panel sizing

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
i just bought an 85 watt panel with 10 amp controller. i have a duracell 600 powerpack battery that i was going to charge on this panel. now the folks at xantrex/duracell are telling me that i have to use a formula to calculate the size of panel i can use. 28 amps/5x12 equals 67.2 watt maximum. the controller has a battery "port" and an accessory "port". can i still make this work? should i connect a larger battery and then connect the duracell to the accessory port by way of an inverter and the original ac adapter i charge with at home? it is really confusing. or maybe i should return the panel.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #2
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    Re: panel sizing

    I don't have any details on the 600 power pack... But it sounds like a 28 AH battery running at 12 volts and they are recommending a maximum of C/5 charge rate (20%).

    Certainly, 20% is probably about the largest charge rate you would want for the battery pack--you may also run into current limits of wiring/internal fuse/breaker, etc.

    An 85 watt solar panel+charge controller will probably an average of 65 watts or so maximum--So, you are probably pretty close to what they recommend. Especially if this is a PWM charge controller (simple, less expensive than MPPT type charge controller).

    Another way of looking at the specifications (using generic 85 Watt solar panel Vmp/Imp), your actual maximum charge current is probably around 5 amps (5 amps*14.4 volts = 72 watts).

    As long as your fuse/breaker/wiring supports 7 amps or more, I would not worry.

    Unless this is a multi-stage charge controller (bulk, absorb, and float) with a sealed battery setting, I would not leave the solar panel/charger plugged in permanently but only charge with the solar panel when needed--you would run the chance of over charging the internal battery with typical 14.4 volts of a standard PWM controller. AGM batteries are sensitive to over charging (causing them to vent will kill them) and need a slightly lower charging voltage and would be much happier if "floated" at ~13.0-13.6 volts for long term storage/charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: panel sizing

    the battery is agm and it will take a higher charge than 20% and 20% is pushing things for an fla type. your charge rate is at 17.85% with that pv so imho you can keep the panel.:D now as to the controller you may wish to not leave this on for prolonged periods after the battery is charged as it sounds as if it may be the sunsaver 10 for that cc does not go to a float charge, but rather tapers the current back some. by that i mean if the battery is not being used every day and the pv is constantly connected everyday it could be too much for the battery. agms are efficient at charging and hold their shelf life better than the fla types so you can top it say once a week.
    to add if you are using the battery power then be sure the battery gets its full charge before you decide to disconnect it.
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