PV Gap

Elizabeth Said:

How to use solar panel to charge 2 battery packs simultaneously?

We Answered:

Series would mean that the two battery packs would have a total of 24 volts. The 12 volt panel would not charge the batteries.

You need to put them in parallel. Match the polarity of the PV panel and the battery packs. All the + together and separately all the - together.

Depending on your connectors you may be able get a Y adapter that would allow you to connect and/or disconnect each battery pack or device seperately.

Sidney Said:

Can a solar panel be used as a NiCd cordless tool battery charger?

We Answered:

Your 5W solar panel has to put out about 15 volts or higher to charge a 12 volt battery. 5 watts at 15 volts is only 0.3 amps, which is only enough to handle the internal leakage inside a large battery, plus a bit.

If you have a 100 amp-hour battery, that panel would take 300 hours of bright sunlight to charge it. But I do agree that it will keep the truck battery charged as long as it gets sun.

Make sure you put a diode in series between the panel and the battery to prevent the battery from discharging through the panel when the sun goes behind a cloud.


I'd be worried that if you charged the 18 volt battery frequently, the panel would not be able to replace the lost charge, and your 12 volt battery would wind up discharged. That 18 volt battery is 1.2 amp-hrs (if I got the correct one). That is 27 watt-hours. Allowing for losses, you car battery will have to deliver over 30 watt hours to charge it. Your solar panel will take over 6 hours of bright sun to make up that difference. That is over 24 hours this time of year. So if you recharged it more than once every 2 days, you will lose charge in the truck battery.

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Dora Said:

Will a 3w Solar Panel Charge A 55ah Car Battery?

We Answered:

Quite a while. I am assuming you are using 12 volts as your buss power.

The small panels were intended as a "float charge" for batteries to keep them from discharging over a period of time. 3 Watts means only 1/4 Amp. Normally when I do slow charging of batteries, I am using right around 1 amp, and that takes about a week to bring up a battery that was discharged past 80 percent capacity.

When you factor in losses from corrosion, battery self discharge, and loose connections, you will likely want to add more panels.

using your 55Amp/hour battery, a 1 amp charger running constant in a perfect world would take 55 hours. Real world, probably closer to 64 to 72 hours. That for simplicity is 15 Watts constant charge power. Now you are using 1/5 of that with your current setup. so 5 times longer, whichh puts you in the 300 hour range of real world, or 220 hours of perfect world. This time of year, you may have about 8 hours worth of charging light, which puts you at close to a month.

Don't fret. If you are using it for lighting in a shed, Power LEDs and tethering some of the inexpensive LED lights to the 12 volt source will give you plenty of light for a very long time, the panels will help some, but you will likely need to put the batteries on a charger, or you can build a gas powered 12 volt generator easily enough. Charge it up only when needed.

Judith Said:

Can a 5W solar panel directly charge an 18v 1.5 amp NiCd Black and Decker Firestorm battery?

We Answered:

You can connect the panel and it may charge the 18V battery sometimes. You should have a multimeter to measure the current in series, so you know what is happening. However the solar panel will get hotter due to being in the sun, and this reduces its voltage, so it will probably not charge once the panel is hot. They normally come up to 50C or 60C depending where you live - that is very hot to the touch. Make sure it is well ventilated. However I don't expect it will work very well at all. It is meant to charge a 12V battery, and can only charge the 18V battery under certain conditions, like when the battery is low and the panel is cold. Don't worry about diodes, they only reduce the already starving for voltage situation you will have.