Generator only runs while Sprinter is running

[markopolo]

Originally Posted by GeorgeRa

............ Linking the starter battery replacement with the generator failure is rather unlikely, ...............

Generator hasn't really failed. It runs when it gets 12V when the Sprinter engine is running. Shutting off the Sprinter engine interrupts that 12V likely because there's an isolator or Separator.

LP solenoid etc. all work when 12V is present so no failed parts.

Starting battery and House battery are seen as one battery when combined by the separator so the generator sees 12V. Interrupt that 12V (turn off Sprinter engine) and the generator quits (lack of fuel as LP solenoid closes when 12V not present is my guess).

12V to the generator needs to be restored as Harry pointed out. Very likely explanation is that the House battery to chassis ground was removed as a safety precaution when the Starting battery was replaced. Or maybe they tested the House battery during the same visit.

12V still gets to the Coach systems because that wiring still present. (most) Coach systems don't require a House battery to vehicle chassis ground.

Missing House battery to chassis ground seems to be the most likely cause of this problem.

Edit: 12V path to generator now with Sprinter engine running:
(neg) Chassis to generator
(pos) Starter battery to separator to House battery positive to generator positive.

[GeorgeRa]

Originally Posted by markopolo

Generator hasn't really failed. It runs when it gets 12V when the Sprinter engine is running. Shutting off the Sprinter engine interrupts that 12V likely because there's an isolator or Separator.

LP solenoid etc. all work when 12V is present so no failed parts.

Starting battery and House battery are seen as one battery when combined by the separator so the generator sees 12V. Interrupt that 12V (turn off Sprinter engine) and the generator quits (lack of fuel as LP solenoid closes when 12V not present is my guess).

12V to the generator needs to be restored as Harry pointed out. Very likely explanation is that the House battery to chassis ground was removed as a safety precaution when the Starting battery was replaced. Or maybe they tested the House battery during the same visit.

12V still gets to the Coach systems because that wiring still present. (most) Coach systems don't require a House battery to vehicle chassis ground.

Missing House battery to chassis ground seems to be the most likely cause of this problem.

Edit: 12V path to generator now with Sprinter engine running:
(neg) Chassis to generator
(pos) Starter battery to separator to House battery positive to generator positive.

….and to continue Booster’s and your posts, perhaps installer indeed made a mistake and started changing "starting" battery from under the hood, disconnected the ground then realized it was a wrong battery and replaced the battery from under the floor but forgot to reconnect under the hood battery to the ground. All this while OP is MIA.

[hbn7hj]

Originally Posted by GeorgeRa

The attached document is old but likely still valid.

It always amazes me the knowledge you guys are able to dig up. I suspect the upfitter’s aux battery document holds the key to the solution.

Interesting that generator stopping could be caused by LP delivery failure rather than ignition failure. Probably caused by both depending where the LP solenoid is.

[markopolo]

Re: LP solenoid - Just for clarity, I'm assuming there's one on the generator itself. I'm not referring to one that turns LP on or off for the whole coach.

[DAWg134]

I suspect the installer disconnected the ground from the house battery when he replaced the vehicle's engine battery. Given that the two battery systems are interconnected by the battery separator whenever the voltage is above a certain threshold, then the positive cable would've otherwise been "HOT" even with the vehicle battery removed... not good when loose cables are bouncing around inside that compartment. The installer probably forgot to reconnect the house battery ground afterwards.

Ergo, as others have surmised, the only time the generator is getting the 12 Vdc it needs to run is when the vehicle's engine is running and the alternator is producing sufficient power to raise the battery voltage above the battery separator's threshold for the relay coil.

A similar failure could also result if the installer removed the house battery POS terminal from the battery separator; once again, to avoid having a HOT cable bouncing around.

A third possibility is a possible failure of the battery separator itself, that may have been related to the vehicle's battery replacement or could simply be an unrelated coincidence.

[hbn7hj]

We will never know. The originator of the thread quit talking to us. It has been an interesting exercise and embarrassing to realize how long it took us/me to come up with the simple, probable, solution.

[JRForster]

I've got the same or similar problem with my Roadtrek 2015 SS Agile Sprinter; generator won't start unless engine is running. It will turn over but not fire. So maybe a similar ground issue, but with the solenoid? I can't try things right now as I've lent it a friend.

[Charlie1]

I am having the same problem with my Dodge widebody I am hoping someone out there knows where to look
Charlie

[Traveling peeps]

Originally Posted by gks314

This is a new issue on my 2017 Midwest Auto Sprinter Weekender, with an LP Onan 2800 generator.

Everything was working fine until I had the starter battery replaced at a national chain. Beginning immediately afterwards, the generator will not start unless the RV is running. And once the generator IS running, it shuts off instantly when the RV is turned off.

This happens even when connected to shore power.

While the generator is running, it supplies AC power to the RV just as before, running the air conditioner or microwave, for example, without problems. While running, the generator also charges the house batteries just as before.

In other words, the genny seems to be behaving normally once running, but it will only run if the RV itself is running.

What could have happened during the starter battery replacement to explain this behavior?

All fuses and breakers appear to be good.

Thanks in advance,
--Greg

Hey, I was just searchig the web and found your post. I have the same exact problem with my MAD sprinter. Just wondering if you figured out the problem you were having? If so I would be interested in the results of your findings.

Thx in advance,
Todd