Battery charging problem

[1987_345]

Just got back from the coast and going down everything appeared fine. Coming home I noticed the cranking (chassis) battery was discharging. I was running the lights and dash air. I assume the amp guage is representing only the cranking battery and not the coach batteries. Anyway with the genset running the cranking battery discharges. If I flip the switch in the glove box connecting all the batteries together and hold it there, things return to normal. If I turn off the genset everything returns to normal. I had thought maybe the battery had a short in it, but llike I said if we don't run the generator everything works fine. Any thoughts?

[dadstoy]

Originally Posted by 1987_345

Just got back from the coast and going down everything appeared fine. Coming home I noticed the cranking (chassis) battery was discharging. I was running the lights and dash air. I assume the amp guage is representing only the cranking battery and not the coach batteries. Anyway with the genset running the cranking battery discharges. If I flip the switch in the glove box connecting all the batteries together and hold it there, things return to normal. If I turn off the genset everything returns to normal. I had thought maybe the battery had a short in it, but llike I said if we don't run the generator everything works fine. Any thoughts?

I have the exact same problem with my '82 280 when I run the GenSet! I need to be able to run GenSet and roof A/C in summer when it is 100+ up here. I would love to solve this one too.

[1987_345]

Well I can tell you how the PO of my coached fixed it. Actually I'm not even sure he did this to address the problem we're having but he had an extra battery cable running from the positive post on the cranking battery to the positive post on one of the coach batteries. Completely eliminates the problem only if you ever run down the coach batteries while camping somewhere, the cranking battery goes down too and you're stuck there...

[t7389sg]

The genset when running supplies 115 volts to the coach. You then have a 115 volt battery charger plugged in that charges the two house batteries. The genset also has an alternator that charges the one battery that starts the motorhome and the genset. At least that is how it works on my 91 350LE. I wonder if the alternator on the genset has failed and the genset is sucking juice from the starter battery to keep it running.

[dadstoy]

Originally Posted by t7389sg

The genset when running supplies 115 volts to the coach. You then have a 115 volt battery charger plugged in that charges the two house batteries. The genset also has an alternator that charges the one battery that starts the motorhome and the genset. At least that is how it works on my 91 350LE. I wonder if the alternator on the genset has failed and the genset is sucking juice from the starter battery to keep it running.

In that case, I wonder why the alternator on the 454 does not keep the cranking batt charged?

[t7389sg]

That's a fair question. It may be trying. What do we have for the 454 60 amp? I am not sure what the genset draws to keep running.

[jdalrymple]

I don't own a motorhome, but have you looked at the battery isolator? It may have a diode shorted or open, and allowing current to flow somewhere unintended. As far as I know, it is the only connection between the two systems, other than the back-up switch in the glove box.

Just an idea.

[dadstoy]

Originally Posted by t7389sg

That's a fair question. It may be trying. What do we have for the 454 60 amp? I am not sure what the genset draws to keep running.

I have a 220 amp alternator and a 240 amp isolator.

[dadstoy]

Originally Posted by jdalrymple

I don't own a motorhome, but have you looked at the battery isolator? It may have a diode shorted or open, and allowing current to flow somewhere unintended. As far as I know, it is the only connection between the two systems, other than the back-up switch in the glove box.

Just an idea.

Isolator and alternator are new

[jdalrymple]

Not to be the guy from outside that is a know it all, but....

I am aware of the relay that connects the genset to the coach, and disconnects the shore line when the genset is running. Is said relay perhaps powered by the coach battery for some reason?

And, what charges the coach battery when there is AC available?

Just trying to help, and learn.

JD

[ROBERT CROSS]

What's the rating of the new alternator? Was it replaced for this concern?
It should have a charge rate of 14.2v+.
Grounding the alternator field wire will give you the maximum charge rate.

Bob

[dadstoy]

Originally Posted by jdalrymple

Not to be the guy from outside that is a know it all, but....

I am aware of the relay that connects the genset to the coach, and disconnects the shore line when the genset is running. Is said relay perhaps powered by the coach battery for some reason?

And, what charges the coach battery when there is AC available?

Just trying to help, and learn.

JD

The transfer switch works off of sensing power from either shore or genset and is not connected to any batteries. The coach batteries are charged via a 120 to 12 volt converter.

[1987_345]

WOW Lots of good replys. Thank-you. I believe I will start with how much current the genset draws while running. That makes the most sense to me. If I don't find anything there it might be over my pay grade!! I'll probably have to get a pro to look at it. Thank-you again Kenneth

[jdalrymple]

In an attempt to understand, I have reviewed the operation of a standby generator we own.

It is actually the 12 volt battery which starts the genset that supplies the voltage to the transfer switch. If this were not true, when grid voltage failed there would be nothing to supply electricity to the relay and logic board to tell the genset to start.
In other words, the un-energized transfer switch is in the position to allow the grid (shore line) to supply power. When the generator starts and takes the load, the logic board uses 12 volts from the starting battery to hold the transfer switch in the position that allows the generator to supply current to the load. And, a battery charger keeps the starting battery charged.

I assume the system is similar in a motorhome, as the shoreline operates much the same as grid power.

The original post did not say how long it took the coach battery took to drain, but my guess is that the device and/or circuit that charges the coach battery while the genset is running has failed, and the battery drains while supplying current to hold the transfer switch in the normally open position.


Just a guess, but I hope it helps!


JD

[dadstoy]

As "1987_345" described his situation,it is exactly the same issue I've been having. To clarify a couple of things, it is the engine battery that discharges, not the coach batteries that discharge. This happens with engine running and generator running at the same time. Honestly I have not yet checked to see I'd the engine batt gets charged by the genset with engine not running. Also, the transfer switch transfers power solely based on sensing 120 volts from shore or genset. There is no 12 volts wired to the switch.