# I need a Prestolite motor stat



## grouster (Nov 20, 2008)

Hello

I've been lurking here for a bit and thought I'd join in on the fun. I was given a motor from a friend at work for doing some gun repairs, after mentioning that I wanted to try my hand at a small EV build, and would appreciate any help on getting the motors specs.

It is a Prestolite 36V permanent magnet drive motor from a 1974 Sears electric lawn tractor Model# 917.25790 ...
I can't read all of the motors tag, part no. M*G-4001-*5 it also has 663 A97 in another box.
It is 5.5" dia and 8" long, not including a 1.5" long slotted shaft.

It has the standard four brushes, but three power connectors. I was told that 1 was ground, 1 was power and the 3rd was starting power under a different timing to give it better starting torque ?? He used the tractor for years to pull boats at a marina and said he could out pull a gas 10hp John Deere, so I'm guessing 2HP ?

I have an old Honda that I've taken the dead ice out of, and want to start a 48-72V build this next spring for fun. Any ideas on what I have, or its RPM or HP specs???


----------



## major (Apr 4, 2008)

grouster said:


> It is a Prestolite 36V permanent magnet drive motor from a 1974 Sears electric lawn tractor Model# 917.25790 ...
> I can't read all of the motors tag, part no. M*G-4001-*5 it also has 663 A97 in another box.
> It is 5.5" dia and 8" long, not including a 1.5" long slotted shaft.


Hi grouster,

Yeah, I know a little about that motor. Likely part number MPG-4001.



> It has the standard four brushes, but three power connectors. I was told that 1 was ground, 1 was power and the 3rd was starting power under a different timing to give it better starting torque


If one terminal is ground, use the other 2 for power. There would be no connection for extra torque.



> I have an old Honda that I've taken the dead ice out of, and want to start a 48-72V build this next spring for fun. Any ideas on what I have, or its RPM or HP specs?


That motor would suck big time for anything bigger than a lawn tractor. It was 36 volts. You might get away at 48. Probably has a speed about 4000 no load and 3500 loaded. My guess is about 3/4 hp rated. Not good for over loads. You want to do a car EV conversion, get a larger wound field motor.

Regards,

major


----------



## grouster (Nov 20, 2008)

I should have stated it was a 450 Honda motorcycle not a car lol. Still, maybe it is still too small for that also. Do PM motors use the same controller as series motors do, or are there better controllers for them?


----------



## canthony (Jan 15, 2009)

Grouster, is it this motor:
http://www.surpluscenter.com/item.asp?UID=2009011513225259&item=10-1899-A&catname=

That is, supposedly, an MKF 4001. Those are rated at 2.7HP there, so if that's the case I imagine it would do well enough for a motor cycle. 

Let me know if you find a spec sheet on that, I'm looking for one for myself too.


----------



## major (Apr 4, 2008)

grouster said:


> It is a Prestolite 36V permanent magnet drive motor from a 1974 Sears electric lawn tractor Model# 917.25790 ...
> I can't read all of the motors tag, part no. M*G-4001..


Hi grouster,

That would be MPG-4001. Prestolite made a lot of great motors back in those days. Unfortunately, this was not one of those good ones. In fact, it sucks in my opinion. Surprises me it still runs. And that the previous owner liked it. Oh well. I suspect the thing has a rating of about 1/2 hp at 36 volts, maybe good for 3 hp peak, only for a short time. It used a shell commutator having thin copper segments. A little too much current for too long will melt the plastic under the copper on the comm. It also has pretty small gauge wire in the armature. With those big ceramic magnets, heat has a hard time getting out of the armature. I'm guessing it has a no load speed of maybe 3500 RPM. PM motors don't overspeed like series motors, so hook up a battery to it and measure the speed. Just do it at 12 volts and multiply by 3 for 36 volt RPM. And then RPM will sag under load. Again, a guess, it might be good for like 20 amps on long runs, an hour or so, and maybe 50 amps for a few minutes.



> It has the standard four brushes, but three power connectors. I was told that 1 was ground, 1 was power and the 3rd was starting power under a different timing to give it better starting torque ??


I doubt that. It only has the 4 brushes, so no timing issue there. My guess is 2 for power and 3rd is a ground. You should be able to verify with a continuity checker.



> I have an old Honda that I've taken the dead ice out of


A Honda car? Forgetaboutit. Not with this motor. 

It might last a while on a small lawn tractor (propulsion only) or bike, but nothing bigger, or fast.

Regards,

major

edit...I thought this looked familiar. Guess I answered it twice now. Just saw the first post when I clicked on it.


----------



## major (Apr 4, 2008)

canthony said:


> Grouster, is it this motor:
> http://www.surpluscenter.com/item.asp?UID=2009011513225259&item=10-1899-A&catname=
> 
> That is, supposedly, an MKF 4001. Those are rated at 2.7HP there, so if that's the case I imagine it would do well enough for a motor cycle.


Hey canthony,

Prestolite made a lot of different motors over the years. This MKF is another example of a "not so good one". I'd stay away from it. It is 2 or 3 times better than that MPG, but still a bad buy. You are much better off getting a modern golf car motor. They can be had for less money, like off eBay. You'll still have mechanical issues with it not having a bearing at the drive end.

major


----------



## Qmavam (Aug 17, 2008)

major said:


> Hey canthony,
> 
> Prestolite made a lot of different motors over the years. This MKF is another example of a "not so good one". I'd stay away from it. It is 2 or 3 times better than that MPG, but still a bad buy. You are much better off getting a modern golf car motor. They can be had for less money, like off eBay. You'll still have mechanical issues with it not having a bearing at the drive end.
> 
> major


 Hi major,
I have one of the MKF 4001 motors, I was surprised to see it only has two
field coils. It has four poles but only two coils.
I was hoping to use it on a gokart.
Mike


----------



## major (Apr 4, 2008)

Qmavam said:


> Hi major,
> I have one of the MKF 4001 motors, I was surprised to see it only has two
> field coils. It has four poles but only two coils.
> I was hoping to use it on a gokart.
> Mike


Hi Mike,

Yeah, the two poles without coils are called consequent poles. It is still a 4 pole motor. It might do o.k. for a G-kart.

Regards,

major


----------

