Generator only runs with engine on

[MDalton43]

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 :?

[Bobbo]

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.)

[LittleBill]

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.

[Rvpapa]

Where does the generator get its fuel from?
Art

[MDalton43]

BTW the RV is a Class C 2008 Georgie Boy Maverick 32 FT

[CA_Traveler]

BTW A $20 digital volt meter would go a long way is isolating the problem. Maybe less at Harbor Freight.

[MDalton43]

Thanks for all the replies. I’m going to work on it Friday. After reading everyone’s post it is leading me to the coach batteries. I will let you know what I find out. The fuel pump AC/DC power “paraphrasing” would answer why it runs for 10 mins then stops. I think it’s something to do with the battery disconnect switch file the house batteries n them being dead. Thx everyone!!!

[ajriding]

I don't want to say right off that your coach batteries are dead. How old are they? There are other issues that could come up including corrosion, or loose battery connectors that will cause good/charged batteries to not power anything. Sometimes corrosion is not so obvious either, just a light film of corrosion on the battery terminal can prevent current from flowing. Ask me how I know..
Clean the battery terminals and the clamps and charge the batteries if necessary.
If batteries are over 6 years old then suspect that they are getting old, of over 8 or 9 then likely they are just dead from old age.
Check the water level in the batteries, have you ever topped them off with distilled water? They could be dry.

Most generators put out some 12 volt DC power, but not necessarily all of them. The 12v they do put off is not a lot, but should be enough to keep a battery topped off, yet not enough to do a good charging - or should be enough to provide the fuel pump enough power to run, but again, not necessarily and completely dead batts could negate this.

Yes, the RV's battery charger/converter should provide plenty of DC power to run everything even with a dead battery, but if the battery (batteries?) are wired some way then maybe not.

The vehicle motor running means there is DC power provided across the battery terminals or connectors, and this is from probably a 90-130 amp alternator, so power is available, and much much much more than what the gen puts out. Your issues is from a lack of DC power, but track down the easy to fix, free to fix possibilities first before buying new batteries.
Even if you have new batteries, if you let them go completely dead, then you likely will need new batteries. True deep cycle batts can go dead and be charged again, but to go dead and stay dead for weeks is not a good thing.

[pianotuna]

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

[CA_Traveler]

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 battery

Yes 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.

[wa8yxm]

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 this

House battery---Fuse or breaker---Switch---Everything in the house (With a couple possible exceptions)

"Everything" includes the generator
If 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 pump

Shut 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

[enblethen]

Check your chassis battery disconnect

[wanderingaimles]

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