I believe that just because a battery cell test shows a full charge, doesn't
mean that the full charge can be gotten out of the cell (imbalance).

Checking ESR at random intervals could indicate if cells are unbalanced, I
think.
Charging at C/10 is said to balance cells, but how often? Having a means to
indicate (actually see) imbalance would give the user an idea of how often.

I prefer to test capacitor ESR and other parameters before I install them,
as there are always inconsistencies in manufacturing.
No, I don't routinely retest them at regular intervals after installation,
but when circuit performance is poor, ESR testing is generally the first
step.

The only reason I would want to zap nicad cells is to actually see if the
internal resistance is improved/lowered. I believe an ESR test would be a
good indication of any change that takes place.

Otherwise, an ESR test after cells have been used a while, may be a better
indication of it's condition, and possibly it's reliability.
I suspect that an unbalanced cell in a battery pack is bad for all the cells
in the pack, as it's likely to generate more heat, and possibly result in an
incomplete or overcharged state.

Your test fixture seems like a reasonable test, as a quick accept-or-reject
type of test.

I wouldn't want to automate tests, although it can be accomplished with the
right equipment and quite a bit of effort, by someone brighter than myself.
A dedicated analyzer/tester/reconditioner may be a better solution, but
costly.
I don't have to deal with so many batteries that a dedicated analyzer would
be practical.

I've seen a lot of inconsistent statements regarding battery maintenance and
performance.
One source that appears to be reliable is
http://www.buchmann.ca/default.asp

--
Cheers,
WB
..............


"mike" wrote in message
...
Wild_Bill wrote:
I've been doing a lot of reading wrt battery cell testing, but have only
seen one (affordable, reasonably priced) recommendation for testing
rechargeable cell ESR.. the Bob Parker ESR Meter.

http://www.flippers.com/esrkthnt.html (near the bottom)
http://www.prc68.com/I/BatTst.shtml#EVB


Your statements are contradictory. For low current applications, the
ESR of the battery should be largely irrelevant...unless the cell is dead,
dead, dead.
Why do you need to zap cells to lower the ESR unless you're discharging
them VERY RAPIDLY?

I built a jig for sorting Lithium Ion cells for ESR at a junk dealer.
Just used a DVM to measure the voltage and a switch in series with
a light bulb to limit current from a eight-cell NiMH power supply.


Just read the volts, press the switch, read the volts again.
I needed the power pack because the cells were not charged.
If your cells are charged, you can just load the cell to ground.

I had good luck matching cells for building laptop battery packs.

A Tektronix 576 semiconductor curve tracer makes a great tool for
quickly evaluating ESR of cells.

A pulse generator and a scope will measure ESR. Just look at the
amplitude of the voltage step when you hit it with the known current
pulse. You can automate this to any degree you want with a sample-hold
and a microcontroller. If you use a square wave current, you can measure
the
P-P voltage at the cell and even plot it as a function of charge level.

I tried to do this with a GPIB programmable power supply. Problem
is that the battery voltage changes continuously when you turn on the
current. To get repeatable measurements, you need to accurately control
the time between turning on the current and reading the voltage.
I couldn't make this work with all the variable latencies
in the windows OS and the GPIB controller and the supply. My
light bulb scheme worked about as well in practice.

The guys who are fanatics about this reside in the model car racing
groups. But you have to do a lot of sifting. Many people have no idea
what they're doing and just post anecdotes of how they got 100A out of
a cell with no real verifiable
experimental results.