Hi, Matt.
You apparently posted this on 4/24, and this is one that I was missing.
I finally went back to Docsplace and reset msg pointers yesterday 4/26,
and downloaded the last 375 or so msgs in this Echo, and it showed up
this time.

-=> MATT MC_CARTHY wrote to MARK LEWIS <=-

 ml> i've several 12volt, 11Ah batteries here that i'm wanting to
 ml> charge and load test...
 ml> can i charge them with a standard car battery charger? what
 ml> settings should i use?

 MM> You didn't state what type of battery, but from the context I assume
 MM> gel-cell type.

Yes, that's what I'm talking about also.

 MM> With a lot of care, you CAN use a car charger, but you MUST use a
 MM> current limiter.  11AH batteries should be charged at 1.1A for 10
 MM> hours.

In my ignorance here, I have an old Sears Craftsman 6A automotive type
charger, 6V/12V, and I've used it a number of times in testing/charging
gel cels. From memory, when I connected to the commonly-used 12V 7AH
batteries which would take a charge, it would typically start out
showing about 3A on the meter, then taper down pretty quickly to 1A or
so. AT those charge rates, battery would typically get warm, but not hot
enough to split the case, or any other disasters.  I've heard of gel
cels 'blowing up" when being charged too rapidly.

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

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

 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.

I haven't seen that problem with this Sears charger - maybe it has
current-limiting circuit which keeps the thing from getting away?  The
only swollen and even cracked battery cases I've seen were in batteries
already apparently 'dead', which wouldn't begin to take a charge.

 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.

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

 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.

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

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

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

 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.

Where to find a 2 Volt charger?  Do they use those at the golf course?
I dunno if Mark's charger has an ammeter on it, but I wouldn't hesitate
to hook up the good old Sears 6A charger here to one of those 12V 25AH
battery packs, and watch the ammeter carefully, esp at the start.  If
all went well, I could go back and check individual cells later.

 ml> when it all comes down to the end, i'm wanting to tie these all
 ml> together in parallel to go for 12volt, ??Ah so as to boost my
 ml> uptime on my UPS' when commercial power is off...

 MM> Sounds good.  You have three 12V {at} 11AH, for a total of 12V {at} 33AH, and
 MM> two packs that together will give you 12V {at} 50AH.  With_everything_
 MM> connected, you would have 12V {at} 83AH.

And a rat's nest mess of 5 batteries and batt-packs spread all over the
floor?

 MM> Your computer will need about 120 Watts to run with monitor, a wee bit
 MM> more to start up, but lets not worry about that, as it will already be
 MM> running in most cases.  Excluding lots of annoying formulas, Watts is
 MM> basically Volts times Amps.  To get 120 Watts from a 12V system, you
 MM> will need to be pulling 10 Amps.
 MM>  If you do that for two hours, you have used 20 AmpHours.  If all your
 MM> cells are working and fully charged, you should have about 83AH, and
 MM> get about eight hours running time for the FULL computer.  Triple that
 MM> with the monitor turned off, or about 24 hours.

Sorry, this sounds pretty optimistic to me.  All cells fully charged,
and all able to deliver AH as specified for new ones? And where do you
get 120W for a full system with monitor?

 MM> 12ga wire is rated for 15 Amps, and that would probably be good enough,
 MM> but those cells can easily put out 100A if shorted, and you are
 MM> paralleling a bunch of them.  I would recommend 8 gauge, and in any
 MM> case, nothing smaller than 10 gauge.

 MM> As far as the connectors, my "standard" UPS uses 14 gauge wire to
 MM> connect to 7AH batteries.  In your case, I would get connectors that
 MM> will crimp to 12 gauge wire for the 11AH batteries, and use 12 gauge
 MM> for each of the 11AH batteries.  Use 10 gauge for connecting the 25AH
 MM> batteries, then clamp or bolt all the (+) ends to a piece of 8 gauge
 MM> wire for connecting to the UPS.  Same for all the (-) ends.

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

 MM> There's nothing more unsettling than having the lights go out, then
 MM> smelling wire burning!

Yep, I _hate_ it when that happens! (especially when the rest of the
house is in the dark).  [;-D.

 MM> You also have to consider the increased load on the UPS's internal
 MM> charger when the power comes back on.  All those batteries will likely
 MM> cook the UPS while trying to re-charge.

Yep, and I don't know that I've seen a reply to his question about
putting a diode in the recharge circuit, which would prevent recharge,
but what good would that be - to have a UPS which couldn't keep
its own battery (ies) recharged?

- - -  JimH.
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