JIM HOLSONBACK wrote in a message to MATT MC_CARTHY:

 JH> In my ignorance here, I have an old Sears Craftsman 6A automotive
 JH> type charger, 6V/12V, 

A good choice for those gels.

 JH> and I've used it a number of times in testing/charging gel cels. 
 JH> From memory, when I connected to the commonly-used 12V 7AH 
 JH> batteries which would take a charge, it would typically start out 
 JH> showing about 3A on the meter, then taper down pretty quickly to 
 JH> 1A or so.

Sounds about right to me.

 JH> AT those charge rates, battery would typically get warm, but not 
 JH> hot enough to split the case, or any other disasters.  I've heard 
 JH> of gel cels 'blowing up" when being charged too rapidly.

You have to be pushing them pretty hard for that to happen.

 JH> FWIW, and IME, 'bad' gel cell batteries I've seen would generally
 JH> not even start to accept a charge - the bad ones I've seen seem to
 JH> have failed to an "open" condition.

Either that or they were simply not likely to want to accept any charge. 
I've seen stuff (of both gel and "wet" variety) that would act
that way for quite a while,  but if you were to leave the charger connected
long enough it would take some charge,  eventually.  We used to have
"series chargers" at the battery store,  which were kinda nifty, 
you had a selector switch with a *lot* of positions,  and a transformer in
there with a whole mess of taps on it,  and you could connect as many as
5-6 batteries in series,  to charge them all at the same rate all at once. 
Sometimes that unit was handy to "push" batteries a bit,  if they
needed it,  though that technique was better left to the automotive types
than gels.

 JH> So I think Mark is pretty much safe if he sets his charger to the
 JH> 2A rate.

Probably.

 MM> Gel-cells have a thermal runaway problem when they get near their full
 MM> charge point, they will overheat and then short out, killing the
 MM> battery and causing a lot of swelling of the plastic case.

 JH> I haven't seen that problem with this Sears charger - maybe it has
 JH> current-limiting circuit which keeps the thing from getting away?

Does it say "Automatic" on the front of it anywhere?  If so, 
then it does taper the charge off some.  The other type doesn't have that
ability,  and will push a battery harder,  in the long run.

 JH> The only swollen and even cracked battery cases I've seen were in
 JH> batteries already apparently 'dead', which wouldn't begin to take a
 JH> charge.

Cooked dry,  I guess,  or discharged at *way* too high a rate.

 ml> what's the best way to load test them to see if they are still
 ml> good?

 MM> Put a 12V automotive bulb on them that draws about two Amps, like a
 MM> dome light bulb.  A tail light will run about three Amps, a stop light
 MM> about 5 Amps, and a headlamp about 8 Amps.

 JH> Hee. Our Director where I volunteer, after they appear to be
 JH> recharged, just says to put them in a UPS and plug a 3/8" electric
 JH> drill into the UPS.  If the drill spins OK, he says that is a good
 JH> battery.  I don't always agree with that fellow, so I put them into
 JH> a UPS, plug in a computer and monitor, and then unplug the power -
 JH> - if the 'puter keeps running, I figure that is at least a "good
 JH> enough" battery for the stuff we give away.

For how long,  though?  With a new set of batteries the UPS I had would go
for maybe 20 minutes to 45 minutes,  depending on the state of charge and
on the load.

 ml> what does the 11Ah (Amp hours) really signify?

 MM> Exactly what it says, Amps x hours.  That 11 AH should put out 1.1 Amp
 MM> for 10 hours, or 11 Amps for one hour, or 5.5 Amps for two hours, etc.

No,  that's spec'd at a 10-hour rate.  For higher draws you get less than
what you'd think,  and for lower draws,  you get longer.  Some of them are
spec'd at the 20-hour rate.

 JH> OK but I think the battery capacity isn't that linear - - probably
 JH> tapering down during more rapid discahrge rates.

 JH> So what could it be expected to put out for 15 minutes or so, which
 JH> I think is about what most of these consumer/small office UPS units
 JH> are designed for?

 JH> The APC 420 Smart UPS Pro unit I have here just uses a 12V 7AH
 JH> battery - - just 84 watt-hours of power. Figure in my system unit
 JH> and this 17" monitor, and if those suck up 240W or so of power, I
 JH> figure I'm down in the 15-minute range of reliable backup power,
 JH> with this battery now a couple years old. Looks to me like this
 JH> type of UPS unit is clearly designed just to give a user time to
 JH> shut things down just after the power goes off, not to provide
 JH> multi-hour protection and continued operation.

That seems to be the case with most of them these days.

 ml> i've also two "speciality" packs... they are 6 2volt 25Ah all
 ml> tied in series to give a single 12volt unit but i don't remember
 ml> (as above) which way the Ahs go... i'm wanting to charge these as
 ml> well and ensure that they are all up to snuff...

 MM> In series, the AH remains the same, but the voltage increases, just as
 MM> you have stated.  Charge rate is always 10% of the AH, so those
"packs"
 MM> would be charged at 12V, 2.5 Amps for 10 hours.  If you have a 2V
 MM> charger and have access to the connectors between the cells, you would
 MM> do MUCH better to charge and test each cell individually.  So long as
 MM> the pack is not connected to anything else, there is no need to
 MM> disconnect the connectors between cells for individual charging and
 MM> testing.

 JH> Where to find a 2 Volt charger? 

Connect 3 cells in series and use a 6v charger?  Or put a bulb or other
current limiting thingy in line with it...

 JH> Do they use those at the golf course? 

Golf cart batteries are 6v,  and *big*.  Had a guy come by for a set of six
of those,  and he had his whole family in his Caddy.  Took three of them
with him, and came back later for the other three.



 JH> All OK, _if_ he can find female "spade lug" connnectors of right
 JH> size to connect your wire sizes to the lugs on those batteries and
 JH> battery packs.

The yellow ones (?) seem to be able to deal with 10-12 wires,  I guess.

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