Converter or Battery or What?

oletimer · December 1, 2015

I posted this in the tech forum, but thought I would also ask here. Thanks

I received a call from one of our Granddaughters two nights ago about a battery problem in their 2007 Keystone/Montana 3000RK 5th. They are in the Pacific NW (20* nights) and at first I thought they were just trying to use to much juice. They are newly married, in their mid 20's, hard working, and trying to get ahead, so trying to use as much park power as they can. Started blowing a 15 amp 120V breaker first, then at about 3 AM night before last woke with a burning smell, and called my son(her father), and he 1st told them to GET OUT, and unplug shore power!!! Things cooled down, so told them to unhook + battery cable, as the battery had been boiling over, and the ground cable was fried. Soo, unhook the positive cable, then restart shore power, making sure cable isn't touching anything. Turn off 1500W heater, electric hot water, dehumidifier, etc. All was well, THANK YOU LORD, no fire. Had battery checked yesterday, BAD, replaced it, and also the ground cable. Everything was fine until 5 AM this morning, then same thing. Battery boiling over! Could this be as simple as a bad converter? Why the ground cable? All of our family has been warned about a camper fire, and me and my son both are 1,200 miles away, so I fell so helpless. Don't want to keep tempting fate. Any Ideas? Does anyone know where the converter is on a unit like this? Could the converter overcharge a battery that quick to the boiling point, and if so, would it be the ground that would be getting so hot along with the battery? They are in a kinda' remote area, so I'm not sure if a local repair is available. Thanks, Dick T

peety3 · December 1, 2015

If nothing else, the converter (aka charger/inverter/controller) is the gateway device between the 120V/240V in, the 120V/240V out, and the 6V/12V/24V in/storage/out, so I'd shine a spotlight there to start.

porky69 · December 1, 2015

I had a converter go bad on me 5-6yrs ago. Visually unit appeared good but would boil a battery in a matter of minutes, put a digital volt meter on it and it was putting 90volts into the battery. Replaced converter and no more boiling.

Also cooked the control board for the fridge at the same time, gave me the opportunity to upgrade to a Dinosaur board.

NeverEasy · December 1, 2015

I only have had experience with one Montana. The Montana I worked on does not have an inverter, just a charger/converter. Assuming that to be the case with the one at issue here, you can ignore the 120 volt AC side. Test by disconnecting shore power and try something on the AC side to be sure there is no AC present.

I think the place to start would be to turn the breaker off to the converter. That is very likely the 15 amp breaker that was tripping off.

"Battery boiling over" could be an overcharge coming from the converter but it sounds more like a serious overload on the DC system evidenced by smoked ground cable and a tripped breaker on the converter if in fact that was the tripped breaker.

Unless someone really screwed up the wiring, all the components are protected by fuses. With enough current to smoke the negative lead (twice) any component that had a problem would have blown its fuse. Therefore there must be a short on the positive side of the battery to ground.

The place to start looking is the positive side of the battery and chasing that lead to each of the fuses. Make sure none of them has rubbed through to ground.

I forgot something very important. If the battery is smoking there will be a lot of hydrogen gas around. DO NOT cause a spark. Disconnect the NEGATIVE side of the battery before beginning any tracing.

Is there a digital voltmeter availabe to your grandson and does he know how to use it? A DC clamp-on Ammeter would be a real help about now.

oletimer · December 2, 2015

Chet,

That sure makes sense. I called them tonight and relayed that info. They have the battery disconnected, and the converter is converting OK, but without the battery bank they cannot run the furnace, etc., but can run the controls for the fridge, and hot water, They are at least out of danger for now. It has warmed up some (50*), and I told them to run a HD cord through the window to the outside pedestal 15amp 120V, for their 1500 watt elec heater to get them by for tonight. He will trace, and inspect the 12V positive cables for a short to ground before ordering a new converter. I don't think it could be a "dead" short, because I told him to check for sparks yesterday when he reconnected the new battery, but he did say there was a small spark. Will let you all know later. Thanks to all, Dick T

NeverEasy · December 2, 2015

If the size of the ground cable battery to chassis were known the amount of current it would take to overload it could be determined. For example: A 4 AWG wire, 3 feet long, will handle 60 amps before it is overloaded. If the battery was boiling and the negative cable was fried I would say you are looking at a dead short.

Source of info:

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

How did he determine the converter is OK? If the converter is running the controls for some of the items, its positve cable is still tied to the positive cable on the battery via the fuse (see the schematic attached earlier) even though the battery is disconnected. Therefore, the ground should still be a problem. That fuse (actually a self resetting breaker) should be constantly tripping if the battery side of it is grounded.

The 1500 watt heater should have nothing to do with this problem as it is an AC device. However, I have cautioned other Keystone owners about using a 1500 watt heater in their RV due to the wiring size. Keystone ran a 14 AWG wire to my fireplace outlet and ran it with a 20 amp breaker. I recommend installing another 20 amp breaker and running a 12 AWG wire to a dedicated receptacle mounted near the power panel (shortest distance).