Generator stalls & main 12 volt circuit breaker trips

I can tell you why the generator stalls. but not why the breaker is breakering.

The generator uses 12 volt BATTERY/CONVERTER power for the fuel pump and for ignition control.. So if it looses the 12 volt feed due to the main breaker tripping, It's the same as pressing the OFF button. or turning off the ignition on your car.. It does not "Stall" it is "Shut Off".

But I have no idea why the breaker is breakering.. Possible converter issue. that is the only thing I can think of, is a converter issue.

Where exactly is this 12vdc breaker located?

is this a TRUCK camper or a TT with the generator option ?

the typical 12v thermal breaker auto reset on a TT is 40amps
if the charger/converter power is greater than that it will trip

if this is a class B or C
the generator might get starting power from the engine battery

Pull the shore cord and simply discnnect the 120V gen output toI isolate between 120V load vs gen/12V issue. What happens?

When operating the 12v just on the convertor (batteries switched off to avoid overcharging by the old style fixed rate charger) I can try starting the generator and it tries to crank but there isn't enough power to start it. That may be the condition causing your rig to trip the breaker. If I switch the fully charged batteries on, I can crank the generator with no problem even when it takes awhile to start.

I think the Onan generators need 12V to generate power, though typically I wouldn't think they'd be wired through the main house 12V disconnect as the generator starter motor takes a pretty large current.

If the batteries are low and the converter is a large unit and the wiring is low impedance, possibly the converter is trying to output more current than the 12V self-resetting circuit breaker is rated for. Possibly the circuit breaker is malfunctioning and kicking out at too low of a current. It would be helpful to locate it and see what the currents are (and what direction they are flowing) when the 12V supply goes dead.

It may also be that there's a fault in the generator circuitry. While a 120V overload could stall the generator, I don't see how that same overload could normally cause the 12V system to shut down unless there was also some other fault.

sounds like to me it might be shorted cells in the battery bank... But you say when on shore power both AC side and DC side (with batteries connected) works ok. Only happens when you start up the generator which switches the shore power transfer switch and selects generator to run the AC Distribution Panel.

Something not adding up here. The shore power and the generator feeds the same point depending on which position the transfer switch is in...

Keep in mind both the converter/charger DC output and the 12VDC coming from the batteries both feed the same point on the 12V Distribution Center... The 12VDC circuit breaker is only on the battery side...

Sounds like a big load is causing the the generator to trip out...

The only MAIN 12VDC Circuit Breaker I can think of is in-line between the battery and the 12V Distribution Panel mounted close to the battery terminals. Its purpose is to protect the wiring in case a cable short to frame ground.

This is a very simplified block diagram of the 30A AC and DC Power Distribution in a regular trailer setup... Might give you a clue...


Roy Ken

MrWizard wrote:
12v main circuit breaker ?

you have 12v power, until you start the generator ?

then this 'breaker' trips and everything goes black ?

are you on shore power ? how are the batteries charged

yes .. there is a load, the converter will come on as soon as the timer on the ATS kicks in, also possible is any switch that might accidentally be on, like water heater or fridge
a bad converter or two many items in the on position, will cause a small generator to stall, 2800 is NOT a large generator

Thank you for your thoughts. The inverter is in the "off" position so no instant load there. Refrigerator and water heater in off position. Microwave off as well. Water pump off. Air conditioner also off. What else is there? Yes, it is a small generator and I only run one load at a time. Not on shore power at the time. Yes, everything goes black, then a automatic resetting circuit breaker (I assume) cuts all 12 volt off. After about 5 minutes, 12 volt returns.

12v main circuit breaker ?

you have 12v power, until you start the generator ?

then this 'breaker' trips and everything goes black ?

are you on shore power ? how are the batteries charged

yes .. there is a load, the converter will come on as soon as the timer on the ATS kicks in, also possible is any switch that might accidentally be on, like water heater or fridge
a bad converter or two many items in the on position, will cause a small generator to stall, 2800 is NOT a large generator