Solar panel car charger question

I bought a small solar panel intend to maintain my car's battery in winter since I don't drive it often, it's only 1W (80mA) max. I hooked it directly up to the battery with wire running across firewall so panel is placed inside cab, and a 1 amp fuse inline. When I measured everything with multimeter I noticed even thou the panel is only generating about 7 or 8 mA in cloudy days, the voltage is about 22 volts. Does this sounds right? Seems really high given car battery is 12 volts, and the panel voltage will be even higher on sunny days.

jzmtl said:

I bought a small solar panel intend to maintain my car's battery in winter since I don't drive it often, it's only 1W (80mA) max. I hooked it directly up to the battery with wire running across firewall so panel is placed inside cab, and a 1 amp fuse inline. When I measured everything with multimeter I noticed even thou the panel is only generating about 7 or 8 mA in cloudy days, the voltage is about 22 volts. Does this sounds right? Seems really high given car battery is 12 volts, and the panel voltage will be even higher on sunny days.

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I think that sounds about right, if you measured the panel when it was not connected to anything.

When you connect the panel to a battery (through a diode to prevent the panel draining the battery in reverse), then when the panel voltage rises above the battery voltage the diode will switch on and the panel voltage will get clamped at the battery voltage. The panel will then deliver as much current into the battery as it is able, according to the amount of light falling on it.

I'm using solar battery maintainers for a car and a riding mower.

The panel, on my desk receiving light from the office window on a cloudy day, reads about 4.5 VDC.

I connect the car via the cigarette lighter.

For the mower (panel connected directly to the 12 battery), reading between the solar charger lead and one battery pole it get 2.5 VDC (panel and mower are in the garage with the garage door open with cloudy sky).

The instructions say that on sunny days, with the panel in full sun, the VDC should read from 16 to 25.

My panels have reverse, battery draining, protection.

Thread on my Costco solar battery maintainers here, with pics: http://www.cpfmarketplace.com/mp/showthread.php?t=187929

oregon

25 VDC is what I get with the solar panel in direct and full sunlight reading across the cigarette lighter, torpedo-shaped, plug while disconnected from the car.

I got lucky and a patch of blue sky came between me and the sun up the hill where I get southern exposure unobstructed by the tall fir trees.

oregon

Heh, mine looks exactly the same as the costco one but with two ring terminal connector instead of cig lighter, which might as well since my car shuts lighter socket off when keys are out.

So it seems the voltage is normal, thanks, now I don't have to worry about coming home to something on fire.

jzmtl said:

my car shuts lighter socket off when keys are out.

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I wanted to make my car's (2008 Honda Element) rear electrical utility outlet live at my discretion, regardless of whether or not the ignition was on or off.

So I installed a remote switch into the relay controlling that outlet. It works even 50 feet from the vehicle. Originally I was going to install a dash switch but couldn't decide where to mount it. So I got a remote switch, off the ebay, and I couldn't be happier. I have one clicky on my keychain and the other clickie on the dash being held in place by a magnet which I stuck onto the dash.

The 12V remote control kit was inexpensive, less than $20 with shipping, and robust (15 amp maximum). It comes with the small black switch box, two clickies and instructions.

Pics of the 12VDC remote control switch kit:







Link to the vendor I bot from (I have no complaints): http://cgi.ebay.com/12V-15AMP-Relay...photoQQcmdZViewItemQQ_trksidZp1713.m153.l1262

oregon