WendellB

I am working on a 1978 GMC Royale with an Olds Toronado 403 and 425 TH trans. My motor home has dual batteries one for the house circuit and the other for the engine. My manual says to ground the engine compartment to the engine but and the other system to the frame. However, the battery for the house part is over charging and when running the voltage across the battery is 18.5 volts. The engine compartment works fine but am having issues with measuring the voltage from the alternator, which it seems like there is a problem with the engine ground because the voltage fluctuates all over the place. Any ideas would be appreciated. Also, the red cable from the starter relay and the engine ground both bolt onto the engine in the same place. Could there be a problem with the insulation at this point?


Earlier after the installation of a new alternator the Supper Accel coil shorted and fried the wires on to the distributer so I have a new HEI distributer and coil.

MDchanic

I don't know how RVs are set up, so unless there's someone here who knows that they're all the same way, I would say that we need a wiring diagram before any of us can say anything intelligent about this.

Unless the two batteries are charging through two different systems, there is no way that the alternator can be feeding the correct voltage to one battery and the wrong voltage to the other.

- Eric

don71

Does your manual talk about an isolator? Its for use with a starting battery and house battery with proper charging, of course. I would look there first.

Read up on it. I did a simple google search and came up with lots of things to read about your problem .


http://www.vanner.com/brochures/Batt...rs-PB-6-01.pdf

joe_padavano

The first question is, what is the voltage output at the alternator? If it's more than 13.8V or so, you have a problem there. If the alternator is putting out 13.8, is isn't physically possible to get more than that elsewhere in the system unless you have a step-up transformer, so the second question is, are you measuring voltage correctly?

RROLDSX

The two battery systems are the "chassis" system and the "house" system. The chassis system operates like any car or truck. The house system is isolated from the chassis system using a battery isolator switch. I would check the operation of the isolator. If you are getting that much voltage there must Be a connection between the two systems that should not be there. There may also be a switch somewhere on you dash that allows a "boosting" circuit to enable using the house batteries to start the engine, but chances are you have a bad isolator or someone has incorrectly connected the two circuits together somewhere. Hope this helps. I've also found RV.NET to be helpful.

Randy

WendellB

Thanks all for your help it is appreciated. The problem was the battery isolator and after replacing it the voltage was 14.5 to each battery. Am planning on going up the coast on Memorial day to see the oil slick and check out the beaches. Will stay at San Simeon Beach RV park so if anyone is in the area come by for a beer (Stellas) or glass of wine (Russian Valley Chardonay).

MDchanic

I knew one of our excellent members would have an answer for you.

Have a great trip!

- Eric

BILL DEMMER

step-up transformers only function in AC circuits, not in DC circuits.


Bill