No charge to auxiliary battery

[Brandonitis]

Hi all. I recently purchased a AGM battery in hopes of it lasting a long time in my 21ft 1978 Chevy Itasca class C. I've been slowly remodeling the interior and while doing so, I've been using the cabin lights and intermittently checking the voltage on the auxiliary battery. I noticed it came down from 14 to now 10volts, so I flipped the switch as my manual says to charge the aux while driving. I noticed after taking it to Menards for supplies that it didn't budge from 10 volts. So I unhooked the positive cable from the aux, and with the rv running, hooked a test light up to the positive cable, nothing lit up.
I don't know a thing about what to do next. Any help would be much appreciated.

[tenbear]

Brandonitis wrote:
I found the solenoid (also called a battery isolator?), I'll voltage check it today to see if I'm getting power there, meanwhile I've got my battery on the charger to see if that'll perk back up. I found a new solenoid online for about $75, that seems high to me, anyone agree?

I found several solenoids on Amazon for much less than $75.

The solenoids come in 3 and 4 wire. Here is one I found. I have no idea if this is the one I bought and I know nothing about it other than what is listed in the Amazon add. The 150A continuous rating seems good. They also have 3 wire solenoids.

[Brandonitis]

I found the solenoid (also called a battery isolator?), I'll voltage check it today to see if I'm getting power there, meanwhile I've got my battery on the charger to see if that'll perk back up. I found a new solenoid online for about $75, that seems high to me, anyone agree?

[tenbear]

Mine has a solenoid (relay) that connects the chassis battery to the coach battery when the ignition is turned on. Some Class Cs also have a switch that actuates the solenoid for additional power for starting the engine. The solenoid failed and I replaced it and it has been fine since.

Use your multimeter to determine if the solenoid is bad if you have the same system.

[Gjac]

If you are charging when plugged in and not while driving(if I understand your post) then I would suspect a bad solenoid. Check voltage on either side(2 large wires) to see if contacts are burned. You should have 14 v on either side with engine running and 14 v at battery if all is well.

[Brandonitis]

I plugged it into shore power to see if the power converter was pushing power to the aux battery, which it is. So at least I know the power converter is working, still not sure if it still has some charging capabilities left in it or not, I'll find out tomorrow. As for the battery, I hope its not too late. I'll put a charger on it in the morning and see what happens.
The switch I was referring to is located to the left of the driver's seat and the manual says in the dual setting it will charge the aux while driving, the middle part of the switch is for when the RV is not running and the other setting is to have the aux assist the main battery in emergency starting.

[DrewE]

You need to get the battery charged ASAP; 10V is very, very low, and it may already be more or less damaged. A standalone car battery charger would work if you don't have something else handy (like a working converter/charger—and if it's the original 1978 converter/charger, it may well be not working or not all that effective as a charger if it is working).

As for why it wasn't getting any charge while driving, it's hard to suggest exactly what might be going on without a bit more information on the electrical system. Broadly speaking, the vehicle chassis and house ("aux") electrical systems are isolated from each other most of the time, with a solenoid switch or some other device to connect them together when the engine is running to charge the house battery. You apparently have (or at least think you have) some manual switch to do this, I take it. Whatever the system, it's a matter of tracking down the wiring for it and verifying that it goes where it should, that any fuses are not blown, that the switches and relays and stuff are all working, etc.—standard electrical system troubleshooting.