Onan generator running without issue while to Ford E450 motor is running. Turn the motor off the generator stops running any where between 5-15 mins. The generator will not start off the house/coach batteries. The motor has to be running. So I think it is safe to say the house/coach batteries are dead. But why would the generator stop running once started off the motor battery? The generator doesnt need the house batteries to stay running, correct? any help would be great! thx :?

What is the rig? Nobody with a similar unit can answer since you dont say what you are referring to.

Check your chassis battery disconnect

Will the generator CRANK off the house batteries? If the answer is NO then I have a SUSPECT.. And I stress suspect.Many RV's are wired like thisHouse battery---Fuse or breaker---Switch---Everything in the house (With a couple possible exceptions)"Everything" includes the generatorIf the fuse is blown or breaker tripped if the Switch is OFF.... Well then the house batteries are basically Absent with (Swich) or without (Fuse/breaker) Leave. NOTE in this case house lights. and such will also NOT work unless engine is running or plugged in So with engine running: Chassis electrical is "Bridged" to the house and powers among other things the generator fuel pumpShut the engine off. the generator fuel pump no no longer has power.However note.. this only applies if house lights ONLY work with engine running or plugged in ... That said. With the genny running ... the converter SHOULD supply power to the fuel pump... So .....NOTE this is only a suspect and not all that good of one

First step is to load check the batteries, free at most auto stores. Because weak batteries can cause various strange and unexpected problems. Your post seems to suggest the engine starts OK on the chassis batteryYes most/many gens do not generate DC but need DC for say fuel pumps etc. But their AC output is used for the charger to create DC for the batteries and lights etc including the gen that use DC. So engine off, weak battery voltage drops and gen quits as it should. Gen not cranking also suggests a battery problem, charger problem, wiring problem etc. My guess: The engine alternate charges both banks as it should. There can be a variety of reasons why the house batteries aren't being charged or barely charged and your post suggests the house batteries are not being charged from either the alternator or the gen/charger.

If it won't crank, have the house bank load tested (one at a time please, no shoving)

Generator only runs with engine on | Good Sam Community

LittleBill
Explorer
Nov 18, 2021
sounds like the onan onboard fuel pump is dead. or if the definition of doesn't start means not crank. then on the board charging system is not working/powered and the batteries are going dead killing the fuel pump as well.

for those of you saying the onan has a charge circuit, it doesn't, at least not on the 4k onan.
Bobbo
Explorer II
Nov 19, 2021
You folks need to read the entire thread.

OP says the ONAN will run as long as the chassis engine is running (providing 12v power to the fuel pump).

OP says the ONAN will run 5 to 15 minutes AFTER the chassis engine is shut off. That means the fuel already pumped up to the ONAN is being used up, but no additional fuel is being pumped (fuel pump is not running).

The upstart of this is that the fuel pump gets 12v power when, and ONLY when, the chassis engine is running. ERGO, no power to it from the batteries. Either the batteries are dead, the disconnect switch has them disconnected, or there is a blown fuse or break in the circuit between the batteries and the fuel pump.

(The ONAN doesn't have an alternator or generator because it depends on the batteries for its 12v power, knowing that the converter/charger is keeping the batteries charged.)

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