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Old 09-21-2014, 04:17 PM   #1
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Dash battery light

I have a gas class A with a converter. When traveling if I start the generator to power the air conditioners, refridgerator,etc the dash battery light will come on after just a few minutes. What wood be causing this?

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Old 09-21-2014, 06:53 PM   #2
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You didn't mention the make and model of generator, so its hard to be very specific.

The generator typically draws 12v power from the chassis system for starting and its fuel pump, but is supposed to be self-sustaining after it begins running. Does the coach and generator engines die if you leave it running that way? Might take awhile, but those dash "idiot" lights usually indicate a negative amp flow from the engine battery, so they will probably die after a while.

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Old 09-21-2014, 07:44 PM   #3
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It is a Onan 5500. I've never let it run long enough to see if they die. What would cause a negative flow?
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Old 09-21-2014, 08:19 PM   #4
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I've never been able to verify the configuration of an "alternator failure" light, but I think it is a diode circuit that illuminates the light when the battery voltage exceeds the alternator output voltage by some minimal amount. When running just the main engine, I understand, all is well. When you start your auxiliary generator the light comes on. That tells me that the aux gen is feeding the converter (after a short time delay) which in turn is charging the chassis battery at a voltage that is greater than the alternator output. You can test all of this by putting a large load on the battery when the Alt light comes on. Headlights, heater high speed fan, etc.

I don't know your coach's electrical system but I don't think the generator should charge the chassis battery until the coach batteries are fully charged. So look for crossconnect between coach and chassis battery, like the auxilary start circuit.

Hope this helps. Let us know what you find.

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Old 09-22-2014, 07:15 AM   #5
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I think the alt. light is designed to have 12V from the battery on one side of the bulb and 12V from the alternator on the other side. There is a shunt to provide a ground circuit. If the alternator voltage drops it allows the battery voltage to ground through the shunt and lights the bulb. If the convertor is providing power to charge the chassis battery with a BIRD system, or similar, and it is higher than the battery voltage, could light the alt. light. I would try running the engine while plugged in to shore power and see if the light comes on. Also check the AC voltage from the generator and DC voltage from the convertor when plugged in and also with the generator. Maybe the generator is to high.
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battery, dash

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