On 01/03/2020 17:49, The Natural Philosopher wrote:
On 01/03/2020 11:25, Jeff Layman wrote:
On 01/03/20 09:09, The Natural Philosopher wrote:
On 01/03/2020 08:53, Jeff Layman wrote:
Clearing out the shed I came across my old 4.8v Challenge Extreme
powered screwdriver, which I hadn't seen for at least 6 years (I use my
Hitachi drill/driver instead). When I opened the box and took out the
screwdriver I accidently touched the trigger and was amazed when the
motor turned. I though it might be the dregs of a charge in the cells,
but I tried again and it turned. In fact, it was not possible to
stop it
turning by gripping the shaft.

I have no idea what brand NiMH cells were used in this cheap
screwdriver
(Argos), but for the four of them to retain a good charge for 6 years
seems very unusual to me.

Probably Nicd then

They are. Nothing on the device itself, but I dug out the instructions
and they say they are NiCd. The instructions are dated 4/2006. I guess
I bought it within a year or two of that date; I'm surprised that
NiCds were still around them, but I guess they were still using them
on low-end products.

Sites vary in what they state is the self-discharge rate of a NiCd
cell. The best is 10%/month, but the most common is 15 - 20%. Not in
my experience - it's around 1.5% if those cells were last recharged
about 6 years ago! :-)

no. NiMh are theÂ* 10% a month

I don't observe that even with cheap 'unbranded' cell bought from CPC in
about 2001/2. I built several battery packs for Icom handhelds plus a
special for an IC202S (another transceiver) - 7 or 8 cells in each pack
and 10 in the special. When I check them every couple of months or so,
they show hardly any sign of discharge. I sometimes miss a check-
especially if we are away- and even then they show little signs of
discharge when I get around to checking them. I sometimes give them a
discharge cycle and a charge, others just as brief top up.

Conversely, when I used to use NiCads, I bought (supposedly) quality
ones and treated them like cherished offspring. They were still unreliable.

I've observed the same with commercial, ready built, NiCD and NiMH packs
for another handheld bought around 2005 or 6.

I have had NiMH cells fail, including ones which have a good name, but
only rarely. I'm currently trying some Ikea ones which have a good
reputation and, so far, seem reasonable but I've only had them a year or
so. The Ikea 'wall charger' which not only charges them but keeps them
'topped up' until needed seems pretty good.