On Tue, Oct 15, 2013 at 08:57:38AM -0700, Denny Esterline wrote:
> AIUI he already has several standard car batteries available.
> >
> > I would be tempted to set up three of them with a diode arrangement, an=
d
> > some form of timer that is run from the first one, operates a relay to =
turn
> > the second one on after 24 hours, which won't back feed the first one
> > because of the diodes, and then after another 24 hours turn on the thir=
d
> > one which won't back feed the first two because they have diodes. That
> > should just about get you through the four days if you can find some
> > suitable latching relays so you don't need continuous coil current.
> > --
>=20
>=20
>=20
> Curious - Why?
> If you already have multiples and you already have backfeed diodes, why a=
dd
> a layer of time division? How would this be better than just tying them a=
ll
> to the load with the backfeed diodes?

Of course this begs the question of why the diodes at all. Tie them all in
parallel, charge them up, let them go. They will balance automatically. I'd
suggest having a low voltage cutoff at 11-11.5V that shuts the entire
system off. At that voltage, they are pretty much depleated.

Just would like to point out again that even if you have the starting
batteries, that deep cycle is perfect for this application. Unless this is
a one time exhibit, it would be better to invest in batteries that can deep
cycle. As pointed out in an earlier post, 4 40 Ah LiFePo4 cells either
in a 4S1P (14.4V) using a buck regulator, or a 2S2P (7.2V) with a linear
regulator with minimal overhead would be ideal.

BAJ

>=20
> -Denny
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Byron A. Jeff
Chair: Department of Computer Science and Information Technology
College of Information and Mathematical Sciences
Clayton State University
http://faculty.clayton.edu/bjeff
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