Got 3 small solar panels, wondering which(if any) are ok to leave on a car which doesn't move much to maintain battery. All plug into the cig-lighter ,(which does not go through ignition switch). Battery is medium size 670CCA 1) smallest reads 14.7v and 0.06A 2) middle one reads 16vand0.01A 3) biggest reads 19v and 0.3A. Any advice appreciated, muzz.
jason_247,
Jan 24, 2:13pm
if they are plain panels then the 14.7 would not run the risk of over doing it. the other may be abit high
though best bet is to get a proper solar maintanence charger as they charge but then switch to float mode so no chance of over charging. start at around $20 as supercheap.
ceebee2,
Jan 24, 2:51pm
Definitely need a solar regulator so that when the battery is fully charged the reg will switch off otherwise they will overcharge and eventually "boil" the battery dry.
kenw1,
Jan 24, 3:40pm
All three will only make 370mA, so unless the battery is 100% and you leave them in bright sun and track the sun all day it would be miracle to boil a battery with that current.
Put all three in parallel and make sure you have a diode in the line to stop any backward current flow. The diode will loose 0.7 volts anyway.
tony9,
Jan 24, 4:50pm
Something wrong there. 19V across a 670CCA is going to draw several Amps, as it cooks the battery.
kenw1,
Jan 24, 5:36pm
The voltages are all probably off load. Do you have a meter? put the biggest panel onto the battery the 19 volts at 300 milli amps and see how much current it really will deliver.
If you want to be real cautious (I would) use a whisker of the wire just at the end to test the current delivery, like a short piece of fuse wire.
kenw1,
Jan 24, 5:36pm
It will not be drawing current, it will deliver current.
muzz67,
Jan 24, 7:07pm
Yes, test done without being connected to battery, with small multi-meter. So I should hook it to the battery and see if the combined voltage goes up at all? Thanks.
poohy99,
Jan 26, 12:48pm
Hook 'em up and as long as the battery voltage doesn't go over 14.0 V you will be fine.
eagles9999,
Jan 26, 1:58pm
If you don't use the car often the 14v one should be adequate
muzz67,
Jan 26, 3:28pm
Thanks for the help folks,, hooked up the biggest panel for 3hours today, in good angle to sun. Battery went from 12.6v to 12.75V, so stuff all difference really. safe to assume its capable of maintaining but may not charge I guess.
I used one of those dash top solar trickle chargers very effectively last year
intrade,
Jan 27, 6:22am
my mate put one of them solar panels on his car went away for 5 month . dispite me telling him all he needs to do is fully disconnect the battery and it be fine. Anyhow he came back and the battery was. flat. do you need more of a idea now if you should buy the junk or not?
intrade,
Jan 27, 6:25am
you need a big panel to charge it and a controller so it dont boils the battery. small ones will deplet the battery while the constant use of the standby is just the same as what the cheap panel puts in the battery , once you have 2 days of no sun in winter = you depleted it by that and it wont be able to bring it back. down and down it goes like this.
kenw1,
Jan 27, 3:37pm
The best tool to check the state of charge of a lead acid battery is the good old hydrometer.
The panel will not discharge a battery if there is a diode in series with it.
johotech,
Jan 27, 3:52pm
It is very difficult to measure the battery voltage accurately. It also depends how long after you disconnected the panel, that you measured the voltage - and the accuracy of your meter - any meter under at least a few hundred $$$ is unlikely to be accurate.
Anyway, if your battery actually did charge from 12.6V to 12.75V, then you have gone from roughly 90+% to pretty much 100% charge. But there are a lot of variables, so I doubt your figures are actually accurate. The only thing you have shown, is that it probably charged a reasonable amount for 3hrs on the panel.
Also, most solar panels have a diode built in, so it's not usually necessary to add one yourself. You can test this by checking if the current reverses (using your meter on milliamps scale in series with the panel & battery), when you cover the panel.
jason_247,
Jan 27, 7:20pm
wow so an internet cowboy has a mate who used something once and it didnt work.
better ditch the whole idea of ever using one.
i hope you dont take your own ideas that seriously.
they are simple and work. Maybe his battery was poked. maybe part of his car was drawing more power because it was faulty. maybe he didnt hook it up right. (cig adaptor doesnt work for all cars when ign off) or maybe coz you know a muppet everyone should go back to what? hand wiring old shit panels together? seems way more legit.
fordcrzy,
Jul 16, 6:54pm
i have a 5watt one on my car and it does a great job of maintaining the battery all year round
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