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Old 09-02-2012, 04:48 PM   #1 (permalink)
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Will 15watt solar panel cook battery

so I have this 15 watt solar panel. . It's cranking out 23 x
Volts. Will this cook my 12 volt battery? Sc

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Old 09-02-2012, 08:10 PM   #2 (permalink)
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That is around an amp and a quarter, for 4 sun hours per day (assuming it's pointed at the sun!) you are going to get 60 watt hours from a 15 watt panel, when I put a meter on my car to see how much power everything drew, just the cars ECU drew around 80 watts, head lights are 65 watts each, it seemed like while the engine was running I could expect around 200 watts draw on the battery so 60 watt hours going in to the battery is not going to charge it much more then about 10 to 15 minutes of driving after you factor in the starter as well.

As for your original question of if it will cook the battery or not? no, it should not cook the battery, even a small 40 amp hour starting battery is going to be able to handle a 1.25 amp charge and as the battery reaches full charge that charge rate is going to drop off to less then an amp.
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Old 09-02-2012, 10:34 PM   #3 (permalink)
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I ran 3 solar panels wired for 22.5ocv at .4amps onto my batteries for several months.
Those solar panels could float the battery voltage up to about 13.5 volts after sitting all day, but this was with 2 big truck batteries.

That setup will over charge a LiFePO4 battery.
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Old 09-03-2012, 12:10 AM   #4 (permalink)
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Quote:
Originally Posted by SmellyCat View Post
so I have this 15 watt solar panel. . It's cranking out 23 x
Volts. Will this cook my 12 volt battery? Sc
Solar panels are current limited. Though the open circuit voltage is very high, it won't ever see it when connected to your battery.

No, it won't overcharge your battery. The amperage that panel can put out is just over an amp as the other person said, and only at the brightest part of the day with the sun overhead. Put it inside your car and it will be even less with the window attenuating the sun.
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Old 09-03-2012, 11:57 AM   #5 (permalink)
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You can always put a volt meter on and see what the voltage is.
also, don't forget to check the water in the battery once a month if you are cycling it every day.
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Old 09-03-2012, 12:39 PM   #6 (permalink)
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Alright, great info.. here is what the the panel looks like on the roof. Do you think I need to mount it different? SC
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Old 09-03-2012, 01:51 PM   #7 (permalink)
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Ideally you wouldn't have anything over top of the panel (reduction of surface area), but even passing clouds have a effect. Also for optimal output is supposed to be angled. That said mine just sits flat on the deck in the back window. I'd be more concerned with movement at speed or emergency braking, looks like the only thing to arrest movement is the tape. Can it also be fastened to the straps. This may not be a concern if it is light enough. The panel I have is quite heavy and is not in use when moving (not secured). What is the physical size and weight of that panel?
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Old 09-03-2012, 02:35 PM   #8 (permalink)
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It's about a foot by 3feet. 15 watt. I have down force with the straps and the tape should stop any sliding around. I hope. Sc
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Old 09-03-2012, 09:48 PM   #9 (permalink)
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I gave my parents a PV panel to keep the 12v battery on their electric car charged, it's held on with just a rare earth magnet out of a computer hard drive, it's a much thinner panel and is only 10 watts instead of 15, but the magnet does a fine job on the hood of their car so a few magnets of that type might do well to hold yours in place.
Shading is an issue, any area of a PV panel that is shaded is not just a reduction in output but it becomes a load, so shading half of a panel doesn't cut the output by half it cuts it's output to almost nothing.
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Old 09-03-2012, 10:00 PM   #10 (permalink)
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If you are going to mount multiple panels then the roof is the way to go, but for one, maybe not so.

Not sure what your driving or if this would work.
I have pretty much the same solar panel as you sc i covered the frame with some water pipe foam insulation and secured the panel on top of the front dash board. The rear dash may work better for some of the cars.

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