2CM77 questions

e^2 said:

Does anyone know what a GE 2CM77 motor looks like? I believe that is what I have in this car I picked up. I tried googling lots of different ways but cannot find a picture of one and there are no numbers on this motor to help identify it. There is 4Awg on the E-, C+, with a small 10Awg on A+. It runs just fine this way but if there is another way to do it, I'm interested.

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From the terminal block, it looks like an old aircraft starter-generator. They were made by several companies to maybe the same spec. I've seen a number of conversions using them, mostly from 20-30 years ago. You'd likely have better luck searching for the Jack & Heintz version. There's been a few related discussions on this board. They're pretty rugged.

major

The numbers on it are all GE numbers and it has new brushes and assemblies. All I'm trying to do is get a different motor controller for it, a new lithium battery pack, and clean it up. As this appears to be a sepex motor I need to know if this thing is wired up correctly or not.

major said:

From the terminal block, it looks like an old aircraft starter-generator. They were made by several companies to maybe the same spec. I've seen a number of conversions using them, mostly from 20-30 years ago. You'd likely have better luck searching for the Jack & Hines version. There's been a few related discussions on this board. They're pretty rugged.

major

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Interesting - I had never heard of these.

By the way, it looks like the company is "Jack & Heintz" (makes searching easier).

e^2 said:

The numbers on it are all GE numbers and it has new brushes and assemblies. All I'm trying to do is get a different motor controller for it, a new lithium battery pack, and clean it up. As this appears to be a sepex motor I need to know if this thing is wired up correctly or not.

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Yes. Wiring and control is tricky. I believe it is a compensated shunt wound generator. But was used for cranking aircraft engines so able to put out high torque as a motor. I think there is internal schematic for the J&H version somewhere on the interweb and GE might be same. Not sure but I think Westinghouse also made a version.

Thanks Brian. Correction made.

major

Thanks guys. I agree, it does look to be complicated but I did find the original builder here! http://www.evalbum.com/204
I still need a diagram to hook this up so I'll check my local motor shop here in town and see what they say.

e^2 said:

Thanks guys. I agree, it does look to be complicated but I did find the original builder here! http://www.evalbum.com/204
I still need a diagram to hook this up so I'll check my local motor shop here in town and see what they say.

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You might try the EVDL. It was a long time ago but I recall helping a guy named Michael in Texas or OK get his J&H wired up correctly. There's others on that list who've used those genneys. Maybe a guy named Lee Hart will chime in. He knows his way around those. I think he is also a member here.

major

Thanks Major. I'll keep sleuthing around and see what I find. I got through some of the EVDL and found that one of the coils needs 28VDC to make it work. Currently, the motor is running on a DC PWM motor controller, it just has very little torque to get going. If I could just get an internal diagram for this I'd know what to do.

e^2 said:

Thanks Major. I'll keep sleuthing around and see what I find. I got through some of the EVDL and found that one of the coils needs 28VDC to make it work. Currently, the motor is running on a DC PWM motor controller, it just has very little torque to get going. If I could just get an internal diagram for this I'd know what to do.

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Yeah, that's the problem Texas Michael had. Running a shunt motor on voltage control starts it out with a very weak field meaning low flux meaning low torque. Solution was/is to separately excite the shunt field with about 30V. IIRC requires an internal wire relocation. Also because it compensated (compound) you need to get the series winding polarity correct.

major

I was thinking of just running a home built pwm box running on my intended 120VDC rail. The exciter seems to be lowish current.

Just because I was curious, I looked up the APU (auxiliary power unit) on a 737, which also has an electric start / generator. They use a Honeywell unit that is three phase, so not what I am doing at all. However, it does have an exciter circuit that just gets 18awg wire. The generator itself has a 2awg output just for comparison.

I'll start measuring currents and see what I can do.

I measured the voltage on the A+ terminal of the motor with the 14 awg wire. It is connected to the rail voltage at 96VDC. I didn't measure any current draw but the shunt was huge. Maybe the field winding is burnt out if it is supposed to be 30Vdc.

With the shunt fields of your motor burned out, maybe the compensating coils are acting as series coils, like in a series motor. They might be too small and out of phase with the brushes for the motor to work as a proper series motor. Could this explain how these aircraft generators seem to work with PWM controllers designed for series or PM motors, but with poor performance?

So I've done some soul searching, talked to Rich at http://www.manzanitamicro.com/ as he was the original builder of the car back in the 90's!

The motor controller for this motor is not your standard issue controller and the efficiency of this motor won't work for what I want to do with it, which is drive it.

So, i'm going to get a WarP 9" and a series dc controller and go from there. I'm not sure if this motor is going up for sale or not. I'm for sure going to document as much as possible about it so that if I ever do sell it, someone will know exactly what they are getting. Or maybe I'll make a go kart out of it. Who knows.