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Author Topic:   Thoughts After an Electrical Fire

AZdave posted 10-13-2013 11:18 PM ET (US)
Our truck camper was severely damaged by an electrical fire a couple of weeks ago. The camper’s electrical system mimics that of larger boats. It is powered by a pair of 6V batteries connected in series, and they are recharged by an alternator, in this case on the truck rather than an outboard. The batteries are connected to interior lights, a water pump, a three-way refrigerator, and a furnace.
The furnace had been giving trouble in a way that suggested it was being supplied low voltage. I replaced the older of the two batteries but was not able to line up diagnostic work while on the road in Alaska. The problem persisted, and eventually the lights would dim when the furnace came on. On the way home, I noticed a smell in the camper after a stop. I had forgotten to turn off the 12V supply to the refrigerator, which normally powers the refrigerator while driving. I made no special note of the smell, and two hours later we were flagged down by a trucker who told us we were on fire.
The fire started in the primary wiring near the batteries. We were able to control it with the fire extinguisher and some added water. We did not lose the truck, and owe that to the trucker and the volunteer fire department that responded.
With the usual 20:20 hindsight, I should have:
--carried a good voltmeter. I might have found the voltage drop in the wiring;
--been suspicious of the primary wiring. In retrospect, I think some of it was added by an owner along the line;
--heeded the obvious sign of low voltage in the lighting when the furnace started;
--persisted in seeking out competent help, even if our trip was interrupted; and,
--chased down the “hot” smell, even though that meant moving supplies and getting under the camper furniture.
I hope this might be of instructional value to another reader.--Dave

Jerry Townsend posted 10-14-2013 11:32 AM ET (US)
Dave - I suspect the problem was not caused directly by the low voltage.
Your furnace and refrigerator are operated by propane, and both via burning propane controlled by electrical thermostats and control valves. The dimming lights when the furnace started was caused by the low voltage when the furnace blower motor started, and were indicative of a low battery voltage, or a high electrical resistance of a bad or poor electrical component or blower motor.
But, while driving, the electrical power is supplied from the vehicle alternator. Had there been a problem there, you would have seen that on the vehicle's instruments. --- Jerry/Idaho
AZdave posted 10-14-2013 07:42 PM ET (US)
Jerry, I think you are exactly correct. The batteries were maintained at the proper voltage and had ample ability to supply current. The defective wire acted as a resistor in series with everything else in the camper. When only the lights were being used, their resistance was much higher than the defective/frayed wire, and there was little effect. As we drove along with the refrigerator in operation it was being powered by a resistance element at the back of the unit. This device had a lower resistance and current flow was larger. The larger current flow (and voltage drop) through the defective wire caused heating, until combustion occurred.

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Author	Topic: Thoughts After an Electrical Fire
AZdave	posted 10-13-2013 11:18 PM ET (US) Our truck camper was severely damaged by an electrical fire a couple of weeks ago. The camper’s electrical system mimics that of larger boats. It is powered by a pair of 6V batteries connected in series, and they are recharged by an alternator, in this case on the truck rather than an outboard. The batteries are connected to interior lights, a water pump, a three-way refrigerator, and a furnace. The furnace had been giving trouble in a way that suggested it was being supplied low voltage. I replaced the older of the two batteries but was not able to line up diagnostic work while on the road in Alaska. The problem persisted, and eventually the lights would dim when the furnace came on. On the way home, I noticed a smell in the camper after a stop. I had forgotten to turn off the 12V supply to the refrigerator, which normally powers the refrigerator while driving. I made no special note of the smell, and two hours later we were flagged down by a trucker who told us we were on fire. The fire started in the primary wiring near the batteries. We were able to control it with the fire extinguisher and some added water. We did not lose the truck, and owe that to the trucker and the volunteer fire department that responded. With the usual 20:20 hindsight, I should have: --carried a good voltmeter. I might have found the voltage drop in the wiring; --been suspicious of the primary wiring. In retrospect, I think some of it was added by an owner along the line; --heeded the obvious sign of low voltage in the lighting when the furnace started; --persisted in seeking out competent help, even if our trip was interrupted; and, --chased down the “hot” smell, even though that meant moving supplies and getting under the camper furniture. I hope this might be of instructional value to another reader.--Dave
Jerry Townsend	posted 10-14-2013 11:32 AM ET (US) Dave - I suspect the problem was not caused directly by the low voltage. Your furnace and refrigerator are operated by propane, and both via burning propane controlled by electrical thermostats and control valves. The dimming lights when the furnace started was caused by the low voltage when the furnace blower motor started, and were indicative of a low battery voltage, or a high electrical resistance of a bad or poor electrical component or blower motor. But, while driving, the electrical power is supplied from the vehicle alternator. Had there been a problem there, you would have seen that on the vehicle's instruments. --- Jerry/Idaho
AZdave	posted 10-14-2013 07:42 PM ET (US) Jerry, I think you are exactly correct. The batteries were maintained at the proper voltage and had ample ability to supply current. The defective wire acted as a resistor in series with everything else in the camper. When only the lights were being used, their resistance was much higher than the defective/frayed wire, and there was little effect. As we drove along with the refrigerator in operation it was being powered by a resistance element at the back of the unit. This device had a lower resistance and current flow was larger. The larger current flow (and voltage drop) through the defective wire caused heating, until combustion occurred.