SOLCHG.THD --- Copyright 1987 by Phil Wheeler An original compilation of Compuserve Model 100 Forum messages for use by Forum members only. The promise of using the sun to recharge batteries is always intriguing -- sort of something for nothing (well, AFTER you own the solar cells). This file is a series of technical messages addressing the ins and outs of solar charging, with the final message a from a user who has done so. Message range: 154268 to 154293 Dates: 8/6/87 to 8/7/87 Sb: #Need Electr Engnr Advice Fm: DAVE SCHNEIDER 75725,1204 To: All I'd like to wire a solar cell to a 12 volt battery we use to power a CB radio and a few marine lamps at our vacation cottage. There's no electricity there, and I'd like to find out whether the solar cell can be used to trickle-charge the battery. I've never understood electricity too well, since I can't see it. Anyone willing to advise me on how/whether this can be done? The solar cell is about 8X10 inches and has some performance characteristics on the back, but I have no idea what they mean and there are no instructions. I'd welcome advice (or willingness to try to help) here or by EMail. If anyone answers I'll describe the solar cell in detail. Thanks. Dave Fm: Wayne Day 76703,376 To: DAVE SCHNEIDER 75725,1204 There's hardly any way that such a small solar cell would be able to directly power a CB transceiver (which would draw a couple of amps at 13 volts) or your marine lamps (which would probably draw quite a bit more power). What you're probably going to have to do would be use the solar cell in a charging circuit to keep a 12v car or truck battery charged. The schematic of such a charger isn't super-extensive, but it's probably a bit more than could be easily explained in one or two messages... you might wanna dig out a text on solar cells from your library, or look through past issues of Popular Electronics and 73 magazines for suitable circuits. A note on HAMNet (GO HAMNET) might find someone with an extensive 73 library that would be willing to do the research for you, though a trip to your local Radio Shack might be quicker (they do sell a solar cell system, but I don't know what it involves...) Fm: Tony Anderson 76703,4062 To: DAVE SCHNEIDER 75725,1204 The solar cell probably doesn't have enough capacity to recharge your battery after any significant use, because of the small amount of current available from it. Small solar cell arrays are more likely to be useful in charging flashlight batteries and the like, rather than car batteries; just not enough current. Typically, your solar cell would put out enough current in a day to power a single automotive type light bulb for an hour or so. With that type of performance, your battery is going to go dead rather quickly. Larger solar cell arrays cost much more money, of course... some that are used on satelites, etc., cost upwards of $40,000. There is a forum on CompuServe that might have the sort of information you need; it's the Good Earth Forum, and they cater to survivalists, "Back to the Land" people, and others who are interested in living simply, away from modern societies complications. They were originally sponsored by the people who printed "The Whole Earth Catalog" series, if that rings a bell. You can try GO EARTH to get there, or perhaps use the FIND command to locate the correct forum name. Fm: DAVE SCHNEIDER 75725,1204 To: Wayne Day 76703,376 Thanks for the quick response. We currently drive the CB off a car battery that we charge at the beginning of the summer and leave at the local marina all winter. It normally works all summer on the one charge since we only use the radio occaisionally. I found the solar cell on sale and thought there might be a way to give the battery a little help. (when I thought of trickle-charging, I guess I really meant trickle!) All I'm really trying to do is keep from turning the solar cell into a short lived frying pan or flash gun when I hook it up. Fm: DAVE SCHNEIDER 75725,1204 To: Tony Anderson 76703,4062 Thanks for the quick response. I'll take your advice and try EARTH (used to love their books -- we have a number of them at the cottage, though, as my query suggests, I'm not opposed to comforts.) We don't use the current rig much, so one charge of the battery in June keeps the CB radio going all summer. It seemed the trickle, however small, would help, particularly if I put up a couple of small reading lamps, like the dome light in a car. Some of the navigational markers up there -- flashers -- seem to have a solar cell device to keep their batteries charged. Fm: Marlin Bially 74240,126 To: DAVE SCHNEIDER 75725,1204 To figure out if your cell will do you any good check the specs for it's amperage output. look for something like .2A, 200mA, 100 milliamperes once you get that you can do some quick math. If your 'system' is 100% efficient and your cell puts out 100mA (100/1000 of an Amp) and you charge your battery for 10 hrs you have put 10 x 100mA/hrs into your batt. or an equivalent would be 1Amp/hr (10x.1=1) Now if you run a reading lamp that 'draws' 1amp for 1hr you just used up that 10 hr charge. The idea is the batt. stores the energy slowly but you can use it fast. So if you use your solar cell to chrg all day. You could read for a couple of hours at night and not run down your batt. Most the things that 'draw' power are also marked with amp ratings, so just multiply by how long you thing you'll use it. The main idea here is like a checking account balance what you put in and what you use or 'draw out' If you find your going to need say 2amp hrs a day but can only charge 1.5 per day eventually your battery will run down it has to make up the .5 differance and it can't do it forever. REALITY: we're assuming alot here. your system will probably be closer to 85-90% effective on the charge end also on cloudy days you won't get the full out put rating (probably less than half) But even a small 100mA cell would allow you a couple of short conversations a week even with a 2-3 amp CB with out depleting your batt. Fm: Wayne Day 76703,376 To: DAVE SCHNEIDER 75725,1204 Should be fairly easy to do just that, Dave -- a couple of diodes and a voltage regulator.. Fm: Joe Holland 73720,1605 To: DAVE SCHNEIDER 75725,1204 The solar panel I have cost me about $130 and is 11 iches by 20 inches, and is about the minumun size to be useful for your application. It produces about half an amp in full sunlight. This means if it is in the sun for 8 hours, charging a storage battery, it will run 1 (one) light the size of an automobile dome light for 3 or more hours. It would also run a 600 portable continuously, since that is near the same current as suplied by the 600 power supply. My panel has 32 cells. The optimum number might be 34, but I haven't re-examined that lately. A smaller number would do to power the 600. Another solution is to buy a deep cycle storage battery of the type made for electricly powered trolling boats. I got mine at K mart on sale for $60. This has twice the capacity of ordinary car batteries. You then put it in your car for the long drive to your summer home, a trip that mqy overcharge smaller capacity batteries. You take your regular battery with you, and reinstall it in the car when you get there, and move the deep cycle battery to the cabin, where it will run the lights for three or four evenings. You will need a battery hydrometer to keep track of the charge. Avoid "service-free" batteries (nonsense) that you can not get into with the hydrometer. My next solar panel will cost about $160 in cells, and will supply over one amp. I will supply data and sources, if there is interest. You may hook up a 12 volt rated solar panel directly to the battery, provided you connect the positive line, usually red, to the battery positive. It will leak backwards a little when there is no sun, draining the battery only slightly. Either disconnect on no sun or use a diode in series, with the cathode to the battery positive, and the anode to the red wire. No regulator is needed. Rather, use the hydrometer and stop the charge when you get into the green region.