Re: NiCd Battery Storage

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

> I read

	Where?
	There is much 'hooey' writ about batteries.

> that NiCd batterys should be stored uncharged.

	Last manufacturer's data i saw (NOT real
	up to date) was that either was OK, with a
	MILD preference for discharged.

> Is this still true for older nicads that have been charged

> and discharged a number of times?

	I've seen no data.  A charged battery, over time,
	will become a discharged battery, by itself.

> What about storing a newer battery that has seen only one or two
> charge/discharge cycles?

	Same answer.


> What would be a good proceedure for discharging a battery pack?

	cf below, per manufacturers recommendation (last I
	had).

> discharge until the output voltage drops off then stop,

	This one.  Specifically, look for a 1.2 V 'step'
	drop in battery (cf below) output.  (1 V drop
	is ok) then STOP.  eg a nominal 6 cell/7.2 v
	battery should not be discharged below (7.2-1.2)
	or 6V.  Reasoning:  one cell will drop out first,
	go thru zero V, then _reverse_ as the remainder
	force current backwards.  This is BAD for the
	reversed cell.  If discharging lots of current:
	VERY bad.
	(Yes: Manufacturers more or less match the cells.
	One will still drop out first...)

> or continue discharging until current flow is minimal?
	I wouldn't.  cf above.  I'd expect damage.


> BTW, I use 9 volt nicads for portable operation of a SSTC

> pulse generator, and to run a MOSFET driver circuit.
	How many cells?

	7? 8?

	1) I'd be tempted to store them charged but NOT
	try to 'float' them.  Let them discharge by
	themselves.
	1a) Lead-acids tend to be stored on a 'float' charge.
	This tends to overcharge and dry out nicads, leading
	to early death, leakage, etc, unless done VERY
	exactly...  Simplest is to 'leave 'em', next
	simplest _controlled_ (V- 1.2V) discharge.)

	2) Minor point of usage:
		Cell: a single unit.
		Battery: A buncha cells.
	If dealing with individual _cells_, can discharge to
	zero.  If dealing with _battery_, BAD thing to
	discharge to zero, as this means some cells are
	having current forced thru backwards....

	best
	dwp

...the net of a million lies...
	Vernor Vinge
There are Many Web Sites which Say Many Things.
	-me