Is a 40 watt Solar Panel Battery Charger Kit with a Maximum Power Voltage of 17.5V
Maximum Power Current of 2.29A with Open Circuit Voltage of 21.5V, fitted with a battery protection circuit to prevent overcharging of batteries?
Or is it recommended to have a Solar Power Charge Controller?
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Hey Dave, it depends on the, “Kit,” you are speaking of, but generally, no, they do not have a circuit to prevent overcharging batteries. This would be the same as a charge controller. I don’t know which kit you are speaking of, most manufacturers make several sizes of them. Kyocera has a 40 watt kit with a panel, mounting hardware, cables and connectors. Most panels today do have something called, “Bypass Diodes” installed. A diode is nothing more than an electrical check valve, allowing current to flow in one direction, toward the battery, but not the other. This prevents the battery from discharging into the panel at night.
There are instances where you do not need a charge controller. In short, if the panels maximum current rating, called short circuit current, in amps, is no more than 2% of the battery banks amp hour capacity, then a charge controller is not needed. We have two installations here that work that way. Our small home system which provides 12 volt power for cabinet lights, garden lights, and some small 12 VDC electronics in the home uses 4 golf cart batteries wired for 12 volts. This gives us an amp hour capacity of 440 amp hours. Since our 3 panels add up to a maximum of 8.2 amps, well below 2% of the 440 AH rating of the battery, we do not use a charge controller. It has worked well for over 11 years now. The only thing we have to do is make sure the batteries are well watered each month, particularly in warm weather.
There is an excellent book on the subject at your local library, called, “The Complete Battery Book,” by Richard Perez. If you pick it up, just pay attention to the chapters on flooded lead acid batteries, which are almost always the type used in solar applications. Richard also happens to be the founder and edtior of Home Power Magazine, a periodical that gets into the nuts and bolts of home grown energy. I recommend subscribing if you are really going to tinker with this technology. You’ll find great articles and ads for exactly what you are trying to get into. Some other links are posted below.
Whatever panel you end up with, if it doesn’t have diodes or a charge controller, you can get diodes at Radio Shack pretty inexpensively. If the panel is not rated over 4 amps, just get the 6 amp silicone diode, for about 89 cents, and put it right in the junction box on the back of the panel. Make sure the positive output of the panel is first routed through this diode before going to the battery. Hook it up when the sun is out, and see if the battery is getting a charge. If not, you probably have it in backwards, just turn it around. That’s all the charge controller we have on our little system, one diode in the back of each panel.
If you do subscribe to Home Power, you can use their online search engine to look up old articles. Back in 2000 they were so taken with our low cost ultra simple system that they ran an article on it. Use the websites search to look for Small System First if you want to check it out. Good luck Dave, and take care, Rudydoo