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Barsuhn · 11-17-2021, 02:24 PM

I have a Class C 2005 Winnebago Minnie 26a. My house/coach batteries are not charging when I am driving. I took the positive post off the batteries and tested for voltage between the positive cable and ground. There is no voltage when the engine is running. There is good voltage if the motorhome is plugged in. The battery switch left of the steering column on the drivers side doesn't make a difference whether it is in the engine or house position. I checked all of the fuses both under the hood and in the converter visually and with a VOM. One weird thing that was in the fuse block was a little black thing that looked like a fuse without any amp marking and one leg was turned 90 degrees to the other - diode? It tested negative for continuity. I boondock fairly often and use a bi-pap with a 12 volt adapter (not an inverter) so having fully charged batteries when I arrive somewhere for the night is pretty critical. BTW the batteries were new last spring and they are typical deep cycle batteries. Previously the bi-pap barely put a dent in them. I thought about running a special line from the chassis battery to the coach batteries with a diode so it would be charge only but I also realize that with the override switch from engine to house that could be a problem, not to mention the possibility of depleting the chassis battery. Any ideas?

wolfe10 · 11-17-2021, 02:29 PM

Quote:

Originally Posted by Barsuhn

I took the positive post off the batteries and tested for voltage between the positive cable and ground. There is no voltage when the engine is running.

You are VERY lucky if you did not blow the diodes in the alternator. Alternators HATE to feed an open circuit/be disconnected from the battery.

twinboat · 11-17-2021, 02:32 PM

Find the continues duty solenoid that does the battery to battery charging and see if it's getting 12 volts to the small terminal while the engine is running.

If it is getting power, then the solenoid may be bad. Very common for the internal contacts to burn up.

That solenoid will have cables from the house battery on one side and chassis on the other. It closes with the key on or when you use the switch in the cab.
That's how they work.

twinboat · 11-17-2021, 02:35 PM

Quote:

Originally Posted by wolfe10

You are VERY lucky if you did not blow the diodes in the alternator. Alternators HATE to feed an open circuit/be disconnected from the battery.

Alternator is connected to the chassis battery. He removed the house battery cable. No harm to the alternator.

wolfe10 · 11-17-2021, 02:40 PM

Quote:

Originally Posted by twinboat

Alternator is connected to the chassis battery. He removed the house battery cable. No harm to the alternator.

Hopefully you are correct and I misunderstood what he said.

He said: "I took the positive post off the batteries and tested for voltage between the positive cable and ground."

jl.kauai · 11-17-2021, 09:17 PM

My Lazy Daze 2003 was equipped with an isolator mounted up under dash. This will have a connection from your alternator into it and a connection going back to house batteries. I would check the terminal in for voltage with engine running and check connection going out to the coach batteries. Provided you have this set up. Isolators can go bad. Travato John

Barsuhn · 11-18-2021, 09:53 AM

By batteries I meant the two six volt deep cycle batteries not the chassis battery. Your comment though is a good reminder about protecting the alternator by having a load present.

DRM901 · 11-19-2021, 06:34 AM

I suspect you need to install/replace a BIRD (bidirectional relay). I just purchased one from Blue Sea (ML-ACR) to replace the Magnum one that died soon after I installed it.

Hoof-hearted · 11-21-2021, 08:55 PM

I have a 1999 FW Discovery Pusher and had the same issue. I could not trace it. Took it to RV shop. They knew the system and found that the control panel had a failure, were able to correct it by making a simple jumper. Worked great last couple years. If you'd like a picture, I can add one upon request...
Jim