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Old 04-11-2021, 09:20 AM   #57
Bob Nodine
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Brand: Thor Motor Coach
Model: Quantum JM31
State: Tennessee
Posts: 686
THOR #21926
Quote:
Originally Posted by Fullabunk View Post
I unplugged the MH from 50a service and let the batteries drain 10-15%. The next morning the panels began charging real well with 8-9.5 amps. That is about the best I can get with 760 watts on panels and getting 84 volts. Today I added 3 additional AGM batteries. I know have 7 for about 700 amp hours capacity.

I have a question. During this discussion I mentioned my panels are wired in series to keep the amps within the 10awg wire and to allow for adding a few more panels later if needed. It was suggested I change to a series/parallel structure to get the amps closer to 30. I was wondering why? My controller seems to handle any volts or amps(within reason) and outputs 12 Volts to the batteries. Am I missing something?

Thanks for all the suggestions.
As long as you stay with the specs of the MPPT controller the higher voltage will reduce the loss in the wire running from the panels down to the MPPT controller. The controller does the job of converting back to the 12 volt range. Power is power. The equation is P=I x E or power is the current times the voltage. 20 amps times 12 volts equals 240 watts and 5 amps time 48 volts equals 240 watts. What is left out of the equation is the resistance of the wire. 10awg wire is about 0.000999 ohms per foot. If you have 20 feet of wire from the panels to the MPPT controller the loss is P=I (squared) x R. At 20 amps the loss in the wire is about 8 watts but at 5 amps it is 1/2 watt.

Bob
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