DN1• 20
begin the Fast Charging mode.
The Benchmark IC will constantly monitor the pack and turn off the fast
charge when the cells are charged just to full capacity. Once this is
accomplished, it will periodically “top off” the cells with a high current burst,
and allow a slight trickle charge to flow.
Unfortunately, about the only thing to do for this initial check out is to watch
the lights blink - but it is also a good time to “measure” the capacity of your
cell. Start “timing” the charger just when it goes into fast charge mode.
Knowing the charge current rate (whatever you previously set it up at) and
the time for a full charge, (Amperes • Hours), you can get a fairly good
approximation of the health (capacity value) of your batteries.
What about those “mystery” batteries ?!
Often times the batteries are “hidden” in elaborate packs designed to fit in
video cameras, cordless phones, or RC racecars. The easiest way to
determine the number of cells in such a pack is to take the nameplate
voltage and divide by the number 1.2, the voltage of a single cell. For
example, a 7.2 V pack contains 7.2 ÷ 1.2 = 6 cells.
It can also be quite frustrating to connect the charger to these “oddball” type
packs. An inexpensive design idea is to fabricate your own holder with
assorted bits of wood and plastic. Surely a kitbuilder like you already has a
“junkbox” full of those priceless gems just waiting to be put to use to hold
your batteries. For example, an old discarded relay usually contains some
high current spring loaded contacts that make great connecting terminals for
such packs.
Be absolutely sure that you have the proper polarity identified on the battery
pack. Most are marked with a sticker or mark in the plastic case. If you can’t
figure out the charge capacity, go to your local home electronics store. Ask
about replacement cells; most likely the salesman will know what you need.
BATTERY WORKOUT
To keep your NiCad cells at their peak capacity, here are a few suggestions:
1) Alway deep cycle your batteries. Run them until they just begin to quit. It
is best to depress the “discharge” pushbutton after you initially hook up
the pack to Dr. NiCad.
2) Even when not in use, periodically “top off” the pack. This is also