Re: balancing buddy pairs

[Lee Hart <leeahart@earthlink.net>]

Michael Haseltine wrote:
> Unfortunately, that sort of process would take me 6 months of my free
> time... doing it as two 120v strings should be as good and take a hell
> of a lot less work.

The fundamental problem is that you are charging and discharging the
batteries in series at identical currents, as if all the batteries are
identical.

But they are not. They have slight differences in amp-hour capacity,
internal resistance, temperature, charge/discharge efficiency, etc. As a
result, they wander apart, and aren't at the same voltage or state of
charge. You get less range (limited by the least-charged battery) and
less life (limited by overcharging the most-charged battery).

To correct this imbalance, you have to charge or discharge the batteries
differently, to bring them back into balance.

The easiest way to do this is with a good automatic charger. It will
charge each 12v battery, and shut off consistently at the same state of
charge. It should not be a float-type charger, but rather one that does
an equalizing charger (high voltage at low current). Each day, connect
it to a different battery and leave it until it shuts off.

If you want to get the job done quicker, you can measure the individual
battery voltages, and connect this charger to whichever one is the
lowest. Move it to the next battery as soon as it turns off.

I generally measure battery voltages about one hour after a drive,
before charging. The lowest voltage indicates the most deeply
discharged, or weakest battery.
--
Lee A. Hart                Ring the bells that still can ring
814 8th Ave. N.            Forget your perfect offering
Sartell, MN 56377 USA      There is a crack in everything
leeahart_at_earthlink.net  That's how the light gets in - Leonard Cohen