PV Gap

Janice Said:

How long does it take for a 12-volt, 1.5 watt solar panel to recharge a 12 volt battery?

We Answered:

Nata's math is a little off - the units don't work out. If a 12 V battery does indeed have 50 wh of energy in it as he suggests (that sounds right to me), it will take 50wh/1.5w = 33 h. Nata converted to amps and then ignored the voltage rating of the battery, thus messing up the units and giving you a wrong answer.

33 hours is quite a bit more reasonable than 400. Figure on three or four days of charging to get that (~8 hours of good sunlight/day).

Fernando Said:

Can a 12-volt battery be charged from a 6-volt solar panel?

We Answered:

If you charged two 6-volt capacitors in parallel, then put them in series, you could produce 12 volts. You could theoretically make a DC-DC converter in this way, by using transistors to alternate these logical connections. However, such a circuit would be lossy.

A much better circuit would be a boost converter using an inductor. The basic idea is that you build up current in an inductor, then quickly switch the inductor over to the battery. In theory, the same current keeps flowing for a while, no matter what the voltage of the battery. There are limits, but you need not worry about them between 6 and 12 volts. Look up the AP34063 on the web, that would be a good part for boosting 6 volts to 12. There should be sample circuits included on the data sheet. You wouldn't even need to set the output voltage, as the battery being charged would do that for you, and you would just be pumping current into it.

Honestly, if you don't want to fuss, it would be much better to just get a panel designed to charge a 12-volt battery, which would be more like an 18-volt panel.

Leonard Said:

Can you charge a 12 volt battery with a solar panel and can you use different sets of wires and such?

We Answered:

Yes. All you need is a solar panel that outputs about 14 volts, the same as an alternator. You can buy one to plug into your cigarette/accessory socket to trickle charge your cars battery.