[aprssig] Re: OT - DC Auto Charger with auto cutoff

KC2MMi kc2mmi at verizon.net
Mon Jul 19 22:06:23 EDT 2004

<When considering operating mobile/portable do not overlook the DIRT CHEAP
uninterruptible power supplies that are showing up in junk piles and at
hamfests. >

 Um. Except many.most of the cheap ones are designed to run off gel cells,
which run at a significantly lower voltage than wet lead or AGM batteries.
They will not optimally charge "vehicle" batteries, and although they make
great cheap inverter/chargers...they're also designed to recharge that lower
voltage gel cell usually at something like a 20-hour rate, a very slow

 Robert, consider this. There is nothing in your car which "shuts off the
charge" to the car battery itself. Just the alternator regulator, sensing
14.4 volts and trying to sustain it. If you plug your deep cycle (not
starting!) battery into that rear lighter, it will work. It won't ever quite
see as much voltage as the battery up front, because the interior wiring
isn't sized to run a battery. So it may always run .2-.4 volts low, and it
may keep the alternator voltage higher, longer, than the starting battery
would prefer to see. Net result, it should work more or less, just make sure
the starting battery isn't boiling off too much electrolyte and top it up if
it does. For a quick and dirty temporary solution, that will work. (Check
the voltage on both batteries to see how well, or not.)

Ideally, you need to get into a wiring project. Ideally <G> you'd replace
the alternator with one that has dual outputs, with a separate regulator
feeding each battery and no loops between them. Ideally, you'd probably run
0AWG cables to the rear battery, with a high capacity fuse or breaker
mounted on the rear battery. (Do that anyway!) And, you'll want to use an
AGM battery in the rear so there is no danger from acid in another wreck.
Firmly bolted down.

And of course there are lots of options in between. It just depends on how
much time and money you want to put into it, and how well you want that back
battery to work.

More information about the aprssig mailing list