Strange electrical problem

norwestie · 11-21-2011, 09:46 AM

A few days after running the coach and having full charge on all batteries, I will return to the storage yard and unlock the Dynasty. Flipping the battery disconnect switch has no effect on restoring DC power. The dash radio, lights, thermostat and other fixtures will not work. I can start the generator, but still no power. It is only after I start the engine that battery power comes back on.
The status panel in the bedroom lights up only after the engine is running and shows 98-100% charge. I can shut off the engine and all will continue running on battery. So I have full charge on the house and chassis batteries but no initial power. What gives?

**RJay** · 11-21-2011, 09:52 AM

Check the automatic throw over switch at the end of your power cord. You didn't mention if power returned if connected to shore power.

norwestie · 11-21-2011, 11:31 AM

I have no shore power at the storage yard.

Barlow46 · 11-21-2011, 11:48 AM

Which battery disconnect switch? The main one in/near the battery bank or a "salesman" switch just inside the entrance door?

Robi.1014 · 11-21-2011, 06:21 PM

My guess is that you have a finicky "House-Disconnect Switch" (typically located up near the driver....in an outside bay)....which is controlled by the at-the-door "Salesman Switch". I don't believe the "cut-off" switches have any fault here (just to say it: cut-off switches are located in the battery-bank bay....and are manually operated).

A "finicky" switch is just below "fully operational", but is above "intermittent" and is way above "kaput".

My thought is that the "House-Disconnect Switch" (which is a solenoid-operated "latching" switch) is not latching to the ON position when it should. I think your scenario is like this: You return to the RV and flip the Salesman Switch ON, but the 12.6 battery Voltage applied to the "House-Disconnect Switch" is not enough to make the solenoid complete the "ON throw" (the "finicky" state of failure). Hence no 12VDC lights, thermostat, etc.

But by starting the main engine, battery-voltage jumps upwards of 13 volts due to alternator charging (even tho you do indeed have a 98+ % charge on the batteries). With this additional voltage (13.8 vs 12.6), this allows the "House-Disconnect Switch" to complete its ON throw. Once you shut off the genset and/or the main engine, the "House-Disconnect Switch" stays in the ON position.....because it's a latching switch. A "Latching Switch" only needs current when being "told" to turn ON or OFF....and at other times, it uses no current to maintain its last state. This is perfect for us dry-camping guys.....because we're always concerned about every milliamp being drawn from the batteries.

Troubleshooting:
My "finicky" definition could be tested by hitting this solenoid-switch with a rubber hammer. Testing voltage drop across its main terminals also lets you know whether the "House-Disconnect Switch" is closed (very low voltage drop) or open (12 volts or so).

Fuses? There are some fuses here to think about, but YOUR situation implies the "House-Disconnect Switch" is mostly working....just not exactly when you want it to. Can't blame this on a fuse.