Community Forums

DDDonkey · 03-09-2016, 06:15 AM

Can someone please tell me how to test the battery isolator in my motor home. I want to ensue that it is working correctly and not stuck in the closed position. When I have the DW hit the emergency start button I don't hear a click (should it) with the key on or off. Thanks for the help!

Gary RVRoamer · 03-09-2016, 08:17 AM

You may or may not hear a click, depending on where the solenoid is and your hearing.

You could disconnect the hot wire from the chassis battery and see if you still have engine 12v power to start and run without using the emergency start switch. If so, it must be coming from the house batteries via that solenoid. Or you can check the output side of that solenoid with a voltmeter, if you have one and know how to take a valid reading there.

**Lt Dan** · 03-09-2016, 08:38 AM

Another way would be to check the voltage on the battery cables at both sides of the relay with a digital voltmeter. If they are exactly the same without pressing the battery boost switch, chances are the relay is stuck. They should be the same only when the relay is active and the contacts are good. The odds of both the house and chassis batteries being exactly the same are pretty small. I would also test them while the DW presses the battery boost button. The key may have to be on for that to work, depending on how yours is wired.

frede · 03-09-2016, 08:52 AM

When I measured the voltage across both sides of my Isolator/aux start/charge solenoid with a digital voltmeter it showed a 1.23v differential regardless of the auxiliary start switch position. I changed the relay and it now reads 0v when the auxiliary start switch is pressed.

bobmac · 03-09-2016, 02:07 PM

Quote:

Originally Posted by frede

When I measured the voltage across both sides of my Isolator/aux start/charge solenoid with a digital voltmeter it showed a 1.23v differential regardless of the auxiliary start switch position. I changed the relay and it now reads 0v when the auxiliary start switch is pressed.

The zero volt reading tells you the solenoid is operated and both batteries are connected together. You can also verify proper operation if you have voltmeters inside the coach measuring your house and chassis batteries. When the switch is operated or the engine running with both batteries bridged, you should see identical or near identical voltages on both batteries.
The charge solenoids fail frequently as the contacts get pitted from arcing when çonnecting or disconnecting. You might want to consider carrying a spare particularly if you have a residential fridge and want it to operate when travelling with the alternator charging the house batteries to feed the inverter. Good luck,