electrical problem

I'm hoping some of you pros can help me solve this one. PLEASE!!!

Symptoms: 12v system drops to 1v when I run anything at all, tv, water pump, lights. Everything 12v works perfectly if I'm plugged in or if I run the generator. Although, when I unplug or cut off the generator the 12v system goes dead completely. If I start the engine, plug in or start the generator again, I get 12v power back (sort of, see the last symptom). If for any reason I cut off the 12v to the coach, I cannot turn it back on unless I'm plugged in or the engine is running. In short, I can't dry camp on 12v alone. I do have 12v in the coach. The LEDs are all lit up. If I don't start anything, I have 12.6v at every 12v fuse. But when it drops to 1v if I turn something on, it's dead. If I turn it off, the LEDs come back on and again I have 12.6 volts.

What I've done: Checked the Low Voltage Disconnect. It has 12.6 volts at the "sens" and at the "Vin" posts. Seems the LVD is fine. Cleaned a ground connected to the chassis near the battery compartment. Found a loose cable connected to the negative of the battery (I could actually pull the wire out from the battery connector) and tightened it with plyers. I checked the two coach batteries and both have 12.7 volts.

I suspect a bad ground, but I don't know where else to look, and it would have to be really bad... really loose.

Where would you look? What would you test?

2002 Chinook Concourse

Re: electrical problem

Did you check the batteries with a load tester. That will give you a much better idea of the battery condition. It may not be the answer but a good start. Good luck
Re: electrical problem

You could have a nick in the12 volt postive wire were it goes thru a hole in metal causing the voltage to go to ground This happens when you turn something on otherwise the voltage will read fine with everything turned off.
Re: electrical problem

Batteries are new. No liquid type. I'll have them load tested. I don't have that equipment.

I think the positive comes from the batteries direct to the LVD first, so that's a short distance to check. I'll work on it.

Thanks for all ideas.


Senior Member
Re: electrical problem

As an electrician, the leak to ground theory seems pretty far out since a short would always be a short. But voltage from a battery is very much the same as the pressure in a water line. In the case of water, if no water is running, the pressure will equalize to what ever the supply pressure happens to be. But if you have some restriction in the water line, as soon as you start to run some water, some part of the driving pressure will be dropped at that restriction and the pressure seen at the point of use will be much less.

The very same thing happens with electricity if you have a bad connection at some point. With no current flowing, you will read the supply voltage at any point in the circuit. Once you turn on some item in the circuit, that voltage will also drop if there is a high resistance connection in the circuit, even though you can't detect it when nothing is operating.

I suggest that you try removing the battery cables and clean both very carefully and completely. To drop that far would indicate a very poor connection if that is the problem, but it is possible. A load test is a good idea as that may eliminate the battery as part of the problem. There are some RVs that use a converter or inverter that has a separate battery charging circuit also then have a transfer relay inside of them which removes the battery from the circuit when it is being charged from another 12V source and then connect it when no outside source of 12V is available. Those relays have been known to fail.

Should it be such a relay, there would be 12V up to the connection at the device, but not leaving it once the outside source of 12V has been removed.
Re: electrical problem

Kirk --
Thanks a bunch for that explanation. I wondered if the problem were somehow in the converter area. I have removed the battery cables already, and the batteries are new, and even though that doesn't eliminate that as the source, I think for now I will focus on the converter.
Ever since I bought the camper in May of last year, it always hesitates when I switch from one power source to another, then it clicks and the coach power comes on. I have wondered where that was happening, and your "transfer relay" sounds like the source. But you say that there "would be 12v up to the connection at the device, but not leaving it once the outside source has been removed" and I actually still have LEDs burning until I put a load on the system, so the 12v does actually leave the device.
Does that make sense?
Is there a way to test the converter or relay somehow? I don't even know how to get to it. It must be behind the electric fuse panel somewhere, right? Sounds like a lot of money, but I've already wasted about $500 at RV service with no cure.
Kirk, could you give me some advice about what you would do?
Re: electrical problem

P.S. Kirk, the exception is that if I plug in I have coach power, and as soon as I unplug I have no power. If I run the engine I have coach power, and if I cut off the engine, I still have LEDs burning.
Re: electrical problem

If I cut off the engine, I still have LEDs, but not for really long -- maybe about 6 hours max. Then everything goes dead.
Re: electrical problem

When I installed two way radios and the old mobile phones for a living, a leak to ground was not all that uncommon. Most of the time it was in the back seat where the 12 vot wire ran. Some large person would sit in the seat pushing the frame down on the wire and crushing it. When they got out it relieve the pressure and the wire would not be grounded anymore. Also we would find them going thru the firewall were the hole was not insulated
Good Luck


Senior Member
Re: electrical problem

What you tell me does sound like the converter has such a relay. The first step is to locate the converter and to also see what make and model it is. It it is a hung transfer relay it would give the symptom that you have. An LED draws so very little power that a capacitor in the power supply could easily keep a few of them lighted for some time if nothing else was on. As to locating the converter, you should be able to trace the cable from your battery back to it. Also, very often a converter will hum when under load so if you were to run the furnace or such to load it when on shore power, then listen very carefully. The 60 cycle hum would probably not be loud but should give some hint where it is located.

Quite possibly if you post the make and model of RV. someone here may very well know where to find the converter. It is pretty common to find them in the same area as the 120V distribution panel and/or the 12V fuse panel.

If you locate the converter, there is an easy way to test the relay, as long as you are able to determine which connection is which. There should be a terminal block where the cable from the battery connects, and also one that goes out to the RV loads. It is fairly easy to lift both of them and temporarily connect the two together. If you then get 12V power to things, you will know where the problem is.
Re: electrical problem

I'm afraid the converter is behind all the walls and shelves to the left of the sink ... completely closed in and a major job just to expose.

I'm going to trace all the 12v lines I can and see if there's any sign of a leak there. If it's the converter I may have to live with the problem.