On Mon, 4 Apr 2016 08:18:08 +0100, RJH wrote:

On 03/04/2016 19:58, T i m wrote:
On Sun, 03 Apr 2016 14:39:40 +0100, pamela wrote:

snip

snip

LED flashes red "Error" - faulty battery or alkaline battery
detected

Duff. ;-)


I've managed to 'kick start' error reading AA/AAA batteries using a
cheap 'dumb' charger.

I think in this (error) case is more the 'I don't seem to be able to
get it to full charge in the time set' more than the 'I'm not going to
start charging because I don't like the battery for some reason'.

Batteries seem to recover fine.

Whilst I have had some cells that initially appeared 'dead' recover to
the point where they seem to work again, I think in most cases they
continued to be duff in time.

Like, the previously considered 'duff' cells works ok when you are
using the pack at a reasonable rate and regularly but if you leave
them for a while, that same cell will go bad again.

I think they
discharge to such a point that the smart charger can't do anything with
them?

I think I can depend on how 'smart' the smart chargers are. Like the
later Optimate (12V) chargers first test to see if there is a voltage
there (and there may be a minimum threshold but if below that the
battery is probably a goner anyway (especially with Lead Acid) and
then will do all sorts of high voltage pulsing and other cycle - test
- cycle type processes in it's attempt to recover it. Now, whilst I
have pulled a few batteries back from the brink with chargers like
that, I'd say they would generally be either very low capacity or high
levels of self-discharge after that.

I now look upon lead acid batteries (particularly) as straight
consumables.

In fact I've successfully done this when the smart charger failed with a
car battery recently.

Yes, some of the more basic smart chargers do sometimes need a bit of
a helping hand to get started if the battery terminal voltage is below
a certain threshold. I do what others here have mentioned and either
(carefully) put a good battery in parallel for a while or use my bench
PSU on a lowish current but a high voltage (well, sub 30). ;-)

It's interesting to see the current climb and then the voltage drop as
the battery 'wakes up'. ;-)

The thing with the small individual cell charger, discharger and
calibrator is you can mark the cells with the outcome of the tests and
it's then very easy to spot the runt of the litter and discard it. If
you have say 12 identical cells and they can be used in 2's and 4's
but taken randomly from the pool, you never know where that weak one
or two cells are and they will make the whole set (they are with at
the timer) appear bad and will be being made worse themselves at the
same time (reverse charging etc).

The 'You can manage what you can measure' saying is very appropriate
here. ;-)

I would like such a charger for the C and D sized cells but I'm
guessing it would be pretty expensive (and to be fair I don't have
that many C/D's, compared with AA/AAAs anyway.

Cheers, T i m

p.s. When I designed, built and raced my electric motorbike (endurance
racing rather than speed) I was able to borrow a batch (10 or so)
identical 12V car batteries from my local car spares place. I put them
on my test jig one at a time and measured the reserve capacity,
finally picking the two batteries that had the highest capacity and
the most matched characteristics (as they were used in series on 24V).