Hi all,

I was attempting to learn two things:

I wanted to know if I could effectively run my block heater for some period of time via my inverter and battery banks.

The chemical reaction in a lead acid cell is endothermic--but there is internal resistance in the batteries. At some point the resistance may produce more heat than the reaction absorbs. I wanted to know if any "heating" would happen in the battery bank compartments.

Here are the results.

Friday Dec 18 at 9:10 a.m. temperature -16.4 C outside and battery bank -16.4

The system consists of seven 125 amp hour Walmart batteries made by Johnson Controls. They do not have a "cold cranking amps" rating. No solar charging was being done--panels covered in snow output in bright sun *zero* sad.gif . The inverter is a Cobra 2550 (2500 watts, 5000 surge).

I have placed a minimum maximum thermometer on top of one battery in the four battery bank, and I'll be running the inverter from both banks. Voltages are measured by the reading on the 3024di Blue Sky controller, and by a cigarette lighter voltmeter unit plugged into the tv power outlet.

Battery banks at 12.7 volts at rest
Battery banks at 12.5 volts when inverter turned on
Battery banks at 12.3 volts with 60 amp load from block heater (584 watts).

Friday Dec 18 at 10:40 a.m. temperature -14.2 C outside and battery bank at -14.2

Battery banks at 11.9 volts under 60 amp load
Battery banks at 12.2 volts no load (inverter turned off)

Friday Dec 18 at 11:10 a.m. temperature at -13.6 C outside and battery bank at -13.6

Battery banks at 11.8 volts under 60 amp load
Battery banks at 12.2 volts no load (inverter turned off)

I will be going back in three hours and checking the no load voltage.

Friday Dec 18 at 2:00 p.m. battery banks at 12.5 volts.

Conclusions so far:

875 amp-hours with a load of 60 amps produced no measurable temperature rise in the battery box. Load per battery is ~8.6 amps.

Even a small load such as 8.6 amps per battery for two hours shows a rise in voltage if the batteries are allowed to rest for some time.

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