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Re: [Shop-talk] Solar car battery chargers

To: <shop-talk@autox.team.net>
Subject: Re: [Shop-talk] Solar car battery chargers
From: "Randall" <TR3driver@ca.rr.com>
Date: Mon, 11 Oct 2010 10:34:24 -0700
>   Hm.  In attempt to keep it simple, can I just buy two and plug one 
> into the power port (a cigarette lighter) and one into the actual 
> cigarette lighter spot?  Assuming, of course that I can 
> manage to keep 
> the cigarette lighter itself in an 'always on' state?

Sure, if that is "simpler".  You could even buy one of those "Y" cables and
run both panels into the same outlet, if that's what works for you.

My guess is that you'll want bigger panels than the one you linked to on
Amazon anyway.  I couldn't find a rating given, but their "quickly starts
your engine" claim borders on fraud IMO, so I'd look for something else that
at least gives some indication of capacity.

How much you need depends on a lot of things that are kind of hard to
analyze; probably easiest is to just start with one big panel, then add a
second if the first one isn't enough.

Wikipedia estimates self-discharge for a starting wet lead-acid at 3-20% per
month.  If we assume 10% and ignore a whole bunch of other factors (and I
didn't slip a digit somewhere), then you can add together the RC of your two
batteries and multiply that by 1.25 to get (very) roughly the number of mAh
per day you need.  Of course, you'll need to add to that any parasitic drain
from the truck (which you can measure).

Then you have to convert whatever rating you get with the solar panel into
average mAh per day for your conditions, which is a whole nother can of
worms.

Randall
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