Is a 5 Watt Solar Charger Enough to charge a Car Battery?
If I bought a random crap car battery would this be enough to charge it completly over time. Just putting it in the sun and hooking the red and black to the battery? Will this do that job. thanks
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=41144
I will be up in my tree house once a week to spend the night. Will this charge it fully by the end of the week so I can have lights, music, and basic electricity up there for about 12 hours?
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4 Responses to “Is a 5 Watt Solar Charger Enough to charge a Car Battery?”
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If the battery is completely dead or near dead, it would take a few days or more for that thing to charge it up completely assuming the days are sunny. And assuming the battery is somewhat good and chargeable.
At 13 volts and at peak output the solar charger will only be delivering slightly more than 1/3 of an amp. (Ohm’s law: 5 watts divided by 13 volts = 0.36amp) Less on partly sunny days.
But just for keeping a battery charged while in storage that should be ok.
those solar charges are only meant to keep batteries from losing their charge that results from disuse, not to continually recharge a discharged battery incase you ar e wondering.
Do the math. Typical car battery is 70 amp hours (your battery will say). 1 watt = 1 volt x 1 amp. 70 amp hours @ 12 volts = 840 watt-hours.
So your 5-watt solar charger will take 168 hours of full-on sunlight to fully charge that battery. 168 hours is exactly 1 week (24 x 7 hours). However most of the time the sun’s not out, and even if it is, the charger may not be working at its full 5 watts, because it’s a Harbor Freight piece of junk made in China.
However, it works in your favor that you probably won’t drain that battery all the way down. (regular car batteries can’t survive being deep cycled, about 10 deep drains and the battery is ruined.) So if you only use 25% of the battery’s capacity, you should be fine. That’s 210 watt-hours or 50 watts for 4 hours. (I’m assuming you won’t have lights/music while you’re sleeping.)
I don’t know exactly what car battery you have, but in general, I think that they need about 2A at least in order to absorb charge. I’m pretty sure that the Harbor Freight panel doesn’t put out that much. If you can find out the amp-hour capacity of the battery, take 5% of that as amps, and try to find a panel that will put out at least that. A 60 to 100-watt panel is probably appropriate.
For any lead-acid battery, there is a minimum charge rate. If you go below that, you can maintain the charge that’s already there, but no more.