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rcurl
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Batteries and Chargers
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Apr 1 23:37 UTC 1999 |
For discussion of batteries and chargers.
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| 39 responses total. |
rcurl
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response 1 of 39:
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Apr 1 23:40 UTC 1999 |
Has anyone used the UDQ-9000 Charger/Conditioner for "ALL packs"? I've
seen one briefly, but am not sure how it connects to any battery pack.
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n8nxf
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response 2 of 39:
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Apr 2 11:47 UTC 1999 |
Nope. But I am looking for a really good charger that will handle a wide
variety of batteries. Mostly NiCad but also NiMH and lead acid. Pulse
chargers were suppose to be good.
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rcurl
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response 3 of 39:
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Apr 6 05:03 UTC 1999 |
I bought a Maha version of what I describe in #1. It is for radio
battery packs - not individual cells - but will charge batteries
put in series in a separate holder, bewtween 3.6 and 12 volts. It
is interesting as it determines the makeup of the pack (# of cells),
and then charges to that at ca. .6 A and then drops to a trickle
charge of 0.06 A. The hardware adjusts to the battery terminals
on most packs.
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n8nxf
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response 4 of 39:
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Apr 6 10:34 UTC 1999 |
That sounds like a pretty aggressive charge rate for smaller battery
packs. A 600 maH pack is usually charged at about 1/10 of the maH
rating, putting the charge current at about 60 ma. Perhaps the newer
cells can take it or, with it being a smart charger, can cut back on
the current such that the life of the pack is not adversely affected.
I don't think my 250 maH pack would like it.
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rcurl
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response 5 of 39:
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Apr 8 06:33 UTC 1999 |
Probably not. The charger is meant to provide a rapid recharge in
one to a few hours, rather than the slow 1/10 mah criterion, which
can take 10+ hours. (Corrections: the Maha unit works with packs
between 4.8 and 12 V, and the final trickle is 0.04 A.)
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gull
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response 6 of 39:
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Apr 14 06:04 UTC 1999 |
The main enemy of NiCd batteries is heat. If you can keep them from getting
too hot, they'll take fairly fast charge rates. (The problem is if you
don't cut back the current when they hit full charge, they'll heat up pretty
fast.)
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rcurl
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response 7 of 39:
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Apr 14 17:09 UTC 1999 |
The Maha charger has a "magnetic temperature sensor" to place on the
battery pack to protect from overcharging (heating). No other specs
are given for it. I'm a bit skeptical of the design, as the wire to
this sensor is very thin (1.3 mm) and seems subject to damage.
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rcurl
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response 8 of 39:
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Oct 6 06:18 UTC 2001 |
I was charging a gel cell (nominal 12 V, 2.4 Ah) with an unintelligent
charger. When I checked on it a couple of hours later it was running at
about 0.12 A, but ca. 2 cc of liquid (and bubbles) had leaked out of one
of the cell-plugs. It was, of course, acid electrolyte (it had even
'dissolved' a nylon tie that held the battery in a case). Does this mean
anything in terms of the condition of the battery - or its future
prognosis? (I have two of these batteries - the other charged OK and ended
at 0.04 A when I quit. Voltage checks after resting showed 13.27 V from
the "good" one, and 13.20 V from the one that leaked.)
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n8nxf
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response 9 of 39:
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Oct 9 16:09 UTC 2001 |
Gell cells that leak acid under normal charging conditions (Amp capacity /
5 or 10) are not healthy. I'd discharge them through a constant load (12 v,
250 mA light bulb) to about 11v and measure the lapsed time to see how much
energy they actually hold. You may be able to recover some capacity by
putting them through a few charge / discharge cycles.
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rcurl
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response 10 of 39:
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Oct 9 17:12 UTC 2001 |
What is the nature of the possible "disease" that causes the leak? I
presume it is H2 forcing out electrolyte. What would cause too much
H2 to form in one cell and not recombine?
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gull
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response 11 of 39:
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Oct 9 21:02 UTC 2001 |
I'm not sure, but I've noticed a tendancy for gel cells to "swell" when
they fail. I've been replacing batteries in some of the APC UPS's here
at work, and sometimes they've swelled up enough that it's almost
impossible to slide them out of the case. Haven't seen one that had
leaked acid yet, though...mostly they're ones that have lost the
ability to hold a charge due to old age.
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rcurl
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response 12 of 39:
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Oct 9 23:41 UTC 2001 |
I suppose if a cell became fully sulfated, the only effect of charging
would be to generate hydrogen. I think I'll try Klaus's suggestion, and
see what the capacity is now.
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gull
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response 13 of 39:
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Oct 10 14:47 UTC 2001 |
Re #12: That would make some kind of sense. I've found that a bad lead-
acid battery will often appear to have a reasonable terminal voltage,
but it's just a "surface charge" and will drop sharply when put under
load. I don't recall now if the voltage measurements you gave earlier
were under load or not.
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rcurl
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response 14 of 39:
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Oct 10 16:37 UTC 2001 |
Unloaded.
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n8nxf
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response 15 of 39:
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Oct 10 16:49 UTC 2001 |
The most common failure I see in UPS applications is dehydration. The
chargers in most UPS's do no do a good job of float-charging and boil off the
water with time. They hardly ever go through a discharge cycle either. The
times I've seen one or two cells in a battery boil off electrolyte is when
all the cells within the battery are no longer of equal capacity. Some come
up to charge sooner that others, etc. There are equalization procedures for
wet cells but I don't know how they would apply to gel cells. It might be
a good idea to go to the web site of the Co. the made your battery and see
what they have to say.
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gull
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response 16 of 39:
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Oct 11 15:05 UTC 2001 |
Re #15: I agree about the chargers, but don't see how the lack of
discharge cycles would shorten the life. Aren't discharge cycles bad
for lead-acid batteries? The useful lifespan of the battery in an APC
UPS seems to be around four or five years.
(Of course, with the way Detroit Edison neglects the outskirts of town,
my UPS batteries at home have gone through *several* deep discharge
cycles in the last year.)
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rcurl
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response 17 of 39:
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Oct 29 08:30 UTC 2001 |
I have now done what Klaus suggested in #9.
I discharged the battery through a bulb drawing 0.23 amperes. The
voltage dropped pretty linearly for several hours and then dropped
precipitously. When I caught it the batter was at 9.8 volt, a little
less than Klaus suggested. The total discharge was 1.1 Ah.
This is nominal "12 V, 2.3 Ah" battery. What is the connection between
the nominal Ah rating and the actual capacity? Does it having a capacity
of only 1.1 Ah mean the battery is half-dead (so to speak)?
I then recharged the battery at 0.052 amperes for about 20 hours, when
the cell voltage (under charge) was 15.2 volts (I wasn't able to check
when it went through 13.8 V). The current did change a bit over the
charge cycle, especially at the end when it was 0.035 A. Integrating
the current over time I estimate a total charge of .. 1.1 Ah.
The conclusion seems to be that the battery now has only half the
nominal capacity, but all the cells in the battery appear to be
similar with nearly equal capacities.
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gull
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response 18 of 39:
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Oct 29 16:55 UTC 2001 |
I don't remember how amp-hour capacities are calculated, but it assumes
a certain discharge rate. (To use an extreme example, a 30 amp-hour
battery will probably not supply 120 amps for fifteen minutes, because
of the higher heat losses under heavy current demands.) At a low
discharge rate I'd expect to get fairly close, though. How close you
can expect any one battery to be to the nominal depends on the
manufacturing tolerances. I did a project once that involved testing
deep-cycle lead acid batteries under load, and saw variation of 20%
between different batteries of the same type from the same manufacturer
for one brand, and less than 10% for another.
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n8nxf
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response 19 of 39:
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Oct 29 19:09 UTC 2001 |
I suggested a 250 mA discharge rate because it was about 1/10 th of the amp
hour capacity. The capacity is deratted according to load current but that's
something that specified by the manufacturer. The capacity is usually rated
at 1/10 to 1/20 th of the rated capacity. You may want to try it at 115 ma
and see what you get.
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rcurl
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response 20 of 39:
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Oct 29 19:20 UTC 2001 |
You've got a point there. The fact that charging the battery took 1.1 Ah,
the same as was obtained on discharging it, only means that that was the
effective capacity at 0.23 A. I know the effective capacity is lower at a
higher discharge, but hadn't thought it would be a factor of 2 lower using
the 10-hour rule for discharge.
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n8nxf
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response 21 of 39:
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Nov 5 16:45 UTC 2001 |
I agree. I have a feeling that your batteries are not in the best of shape.
Perhaps a few charge / discharge cycles will bring them back. Only one way
to find out, however.
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rcurl
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response 22 of 39:
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Nov 6 04:10 UTC 2001 |
Re #17: I neglected to mention that with charging at 0.052A, there
was no electrolyte release, even though I was "overcharging" for a
while.
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krokus
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response 23 of 39:
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Nov 10 15:35 UTC 2001 |
Sounds like a goner to me.
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rcurl
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response 24 of 39:
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Nov 10 21:01 UTC 2001 |
Actually, it sounds "OK" to me. What makes you say it is a "goner"? It
holds its charger very well.
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