Battery Question...

paulskirocks
paulskirocks Solar Expert Posts: 84 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
OK, I'm down to needing batteries... I will have 920 watts of panels, 2 strings, into a Morningstar MPPT 45 Amp controller, into a 24 volt battery bank... Looking at the numbers of the panels, each string will be close to 8 amps, so 16 amps max into the controller... Will this be enough to keep 200 amp hours worth of batteries fully charged and happy? It's my understanding that 20 amps would be more ideal, so I wonder if I should downsize my amp hours... Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Battery Question...

    MPPT controller, so the current to the controller doesn't matter; it's what it can put out that does.
    The formula looks something like this: 920 Watt array * 0.77 efficiency / 24 Volts = 29 Amps peak charge current potential.
    That should have no trouble keeping, say, a string of 220 Amp hour 6 Volt golf cart batteries happy. Or even a string of 232 Amp hour 6 Volt East Penns. :D (That's what I have on my mere 700 Watt array; no problem.)
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  • paulskirocks
    paulskirocks Solar Expert Posts: 84 ✭✭✭✭
    #3
    Re: Battery Question...
    Cariboocoot wrote: »
    MPPT controller, so the current to the controller doesn't matter; it's what it can put out that does.
    The formula looks something like this: 920 Watt array * 0.77 efficiency / 24 Volts = 29 Amps peak charge current potential.
    That should have no trouble keeping, say, a string of 220 Amp hour 6 Volt golf cart batteries happy. Or even a string of 232 Amp hour 6 Volt East Penns. :D (That's what I have on my mere 700 Watt array; no problem.)

    Ahhh, OK, I was wondering about that... I need to think watts, not current... MPPT is pretty neat technology... Thanks for the quick reply...
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Battery Question...

    And the Vmp-array needs to be >~35 volts to properly recharge your battery bank. It sounds like your Vmp-array should be around 57 volts--Which is fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • paulskirocks
    paulskirocks Solar Expert Posts: 84 ✭✭✭✭
    #5
    Re: Battery Question...

    Yea, each panel is 29.4 vmp...
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