Battery inter-connect meltdown[RE-wrenches]

[Jeff Yago]

Here is another reason I like battery rooms and not confined battery boxes...

An almost new, off-grid solar-gen-battery system with Outback dual inverters and eight L-16's wired in single series at 48 volt, located in separate battery room having fire-rated drywall interior and ceiling and concrete floor.  Room includes an inline inverter powered DC exhaust fan.   Homeowner only uses this second home on weekends.  When he arrived he found no power anywhere and refrigerator had 4 day old spoiled food.   Irate phone call came next, since I was just there 3 weeks ago to change out a failed power board in one of the two new Outback Inverters.  

When I arrived I headed for the battery room where I found one of the battery inter-connects had all insulation melted off about 50% of its 12" length between 2 batteries, and one end dangling since the bolted connection had clearly melted its way through the battery post until it sprung free and broke the circuit.  Since this home was not occupied and no HVAC equipment operating, the only load would have been a few "wall-wart" cell phone chargers and the refrigerator cycling on and off as needed.  Since the inverter 175 amp breaker did not trip, and since the 300 amp catastrophic fues we always add just before the positive battery cable leaves the battery room did not blow, we are fairly sure this battery bank was not under any large current draw. 

We use 5/16" all stainless steel battery bolts, washers, and nuts, and make sure the battery posts are wire brushed clean just before assemble using a torque wrench.  We also make sure the copper cable terminals are directly against the battery post as I am aware stainless steel is not a good conductor and several past failures I have read about were traced to having a stainless-steel flat washer "between" the battery post and the cable.

Best guess since only the one end was fried and only insulation was burned off, is the crimping of the copper terminal onto the copper inter-connect cable was not properly completed and caused a high resistance connection that over-heated when under current draw for extended period.  Please note we only install UL labeled "factory-made" inter-connect cables and not site-made, although we have the capability. 

Conclucion - Most likely just a failed crimp by someone not paying attention, but I am sure glad this was in a room with an 8 foot high fire-rated ceiling above and not in a plywood box with the wood cover just a few inches above what had to be a nice little fire for several minutes!

I think we should request that all pre-made battery cables should be load tested for several minutes after assembly to check for large temperature rise at the crimps.

Jeff Yago

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