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Steve Steven
05-09-2009, 01:12 PM
I have a friend, Bill Cogger (BigBoy1) in Elizabeth City, NC who built a rotary converter using the circuit I put together. The circuit is shown in my old thread
http://bbs.homeshopmachinist.net/showthread.php?t=33353
and works fine for me.

He has built it and the start circuit works fine, but the motor will not start.

The motor will turn slowly, hum and heats up. We have not run it for more than 10 seconds at a time, not wanting to harm anything.

Some things I have noted:
Bill used the size capacitors as I specificed for a 5 hp motor, but he has a 2 hp motor. He has 50 mf on the run capacitors, and a 250-324 mf on the start. To eliminate some questions, I disconnected the run capacitors, no change. I changed the start capacitor for the run capacitor, no change.

I took his motor, a 2hp 3450rpm motor, and tried it with my rotary converter. It started and ran fine.

I took the start capacitor from my converter, and wired it in to Bills box, no change.

Some voltage readings:

Across the start capacitor: buildup to 110VAC, then no more. Shut down after 10 seconds.

T3 to T1 or T2: 110 VAC

T! to T2: 240VAC

The start relay never opens when attampting to start. Presumably not high enough voltage to open the switch.

Here are some pictures of his unit:
http://img.photobucket.com/albums/v200/Stevesteven/DSCN0143A.jpg

http://img.photobucket.com/albums/v200/Stevesteven/DSCN0141A.jpg

http://img.photobucket.com/albums/v200/Stevesteven/DSCN0144A.jpg

http://img.photobucket.com/albums/v200/Stevesteven/ScannedImage-1.jpg

See next post for more picts...

Steve

Steve Steven
05-09-2009, 01:18 PM
Here are a few more picts...

http://img.photobucket.com/albums/v200/Stevesteven/DSCN0142A.jpg

http://img.photobucket.com/albums/v200/Stevesteven/DSCN0145A.jpg

http://img.photobucket.com/albums/v200/Stevesteven/DSCN0140A.jpg

http://img.photobucket.com/albums/v200/Stevesteven/DSCN0139A.jpg

Anyone got any ideas on what is wrong? I can't figgure it out.

Remember, the start circuit works fine, the run caps are out of the circuit for simplicity (and it didn't work with them in either).

The start cap size is a bit big, but it should still work.

Steve

Steve Steven
05-09-2009, 05:24 PM
I completly dismantled what Bill had wired, and re wired it, testing as I went.

The start circuit worked fine.

I wired up the start capacitor and the start relay with nothing else in the circuit, it started correctly. Only tried it one time, tho.

Wired in both run capacitors, would not start. Disconnected the run capacitors, ran once, then DID NOT START. Ran a test sequence of six starts in sucession, got 4 out of 6 good starts with 2 no-starts.

Right now I am thinking the too-large capacitors might be the problem.

Any thoughts on this?

Steve

wierdscience
05-09-2009, 06:59 PM
If it's for an RPC on a 2hp motor the cap should be 160mf,no more than 200mf.The run cap isn't even needed except to correct power factor.

Rich Carlstedt
05-09-2009, 10:22 PM
I am not a fan of having two run caps, coming from each side of the line.
I know there are those who bless it, but I have found that they sometimes interfer with each other. I suggest you drop one Cap permanently.
I also believe that 3400 motors are more difficult to start, based on my experience

1. If you use a run cap, make sure it is on the SAME LINE side that the start cap is .
2. 100 MF for run is way too high for a 2 HP motor. You want 10-15 MF per HP---MAX.
3. You did not define your start relay ?? it sounds like the relay is dropping too fast. This is common with 3400 RPM motors.
You want a Relay with 185 to 200 drop out voltage rating.
MF on the START is not as critical as RUN. if you over do it(START) , the voltage rises faster and the voltage relay accomodates it. I like 100 MF per HP, but your 250 should work fine.
4. If you intend to start the convertor in rapid sucession, make sure you have bleeder resistors accross the caps to save your relay


Rich

Jeffw5555
05-09-2009, 10:49 PM
I am personally in favor of two run caps, but they are never the same size. I choose the run caps to balance out the voltages dependent upon load. For example, with a 5 HP RPC, I have found that 60 uF on one leg (same side as start cap per Rich's point), and 25 on the other works best. Two 50's are no good for a 2 hp, try 25 and 10, for example as a starting point.

I just tried to look up the relay on Grainger; but the site is down for maintenance. You either drew your schematic incorrectly, or you are using the wrong relay; the relay (and schematic) should be NC. Check this out; if you drew your schematic according to the relay schematic, then you have the wrong relay.

J Tiers
05-09-2009, 11:44 PM
Suggest you take out the run caps, and then work with it that way until it is reliable. Then you can mess with run caps if you want. They are not required.

If the start cap is TOO BIG, it will essentially connect the drop-out relay across the incoming line and give it too much voltage too early, so it might drop out before the motor gets going...... try moving toward the lower end of the range, closer to 50 uF per HP, and see whether it starts easier.

Steve Steven
05-10-2009, 12:07 PM
Good comments, I will suggest to Bill that he get a smaller start cap, not connect the run caps, and see what happens.

Yes, I did draw the start relay wrong, it is a NC type with a 150-180 pull- voltage rating. It is the one recommended by several web sites I had visited.

I had noticed relay arcing when I tried to restart several times in quick succesion, I will try bleed resistors on the caps.

Thanks for all the comments, its a great help!

Steve

gnm109
05-10-2009, 12:19 PM
I'm just curious. In the line drawing, it appears that the Neutral has been tied to L2 from the 240 VAC source. Is that OK? I thought that L1, L2 and Neutral were to be kept separate on a single phase system.

It's possible that my converter is wired the same way but the company that built mine doesn't like to give out their specs. They only give a wiring diagram for hookup so it might be similar to yours inside and I wouldn't know it.

Just wondering.......

Rich Carlstedt
05-10-2009, 12:25 PM
Voltage ratings:
Check your run cap voltages.
I just noticed you have 270V and they should be 370v

Relays:
Lower voltage <180 relays require a bit more Mfd
180-200 volt pull in respond to lesser Mfd ( like 100/hp).
Having Run relays means their Mfd must be used in the calculations
Modern motors with little Copper and lots of Aluminum do change the characteristics of a start circut and make it more difficult.

Just my opinion but:
For balancing legs, try to use amperage instead of voltage.
I have used both.
Voltage is "potential", while amperage is "power" and more closely reflects true performance, as the wave form is not a sine wave

Rich

Rich Carlstedt
05-10-2009, 12:44 PM
Gmn 109
Technically the wiring diagram is in violation of (NEC and many Local) code.
Any 220/240 appliance must NOT use the neutral as an unbalanced circut exists. It automatically means one leg will have a higher amperage loads than they other.
Correct application is to add a 240 / 120 stepdown transformer and use that for control circuts, OR , you can use a 240 volt control circut ( but that is not legal in some localities)
I admit, I have done all of the above, but it is a good idea to always fuse the control circut seperately whether you use the unbalanced method or the transformer

it may also explain why the company will not provide you the info ???

Rich

Why the worry ?
Even the NEC and the Insurance Industry are wrong in some instances.
I worked for a company that had 2 boiler explosions caused by a 240 control circut. What was embarassing was that after the first explosion (200 HP Boiler !) about 6 inspectors( State, Insurance etc) did not pick up the cause which resulted in the second explosion 6 months later.
The 240 volt water control relays when exposed to dampness leaked voltage to ??? - ground. ( 120 potential)
Happens that only one side of the 240 leg was shut off during failsafe operation, but the other leg, leaking to ground, held the relays in--depriving the water pumps from turning on>> BOOM is the result
No one was killed luckily in either case, but lots and lots of damage

The solution was a isolation transformer and all new 120 volt controls..3 million dollars later

J Tiers
05-10-2009, 02:47 PM
Gmn 109
Technically the wiring diagram is in violation of (NEC and many Local) code.
Any 220/240 appliance must NOT use the neutral as an unbalanced circut exists. It automatically means one leg will have a higher amperage loads than they other.
Rich


Someone had better tell that to the stove manufacturers....... they often have 220 in but 120V lights and timers etc.

In fact, there are special 4 wire plugs for those appliances so that the neutral is able to be supplied..... a change from earlier NEC which allowed the neutral to double as an equipment grounding conductor for stoves........

For an incidental load like that relay, the imbalance is below negligible.

gnm109
05-10-2009, 05:04 PM
Gmn 109
Technically the wiring diagram is in violation of (NEC and many Local) code.
Any 220/240 appliance must NOT use the neutral as an unbalanced circut exists. It automatically means one leg will have a higher amperage loads than they other.
Correct application is to add a 240 / 120 stepdown transformer and use that for control circuts, OR , you can use a 240 volt control circut ( but that is not legal in some localities)
I admit, I have done all of the above, but it is a good idea to always fuse the control circut seperately whether you use the unbalanced method or the transformer

it may also explain why the company will not provide you the info ???

Rich

Why the worry ?
Even the NEC and the Insurance Industry are wrong in some instances.
I worked for a company that had 2 boiler explosions caused by a 240 control circut. What was embarassing was that after the first explosion (200 HP Boiler !) about 6 inspectors( State, Insurance etc) did not pick up the cause which resulted in the second explosion 6 months later.
The 240 volt water control relays when exposed to dampness leaked voltage to ??? - ground. ( 120 potential)
Happens that only one side of the 240 leg was shut off during failsafe operation, but the other leg, leaking to ground, held the relays in--depriving the water pumps from turning on>> BOOM is the result
No one was killed luckily in either case, but lots and lots of damage

The solution was a isolation transformer and all new 120 volt controls..3 million dollars later



It's possible that the company that built my RPC did the same thing with the neutral, but it's more likely that they don't want aoyone building them from their drawings.

My RPC does have a start relay but it could be that it operates from the 240 VAC for all I know. We shall see.

All I really needed is the hookup drawing that was supplied with the unit. If it ever breaks down, I'll figure out how it was wired as I rip it apart. LOL

Rich Carlstedt
05-10-2009, 09:30 PM
J
The stove people have their own lobbiests for the code.
It's even specifically covered in the NEC, unlike other home stuff
Yes, they now do use a 4 wire for new installs.
They may have transformers too..but I don't know about that
Check local codes fellows. Here in Green bay, it is not legal to use the neutral on your 220 lathes or mills, or for rotary convertors.
they are classified as appliances/tools
Fires have started from mere neglible loads.

GMN 109
Take the control box apart and record the wire runs.

Rich

J Tiers
05-10-2009, 09:55 PM
There are a number of other items that also use the neutral..... those plugs are used on other things as well, I believe dryers, etc. The application is common enough that a class of plug is sold at any big-box store (type L14-20, IIRC) which includes both hot wires, NEUTRAL, and equipment grounding conductor. Nominally, they are for generators, but.......

30 and 50 amp 4 wire plugs are also sold, similar to the old stove/dryer plugs, but including 4 prongs, for the new stoves and dryers.

Yes the stove people do strange things.

Yes, it is a better idea to use 220 or a transformer, even if simply on the basis of deriving control from the same source as the power, so that it is less likely to fail independently. That is sufficient to account for it being frowned upon without any spurious notions about unbalance.

However, I don't think there is any justification whatever for demanding it on the basis of balance..... That is basically BS.

When any person can plug in 1200W of heater on any 120V circuit, which is an unbalanced load by definition, there is no rational or sane reason for suggesting that a hundred milliamps of unbalance is dangerous and likely to cause a fire. Not unless the neutral is undersized.

While there are some failure modes which could impose 220V on that 120V coil, those failure modes will also smoke at least half of the 120V devices in the structure, so even those reasons are BS.

The transformer is the better choice overall, code notwithstanding.

Sparky_NY
05-11-2009, 06:40 AM
When any person can plug in 1200W of heater on any 120V circuit, which is an unbalanced load by definition, there is no rational or sane reason for suggesting that a hundred milliamps of unbalance is dangerous and likely to cause a fire. Not unless the neutral is undersized.



Pretty much what I was thinking. Your whole house is fed by a 220/240 circuit with a neutral, the service entrance. (as well as sub panels)

Also, lookup what a "multiwire branch circuit" is, its 240 with a neutral and very commonly used in houses. Commercially, its the norm to run 3 hot wires with one neutral to provide 3 different 120 circuits, some inbalance being the norm.

The neutral carrying any inbalance is a normal occurance, no harm done provided its sized properly. It is good practice to attempt to balance the loads between the different phases but that is for another reason (the loading on the power companies transformer)

J Tiers
05-11-2009, 08:47 AM
Yep, in europe it is different, they apparently routinely drastically undersize the neutral. So there, balance can be very important, and the added harmonic current of certain types of power factor loads can severely strain the neutral.

But the grounded conductor (neutral) must , in the US, be the same size as the "hot wire", for branch circuits. For the normal 120/240 20 amp circuit, that is easy, use the same 12 ga wire, which is rated for 30A (THHN type), but is never protected by more than a 20A branch circuit protection device.

Now, nobody ever said the electrical code has to make sense. So some provisions, and some ADDED provisions in certain locations by the Authority Having Jurisdiction (the local podunk town, county, etc, aka the "AHJ"), may be more restrictive, or LESS restrictive, for any number of special reasons.

Use the control transformer, or a 220 coil, anyhow. It's a good idea. It tends to ensure that the controls drop out and shut down the load in case of power failure on the motor circuit, so it won't restart unexpectedly when the breaker is reset.

gnm109
05-11-2009, 10:45 AM
J
The stove people have their own lobbiests for the code.
It's even specifically covered in the NEC, unlike other home stuff
Yes, they now do use a 4 wire for new installs.
They may have transformers too..but I don't know about that
Check local codes fellows. Here in Green bay, it is not legal to use the neutral on your 220 lathes or mills, or for rotary convertors.
they are classified as appliances/tools
Fires have started from mere neglible loads.

GMN 109
Take the control box apart and record the wire runs.

Rich

This is a photo of the hookup diagram for my phase converter. It doesn't use the neutral at all. In fact, I'm hooking it up right now and I'll have to call the manufacturer and ask them what to do with my single phase neutral.

The way it was explained to me is that the unit contains a voltage sensing relay. When power is initiated to the converter by closing the two pole switch, the relay closes and starts the unit. Once the idler motor spins up, the relay drops out and the unit runs until power is cut off. You might call it a bootstrap circuit.

That's what I know at this point.



http://i144.photobucket.com/albums/r188/gnm109/RotaryPhaseConverterXX.jpg

Jeffw5555
05-11-2009, 01:01 PM
Voltage ratings:

Just my opinion but:
For balancing legs, try to use amperage instead of voltage.
I have used both.
Voltage is "potential", while amperage is "power" and more closely reflects true performance, as the wave form is not a sine wave

Rich

Not to nitpick, but amperage is not "power". The voltage x amperage in-phase is power. I measure voltage because it is easier.

Ideally, you would measure voltage, amperage, and phase ratio (power factor) to choose the optimum balance. (I have all the equipment to do so; a Tektronix 7904A set up with multiple plugins)

But this would be of dubious value, because most motors used for HSM purposes run fine without any run capacitance at all...... :D

Carld
05-11-2009, 01:21 PM
gnm109, I use the same circuit for my home made rotary convertor and it has been used for about 25 years by my friend before me and now me. I don't use balance caps and never have.

I have a neutral run through the panel just for the pony motor on 120v but it is only connected to the pony motor. You don't need a neutral for the rotary convertor or the 3 ph motors it runs.

You do need a mechanical ground on everything.

gnm109
05-11-2009, 08:16 PM
gnm109, I use the same circuit for my home made rotary convertor and it has been used for about 25 years by my friend before me and now me. I don't use balance caps and never have.

I have a neutral run through the panel just for the pony motor on 120v but it is only connected to the pony motor. You don't need a neutral for the rotary convertor or the 3 ph motors it runs.

You do need a mechanical ground on everything.


Are you talking about a fourth wire for a mechanical ground?

Carld
05-12-2009, 12:06 AM
Yes, a green wire from the service panel to everything in the circuit and ending at the machines. It will run from the panel to your disconect for the RPC then to the machines.

220 v does not need a neutral, only the two hot wires and a green mechanical ground wire.

There is two terminal bars in the service panel, one for the white neutral wires and one for the green mechanical ground wires. Don't mix the two.

Rich Carlstedt
05-12-2009, 01:11 AM
However, I don't think there is any justification whatever for demanding it on the basis of balance..... That is basically BS.
.
Hey J, your knickers are in a twist.
I never said balance justified it !
I said
"Fires have started from mere neglible loads. "

You have a guy wiring up his motor with 30 amp breakers and no control circut fuse---if you want to tell him it's OK, go ahead.Just don't pass it off as BS !

We can tell people here anything because they don't know us.
I prefer to advise them to stay safe.

You hear all kinds of things here, and it doesn't make them right.
An earlier poster made claims that amperage is not power, he probably never bought a car battery. His answer puts a 12 volt motorcycle battery in competition with a Diehard for your truck.
Life is silly enough guys, without the nit picky crap getting in the way and folks trying to show off.
The man asked for help..answer his question!
Rich

Rich Carlstedt
05-12-2009, 01:23 AM
GMN 109
Your start relay will be a 240 volt relay ( not 120)
When you turn power on, it is in the normally closed mode.
It does not operate until the volatge climbs to ~180 Volts, Then, it closes ,which really opens the Starting Cap circut .

The most effective relays for 3 phase convertors is a timing relay.
I have worked with voltage, and amperage controlled, and the best
is a timer, as it allows you to make adjustments very easy based on
Cap capacity. You generally need a 0 to 5 sec relay with most setups being effective from .5 to 1.5 seconds of time .
Timing relays however are not good if you use them for differential motors,
ie, a 3/4 HP and a 2 HP using the same control.
They are ideal for rotaries as the load for start never changes.
Timing relays generally have small contactor ratings and require an auxilary relay,
but I have used neumatic timers that could handle 40 -50 amps without burning
Rich

J Tiers
05-12-2009, 08:46 AM
Any 220/240 appliance must NOT use the neutral as an unbalanced circut exists. It automatically means one leg will have a higher amperage loads than they other.

Sounded like a balance argument.........

I must have missed the 30A breaker issue here, I looked in the thread but could not find it. What was it?

As far as negligible loads, fires can start from anything that heats up combustibles sufficiently......... obviously..........

But any proper neutral won't be affected by a tenth of an amp, it is designed to carry 200 times that (20A circuit).

I have no problems with proper advice. There is so much total crap on the 'net, sanity is needed somewhere. And often (usually?) the full story is not told by the person asking the question.

However, if a reason is given (instead of just "the NEC says so", which obviously is actually totally sufficient), it should be a GOOD and TRUE reason.... let's don't "cry wolf". :)

Jeffw5555
05-12-2009, 12:53 PM
You hear all kinds of things here, and it doesn't make them right.
An earlier poster made claims that amperage is not power, he probably never bought a car battery. His answer puts a 12 volt motorcycle battery in competition with a Diehard for your truck.
Life is silly enough guys, without the nit picky crap getting in the way and folks trying to show off.
The man asked for help..answer his question!
Rich

Please don't try to belittle others when you have little knowledge of the topic of which you speak. Perhaps if you read up on the definition of electrical power you will come to understand that I was attempting to build your knowledge on the topic, not trying to get your "knickers in a twist". :p

You made an incorrect statement by claiming "amperage = power", 'nuff said. If you do not like being corrected, please become more informed or live with being corrected.

Since you brought it up, you also don't quite grasp the concept of power with respect to lead acid batteries, so I feel obliged to build your knowledge base. :D Theoretically, a motorcycle battery could be built to deliver the same amperage as the Diehard you mention. Yet the motorcycle battery wouldn't be able to start a car. Why? Because the voltage drop would be so great with the motorcycle battery, that the power delivered to the starter (remember, I said that power = Amps X Volts) wouldn't be enough to start the car.

But that is DC, which is simple. AC is a whole different game with phase ratios. I don't want to go there.

Steve Steven
05-12-2009, 06:51 PM
Well, I finaly got the rotary converter running. At first, I used the two run caps as the start cap with them in parallel to give 100mf. This worked fine, started every time.

Then I happened to touch a ground and the case at the same time and got SHOCKED!

I knew this was a problem, and finally tracked it to a to-tight clamp on one of the output wires (T3), shorting the lead to the case. Got that corrected, and very carefully checked it again for voltage on the case. Found 28VAC on the case, and cannot figgure where it is coming from. Grounded the case, and it went away with no effect on the operation. I had been operating without a ground, since the incoming wire has a neutral but no ground.

I will tell Bill it is ready, and he can operate it without balancing caps, the T3 leg operates at about 180VAC.

Thanks for all the help, guys, I appreciate it!!

Steve Steven

Rich Carlstedt
05-12-2009, 07:38 PM
J
The 30 amp refference was in the very first post of the thread--Rich

Jeff
I am not trying to belittle anyone, you were the one to take issue with
the amperage comment before I had any response to you.
You are be-littling sir by assuming I know nothing about the subject.
I have built close to 60 single to 3 phase convertors.
I have built kick start, auxillary motor start,manual start convertors , and automatic ones with timing relay start, voltage relay start, amperage relay start, and even 240 single to 480 Volt three phase systems.
I have gone from 1/2 to 11KVA systems and have done this since 1963
When I offered help to the poster, it comes with real world experience.
I don't know what your qualifications are Jeff, but please do not make assumptions based on dictionary definitions.
This Board is to help people , not confuse them

Rich
PS
The definition of voltage is "Potential"
Voltage never does anything....without amps

Jeffw5555
05-12-2009, 09:17 PM
Rich,

I did not "take issue" with the amperage comment; I corrected you. That is an important distinction. If your goal is to "not confuse people", then you shouldn't say incorrect things.

Furthermore, you stated afterward that what I said was "not right", and implied I didn't know what I was talking about, using a comparison with batteries....

You may have built many, many RPC's, but you have obviously built them by trial and error, not because you understand electrically what is going on. (Let me state that I have nothing against this type of experience; you have given, by a large degree, good advice towards this topic....)

FWIW, I have a degree in electrical engineering (MSEE), and have designed a wide range of devices, from consumer to military applications. The reason I give "dictionary" terms is because they are correct.....

J Tiers
05-12-2009, 10:35 PM
J
The 30 amp refference was in the very first post of the thread--Rich


Ah, yes, ther is no fuse in the control circuit, a fact which I did miss in examining the circuit for basic functionality as a converter.

THAT I will definitely agree is an issue, the more so because I will wager the wiring in that circuit is not 30A rated.

While we are discussing it, I didn't mention the matter of the base of this device to be, apparently, plywood. I don't care for plywood as a base for electrical stuff.

And, the issue of the shocking... that is another matter of concern.


I had been operating without a ground, since the incoming wire has a neutral but no ground.

More than a little eye-opening............. about the small matter of electrical safety at that location.

gnm109
05-12-2009, 11:13 PM
I got my Webb Mill fired up today for a test using a 5 hp RPC that I bought fron an online seller. I verified that I have a good mechanical ground all the way into the machine and after checking all of the wiring from the subpanel to the 3 hp Mill motor, I switched it on and it came right up. A quick check of the motor rotation using the drum switch and I verified that the directions are correct. It rotates clockwise in high range and counter-clockwise in low range like a typical Bridgeport replica. It's necessary to use reverse on the drum switch to obtain correct cutting rotation in low range but you all probably know that.....being uninformed and slow-witted, I learn something new every day. LOL.

I built a stand for the RPC from 1-1/2" angle iron to get it up off the ground and also to make it easier to reach to turn on when using the mill. With the RPC bolted directly to the stand the idler motor was rather noisy. The frame amplified the noise quite a bit.

For test purposes, I unbolted the four 5/16" bolts that were holding the motor to the frame and set it on a rubber pad. Voila, all I hear with the rubber cushion is the whine of the motor which is not unpleasant.

I've located a set of vibration insulating mounts at a local rubber products company. Once those are installed the noise should be acceptable. They are basically just rubber blocks with 5/16" studs on each side.

My RPC has a large idler motor with an 8" X 8" X 4" covered metal box connected to it. Inside the box there is a relay with a 150 mf start cap and two 50 mf run caps, at least according to the company. There is no neutral connection, only 220VAC to L1 and L2 with a ground. Once started, L3 is generated by the idler motor, or so I'm told. I plan on eventually testing the voltage at each line but for now, I'm good.

This has been a very helpful thread. I hope to be making chips very soon. Thanks to all.

Carld
05-13-2009, 02:32 PM
I used a wood base with four lag bolt leveling screws to set my RPC on and it is as quiet as it will get. They tend to have noise issues anyway.