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Old 12-03-2011, 12:45 AM
yikes98 yikes98 is offline
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Location: SoCal
Join Date: Sep 2010
Posts: 111
Mein Auto: e36, e92, e70, e90
Originally Posted by ctuna View Post
so about 3 of these would = one of those if the sun was shinning at a optimum value.
The sun only shines at optimum in SoCal Everywhere else you will need at least 5 panels, just kidding.

Here's the problem (these are best guesses), if the battery discharges around 50 mA while in sleep mode and is a 90 Ah battery, theoretically at 99% SOC to 50% SOC you can get ~5 wks before the battery is no longer happy . Additionally if for example it takes 180 amps to starting that would be ~.25Ah of capacity gone. So to stay charged you need to replace what you use for starting and sleeping based on the alternator can handle loads while driving at a net gain of ~1.25Ah based on 15 min at 5 amps charging of driving per day. Figure a couple starts and a constant drain ~50mA works out to be ~1.7ish Ah/day net loss. About 26 days of this driving cycle the battery will be pissed off. But the good news is you just need to replace about 2Ah/day. So two 12V, 5 watt panels gives ~800mA *.8 sun eff yields 640mA*3.125hrs = 2000mAh or 2Ah. So charging your battery to 90% SOC, use a total of 10 watts of solar, find 3 hrs/day of sunlight and your power budget should be slightly net positive. Or this can be all crap.
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