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Too_Many_Tools
09-23-2010, 01:56 AM
I was just looking at a number of different cordless drills...all different voltages.

While I understand that the battery packs differ by the number of cells they contain, are the motors in the different drills really different?

Do they vary by windings or do they use dropping resistors to adjust the voltages to a common motor?

TMT

macona
09-23-2010, 02:07 AM
Yes, motors are different for a given voltage. Higher the voltage the higher the turn count and lighter wire. If they used resistors you probably wouldnt be able to hold on to it after a couple minutes.

darryl
09-23-2010, 03:37 AM
It isn't an absolute requirement that the motor changes when the battery voltage goes up. I have a pair of drills with the same motor, one is 12v, one is 14.4v. The motor turns faster on the higher voltage pack. I haven't compared gear ratios, but the gears could be the same also. The change is increased rpm at the chuck, and more torque from the motor- but also a higher current drain from the battery.

Those motors range from 3 slot armature hobby motors to industrial quality 12 slot, fan cooled, high strength ferrite magnet motors with flux augmenting ring. I have not yet seen a cordless drill motor with ball bearings, but most have planetary gearsets so there is no real side loading on the bearings anyway.

There is no resistor between the battery pack and the motor, since the resistor would get very hot very quickly. In the trigger is an electronic chopper circuit which varies the duty cycle of the pulses sent to the motor. At the full pull of the trigger, a set of mechanical contacts shorts the speed control circuit so full battery voltage can appear at the motor. This is interesting- if you don't pull the trigger all the way, the speed control circuit has to pass all the current the motor wants, and it's often well over ten amps. The power mosfet can get stinking hot if you're torquing down screws at less than full speed. Some people have that habit of using less than full trigger for the entire time that a screw is being driven. That's hard on the drill. Better to give full pull, then ease up just for the last second or two to stop at the right spot.

The original question might have had something to do with 'can I up the voltage to my drill without hurting it' (something I would try, and have many times :)) Yes you can do that- the motors are pretty rugged basically, just watch that you don't overwork it. Most speed control circuits run a little better on 12 or more than they do on 7.5 or 9 volts, but if you want to run say 18 volts, that could make them fail. So far, all the speed control circuits I've seen use a 50v mosfet as the power device- I'm not sure if the 18 volt cordless drills use a higher rated part or not- possibly so.

Ok, well I went off on a bit of a tangent there-

The Artful Bodger
09-23-2010, 05:39 AM
I have a fairly old 7.5v battery drill that I put a cable on and it runs very happily on 15 to 20 volts but I am very careful not to stall the motor.

Boucher
09-23-2010, 09:25 AM
I have several of the old 9.6V Makita drills that we put a good 1/2" Jacobs chuck on and used to drill 2 3/8" holes with a hole saw in PVC. It was cheaper to buy a new drill with 2 new batteries than to just replace the batteries. The old drills were much tougher than the newer ones which had a keyless chuck and a clickson type overload. The old ones did not appear to have any overload protection. They had amazing torque and held up well. The only thing that has failed is the trigger switch on one. My 18V Dewalt just stripped the gears drilling a 3/8 hole in steel.

Too_Many_Tools
09-23-2010, 05:55 PM
I have several of the old 9.6V Makita drills that we put a good 1/2" Jacobs chuck on and used to drill 2 3/8" holes with a hole saw in PVC. It was cheaper to buy a new drill with 2 new batteries than to just replace the batteries. The old drills were much tougher than the newer ones which had a keyless chuck and a clickson type overload. The old ones did not appear to have any overload protection. They had amazing torque and held up well. The only thing that has failed is the trigger switch on one. My 18V Dewalt just stripped the gears drilling a 3/8 hole in steel.

The 9.6v Makitas have a very good reputation.

I did not know that the newer ones were less than the old ones.

The 18v Dewalt had a good reputation...till now.

ANyone want to weigh in on this?

TMT

Too_Many_Tools
09-23-2010, 05:57 PM
Anyone have any opinions of what cordless drill motors would work great for HSM projects?

I am starting to see a lot of cordless drills surplus because the batteries are dead and it is cheaper to buy a new set.

TMT

Dunc
09-23-2010, 07:54 PM
Based purely on personal opinion (alright, bias)

I use my cordless drills for the routine stuff. If I want to do serious drilling I reach for a corded one. Have DeWalt, Bosch, Milwaukee. No prefs: whatever is closest & has a charged battery.

kf2qd
09-23-2010, 08:10 PM
My son and wife got me a Makita Impact & Hammer Drill combo 2 Christmas's ago and they are both workhorses. 18V Polymer batteries and they hold up great - so far. I have an 6 year old DeWalt Drill that I used to rebuild a house in indiana, only problem with it is the batteries won't hold a charge any more. Work well after charging, but a couple days later it's dead. What I liked about the DeWalt is that it is a 3 speed while the newer Makita i have is only a 2 speed. Oh - and the Makita has the Hammer feature that has been used to put oak thresholds on the concrete floor here in Texas.

The impact is the greatest thing when driving long screws into hard wood, and working on lawnmowers... Got the Harbor Freight socket adapters and use them often.

aboard_epsilon
09-23-2010, 08:27 PM
I've got a couple of 9.6 volt makita's and love them ..they are good drills ..i did have three up to two weeks ago :(

i also have a Bosch 24 volt one and hate it

because despite it being 24v has less power somehow than the makita

it has a torque ring behind the chuck.........but no place on it for full power without the torque limiter.

so on its highest torque setting ..its got less that the makita, that has a position without torque limitation ..so you never get to use all the power on this Bosch. stupid ...it can barely drive a screw fully home .

so, if you're looking for drills ..this is something to look at.

all the best.markj

Boucher
09-23-2010, 08:54 PM
Eventhough I trashed the Dewalt 18V, I think it is one of the better drills now avaliable and bought another one. The cordless were so much more convenient in my work. Now I am finding that the corded drill works better. Most of mine are also Mikata. The old 3/4" B&D still is the go to when things get hard to turn. It has slapped me silly a couple of times which teaches you to have a good hold on things when you punch the trigger on a big drill.

Fasttrack
09-23-2010, 09:12 PM
Instead of buying a whole new drill kit when your batteries die, why not have them rebuilt?

There is a "Batteries Plus" store near my parents' house that rebuilds cordless drill batteries for about 30 bucks. You get the old housing back with new cells. I had a Milwaukee 12 volt drill battery rebuilt and I also bought a replacement (about 60 bucks). The rebuilt one had a higher ampere-hour rating and lasted longer than the new one. Within about 2 years, the one I bought stopped holding a charge, but the rebuilt one was still charging.

Too_Many_Tools
09-23-2010, 09:32 PM
Eventhough I trashed the Dewalt 18V, I think it is one of the better drills now avaliable and bought another one. The cordless were so much more convenient in my work. Now I am finding that the corded drill works better. Most of mine are also Mikata. The old 3/4" B&D still is the go to when things get hard to turn. It has slapped me silly a couple of times which teaches you to have a good hold on things when you punch the trigger on a big drill.

I know of several people who lost teeth when they did not respect their old B&D drill.

TMT

wierdscience
09-23-2010, 10:16 PM
3/4 B&D?Hehe we have a 1-1/4" B&D drill at work that gets used as a last resort.It carries a #3MT socket with two drive tangs.Seen it pick a guy off the ground while drilling some 7/8" holes in stainless:D

The problem I see with the new cordless drills is the mfg spends more on the gawdy plastic cases than they do on the gear heads and motors.

My most recent additon was a 1/4" hex impact driver.I bought it since 90% of the time I am driving screws and it will drill 1/4> holes in steel faster than a cordless drill.Plus it's lighter,smaller and lith-ion.

Dr Stan
09-23-2010, 10:18 PM
My favorite cordless drill is made by Bosch, in fact I have a matched pair of 3/8" 18 volt drill/drivers. They're great for carpentry work when I'm drilling pilot holes then running in screws. I blew out the clutch/gear train on one and was able to find a replacement on line.

You may want to look at what is offered at CPO tools.

whitis
09-23-2010, 10:41 PM
With a pulse width modulation (PWM) motor controller (used anyway for speed control) with current limiting you can use a lower voltage motor. If the same sized motor (regardless of voltage) is used on different models, though, you may not get much additional torque from the bigger battery pack though you should get longer battery voltage. You might also get some additional speed as the higher voltage can overcome the inductance and back emf of the motor.

The battery voltage is not necessarily an indication of how much energy the battery, let alone the drill, has. For a given battery type, the voltage is an indication of how many cells are wired in series but not how big they are. Your typical 24V drill battery does not have as much ooompf as your 12V car battery, for example. I have used cordless drills that had a waist mounted battery pack that was about the size of a motor cycle battery, though.

TMT, you might want to be more specific about your projects. I would warn that on many cordless drills, the plastic case of the drill itself is the structure for the gear train so you have some work to do if you discard it.

darryl
09-23-2010, 11:58 PM
Lots of uses for old cordless drills if you're into robotics, or you want to make an RC vehicle of some type. So many times I've thought to take two identical drills and make each one drive an axle directly with a rear wheel on it. You might use two speed drills and get a low range out of it-

You might throw away the cases and just use the gearbox and motor, which might mean having to find a way to mate the two together. Sometimes you won't need the case. Most drills these days have the planetary gearbox, and usually that mates to the motor. If yours has spur gears, you will need the case to keep it all lined up. You could just cut the handle off the drill to make it more compact.