amp hour?

bigcountry
bigcountry Registered Users Posts: 22 ✭
in Solar Beginners Corner #1
Was wondering what amp hour battery is ideal for 80 Watts of solar?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: amp hour?
    bigcountry wrote: »
    Was wondering what amp hour battery is ideal for 80 Watts of solar?

    That's sort of the wrong way 'round. Normally you determine how many Amp hours your battery needs to be (or is) and calculate how much panel you need to charge it.

    Voltage come in to play too, as panels are measured in Watts which are Volts * Amps.

    Assuming a 12 Volt battery, an 80 Watt panel would be good for charging about 50 Amp hours.
    That is also assuming 77% efficiency of panel/wiring/controller, good insolation, 4 hours minimum equivalent good sun, 10% peak current, no greater than 25% DOD, recharging in one day ... et cetera.

    Sorry it isn't a straightforward there's-only-one-choice answer. :blush:
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  • bigcountry
    bigcountry Registered Users Posts: 22 ✭
    #3
    Re: amp hour?

    This set up is on my off road trailer i pull behind my Jeep when i take trips will be using it to charge laptop & cell phone and maby a little fan at night the panel is what could fit on top of it and can afford
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  • bigcountry
    bigcountry Registered Users Posts: 22 ✭
    #4
    Re: amp hour?

    When not using my system can i use it to maintain my batteries for my boat?
    1 is a deep cycle starting battery and 1 is a trolling motor battery i think its a 12590 amp hour battery
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: amp hour?
    bigcountry wrote: »
    When not using my system can i use it to maintain my batteries for my boat?
    1 is a deep cycle starting battery and 1 is a trolling motor battery i think its a 12590 amp hour battery

    The RV/Marine batteries tend to be around 100 Amp hours. Very often you won't even find such a rating on them as they don't consider that number to be important in the application.

    With a proper charge controller the panel should be able to maintain such a battery. Basically you're looking at:
    80 Watts @ 77% typical efficiency = 61.6 Watts / 12 Volts nominal = approximately 5 Amps peak charging current. That should suffice for maintaining a 100 Amp hour 12 Volt battery. This would be the minimum controller for the application: http://www.solar-electric.com/sg-4.html
    You might want to have a slightly higher capacity one in case you can get better efficiency than 77%:
    http://www.solar-electric.com/ss-6.html
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