I have one of those 12 volt solar panels. It was on a electronic solar fence charger for farms. The rest of the fence charger was dead, but the solar panel works. I want to connect it to a 12V car battery. Do I just connect it directly, or does there need to be a diode or other parts in between, so the battery dont fry the solar panel?
Thanks
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First thing off you need to know that a 12 V car battery is actually a
13.2 volt battery. The cells are 2.2 colts each so do the math. It takes about 13.5 - 13.7 to keep the batteries on float charge, just enough to keep them from self-discharging over time. I have 2 batteries in my office room and they are at 13.5 and still good after 2 years. Also, don't believe that old mechanics tail that concrete sucks the charge out, total B.S. to cover their own butts for not keeping them charged. Bill Baka
Read this, it may give you some insight.
On Sat, 12 Jul 2008 17:42:07 -0500, snipped-for-privacy@none.com put finger to keyboard and composed:
You need a diode with a low forward voltage drop, eg a 1N5817 Schottky rectifier. The open circuit voltage of the solar panel can be quite high but you might get away with not using a voltage regulator if the short circuit current in maximum sunlight is below the continuous charging current that your fully charged battery can tolerate. Be aware that solar panels are really only useful for keeping your car battery topped up. A 100mA panel would take 400 hours to charge a flat
40Ah battery. That's at least a month of sunny days.- Franc Zabkar
Cool....how many colts = one horse? If I assume about 3 colts = 1 horse, then the battery should supply about 2 horsepower or about 1500 watts. But for how long? .... lets see.....1500 watt drain (125 amp) on a 65AH battery is about 30 minutes.
Seems to me your just horsing around.
(sorry, the devil made me say that)
Just colt not resist, I see.
That's because its got to be a COLD (-20" ~30' Celcius) concrete floor in a heated room to set up a temperature gradient in the battery where the Specific Gravity at the bottom of the cell is higher than the top of the cell. The battery then tries to come to an equilibrium with the S.G. difference between the top and bottom of the Cell, powered by the Potential Difference caused by the different S.G. between the warmer top and colder bottom of the Cell.
Yukio YANO
That is a believable temperature gradient effect, but much the same, and more, happens under the hood of a car. Concrete may make a faster self-discharge, but as I said most of it is the mechanics tossing them in a spare parts area and forgetting to charge them once in a while. In a car, most lots/shops remember to start the car at least about once a month to make sure it will start when a customer wants to buy it. Not always true with the used junker fixer uppers, and there are plenty of dim mechanics here stateside. Bill Baka Even a Ni-Cad will corrode after a year or 2 in a drawer. I haven't got any old NiMH or Lithiums that old yet.
The question was simple, but the problem is not. Depends on the ratings of your panel and battery.
A solar panel sized to charge a battery in reasonable time can easily cook a battery.
We could make assumptions about all that, but you know what happens when we assume...
alt.energy.renewable, alt.solar.photovoltaic, alt.energy.homepower might have answers. mike
If the panel is large enough to produce a meaningful charge into your battery it will need some form of regulation to prevent overcharging the battery.
at least a diode, one for/from a switch mode power supply or an old Germanium one , so only dropping 0.2V or so
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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