> BB> I've also been working with some gel cells and getting fair
> BB> results recharging those at pretty high voltages of 60 volts or
> BB> so. It's a lot harder to get much current through those than it
> BB> is car batteries.
 
> What amp-hour rating are the gels you're talking about?  I didn't think
> that those were really designed to do all that much with high currents...
 
Most of them are in the 2 to 7 ah range and most are 12 volts. They don't
pass much current at all (milliamps usually) and when "dead" probably
won't pass anywhere near their normal amount. I find that I can take
a single 12 volt 6-7 ah gelcell and using the same charging setup I do
on car batteries that I can hook up just 1 gelcel across the charger
and get little or no results at all. If I did that with a car battery
I would have fire flying all over the place and likely a blown circuit
breaker or diode. I normally put 8-10 gels in series when starting 
with a fresh bunch of gelcell cores. Then after a few minutes I start
using the voltmeter across each individual cell and pulling those with
very low voltage readings. I replace those until all the cells are
showing me a reading in the 11 to 13 volt range. Then I let those all
charge for about 18 hours or so. I end up with most of those charging
and hopefully ready to return to service. After that, I put another
8 to 10 in series and using the voltmeter weed out the ones with very
low voltage readings. Once I get to that second stage I find that I
am not likely to get any good ones no matter how long I leave them
charging. I have only gotten my mitts on one bunch of about 40 or so
gelcells so I don't have a lot of history to go on, but so far it
looks like it's the way to go on rebuilding gelcells.
 
> I used to sell those for various applications, and there was a guy who
> wanted to use a 7 AH unit to intermittently supply short bursts of 3-4
> amps for as much as a minute at a time.  I recommended that he get
> something a little heavier,  and sure enough,  he was back after a few
> weeks and that unit he insisted on getting was fairly well cooked.
 
I would think so. Seems to me that you would just about need a car
battery to supply that kind of current for even a short time although
I have some 1000 watt UPS systems that *normally* use 4 gel cells of
the 7 ah variety at 12 volts. In the *normal* configuration, they will
supply a max of 5 amps for about 20 minutes to a computer or whatever.
Since I often do things outside of *normal*, I am using one of them
on my bbs system. It has 4 12 volt car batteries hooked up in parallel
with the 4 gelcells and that will run the computer alone for about 3
or 4 days before it gets down to about 95 volts at which point the
computer gives up the ghost and shuts down. Then I just recently
paralled another bank of 8 big computer batteries on top of that.
These are wet cells too and are 6 volts each. They are rated at 100AH
@ 8 hours each. They are Gould batteries and I can't get ahold of
the Gould Co. to ask them how long those batteries would hold up
under a 5 amp load so I don't really have the foggiest idea how
long they would last. I got ahold of one idiot from Exide who told
me that they would last about 20 minutes at 5 amps draw. When I told
him that 4 7ah gelcells would do that then he admitted he didn't have
the foggiest idea how long the big wet cells would last. It looks to
me like that they would stand a draw of 100 amps for 8 hours so
dividing that out for about an actual 3 amp draw they would last for
at least 33.33333333 times 8 hours or something like 250 hours at
which point they would be dead. That means about 10 days of running
except that the computer would go dead at the point where they were
drained down to 95 volts. So ratio-ing that says that 95/122 (volts)
would say that they would only be drawn down to about the 75% level
during any given power outage. So 75% of 250 hours would be more
like about 62.5 hours useful running time. That's about what I have
been getting out of the 4 standard car batteries so with all 3 banks
hooked up to the unit it looks like I might be able to run for about
125 hours or about 5 or 6 days. 
 
Do you think my assumptions are pretty close or not?
 
Bill Bauer
--- DB 1.58/004358
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