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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

US Motors AA21A Generator


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  #1  
Old 10-10-2018, 01:57:30 PM
JohnFM JohnFM is offline
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Default US Motors AA21A Generator

Any of you folks here know the color codes or have a wiring diagram for that old AC Generator?
TIA for any help.
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Old 10-10-2018, 09:38:00 PM
circuitman circuitman is offline
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Default Re: US Motors AA21A generator

is this a gas powered unit? i have a US motors unit, runs good but smokes a lot. really old!
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Old 10-11-2018, 07:10:13 AM
JohnFM JohnFM is offline
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Default Re: US Motors AA21A generator

It's driven by a Briggs ZZ built 7/44.
Yeah, it getting old, almost as old as I am.
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Old 10-11-2018, 11:24:16 AM
JohnFM JohnFM is offline
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Default Re: US Motors AA21A generator

This generator has 4 leads. Green, Black, Red, and bare ground.
This morning I checked voltage at the Red and Black leads again. They're the same. All I can figure is that 2 separate circuits could be run for a total of 13 Amps.
Nowadays that doesn't sound like much, but when this thing was built, that was a LOT of electricity.
My house was built in 1947 and it had ONE outlet in the Kitchen.
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Old 10-11-2018, 01:02:23 PM
Joe Romas Joe Romas is offline
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Default Re: US Motors AA21A generator

Or the 2 seperate circuits output 220 volts maybe??
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Old 10-11-2018, 01:46:02 PM
JohnFM JohnFM is offline
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Default Re: US Motors AA21A generator

Possible. If it was newer that's what I would think, especially with the wire colors.
The plate on the generator reads 115 volts at 13 amps.
Maybe there was another version for 230 volts or 115/230.
I dunno.
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Old 10-11-2018, 02:09:13 PM
Vanman Vanman is offline
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Default Re: US Motors AA21A generator

It's also possible they brought out the DC from the exciter...

Open up the brush cover and have a look. Should do that anyway to make sure everything is clean and all of the brushes move freely in their holders.

There should be two collector rings and a commutator. The two solid collector rings are the AC output, and the segmented commutator supplies DC for the field (excitation).

Follow all of the wires to see where they go, maybe post some photos.
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Old 10-11-2018, 02:20:11 PM
JohnFM JohnFM is offline
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Default Re: US Motors AA21A generator

Yeah, I've had it all opened up to see how things looked inside.
I have it open now trying to figure out where the ground wire was connected.
The end that went inside the generator looks like it was never connected to anything. Don't really know why it wasn't hooked up if they had it installed.
I'll try and get some photos of the internal guts.
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Old 10-11-2018, 04:54:21 PM
JohnFM JohnFM is offline
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Default Re: US Motors AA21A generator

As can be seen there are brushes on all 3 places. It's all still pretty clean in there except for a little corrosion showing on the brush holder springs.
All 6 brushes look like they have a lot of life left in them.

Just taking the covers off is about as far as I want to go. Don't really want to disassemble the thing.

One thing I can't find is where that ground wire that was with the leads coming out might have been attached. I figure there must be a place on the main framework somewhere, but I sure can't find it.

I think I'll run a ground wire from the receptacles to the breaker box ground buss, then to the #9 wire attached to the generator mounting plate, and from there out to a ground rod and see if that shows a correct ground on my tester.
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Old 10-11-2018, 10:08:07 PM
K-Tron K-Tron is offline
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Default Re: US Motors AA21A generator

John,
My AA21 says that it is rated 115volt, 13 amp @ 1800rpm. I have not seen these set up for 230volt before. That sure is a nice picture you uploaded. Your generator is nice and clean inside. I was not aware that it had a DC output of any kind. It is not mentioned on the nameplate, and the engine sure does not need any DC current to run. I wonder if the generator can excite and start the engine if a 12v battery is connected. I did nothing to my generator other than spray the valves with oil, lube the cylinder and add some light oil to the generator grease cups.

Chris
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