Charging batteries from batteries? [RE-wrenches]

[Gary Higbee]

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Wrenches,

I'm scoping a project for the Forest Service that could fund a solar
charging station for electric boat batteries--this to encourage the use of
electric trolling motors rather than obnoxious and polluting gasoline
engines on a pristine alpine lake. This project is particularly exciting, in
that it would bring solar technology to a lot of people, as this is a
highly-visible location. We're also looking at including enough capacity so
that the local concessionaire could provide ice (hmm, for fish or for
beer?).

The idea is to provide around 6 $-operated lockers in which one places their
deep cycle battery, hooks up terminals, and comes back so many hours later
to collect the charged battery. Numerous challenges exist, including:

1) Make the system safe and fool-proof. The battery clips need to be able to
be shorted and reverse-polarity protected. If there are two possible ways to
hook something up someone will figure out four!

2) Have a clear indication that things are hooked up right and that charging
has begun (red light, flashing green light or such).

3) Have a clear indication that the battery is charged (green light or
such).

One aspect I'm scratching my head over is what the best charging method
would be. I vastly prefer using off-the-shelf components than custom
circuits, and DC-DC conversion where possible. I wonder whether it might
make sense to use a small (reverse polarity protected, charge status
indicating) PV charge controller for each battery to be charged--all
supplied from a considerably larger PV-charged battery bank at a higher
voltage.

Do you know of a PV charge controller that:

1) Will accept close to 30 volts (i.e., 24-volt nominal main battery
charging system).

2) Has indicator lights as to when it is correctly connected.

3) Is reverse polarity protected.

4) Is short-circuit protected.

5) Is very reliable.

Does this system make sense? Any other ideas?

I've thought of one--and that is that folks buy two deep cycle batteries,
and need to have one battery in the box and charging by morning so that it
charges during the DAY, rather than the night (i.e., we lock out the system
at night with a timer, and can reduce the battery bank size). Asking folks
to change this much, this fast, might be a deterrent, though.

Your thoughts on this project would be greatly appreciated!

Thanks,

Gary

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                     ~ Windstream Solar ~
     Gary Higbee  (gary at windstreamsolar.com)
                     (541 ) 607-1818 (Eugene)
                        (541) 954-3881 (Cell)
Solar, wind, and hydro site analysis and system design
    Components dealer and installation assistance
 Energy Trust of Oregon contracted system inspector
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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