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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

G.M. Power I-4632 no power output


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  #1  
Old 07-27-2014, 03:25:54 PM
Josephbookshed Josephbookshed is offline
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Default G.M. Power I-4632 no power output

I recently purchased a vintage General Motors genset. The version I have is the 2-71 Detroit, 30KW phone site backup. Generator is model I-4632. The old girl has been sitting unused in a barn for at least a decade.
I spent about a week checking out every possible issue with the engine, which included unsticking an injector to free up the rack, changing oil, filters, oil fuel lines, the 32 volt starter, reinstalling the muffler, etc. Finally fired her up yesterday and she purrs like a kitten.
Now I'm ready to get the generator active and, since the unit has been sitting so long, there is not enough (if any) residual magnetism in the iron to create voltage, so I need to flash the field to reactivate the generator. This is, of course, a brush unit and I don't want to cook something in the head, so I would like to know the best way to flash this particular unit.
I understand from reading here and other sites that normally one can apply DC voltage in the correct polarities to the F+ and F- leads to reactivate the system. That isn't an option here but I have attached pic of the field connection diagram showing the lead ID's. My question is, since one end of the shunt field connects to A1+ and the other end of the shunt coil connects to F2-, could I use A1+ and F2- to flash this unit. If so, should I use 6 volts, 12 volts, or more. I know someone out there can help me out! Thanks in advance!
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  #2  
Old 07-27-2014, 07:36:55 PM
pegasuspinto pegasuspinto is offline
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Default Re: G.M. Power I-4632 no power output

Might need more info, unless someone here just knows this thing. I searched for that part# generator and got links to a brushless unit with rotating diodes. What does the generator tag say exactly on what output voltage it is rated for? This absolutely does have a separate cranking starter bolted on, correct? Does the unit have a voltage regulator of any kind?

More pics of the unit would be good. One thing that strikes me is if this was a telcom unit, it would probably be able to flash itself. No point in a standby generator that may or may not make juice...
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Old 07-27-2014, 09:45:02 PM
Josephbookshed Josephbookshed is offline
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Default Re: G.M. Power I-4632 no power output

Got the info off the tag. Voltage is 208/240 or 416/480. KVA is 37.5
Excitation amps is 11.2 at 125 volts. The unit has an Allis-Chalmers Rocking Contact regulator. There is a starter motor on the unit. It came with a 36volt unit but I replaced that with a 24 volt unit. I can do more pics tomorrow. This is definitely a brush unit. I removed the guards to check for mice/rats/bees/wasps/etc. before ever rotating the motor so I can plainly see the brushes. To satisfy my curiosity, I put 12VDC on A1+ and F2- and the unit made 220V as long as I had power on those leads When I removed the 12VDC power, the unit stopped generating. I await further input from someone with more knowledge than I have.
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Old 07-27-2014, 10:22:23 PM
pegasuspinto pegasuspinto is offline
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Default Re: G.M. Power I-4632 no power output

If you flashed it and it made juice the generator is likely OK. I assumed you looked it over for wiring damage and mice modifications, etc. I think I'd start by cleaning any contacts on the regulator-you don't want to bend anything or stretch any springs as that will cause the calibration to change. Something like cut strips of paper sack-rough enough to clean but smooth enough that it won't remove tons of material or change the gap.
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Old 07-28-2014, 08:33:09 AM
armandh armandh is offline
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Default Re: G.M. Power I-4632 no power output

yes applying DC to the shunt field should get things going
the not shown rheostat will keep it going and adjust the voltage
the series field of the DC exciter and the varying load from the AC section field
makes the system some what self regulating.

should tighter [modern] regulation be needed applying it to the shunt field
instead of a fixed voltage from a rheostat would be easy
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Old 07-28-2014, 06:10:01 PM
Jim Rankin Jim Rankin is offline
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Default Re: G.M. Power I-4632 no power output

I have an old BUDA set with a similar RegOhm regulator and external exciter etc.

I found that the generator would not excite after sitting for a long time unless I switched it to manual regulation (the rheostat) and cranked the voltage setting to maximum. Once it built up, I could lower the voltage to the desired setting and/or switch it to automatic and it would be good from then on.

Of course, the first time I ever got it to build up, it had been sitting for many years and I flashed it with an external battery.

I would check any auto/manual regulator switch (if it has one) and the rheostat that would be in the circuit when switched to manual. Should also be able to ohm through the regulator to ensure there is a circuit through it.

One other thing, if you inadvertantly flashed it with reversed polarity, the regulator cannot pick up when you remove the flashing connection. Seems unlikely, but something to check.

Also it might help to apply some sort of load to the AC terminals while flashing it. This should really get some flux going.
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Old 07-28-2014, 08:04:47 PM
Josephbookshed Josephbookshed is offline
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Default Re: G.M. Power I-4632 no power output

So today I was looking over my genset trying to decide why it wouldn't make power. I opened up the rocking contact regulator, and even though I'd never seen one of these before this, something just didn't look kosher to me. Then I figured out that the needle point on the bottom of the rocker had been jarred out of the little cup that it is supposed to sit in, which kept it from making contact with the brass contact segments above the rocker. I put the needle point back in place, fired up the motor, flashed the fields, and the old girl started making power and kept making power, just like she is supposed to. I guess when the unit was being loaded/unloaded at the various spots she called home between the telecom site and my place, someone set her down a bit harder than she liked and jarred the rocker out of place. I now have a working Deuce-powered 30KW genset! Thanks for your help guys! Now if I can get the old Westinghouse steam engine behind my shop up and running, I'll be a happy camper.
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Old 07-28-2014, 10:09:38 PM
Jim Rankin Jim Rankin is offline
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Default Re: G.M. Power I-4632 no power output

Wow...That thing is clean and neat.

Never seen one with that kind of mechanism. The RegOhm and others I have seen have multiple fingers with contacts....very easy to bend something and change how it works if you monkey around inside there. The
AllisChalmers seems to be a more robust design....except for maybe that little cup
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