance and dynamic power transfer balance. (far superior to something like the opposed boxer).

Then I would have to spend the remainder of my life building one hot airplane to attach it too with two very close and timed counter rotating props, this design would also remove many of the inherent flaws that a typical single engine plane has during flight due to neutral rotational power balance, It would have all the bennies of a twin engine without most of the inherent flaws that they present...

davidwdyer
08-31-2011, 09:08 AM
What size motor?
I want to that for my canoe.

I used a very small one and it turned out to be too small. It moved the canoe, which was a large one with two people and a lot of gear, but a little slowly. I'm quite sure one of the larger models 45cc and up would do a good job on a light canoe which is not loaded to the gills.

I ended up making another one out of a Lawnboy 2 cycle motor. I used a small aluminum prop from a trolling motor. You can order various sizes. That motor was 2hp. The canoe went so fast, you could almost water ski behind it. Seriously, there was a tremendous bow wake, etc.

The 2 cycle motor was chosen because you don't have to worry about lubrification problems as you would with an oil pan/splash system. (A friend of mine burned out several rototillers because of using them at an angle.) This is why a weed whip would make a good choice.

The lawnmower adaptation was used a lot and worked well, but had two problems. One, the carburetor was not made for low speeds. To go really slow, you had to pull the prop up occasionally. Two, sometime in the past, I think someone had hit a rock with the mower and the crankshaft was a little bent. This introduced some vibration in the motor, but nothing so bad that we didn't use it a lot.

Conclusion, the 2hp was almost too big. Therefore, a larger weed whip motor would probably work well and is quite simple to fabricate. Just put a prop on the end of the shaft and a swivel, sort of like an oarlock, somewhere on the shaft. Then you have to have a hole near the stern of the canoe to stick it in.

I recommend it. It turned out to be a lot of fun and turned heads too.

vpt
08-31-2011, 09:24 AM
An alternator of course rectifies AC voltage and current to DC. But as a very rough rule of thumb 12-14 V automotive alternators require about 1 HP for every 20-25 amps of output. The more voltage applied to the field circuit the the more energy the alternator will put out. For example under full load a 100 amp unit will require at least 4-5 HP.

Lots of variables here, but you definitely won't have enough HP to burn out an automotive alternator.



After reading your response I realized I should know the answer but didn't think of it at all. I wasn't thinking of how alternators are listed as 75, 100, 200, etc. amp.

I guess the question I was thinking in my head was if a alternator rewired for strait AC (have a DC port for jumping car batteries) how much or big of AC equipment do you think it could power? I have heard of people making on board welders out of them for off roading (another possible output for it) so they must be able to put out some good current. I couldn't imagine wanting to power to big of AC things with it just maybe a light or drill, saw, small angle grinder, etc.

Sounding like this could be a neat little generator if all works out. AC/DC output with welding capabilities.

Rustybolt
08-31-2011, 09:56 AM
Thanks Dave!
I hunt on a very shallow river.
Going downstream to the blind isn't a problem.
Going back up is.

davidwdyer
08-31-2011, 10:28 AM
Thanks Dave!
I hunt on a very shallow river.
Going downstream to the blind isn't a problem.
Going back up is.

I forgot to mention that I arranged a kind of "keel" of aluminum which went under the prop which was fastened to the shaft with a hose clamp. This was later modified to include some rods descending from the shaft, sort of like the keel, to keep weeks away from the prop.

It might work even better with a kayak.

TGTool
08-31-2011, 12:26 PM
After reading your response I realized I should know the answer but didn't think of it at all. I wasn't thinking of how alternators are listed as 75, 100, 200, etc. amp.

I guess the question I was thinking in my head was if a alternator rewired for strait AC (have a DC port for jumping car batteries) how much or big of AC equipment do you think it could power? I have heard of people making on board welders out of them for off roading (another possible output for it) so they must be able to put out some good current. I couldn't imagine wanting to power to big of AC things with it just maybe a light or drill, saw, small angle grinder, etc.

Sounding like this could be a neat little generator if all works out. AC/DC output with welding capabilities.


Don't forget that the auto alternator is multiphase and frequency will depend on speed. So, it could be like a portable VFD where the throttle will also control the speed of the electric motor - sort of. In automobiles since it's all rectified that doesn't matter. I would guess that use as a welder is on DC.

Willy
08-31-2011, 02:28 PM
Sounding like this could be a neat little generator if all works out. AC/DC output with welding capabilities.

Not wanting to dampen your enthusiasm for a portable generator but automotive alternators are notoriously inefficient, about 50-60% max.
1 HP in a perfect world = 746 watts. Because of alternator design and mechanical inefficiencies you will be lucky to get half of that out.

This is why most practical portable welders use a minimum of 7-8 HP.
Plus they use a more efficient electrical source.

http://www.burco.net/mpm165.htm

Not saying you can't use a weed eater as a power source but by the time your engine spools up the alternator to 7-9000 rpm that the engine operates at frictional and cooling fan drag will leave precious little left for electrical power generation.
Gearing it down will only add to the mechanical loses.

Most 1000 watt generators, which are actually rated 1000w surge, 850w continuous, use a 1.5 HP at 3600 rpm
engine.
Unless you have a big weed eater engine, I think you may be down on power for this application to be practical.

vpt
08-31-2011, 03:39 PM
Thats great info! About what HP is the average cheaper weed eater? 1/3HPish?

MrSleepy
08-31-2011, 03:40 PM
http://www.burco.net/mpm165.htm


Thats a Mosa MagicWeld..made in Italy.

They also make lightweight 2 stroke versions

http://www.mosa.com.au/w_portable.htm

I used to have a TS200...very nice bit o kit..

Rob

Willy
08-31-2011, 04:02 PM
Thats great info! About what HP is the average cheaper weed eater? 1/3HPish?

Don't hold me to this, but having just done some work on one of the neighbor's Ryobi 30cc trimmer, I remember the guy behind the counter that sold me the parts saying it was rated at .8 Hp.
Not gospel but this is what I always assumed was the approximate power.
At this rate, depending on engine size of course, expect .5-1.5 HP at the most for a very large one , I can't envision more than that. And remember these engines develop their power at high rpm, not what you want for a generator.

Willy
08-31-2011, 04:15 PM
Thats a Mosa MagicWeld..made in Italy.

They also make lightweight 2 stroke versions

http://www.mosa.com.au/w_portable.htm

I used to have a TS200...very nice bit o kit..

Rob

Wow, vey nice!
Very capable and powerful for it's wieght.
I wouldn't mind having that one myself.

adatesman
08-31-2011, 04:42 PM
If you get enough of them you could build a motorcycle... This one uses 24 chainsaw engines totaling 1.9l displacement and 170hp.

http://www.transportspecs.com/images/motorcycle_cylinders/dolmette_24_cylinder.jpg

vpt
08-31-2011, 05:19 PM
If you get enough of them you could build a motorcycle... This one uses 24 chainsaw engines totaling 1.9l displacement and 170hp.

http://www.transportspecs.com/images/motorcycle_cylinders/dolmette_24_cylinder.jpg



I saw a video of them starting that one or one like it and driving it a little. It was actually pretty funny to watch.

rbertalotto
08-31-2011, 07:06 PM
My son has a remote control helicopter with a 6' rotor that uses a Weed Whacker motor. It can lift 5 pounds...........And it can lift the cat....:eek:

We put a video camera on it to check our gutters for leaves. If we find any, he just blows them out with prop wash...........

Rustybolt
08-31-2011, 07:47 PM
Thanks Dave. That helped a lot.

flylo
08-31-2011, 11:01 PM
I have the Mosa MSG Chopper welder/generator only in 115V. Quite a lot of power in a small package.

davidwdyer
09-01-2011, 06:10 AM
If you get enough of them you could build a motorcycle... This one uses 24 chainsaw engines totaling 1.9l displacement and 170hp.

http://www.transportspecs.com/images/motorcycle_cylinders/dolmette_24_cylinder.jpg


Somebody has seriously too much time and too much money on their hands.

A.K. Boomer
09-01-2011, 08:41 AM
My thoughts exactly - and even if you ignore all the bulk and weight 170 hp's out of 1.9 liters is an absolute dog by today's power per CC motorcycle standards (unless its a harley or something)

im wondering about the nightmare inside - in wondering how he's got them all tied together and then linked to the final drive. that's also gotta be one heavy twisting throttle:p

poor bastard was so drained he couldn't even afford a decent set of shoe's...

vpt
09-01-2011, 08:58 AM
Almost can bet they are all tied together with a long belt. Probably a V-belt from a mower deck out back.

psomero
09-01-2011, 10:54 AM
there is only one true purpose for weed eater motors: http://www.youtube.com/watch?v=scfxsPFaAO0

impatient people can jump to the 1:05 mark

Dawai
09-01-2011, 12:27 PM
http://www.youtube.com/watch?v=EOqWzefvlfg
Steam engine made from weed eater engine.

HOW? he uses a solenoid and a reed switch to fire it.

WHY? Hook it to a "flash boiler" on your wood stove and keep the released heat to heat your home, keep the energy produced to charge batteries. And, it'd make a lovely cup of tea..

It'd beat the heck out of a wind turbine on the roof. You'd have a controllable way to charge batteries.

Ironheart
09-02-2011, 12:00 AM
Good power pack for an ultra light---basically a motorized glider.

I don't know about powering an ultralight. Mine uses a 40 hp engine...

vpt
09-02-2011, 07:26 PM
But powering you on roller blades, thats another story! :D

30cc(ish) enough for a gas powered 7.5" circular saw?

vpt
09-03-2011, 02:12 PM
Did a little test today with a spare alternator I had laying around.

Warning very crude (not entirely safe) mock up inside.

http://www.youtube.com/watch?v=oZheBQ_VENs

Ironheart
09-03-2011, 02:20 PM
Did a little test today with a spare alternator I had laying around.

Warning very crude (not entirely safe) mock up inside.

http://www.youtube.com/watch?v=oZheBQ_VENs

That worked out right well. What size (amp) alternator are you using?

vpt
09-03-2011, 02:30 PM
The alternator is off a honda H22 motor. I believe they are 65-75amp.


Edit* Did a quick search and people say the stock alternator is somewhere between 90-120amps depending on the car the motor came in.

Willy
09-03-2011, 03:50 PM
That looked good Andy, thanks for taking the time to make the vid.

Try putting about a 200 watt load on it, (four headlamps?) that should require about 15 amps at 13.5 V.

danlb
09-03-2011, 04:27 PM
The nice thing about using it for a jumper is that you do NOT need to provide all the power that is needed to run the starter in real time. This assumes the battery can hold a charge.

If the car is well tuned, you will only need to run the starter for less than a second to get it started. Assuming 150 amps for 1 second at 12 volts, that's not many amp-hours.

If you have a charger that can put out 20 amps at 15 volts (a high charge rate) for a minute or two, then you should be able to crank the car for a second or two. This depends, of course, on how badly depleted the battery is in the first place.

Dan

vpt
09-03-2011, 05:04 PM
That looked good Andy, thanks for taking the time to make the vid.

Try putting about a 200 watt load on it, (four headlamps?) that should require about 15 amps at 13.5 V.



Thats a great suggestion! I had to go out and try it. I whipped out two 55w fog lights and 4 headlight bulbs two of which are 100w and the other two 55w. All sure of myself I hooked them all up right off the bat and started the motor, hooked up the jumper wire, then turned the lights on and killed the motor, lol. So I went on starting with the 1 55w fog light and working my way up. I was able to get two 100w bulbs and one 55w fog light on and keep the motor running steady. With the 255w draw the meter showed a constant 13.0v.

Now there are some variables that I should mention. The battery was pulled from one of our trucks because of a dead cell. It has been sitting for a year and when I first hooked up the meter it showed 11.6##v. So the battery itself is taking power. Second variable is this motor has been hanging on the wall for 2 years since I last used it, the same for about 5 years before that. The motor cleaned out and tuned up a bit may put out a little more. The belt drive takes some power that would be eliminated if all works out and I do build this thing. I assume it would never be enough for any kind of welding but it may still be good for emergency battery charging, maybe enough AC to run a light or small hand tool, and like mentioned a possible air compressor hook up. Possibly more stuff as ideas are mentioned.

Its got me excited! :D

darryl
09-03-2011, 06:27 PM
I don't know if there are any efficiency curves published for ordinary car alternators, but there probably is a range of rpm where they work most efficiently. There is also a range where the ratio of motor rpm to alternator rpm would allow the best of both worlds with the particular weed eater motor and alternator combination.

My preference would be to drive the alternator directly to avoid belt and pulley losses, although this might not be a good rpm match for the combo. It might be at least as good as the results could be if the ratio was optimized, but losses in the ratio transformation were also considered. Simpler is better- some kind of a straight shaft to shaft adaptation allowing some misalignment might be better than belts and pulleys.

If however, the optimum ratio would be something like 3 to 1 or more, then the losses in the belt and pulleys might be overshadowed by the efficiency gain by matching the rpms.

Particularly for a fairly low power output engine and a higher power output capable alternator, you would want to 'gear down. The goal would be to operate the alternator at the low end of it's efficient range of operation, but where the output power is still high enough that it can use all the power the engine is capable of delivering. Obviously you factor in a loss for alternator efficiency- I'm thinking that you would consider 40 amps output at 14 volts to be the equivalent of 1 real horsepower input.

Most likely you would have to guess at the power output of those engines, and at what rpm they would like to turn to best produce that power. Short of having the graphs available, you would have to do mechanical experimentation with ratios to come close to optimum. If you don't experiment, you could easily have a situation where the engine is working hard, but you are only producing a fraction of the power that you could be with the same engine and alternator combo.

Willy
09-03-2011, 06:58 PM
Good points Darryl on optimizing engine rpm vs alternator rpm in order to maximize efficiency, I touched on this in an earlier post also, but you explanation is spot on.


I'm thinking that you would consider 40 amps output at 14 volts to be the equivalent of 1 real horsepower input.

I think in the real world you would be doing well to get about half of that though. Automotive alternators are notoriously inefficient 50-60% max.
In addition to electrical inefficiencies there is also the cooling fan used to get rid of waste heat. Automotive alternators that are subjected to full loads are usually short lived due to overheating of internal components.

Truck and bus alternators are usually oil or water cooled to carry away this waste heat, just as an example to how inefficient they are.

http://www.zena.net/htdocs/alternators/alt_inf2.shtml



Is your engine large enough?
For example, if you are driving your alternator with a diesel engine, and assuming adequate flywheel mass and a 3:1 engine drive pulley to alternator pulley ratio, a high efficiency, high current, 12V alternator will require about 1 hp per 30 amps of output power + about 1-2 hp for engine operating/muffling loads -- when operating at its maximum rated output current.
Therefore, for a 150 Amp alternator, operating at full output, the expected diesel engine load would be about 7-8 hp.
If using a gasoline engine instead of a diesel, with a slightly lower 2 to 2.5:1 drive ratio, figure on a requirement of about 1 hp per 15 amps of output power + about 1-3 hp for engine operating/muffling loads -- i.e., 11-14 hp for a 150A alternator.

vpt
09-03-2011, 07:04 PM
I don't know if there are any efficiency curves published for ordinary car alternators, but there probably is a range of rpm where they work most efficiently. There is also a range where the ratio of motor rpm to alternator rpm would allow the best of both worlds with the particular weed eater motor and alternator combination.

My preference would be to drive the alternator directly to avoid belt and pulley losses, although this might not be a good rpm match for the combo. It might be at least as good as the results could be if the ratio was optimized, but losses in the ratio transformation were also considered. Simpler is better- some kind of a straight shaft to shaft adaptation allowing some misalignment might be better than belts and pulleys.

If however, the optimum ratio would be something like 3 to 1 or more, then the losses in the belt and pulleys might be overshadowed by the efficiency gain by matching the rpms.

Particularly for a fairly low power output engine and a higher power output capable alternator, you would want to 'gear down. The goal would be to operate the alternator at the low end of it's efficient range of operation, but where the output power is still high enough that it can use all the power the engine is capable of delivering. Obviously you factor in a loss for alternator efficiency- I'm thinking that you would consider 40 amps output at 14 volts to be the equivalent of 1 real horsepower input.

Most likely you would have to guess at the power output of those engines, and at what rpm they would like to turn to best produce that power. Short of having the graphs available, you would have to do mechanical experimentation with ratios to come close to optimum. If you don't experiment, you could easily have a situation where the engine is working hard, but you are only producing a fraction of the power that you could be with the same engine and alternator combo.


That is also a good point and I am curious if a chain or gears would take less power to turn then a belt? When I was doing the tests I did notice the meter stayed at 14.20 while idling the motor down and finally started to drop off after about 2000RPM drop. The pulleys I have now are close to 1:1, I agree it would be optimal to run both motor and alternator at their optimum rpm's. I feel the 1:1 is close enough that putting pulleys on would nullify the gains. I plan to use a rubber coupler between the shafts. Each shaft is right hand threaded so it would be easy to screw a sleeve on with the rubber. Brings up another question though, does a alternator function correctly in reverse?

Ironheart
09-03-2011, 07:38 PM
The fan will be turning in the wrong direction.

gary350
09-03-2011, 08:20 PM
I converted one engine to steam. The rotary valve is attached to the engine crank shaft when the piston is top dead center the valve opens and puts steam into the spark plug hole. I use another valve to control steam volume for engine speed. The engine will run very slow maybe 40 RPMs and fast too maybe 7000 RPMs. I built a steam engine drip oiler for the steam line to lube the engine.

I made an adaptor so I can put a model airplane glow plug in the spark plug hole. The engines run excellent on gasoline with a glow plug. You don't need the ignition coil so remove it. The engines sound like they are turning more RPMs with the glow plug I'm not sure if they really are I have not checked them with a tack meter. I sold a few engines like this on ebay. I have no idea what people are using them for.

darryl
09-03-2011, 09:18 PM
Yes, the fan. I just checked a couple alternators I have, and the fan is definitely optimized for one direction. Otherwise I don't think the alternator cares which way it turns.

Another thing to look at is the need for the fan- the alternator usually resides under the hood where it's hot already. In an ambient temperature situation it would not need anywhere near as much airflow to keep it within limits. Have a look at that fan- it's the simplest thing. Make your own, and don't use as many blades. Set the angle to suit the rotation.

Here's another suggestion- in a vehicle with the engine idling, the alternator is turning at perhaps 1500 rpm. It's charging at that speed, even if not at rated capacity. The charge rate will be limited by the field current available, driven by the battery voltage. The field may be fully energized, and the output will be the maximum that can be had given that low rpm. The regulator lowers the field current when the voltage on the output raises to 14 or so volts. At lower currents, the field current is also lower. Unless you are trying for full power at lower rpms, the losses due to field current will be lower most of the time, and at the same time lower current output also means lower losses in the rectifiers.

What I'm suggesting is that the alternator could be fairly efficient at about half or so of its rated output, while being driven at about 3000 or so rpm. Not that much cooling would be needed.

In a vehicular application, given the wide range of operating rpm, the high heat environment under the hood, and the need for high current output much of the time (alternator supplies all the electrical needs at all times when the engine is running) the alternator could well be rated at a lower level of efficiency. If it was always as inefficient as has been stated, it would be burning up in normal use. Why doesn't it-

darryl
09-03-2011, 09:43 PM
I just looked up some charts for alternators- it would seem that the normal situation is a 3 to 1 overdrive ratio from the car engine, that it is producing about 20% of rated output at idle (1500 rpm or thereabouts at the alternator shaft) and it is producing about 80% of rated at 3000 rpm. It doesn't need more than 4000 rpm to produce virtually full output, but it is capable of running at 20,000 rpm on a short term basis. In a vehicle where you have the engine up to say 6500 rpm, testing the cars limits on the open highway, this gets the alternator up to the high end of its rpm range. But of course it doesn't need the last 15,000 rpm of that speed to generate at capacity- all it's doing is tolerating the operational environment.

This puts my previous thinking pretty much on track. Run the alternator at 3000 rpm, maybe a bit more, and do the pulley ratio math based on your weedeater engine rpm vs power output curve. I'm going to suggest a reduction ratio of about 2 to 1 minimum, and 3 to 1 maximum, because those little engines like to run at high speeds, and that is where their power capabilities are on the curve. I would suggest to base your calculations using a figure between 7500 and 10,000 rpm for the weedeater motor.

Willy
09-03-2011, 10:02 PM
If it was always as inefficient as has been stated, it would be burning up in normal use. Why doesn't it-


Because in normal use it is not required to operate at it's maximum output rating. Repeated alternator use for charging a dead battery will greatly shorten it's life. Under these conditions the alternator will be forced to put out it's maximum rated amperage for an extended time.
It won't usually die immediately but it's life will be greatly diminished if repeatedly subjected to this type of service.

Most newer car alternators have higher ratings due to increased electrical loads inherent in newer cars. Plus due to limited under hood footprint allowances they have gotten smaller despite increased output. 120 amp alternators are no bigger now than 60 amp alternators of twenty years ago.
A large truck alternator has almost the same rating as a typical coffee can sized automotive alternator but the component size allows them to be used at higher loads.

If required to operate at maximum output the typical small hi output automotive alternator's life is short.
I have seen more alternator fatalities in the dead of winter at -25C because of the high heat encountered due to trying to pick up a dead battery plus heater and lighting loads, than in the summer.
They are happy at 60%, and normally that is all that's needed.

darryl
09-04-2011, 12:25 AM
One other thing I wanted to mention is that the built-in rectifiers are silicon, and have the typical forward voltage loss of silicon diodes. We have metal oxide diodes now, usually called shottky diodes, which have a much lower forward voltage loss. Amp for amp, they dissipate only about half as much power as the silicon ones. You would need to bring out three wires from inside the alternator, then wire them to a bank of these diodes on a heat sink.

Doing this will improve the efficiency, but maybe more importantly it will reduce the amount of heat being generated and wasted, plus it will get this heat out of the alternator. If you look at where the heat is being generated when the alternator is really pumping, you'll find that a lot of it is in the rectifiers. As Willy said, they don't like full output operation for any length of time, and it's heat build-up that's going to kill it. Take this heat source outside of the alternator, and let the alternator concentrate on removing the heat from the field rotor.

vpt
09-04-2011, 11:26 AM
lots of good info flying around here! The fan is inside this alternator and is the typical metal disc with fins punched and bent out. As I was looking over the contraption I was thinking I could get the motor fan to pull air from both sides (motor and alternator) but I am not sure if it will pull enough air to keep both cool. Right now the shield over the motor fan is gone along with the recoil (which I wish I had) so the fan on the motor isn't pulling anything past the jug and head so the motor gets warm pretty fast while testing. I am not so worried about the alternator going out eventually because I have a few of them around all the time. Plus like I mentioned this thing will be for emergency situations, its not like I am going to be running it all day long charging batteries on my camper.

I think for now I am just going to go strait shaft and get plugs wired for outputs and see how things go. It is going to be simple so later on after I use it a few times and test more stuff out I'll keep a mental note of what needs to be "adjusted" and tear it down and redo stuff later on.

For now I am going to shoot for a 12v output, an AC output, and try to figure out something for an air pump/compressor and see how everything works.

I do need to do some research on wiring for AC output, I have never done anything like it before and have no clue. I do see the alternator has 4 winding lugs that go to the rectifiers. I assume the AC power needs to be pulled from the windings before the rectifiers. But 4 lugs? All confusing to me right now. lol

vpt
09-04-2011, 12:07 PM
My alternator is at the bottom of this page: http://www.alternatorparts.com/quicktifier-remote-bridge-rectifier.html

From what I read people say you can't just hook up AC "tools" strait to the alternator legs because it is not at 60 cycles like a normal house outlet.

What I gather is the alternator actually outputs 3 phase power which is rectified. I know they say it doesn't output 60 cycles but I am determined that I can run single phase off just one leg in the alt. and adjust the motor RPMs to get it close to 60 cycles. Does that sound right?
Seem like a waste of the other two legs but eh. Maybe I can use one leg per AC outlet but I don't think the motor will have enough power to turn the alt. if running two things at once. There is the possibility of just running a dc/ac converter but that would be more stuff and more weight and make the unit bigger. I am trying for cheap, small, and light.

So taking AC power from one winding does the neutral get grounded to the alt. case like the negative does with DC?

Dawai
09-04-2011, 12:43 PM
During the blizzard of 93.. I had a 64 El Camino w/external regulator, I disconnected the
Regulator, ran a hot to the fields, it produced 80 volts dc.. we hooked it to a skill saw and cut
us firewood up. I ran booster cables from my service van sitting next to it to charge the battery.

Skill saw has brushes.. ran fine.

Most people run a permanent magnets in a car alternator to use them as wind turbines. This makes
no sense to me, why don't they vary the fields so they can use any wind speed available?
If rpm < ??? subtract field PWM, if RPM>??? add PWM .

A harley alternator is about a inch wide, has a hollow magnet drum, you could put a flat plate
on the weedeater and mount the coils there, build a adapter for the shaft to drum.. THEN still put a
pulley on the remaining shaft there to run something else.. if you wanna?? I got a 60 amp unit
here on the bench, cost $120 dealer cost.

darryl
09-04-2011, 05:40 PM
I think you'll find that the alternator will have to turn very slowly in order to produce 60 hz. But it can do that, although with very much lower power output. The whine you hear from an alternator is more like 1000 hz.

The difference is in the voltage output. At 60 hz, you could get the full current output, but the voltage would probably be under one volt. Not very useful. Running the field wide open (without the regulator) would improve that, but not by very much.

Now if you wanted to add electronics, you add switching transistors to each phase, and control them to produce a pseudo-60hz output. The transistors replace the rectifiers, and you would switch them with the appropriate timing to essentially assemble multiple high frequency voltage peaks from the alternator coils into a semblance of a 60 hz sine wave. The alternator would have to be spun fairly quickly in order to minimize the deviations from the sine wave. I'm going to call this 'direct rectification' to suggest that you can bypass the normal rectifiers and any other power switching devices such as would be found in an inverter, to gain some measure of increased efficiency. The standard way of doing things would be to use the alternator normally, with a battery, and run an inverter from it. Not only do you have the switching transistor losses, but you also have two rectifier system losses as well. You can do the job using only switching transistors, doing away with the rectifiers entirely.

I have never seen this done, though I'm pretty sure it would work. You might have to add capacitors and filters to the output to smooth the voltage into a nicer sine wave.

As far as getting the voltage up as high as normal wall socket AC, you would have to run the field voltage fairly high, and the alternator rpm also fairly high. I have a friend who has done this with a kit to the alternator in his van, and run skil saws from it. Works well it seems, but I suspect you'd have to run a low duty cycle to prevent overheating the alternator. One reason this works with a skil saw is that you are running it on DC, so a lower than normal voltage can still get it up to speed. If fact if you ran it on 120 volts DC, it would probably cook in no time.

And now the last suggestion for now- you have the option of rewinding the alternator coils to put more turns on. This would directly increase the voltage output and decrease current output in direct proportion, given an equal power output rating from the alternator. To be somewhat practical, you would probably still use a battery, and you'd still need the normal rectifiers, but you'd tap the windings at the same number of turns as original, to get the normal 14 volts output. The ends of the windings, at the full number of turns, are brought out to be used either through higher voltage rectifiers for a higher DC output voltage, or through the switching transistor circuit to generate the pseudo 60 hz output, independently of the alternator rpm. This way the alternator can still supply the normal voltage and current to the field winding, and can still regulate the output.

I think you'd have to call this a fairly significant hack of the alternator-

vpt
09-04-2011, 07:01 PM
Thanks for all the info Darryl! You make an inverter and battery to get AC sound like the way to go. I wish I knew electrical better to know what I would need and how to put together the electrical parts to get them to do what I want. Like when I see pics of peoples single to 3 phase boxes with capacitors, and switches and whatnot and every one is different. I just don't get how you figure out something like how many capacitors you need and also what size. Its all gibberish to me. lol

Like the 60Hz, is that 60 "cycles" a minute or second or? With the alternator it would essentially be 1 "cycle" for every 1 revolution of the alternator if Hz is by minute like RPM, correct?

trying to understand, I never had much interest in it but it would be nice to know and understand electrical circuits!


Didn't get a real lot done today. I spent most of the day welding and machining the shaft snout nuts so I could use a rubber hose for the coupler. After getting it all together I realized the stock starting recoil would be needed. Now the rubber coupler I built is too big the hole in the recoil cover and the cover cannot be opened up or cut or it won't work. So now I am thinking of using a ball and pin joint like in the first pic below. I figure the unit weighs about 17 pounds as it is now.

http://fl2.shopmania.org/files/images/13763/team-vtx-drive-joint-2-vrx-85717~t_13762003.jpg


http://img685.imageshack.us/img685/2967/weedeateralternator2001.jpg

lazlo
09-04-2011, 07:08 PM
Cool idea Andy! Like everyone else, it seems, I have a spare (Stihl) weedeater motor. I was thinking of the same thing: a small generator, but I don't really know what I'd do with it :)

RC boat sounds cool too, but we don't have water in Texas these days...

vpt
09-04-2011, 07:13 PM
Cool idea Andy! Like everyone else, it seems, I have a spare (Stihl) weedeater motor. I was thinking of the same thing: a small generator, but I don't really know what I'd do with it :)

RC boat sounds cool too, but we don't have water in Texas these days...


Yeah I really don't know what I am going to do with this thing yet either. All depends I guess how well it works out. I have a honda eu2000 that I carry around now and love it!

You could build a RC plane, there is always air around. :p

lakeside53
09-04-2011, 07:39 PM
In case you don't know, the weedeater motor idles about 3000 rpm... with very low power, and develops most of it's power 8,500-10,000 rpm. Direct coupling and attempting 60hz output will be probematic.


60 hertz is 60 cycles per second. How this translates to rpm depends on how many poles your alternator has. If it's two poles, then you would need to run it at 3600rpm (Idle). If 4poles, 1800 rpm..

J. Randall
09-04-2011, 07:44 PM
Years ago I was maintaining a fleet of vehicles for an oil co., I had a guy with a meter proving truck that wanted to run an electric impact wrench, and a drill from the alternator. I don't remember the details, but we bought a kit that came with instructions, and I opened the alternator and brought some wires out and wired the box in. Then I put an idle speed solenoid on the throttle linkage, when he wanted to use it he just flipped a toggle switch and the idle kicked up and output was 120 volts. I always just assumed it was DC.
James

vpt
09-04-2011, 08:07 PM
In case you don't know, the weedeater motor idles about 3000 rpm... with very low power, and develops most of it's power 8,500-10,000 rpm. Direct coupling and attempting 60hz output will be probematic.


60 hertz is 60 cycles per second. How this translates to rpm depends on how many poles your alternator has. If it's two poles, then you would need to run it at 3600rpm (Idle). If 4poles, 1800 rpm..



4 pole. Maybe I should still think about running a 2:1 or more reduction? I figured the weed eater motors go up to around 10K rpm but I figured it idled lower then 3K, I thought they idled around 1500ish.

Would a chain be better then a belt as far as taking power to turn?

Also like mentioned by Darryl would the alternator still put out good power (AC wise) at 1800-2000 RPM? The DC side of things I am not to worried about so long as it is able to charge a battery yet out in the field.

vpt
09-04-2011, 09:04 PM
Well this one is small. Looks to be a 2:1 drive as well. He doesn't show it doing anything though.

http://www.youtube.com/watch?v=T7D44i8cJYo&feature=related

Gravy
09-04-2011, 09:16 PM
Andy,

I think you will get useful power out of that alternator setup for the short-duration applications that you have in mind.

What I want to talk about is air compressors. I've been playing with that idea for years now and I still don't have any good ideas. It seems to me that a one-hand-carry engine driven air compressor is a great idea for a home shop project. I just haven't run across a cheap compressor head that can handle the RPM's. If you use another weedeater motor, how do you lubricate it without excessive carryover into the airstream?

Ideas or suggestions, anybody?

darryl
09-04-2011, 09:29 PM
I just had a look into one of these alternators I have, and it has 12 fingers on the rotor. That means 6 norths and 6 souths. One rotation gives 6 cycles, 10 rotations gives 60 cycles. So- ten rotations per second gives 60 cycles per second, or 60 hz. Ten per second is 600 rpm- far too slow to give any meaningful power.

In a typical vehicle with a step-up ratio of 3 to 1, that would mean the engine would be turning at 200 rpm. A bit of imagination would tell you that you couldn't expect to get any charge out of it.

You do need more rpm for substantial power, but you don't need to spin it faster than 4000 rpm. Going direct drive means it will be going at 8500 to 10,000 rpm, and the losses will be greater because of the fan mostly. As you load the alternator down, the motor will slow because of the torque requirement. Now the motor will be approaching the overloaded range, will be running too slow, and will probably overheat. From the figures I've found, and what lakeside has said, you'd want to run the motor at twice the alternator speed, so that's a 2 to 1 step down ratio.

Looks like you won't be able to use the existing alternator pulley since it's quite small, being sized for a step up ratio. If you can find a pulley that's about 5 inches in diameter for the alternator, and 2 or 2 1/2 inches diameter for the weedeater motor, that should let you use a small appliance v belt without too much loss, maybe a 3/8 wide. You could probably use the alternator pulley for the motor, if you can make it fit. If you really want to minimize the belt losses, you would go with a micro v belt and pulleys. The alternator is ok with the side forces from the belt, but you would have to determine whether the weeder motor can take the side forces.

vpt
09-04-2011, 09:42 PM
Yes, thinking about the tests again I did and what you and others have said I think I will somehow do the 2:1 drive. There is no reason to drive the alternator so fast and I should be able to put a bigger load on the alternator.

I have boxes full of pulleys around here. I'll go and get a small 2-3 rib belt and find some good size pulleys to use. I was thinking if I use a belt I could switch it back and forth between the alternator and air pump.

Gravy
09-04-2011, 09:43 PM
Another thought on the air compressor approach: Flywheel effect might be a killer. The rotating mass of the weedeater motor might not be sufficient to overcome the peak pressure pulses of the compressor. Add more flywheel, and getting the engine started might get tough.

Hmm...where can I find a small, high RPM, cheap screw compressor?:eek:

vpt
09-04-2011, 09:46 PM
Another thought on the air compressor approach: Flywheel effect might be a killer. The rotating mass of the weedeater motor might not be sufficient to overcome the peak pressures of the compressor. Add more flywheel, and getting the engine started might get tough.

Hmm...where can I find a small, high RPM, cheap screw compressor?:eek:


It would be nice to find one of those electric compressors for cheap then rob the compressor off it.

http://ecx.images-amazon.com/images/I/51R2VW4KGQL._SL500_AA300_.jpg

vpt
09-04-2011, 09:48 PM
The alternator is ok with the side forces from the belt, but you would have to determine whether the weeder motor can take the side forces.


We'll worry about that later. :D

lakeside53
09-04-2011, 10:03 PM
4 pole. Maybe I should still think about running a 2:1 or more reduction? I figured the weed eater motors go up to around 10K rpm but I figured it idled lower then 3K, I thought they idled around 1500ish.

Would a chain be better then a belt as far as taking power to turn?

Also like mentioned by Darryl would the alternator still put out good power (AC wise) at 1800-2000 RPM? The DC side of things I am not to worried about so long as it is able to charge a battery yet out in the field.


Nope.. they idle around 3k, and have essentially no power until you get into the power band whch is above 6K, and even then it peaks at about 9K. If it still has the centrifugal clutch, that won't engage untill you have about 3200 to 3500 rpm.

Chains at that rpm would be an problem unless you use a larger sprocket (SFM...). Use a belt...


Unloaded the weedeater will run12-14k; loaded at max hp - 9500+/-. You need a govenor... A weedeater max rpm and max power is pretty much set by the length of the cutting string. Best way to burn them up is to remove the guard and cutter to lengthen the string, reducing the rpm - make sure you stay in the power band... (oh.. I'm a Stihl certified tech :) )

Gravy
09-04-2011, 10:07 PM
It would be nice to find one of those electric compressors for cheap then rob the compressor off it.

http://ecx.images-amazon.com/images/I/51R2VW4KGQL._SL500_AA300_.jpg

That's the problem. I've got one or two. They are rated for 3600 rpm at most...and most are limited to 30-50psi and fractional cfms.

I'd be willing to accept a 50% reduction in life expectancy, but I think spinning one of them at 7000-10000 rpm might produce a service life measured in minutes, if not seconds.

lakeside53
09-04-2011, 10:07 PM
Yes, thinking about the tests again I did and what you and others have said I think I will somehow do the 2:1 drive. There is no reason to drive the alternator so fast and I should be able to put a bigger load on the alternator.

I have boxes full of pulleys around here. I'll go and get a small 2-3 rib belt and find some good size pulleys to use. I was thinking if I use a belt I could switch it back and forth between the alternator and air pump.


You may be looking at a 4 or 5:1...

lakeside53
09-04-2011, 10:17 PM
I just had a look into one of these alternators I have, and it has 12 fingers on the rotor. That means 6 norths and 6 souths.
, .


But it's 3 phase, so it's 2 each per phase or 4 pole. Using any one phase I'd guess you'd get maybe 50% rated output (if the wire can handle it) and 1800 rpm gives 60 hz.

vpt
09-05-2011, 10:41 AM
That's the problem. I've got one or two. They are rated for 3600 rpm at most...and most are limited to 30-50psi and fractional cfms.

I'd be willing to accept a 50% reduction in life expectancy, but I think spinning one of them at 7000-10000 rpm might produce a service life measured in minutes, if not seconds.


The drive would have to be reduced like we are talking about with the alternator.

vpt
09-05-2011, 10:44 AM
You may be looking at a 4 or 5:1...


I'll be testing a couple different ratios to see which fairs better.

A.K. Boomer
09-05-2011, 11:25 AM
Thanks for all the info Darryl! You make an inverter and battery to get AC sound like the way to go. I wish I knew electrical better to know what I would need and how to put together the electrical parts to get them to do what I want. Like when I see pics of peoples single to 3 phase boxes with capacitors, and switches and whatnot and every one is different. I just don't get how you figure out something like how many capacitors you need and also what size. Its all gibberish to me. lol

Like the 60Hz, is that 60 "cycles" a minute or second or? With the alternator it would essentially be 1 "cycle" for every 1 revolution of the alternator if Hz is by minute like RPM, correct?

trying to understand, I never had much interest in it but it would be nice to know and understand electrical circuits!


Didn't get a real lot done today. I spent most of the day welding and machining the shaft snout nuts so I could use a rubber hose for the coupler. After getting it all together I realized the stock starting recoil would be needed. Now the rubber coupler I built is too big the hole in the recoil cover and the cover cannot be opened up or cut or it won't work. So now I am thinking of using a ball and pin joint like in the first pic below. I figure the unit weighs about 17 pounds as it is now.

http://fl2.shopmania.org/files/images/13763/team-vtx-drive-joint-2-vrx-85717~t_13762003.jpg


http://img685.imageshack.us/img685/2967/weedeateralternator2001.jpg



That's a crazy looking picture;)

Like stated the weed eater is not going to have the balls to pull that off, you have very limited hp's and need to conserve every bit of it while reducing your gearing at the same time - a belt is going to scrub power some - chain reduction is pretty efficient but still there is side loading of both the engine and the compressor - you can eliminate all side loading and maintain direct alignment by using gears - planetary gears, while at first this sounds pretty extensive it may be simpler than you think, check into the ratio's of an old sturmey archer three speed bicycle hub - it will handle the torque for sure but you might have to seal it off and run 90 wt. inside.
I think first gear might be around a 3 to 1 ratio, could be about perfect and planetary gears are very efficient due to even loading of the drive systems when used in this configuration... (it's actually one of the reasons why some of the newer automatic transmissions have higher MPG ratings than their manual equals - that and lock out torque converters and thinner fluids)

If it all pans out ratio wise then build yourself an oldham coupling between the two - make the center yoke out of delrin AF - this will ensure proper alignment under load even though you will be off some with your mounting - this is critical with this set-up as the worst thing you could do is direct couple the 3 speed unit and put the planetary system in an internal bind - then say good bye to efficiency and most likely some parts as well...

lazlo
09-05-2011, 11:42 AM
In case you don't know, the weedeater motor idles about 3000 rpm... with very low power, and develops most of it's power 8,500-10,000 rpm.

Good point Andy, that's a deal-breaker for me. The noise associated with a generator running at 10,000 RPM...

Guess the Stihl will gather more dust ;)

vpt
09-05-2011, 11:56 AM
That's a crazy looking picture;)

Like stated the weed eater is not going to have the balls to pull that off, you have very limited hp's and need to conserve every bit of it while reducing your gearing at the same time - a belt is going to scrub power some - chain reduction is pretty efficient but still there is side loading of both the engine and the compressor - you can eliminate all side loading and maintain direct alignment by using gears - planetary gears, while at first this sounds pretty extensive it may be simpler than you think, check into the ratio's of an old sturmey archer three speed bicycle hub - it will handle the torque for sure but you might have to seal it off and run 90 wt. inside.
I think first gear might be around a 3 to 1 ratio, could be about perfect and planetary gears are very efficient due to even loading of the drive systems when used in this configuration... (it's actually one of the reasons why some of the newer automatic transmissions have higher MPG ratings than their manual equals - that and lock out torque converters and thinner fluids)

If it all pans out ratio wise then build yourself an oldham coupling between the two - make the center yoke out of delrin AF - this will ensure proper alignment under load even though you will be off some with your mounting - this is critical with this set-up as the worst thing you could do is direct couple the 3 speed unit and put the planetary system in an internal bind - then say good bye to efficiency and most likely some parts as well...



I think I will go with the simple belt for now. It seemed to work out fine in the initial tests and that was 1:1. I think with a smaller belt and getting the 2-5:1 will make it seem like the belt isn't even there. Yes it will put side load on the motor but I'll worry about that problem after we see how long the single crank bushing lasts. Maybe I'll never have to worry about it, maybe the crank will start flopping around after only a few minutes, we'll see. I could always put a pillow block bearing on the other side of the pulley to take some of the load off the motor bushing. Or I could mount the yet to be determined compressor on the other side of the pulley to take some load and do the compressor job.

Is it worth it to put a very very small tank on the unit for the compressor? Like 30oz size. My thinking says it would help for very very short bursts of air tools like an impact where strait hose off the compressor would make any air tool useless.

lakeside53
09-05-2011, 12:02 PM
Your crank isn't the issue - it's the bearing (likely just 1 single row radial) on the output housing side of the clutch (assuming it's still inside). It and the clutch are not designed for any side load - just a support to drive a shaft supported at the distant end. Pulling sideways may tweak the clutch drum out of alignment.

vpt
09-05-2011, 12:15 PM
No clutch in this unit, it was direct drive. Do you think the single bushing for the crank will take the side load for very long using a belt?

lakeside53
09-05-2011, 12:29 PM
Odd weedeater not to have a clutch! Might be a pain to start it with the alternator or compressor attached. Does it have a bushing or a bearing? Bushing is also odd...

No... I wouldn't put a pulley directly on the end. Drive tan arbor/pully with pillow bearings. You could put (on the arbor shaft) a multisheeve pulley.

Willy
09-05-2011, 02:22 PM
I applaud your desire to see this engineering exercise to fruition Andy.
Trust me I'm not here to rain on your parade.

But as I eluded to in several of my earlier posts, you are extremely limited by not only the amount of power at your disposal, but also the rpm band in which this power is available.
In any endeavor of this sort the main ingredients have to be at least somewhat compatible for the project to make sense.

The application you are proposing for this engine, although doable, are not practical. The amount of interface between the main components detracts from it being a viable project.
Envision a bicycle powered with an engine out of a D-8. It can be done...but does it make sense?

It's entirely up to you of course but if it was up to me I would choose an application that capitalizes on the available power the engine has and the speed at which it is produced. There are also other design criteria of course that enter the picture, things like the side thrust or bearing loads that have to be in phase with the original component's design. Anytime you make a modification to circumvent an issue, it not only complicates the project, but also detracts from it's efficiency.

If you think about it, this is probably why you don't see these marvelous little engines in this type of service.

vpt
09-05-2011, 06:07 PM
Quit raining on my parade Willy. :p

I know its not practical especially when I saw a small gas generator all ready to go for $100 at HF. Its just something fun to do that may come in handy some day. At least its doing something with the motor that has been hanging on my wall for 7 years.


Put it back to belt drive today and got a nice little 3 rib belt. With the recoil where it is the shaft has to be about 3.250" long with the pulley hanging off the end. I didn't want to run it to much like this but I wanted to do one quick test. First I set up 2:1 and I hooked up the two 100w bulbs and two 55w fog lights. With the 310w load I was just about able to keep the motor reved. I thought it would have done better but I will move on to bigger alternator pulleys and see what happens.

lakeside53
09-05-2011, 06:10 PM
310 is nearly a 1/2 hp of alternator OUTPUT. Even if you are smack in the middle of the power band, and assuming the motor is the usual 0.9-1.1hp type and is in decent shape, maybe you'll get 500 watts...

vpt
09-05-2011, 06:29 PM
Thats more then enough to charge a battery and run a light or two. If I put a big heat sink on top the head I could use it for cooking too!

aboard_epsilon
09-05-2011, 06:59 PM
If you do pulleys or sprockets or whatever route, just put another outboard bearing in .

What you should worry about with a two stroke is the crank seals ..pulling to one side may wear them out ..then it will suck in air and wont start.

Suppose you've got these motors ..because they were bent shaft weed eaters ..having a cable drive to the head ..that usually ends up snapping.

all the best.markj

vpt
09-05-2011, 07:07 PM
Yeah the heads get all beat up and the motors still run, so I pull them off and throw the rest away.

I was planning on using the air compressor for the outboard bearing. But I was also thinking of using a pillow block bearing and then having the shaft to the compressor keyed so I could slide it toward the driven shaft to engage it and pull it away when I just want to use the alternator.

What do you guys think of the small air tank idea?

Gravy
09-05-2011, 07:14 PM
Definitely add the air tank. Make it as big as you can and still be easily portable.

vpt
09-05-2011, 07:16 PM
2 liter pepsi bottle? Nice and light. :D

aboard_epsilon
09-05-2011, 07:19 PM
disposable mig welding bottles.

will exhaust gases compress more than air ?

all the best.markj

vpt
09-05-2011, 07:30 PM
I thought about how much compression is possible out of the exhaust but being 2 stroke there would be all kinds of oil in it. Or are you suggesting a turbo for more power?

vpt
09-05-2011, 07:31 PM
How about a propane bottle? Not strong enough for 100-120psi?

topct
09-05-2011, 07:55 PM
I'd be looking for the engines with the starter on one end and an actual output shaft on the other. They often have a clutch on the output and so the crank is much better supported. The little throw away chain saws also have a clutch of course. You don't have to use the clutch, but again the crank is much better suited for driving.

I'm waiting for one of these little 4 strokes to show up, or something similar.

http://www.smallenginewarehouse.com/product.asp?PN=21032-0139&desc=Briggs%20&%20Stratton%20Engine%20%202HP%20Weed%20Trimmer%20E ngine,%20Four%20Stroke,%2034CC,%20fits%20Go%20Ped

vpt
09-05-2011, 08:00 PM
I would have opted for a better suited motor if there were some around. Seems only the cheap ones get thrown out.

Gravy
09-05-2011, 09:10 PM
2 liter pepsi bottle? Nice and light. :D

Well, if 2.7psi works for ya:D

Gravy
09-05-2011, 09:12 PM
How about a propane bottle? Not strong enough for 100-120psi?

Probably work just fine. I'd think there would be a hefty safety margin on them...

But I'm not an engineer who stayed in a Holiday Inn Express.

Paintball gun canister?

Gravy
09-05-2011, 09:22 PM
Then again, if you're talking about disposable propane tanks, the fittings are weird and restrictive.

bborr01
09-05-2011, 09:27 PM
Then again, if you're talking about disposable propane tanks, the fittings are weird and restrictive.

Shouldn't be too restrictive for someone with a lathe.

Brian

Gravy
09-05-2011, 09:35 PM
Shouldn't be too restrictive for someone with a lathe.

Brian

Good point, but it will still be weird. (Oh, yeah - remember that the residual propane may still go "Boom" when you open it up.)

I keep thinking there's a common item that would be easier to adapt, but I'm coming up blank.

vpt
09-05-2011, 09:58 PM
Shouldn't be too restrictive for someone with a lathe.

Brian


Yeah they do have a big chunk of metal on them to bore out and thread.

Yow Ling
09-06-2011, 03:54 AM
Refrigarant bottle ?

vpt
09-06-2011, 08:46 PM
Thats all she can give.

I turned another pulley today and ran another test. I guesstimate it is at 4:1 now and can hold steady at 3/4 throttle with a 310w load and showing 14.64v on the meter. I am not sure if the connections for the meter were a bit loose before or if I was driving the alternator past its sweet spot when it showed 13.9#. With the big pulley the motor runs much more free when just charging the battery. I also think the motor shaft with the pulley is rubbing on the plastic housing inside with the side force of the belt wearing down motor output a bit. The outboard bearing/compressor should help that.

Another add on that I was thinking for this thing is a water pump. Also like I mentioned before about making the end of the driven shaft keyed so I could engage and disengage the air pump. I was thinking I could make removable attachments that could just slide into the keyed shaft (like a PTO) and mount to a couple studs with wingnuts or something. That way anything I dream up down the road could be just made into an attachment.


Anyhow a couple pics of the final alternator test. I will weld on the final lower alternator mounts and then on to the compressor. I do have a shorter belt that will bring the alternator in closer to the motor. It was just to short for testing.

http://img831.imageshack.us/img831/151/weedeater3001.jpg

http://img193.imageshack.us/img193/6548/weedeater3002.jpg

http://img200.imageshack.us/img200/6445/weedeater3005.jpg

Gravy
09-06-2011, 08:58 PM
An alternator or a centrifugal pump have pretty low starting torque. An air pump will probably need some sort of unloader valve/compression release for starting. I think that would be simpler than a clutch.

vpt
09-06-2011, 09:02 PM
I forgot to clarify. I wanted to make the air pump keyed so when I don't need it I could back it out of the "PTO" so it would not be turning and taking any power or wear out prematurely.

Gravy
09-06-2011, 09:20 PM
I forgot to clarify. I wanted to make the air pump keyed so when I don't need it I could back it out of the "PTO" so it would not be turning and taking any power or wear out prematurely.

I got that - I was just thinking of trying to start the engine against the inertia+compression load of the air pump. There's not much flywheel effect to overcome the pressure peaks.

What about belt driving the air pump and using a lever operated tensioner as a clutch?

Gravy
09-06-2011, 09:22 PM
I got that - I was just thinking of trying to start the engine against the inertia+compression load of the air pump. There's not much flywheel effect to overcome the pressure peaks.

What about belt driving the air pump and using a lever operated tensioner as a clutch?

Or maybe not - that would be bulky and heavy. Next idea?

darryl
09-06-2011, 09:48 PM
On the subject of tanks for air pressure- propane tanks are easily capable of handling normal pressures with a large safety margin. I tested a 20 lb tank at almost 900 psi and it didn't even stretch. I could tell by the level of water inside- it was the same before and after the test.

For a smaller diameter tank you could use a fire extinguisher bottle- I have a few that have test numbers on them- 536 psi on one, don't recall the numbers on the other. But even the 2 ft tall ones don't hold much air- two shots with a nail gun and the compressor has to run.

2 liter pop bottle- supposedly they can take over 100 psi before blowing up. Not a good choice for an air tank, but the figures are impressive anyway. One day I'll play with bottle rockets- looks like fun.

Gravy
09-06-2011, 09:54 PM
I like the fire extinguisher bottle idea. Empty it, unscrew the valve, measure the threads and make an adapter to fit.

1-800miner
09-06-2011, 10:47 PM
Made a concrete power screed out of one.

Pulled the cutter head off and welded a small weight of center on the rotating shaft so it vibrated.

Bolted a four foot piece of angle iron to it horizontally with some braces.

Fire it up and drag it through the wet concrete,Works like a charm.

vpt
09-11-2011, 09:22 PM
Had a little extra time today between projects and did a little on the weed eater project. Turned a lexan disc for a ground protector, also turned a pole terminal for the jumper cables to connect to. I figure the ground side could be connected anywhere on the frame and doesn't need a pole. Started on a couple switches like the alternator excite 12v and engine kill switch. I was thinking it would be neat to have a small light right on by the alternator switch. It would illuminate the switches and work area. But without a battery how would you light the bulb (12v?) without a battery? Say you are using the unit to pump up tires in the dark so you wouldn't have a battery hooked up to use the alternator so it wouldn't be outputting anything. Ideas?

Some pics. Also did up a quick throttle today.

http://img838.imageshack.us/img838/4167/weedeateralt4002.jpg

http://img402.imageshack.us/img402/7235/weedeateralt4003.jpg

darryl
09-11-2011, 11:20 PM
Just add a small battery to the system, like a garden tractor battery or small motorcycle battery. You can get a 12v 9 A/H for not too much. Then you can have light while you sort out starting the engine.

Then of course you add electric start- :)

Iraiam
09-12-2011, 12:03 AM
You are going to need a battery to excite the alternator windings, I don't know of any way around this, short of using a permanent magnet alternator, but then it will cog badly and be hard to start the engine.

What size engine is that? I made a similar contraption out of a 3.0 hp vertical shaft briggs engine, I over sized the drive pulley for an RPM of about 6500 on the alternator at WOT.

It took all that little engine had to turn it under load with a 40 amp alternator.

looks like a good project

Willy
09-12-2011, 01:11 AM
Nice compact packaging Andy, makes it get used more often when it's small and lightweight the way you've designed it. Very nice.

For a light when you aren't using the alternator/battery and only have the compressor mounted. How about just a simple 9 volt batter/resistor combo powering a high output led through a diffused lens. Lots of light, very compact, and it will last for hours.

vpt
09-12-2011, 09:23 AM
Or I could just remember the flashlight. :D

Iraiam: The motor is a slight mystery, from testing we figure it to be around 1/2-3/4hp. I have it pullied to about 4:1 (4 motor turns to 1 alternator turn). Word is weed eater motor turn about 10K rpms and their power band is around the 8500-9K range. So I am turning the alternator about 2200ish rpm. It is a honda alternator and from what I read it is somewhere around the 90-110 amp. If you haven't seen I was able to get a 310w load on the alternator and still have it showing 14.6v on the multi meter.


Willy: thanks for the compliment! I am shooting for as small and light as possible with the materials I have laying around. Like you said the easier something is to carry and use the more you will use it.

As for a battery I was wondering how small of a battery would be to small to take the charging power of the alternator? I have some 12v cordless drill batteries that I have used for testing 12v automotive relays and switches and whatnot. They are small and light but would charging them with an alternator be too much for them?

lakeside53
09-12-2011, 11:46 AM
If you use the nicads/NiMh or whatever, you need the correct charging regulator or they will blow.

Just get a cheap lead acid NP22 7amp/hr lead-acid battery as found in ups, burgler alarms etc.

Willy
09-12-2011, 12:56 PM
Or I could just remember the flashlight. :D



Well...DUH:o

Sorry Andy, I misunderstood the question.:)
Yeah Lakeside53 is right, different battery technologies require differing charging protocols.
What is right for NiCd, is not right for NiMH or Li-ion.
Lead acid again uses a different set of parameters. I'd stick with a small lead acid battery.

vpt
09-14-2011, 09:25 PM
If you use another weedeater motor, how do you lubricate it without excessive carryover into the airstream?

Ideas or suggestions, anybody?



I have been thinking of this dilemma since I started this project and assumed I would be using another 2 stroke for a compressor.

I had a thought today. Using the one way valve in the spark plug hole like they all do but block off the intake port into the cylinder and use the exhaust port as the air intake. The crank case would essentially be sealed then to which you could add oil and run using the rod as a splash. I assume some oil would be pulled out of the ring when it passes the exhaust port and still make it into the air stream but I can't imagine a whole lot.

Possible? Sound feasible?

vpt
09-14-2011, 09:26 PM
Well...DUH:o

Sorry Andy, I misunderstood the question.:)
Yeah Lakeside53 is right, different battery technologies require differing charging protocols.
What is right for NiCd, is not right for NiMH or Li-ion.
Lead acid again uses a different set of parameters. I'd stick with a small lead acid battery.


Is it possible to use a small capacitor instead of a battery?

Willy
09-14-2011, 09:50 PM
Very good thought!
I have driven motorcycles a long time ago that incorporated such a capacitor. They essentially replaced the battery to save weight. Of course they aren't legal for on-highway use because they can't provide lighting unless the motor is spinning the alternator. The lighting was dim and flickered at idle but looked normal at anything past that.

Not sure how they would work with an automotive alternator, you may need a larger cap. I'm sure someone with a better grasp on electronics will help fill in the details.

Meanwhile do a Google of "motorcycle battery eliminator capacitor (http://www.google.ca/search?hl=en&source=hp&biw=1024&bih=625&q=battery+eliminator+capacitor&rlz=1R2GPEA_en&oq=battery+eliminator+cap&aq=0&aqi=g1g-v2g-m2&aql=&gs_sm=c&gs_upl=2328l4875l0l8531l8l6l0l0l0l0l250l1141l0.3.3 l6l0)", should be some clues there.

lakeside53
09-14-2011, 11:13 PM
Is it possible to use a small capacitor instead of a battery?

Maybe a large capacitor (farads)... and you'd need to keep it "charged" ready for the next start cycle. Just use a acid battery.

jnissen
09-15-2011, 01:08 AM
Radio control aircraft or Boats have used weed eater power for years. Here is an example of a Homelite boat I ran for years. This was a converted trimmer motor and the setup would do just over 50MPH. http://www.jrcbd.com/images/jims/IMG_2314.jpg

lakeside53
09-15-2011, 02:20 AM
Compressor? Poor choice. Splash lube isn't usually done by slapping the crank into the oil; a scoup of some sort is often attached to the rod end. There is little clearance between the crank bells and the case bottom (often a couple of mm), and... 2 strokes don't have oil control rings; many weedeater only have one ring.

madokie
09-15-2011, 04:54 AM
ok heres my input on this stuff, first, for a air tank, ask your friend that scuba dives for a old tank that wont pass certification, and make a high pressure to low pressure tank out of it with a couple of regulators,( 200$ online ).second, making a generator out of one weed motor likely wont work you need at least 5 HP to turn a car alternator,you can go to the epi center.com and look around, plenty of info there, they also sell steel plates(25$-35) that bolt up lawn mower engines and alt.if you want to make a air compressor maybe this might work,use 2 of these weed motors, one on each side of horozontal 3.5hp B&S,one will bolt up to drive shaft, direct, and other will adapt to flywheel nut, also direct drive,flywheel nut comes off and you can makup a longer replacement that weed motor will bolt to.un load compressor, get one motor started, start other motor and then release loader valve.if you have trouble getting weed motor started remember some 5HP motors have electric start, you could use that to fire everthing up.anyone care to make up a powered drill,sander,circular saw, or a miter saw??:eek:or how about a 1/3 scale chainsaw?? with the flexible shaft that come with some, their is an endless supply of things and tooling that could be attached to the end of said shaft.also you could take a larger weed motor, bolt it to slightly smaller weed motor,(direct drive), use large one as a air compressor to supercharge smaller one, i would like to see if that works.did you see the Hot Rod issue this summer where they used two leaf blowers to supercharge a old junky vette??yes it worked 25 HP.maybe use one to supercharge another weed motor??or make up a bank of say 4 weed motors using leaf blower to supercharge all 4??i dont have spare time to try, have to work all the time to pay my bills.ideas though come freely.

vpt
09-15-2011, 08:58 AM
I keep mentioning the second motor as a compressor because it is basically free. An actual compressor I would have to pay for, lol. I have been watching craigslist for a cheapy pancake or tankless compressor. There is a 1/2 sears on there right now that I was getting excited over until I got pics and saw it is way to big.

Before I was worried about the 10K rpms driving the compressor but staring at my concoction the other night I realized I could drive a compressor of the alternator shaft which is reduced to around 2500rpm. But I still have to find a cheap compressor.

Lakeside: I know how the cups work in old car engines for oil pickup. My thought with the 2 cycle motor is just a tiny bit of oil in the bottom that would most likely turn into a mist and get everywhere at 10Krpm. 2cycles I am sure you know use needle bearings at the crank and rod ends and because it is 2cycle it is made to take in very little oil/gas mix when it is running normally. Sealing off the intake port to the cylinder would just keep the oil from being pumped out. I think it would work fine but if I can find a cheap compressor I would rather go that route.


Willy thanks for the tip on the caps in the older bikes, I will look into that! I may end up just skipping a battery or cap all together. Seems like it is going to be to much weight and extra stuff just to have a light. I have one of those shake to charge flash lights, maybe I'll just make a mount on the unit for that light and call it good. :D I'll make the wife charge it up when I need it.


Madokie, go back and watch the video. It might take 5hp to turn a alternator under full load but not at partial load. This thing is all about light weight and cheap scrap parts laying around.