Re: Battery gassing ?

[Michael A Perry <mperry@efn.org>]

Yes, true.  To recap, there are two times when gases are given off, as I
recall.  One is when the battery is very hot in spots (boiling hot) and the
other is when there's enough excess current to bridge between plates.  As in
your HS science class, when enough current is run through water, it breaks
down into oxygen and hydrogen.

I'm getting some late gassing as cells continue to balance themselves.  This
is a drawback to series/paralel battery hookups and having a bad battery in
the pack.

>From having no response, I assume that that balancing circuit I read about
never "flew."  Instead of directly connecting batteries, that circuit would
monitor each battery separately.  In that way, the weaker batteries were not
pulling down the higher batteries, thus allowing each battery to maintain
its max charge, even when sitting between charges.  It was also possible to
throw in a few extra cells (as they do in telephone exchanges) so, when
voltage drops below peak, the fresh batteries are thrown into the loop.
It's sort of a communist philosphy when charging/discharging... to each its
needs, from each its ability.  As I recall, the drawbacks were its
complexity and in developing circuits to handle the peak current... which
equates to $$$.

In telephone use, as I recall, you had 26 batteries.  The DCO pulled from
the first group, providing 48V.  When voltage dropped, each of the spares
was cut in.  The exchange (coil relays stepping the switches and making
contacts) could continue to run quite a long while on its own backup power.
For 96V ringing current, juice passed through an AC converter.

Lee Hart wrote:

> I don't know if we answered this for the more common lead-acids before
> wandering off to nicads and other less-common batteries.
>
> So for the record: No, lead-acid batteries do not normally gas during
> discharge. They only gas during charging, and then only at the end of
> the charge cycle, when they are nearly full and there is nowhere else
> for the energy to go.