RE: parallel packs?

[Larry Elie <lelie ford com>]

----------
From:   vic garza[SMTP:vtr-garza worldnet att net]
Sent:   Monday, January 04, 1999 9:00 PM
To:     Ken Olum
Cc:     elec-trak cosmos5 phy tufts edu
Subject:        Re: parallel packs?

;At 09:25 AM 1/4/99 -0500, Ken wrote:
>
>   I would be careful about paralleling poorly matched battery
>   packs. With a mismatch, you can have one pack drained before the
>   other.  Usually it will be the weakest cell which goes first.
>
>No, battery packs which are more fully charged will have a higher
>voltage under load, so the power will come from the charged battery
>pack rather than the uncharged one.  You can only have a problem with
>over-discharge if different batteries are in series.
>
>                               Ken
>

;Have heard its not a good idea to leave batteries connected in parallel at
;rest, wonder if there's any truth to it?  I've noticed when charging 
smaller
;nicad paks in parallel that one pak will be undercharged after several
;cycles so I have to go back to charging each pak individually-  wonder if
;lead systems are similar? Any other situations where batteries should not 
be
;paralleled?

;--Vic

David already answered this, and he is right about how they work in 
parallel 
(unless you do some other regulation tricks, but that involves some active 
elements), but I do want to point out that NiCad's and lead-acids have 
different memory effects.  I am told are due partly to chemistry and 
partly to geometry.  Newer NiCad's are better in this regard, but part of 
what you see on old NiCad packs is memory.  They don't like to be 
fully charged after a partial charge.  In a series wired pack, one of the 
cells typically doesn't get a full charge once, and has more of a problem 
the next time.  Bummer.

Larry Elie