Solar Battery Chargers

[CraigL]

I have a 26' cabin crusier cabin with two batteries. I am not rigged up for shore power and don't intend to. I am going to be running alot of electronics inside. (TV/VCR, fans, coffee maker,etc). I was planning to install a second battery in the main cabin inside a storage closet. (Probably will have to cut a small vent hole in the side of the hull for battery gases to escape).<br /><br />Questions: I was planning on purchasing a SOLAR BATTERY CHARGER to charge this cabin battery. The solar charger is 1.5 W (about 325mA). Will a solar charger with this wattage charge a half dead battery in a week or two time frame. (This is about how often I get to the lake)?<br /><br />Also, as this charger does not have an auto shutoff (I do not want to overcharge), I was thinking of rigging up a timer circuit that I could set for days or 1 week, such that it would interupt the charging current, if for some reason I did not get to my boat for weeks at a time (I sometimes have work related travel that would take me out of town for weeks and I would not be able to shut off charger before departing.<br /><br />Does anyone know any calculations that would give me an idea of how long it takes, at 325mA charging, to charge a battery?<br /><br />And Yes, I have thought of tieing in this 3rd battery to the existing two, but then I would have to replace the alternator with a higher charging current one (or be constantly flipping the parralle swithes etc and the heavy wires (#4) that would have to be run into the cabin, I have decided that a $15 solar charger may be the way to go.<br /><br />I like the idea of being total self-sufficient with no relying on shore power.<br /><br />Any feedback will be greatly appreciated.<br /><br />THanks

 

[SlowlySinking]

Re: Solar Battery Chargers

CraigL, Maybe! Your solarpanel puts out 1/3 of an amp. So for example a 60 amp hour rated battery would take about 180 hours to charge if it was run down pretty bad, now that's assuming the solar panel to battery wiring has no voltage drop, and the panel is looking directly at the sun all day, no clouds, and how far you are north of the equator; so 10 hours of bright sun a day would pump in 3 and 1/3 amp hours of charge, a week adds about 22 amp hours of charge; so if the battery isn't run down too bad it would likely do the trick in 1 or 2 weeks.

 

[Boatist]

Re: Solar Battery Chargers

Craig<br />Did figure wrong as I only get .125 amps or 125 ma. P=IxE right. That figure would be if your cell tracked the sun and no clouds no shade. Do not forget batteries self drain also. I think you need at least 12 watt to do any good.

 

[petryshyn]

Re: Solar Battery Chargers

CraigL<br />Boatist is right, you need atleast 15w or more pending on requirements.<br /><br />The formulas you are looking for is:<br /><br />amps used X time<br />If you use 20 amps for 4 hours, that equals 80 amp/hours.<br />It will take a 15w solar panel 80 hours of sunlight to replenish the battery. <br />It takes a badass panel to really do the job....60w is ideal.

 

[KenOhki]

Re: Solar Battery Chargers

I dont think a 1.5w panle will do you much good. The way I was taught it, amps x volts = watts,, so, watts devided by volts will give you .125 amps of charge power at 12 volts. so,, 8x .125a = 1 amp. so, it will take 8 hours ( roughly ) to put 1 AH into your batt. mind you this is not accounting for battery self drain either. So 7 days, with 8 hours of solid good light will give you roughly 7 AH charge. were I to do what you are wanting to, I would want a solar pan with 6 12 or 15 watt rateing. providing .5 1 or 1.25 amps respectivly. I feel charging at less then 1/2 amp is not worth wile or effective, even over the week or 2 rest you give it to charge. At 1/2 amp charge I would not worry about overcharging, but at more then 1 amp I might start to worry a little, at more then 2 amps charge, I would definitly worry about overcharge if left alone for weeks at a time.<br /><br />a windmil generater might also provide you with what you need if you have decent wind around your boat, a 21 foot boat might be able to hold one. check out http://otherpower.com/ for all sorts of ways of generating usuable 12 volt power ( notmy websight, I just love it to death thought, very creative people over there )