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Old 05-11-2012

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Re: Solar charger size - trolling motor battery

Let's say that you have taken all 28 amp-hours at 12 volts out of the battery--that's 28*12= 336 watt-hours. Now you want to replace that with 5 days of solar power, at an average exposure of 8 hours per day or 40 hours. In theory you would need a solar panel of 336/40 = 9 watts. However, the solar panel guys oversell their panels (they rate them at 17 volts, but they only charge at 12 volts), the sun doesn't always shine, and there are some efficiency losses.

In reality a better rule of thumb is the watts in the solar panel divided by 3 will give you the amp-hours of charge at 12v per day. Using this rule, you would need 28 /5 *3 or about 17 watts of solar for a full re-charge each week.

Last edited by donradclife; 05-11-2012 at 10:44 PM.