How long does it take to charge a 12 volt battery with a 45 watt solar panel?

Answer 1

It depends on the amp hour rating and discharge condition of the battery to start with. The output voltage of the solar cell should be at least 13 volts. At that voltage the cell has an output of 1.15 amps.

Answer 2

That depends on the capacity of the battery, usually rated in terms of "ampere-hours".

Here's a simplified look at how to think about it:

Very roughly: If you pump one Ampere into the battery for 1 hour, you've stored 1 amp-hour

in it. If it's a completely empty 100 amp-hour battery, then in order to fully charge it, you

need to pump in 1 amp for 100 hours, or 5 amp for 20 hours, or 25 amps for 4 hours, etc.

Your solar panel needs to have at least 12 volts at its output, or else it can't charge

a 12-volt battery. The more it exceeds the 12 volts of the battery, the more current

(amps) will flow into the battery. BUT ... the more current (amps) flow out of the solar

panel, the lower its voltage will drop. So when you hook these things up, everything

will settle down to where it's all in balance. At that point, if you have an ammeter in

the loop, and can measure the amps being delivered to the battery, that'll tell you

roughly how long it'll take to fully charge.

The "45 watts" rating on the solar panel isn't extremely useful, unless you know that

it's 45 watts AT 12 VOLTS ... in other words, it can supply 45 watts without dropping

below 12 volts. If that's the case, then here's a formula you need:

PowerWATTS = (voltageVOLTS) x (currentAMPS)

45 watts = (12 volts) x (amps)

Amps = (45 watts) / (12 volts) = 3.75 amps.

If these are the true numbers for your solar panel, AND you keep it aimed accurately

while the sun moves across the sky, then it'll pump 3.75 amp-hours into the battery

for each hour that they stay hooked up.

Put that together with the amp-hour rating of the battery, and you'll have the answer.

Answer 3

100W divide by 12V=8,333333Ampers. 200Amp divide by 8,33333333333=24 Hours.