Generator &12; vdc output

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Bad Wolf

Minister of Fire
Jun 13, 2008
523
Eastern CT
During the last round of power outages my generator got a good work-out. Since it didn't already have one I decided to install an hour-meter. I figured the simplest place would be across the 12 volt dc output. When I tried it wouldn't work, so I put the volt meter on the output and got zero. Popping the panel out I started working backwards and found that I had voltage on the other side of the circuit breaker, but it was only 8.1 volts. The circuit breaker is supposed to be a self resetting kind so I guess it might have failed. Shouldn't be too hard to find another 12 volt 10 amp breaker to replace it with.

With the hour meter hooked up to the other side of the breaker (which is where the schematic shows it anyway) it worked just fine.

But..... doesn't 8.1 volts seem low? Or is there something weird about outputs on generators? The schematic shows a rectifier so its probably the crudest square wave. I seem to remember reading somewhere that this was an unregulated output and should only be used to charge batteries. I'm assuming its doing that properly because in over 50 hours of use it always cranked over (its electric start) and just like a car if it wasn't charging the battery as it ran it would eventually run down.

I'm just puzzled by the low reading, can anyone explain this?
 
I would only trust a multimeter, I am assuming the 8.1v is what the meter says when its running?

I know the generators I have put out supposedly a very rough wave. The manual says only good for charging batteries.

Chances are the meter isnt getting the peak voltage, all depends on how its sampling. As long as the meter reads the hours, I wouldnt pay attention to the volts.

It could also be watching a 6 volt line that is getting a bit overvoltage.... but i bet not.
 
The battery acts as a huge capacitor, smoothing the voltage. The generator, as you said, puts out pretty rough voltage. Since the breaker is bad, you're not connected to the battery. I bet the voltage readings look more normal once you are connected to the battery again. maverick06 is right, the meter is getting confused. The rectifier is putting out ½ wave AC, and the meter interprets that incorrectly.
 
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