Subject:
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RE: Charging Batteries
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 10 Nov 1998 17:57:22 GMT
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Original-From:
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brett anthony <ANTHONYB@ECS.CSUS.avoidspamEDU>
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Viewed:
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2034 times
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The HB wall plug charger MIGHT do the job, sort of... Generally you need a
charger that makes about 15V under load to charge a 12V (nominal) battery
pack.
Do NOT use an auto battery charger unless you have a way to reliably control
the CURRENT to your battery.
Are you sure your security alarm panel battery is a NiCad and not a gell
cell?
Quick and dirty general charging rules:
NiCads: Charge in 8 to 12 hours at C/10 amps where C is the capacity.
Thus, a 6AH NiCad pack would charge at 600MA. Note that the charge voltage
should be several volts more than the rated pack voltage.
Generally, low cost OEM charger/battery combinations use C/20 to reduce
tha chance of damage to the pack. Fancier ones charge at C/5 or faster, but
use some feedback (usually temperature, sometimes voltage or pack
resistance) from the pack itself to switch the charger to trickle mode when
the pack is full. Reason: NiCads will tolerate a fast charge, but once full
they will overheat rapidly and vent or rupture if the current is not
reduced.
Conventioanl wisdom about NiCads is that they will lose useful capacity
if kept on trickle charge or repeatedly recharged before they are empty.
This "memory effect" is actually much less of a problem today than 10 or 20
years ago, but it is still a good idea to periodically run NiCads till dead,
than give them a long slow charge.
Lead/Acid: Except for vehicle batteries, most lead/acid batteries today are
gell cells; no vents, no spill, but gell cells will not provide the very
high currents (or tolerate a very fast charge) like the battery in your car.
Gell cells can be charged at C/10, but C/20 is safer. The big difference in
charging gospel for gell cells is that they should be kept on full charge
all the time, recharged immediatly after any use, and it's a bad idea to run
them flat. Most users store them on a C/20 or C/40 trickle charger all the
time. Maintained this way, they can be counted on to provide full capacity
for years. I suspect your security panel backup battery may be a gell cell.
It should run the HB just fine...
Brett Anthony
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