On Mon, 29 May 2006 18:19:18 +0100, John Rumm
wrote:

T i m wrote:

I had this exact discussion with Ansmann Chargers and a couple of
battery suppliers.

Terms like 'Fast Charge' or 'Ultrafast Charge' seemed to go against
the recommendations on the cells themselves?

The bottom line from them all ... "Yes, fast charging will generally
sod up yer cells but that's what folk want (fast charge cycles) and
they don't mind buying new ones .." ;-(

There is another angle as well... I was speaking to a bunch of fast
electric boat nuts once[1]. They were all of the opinion that you should
never slow charge a racing pack, since all they care about is getting
the ultimate current delivery from the cells and are not to fussed over
their longevity. They believed that always fast charging resulted in
better high current delivery.

And I agree there is some mileage to that one John (but choose a
compromise myself even on racing packs). It's all well going off like
a rocket as long as you are still there at the end of the race ;-)

[1] These were however into the serious anorak class! A model boat
regatta / event had attracted them, and they were camping overnight in
the park.

Ok, nothing wrong so far ... ;-)

A bunch of the sub 2kg class were whizzing round the lake
trying to avoid getting run over by my 10kg / 4 times the size 10cc IC
engine boat! ;-)

Or drenched from the 'rooster tail' off the back of my Webra 61R /
Agnew 'Z' drive powered catamaran! ;-)

I went and had a chat with some of them after. There
was one chap who came with a boat he had specially designed to have a
crack at a world record which is run round a 500m length course
(apparently the Chinese held the record at something like 9 seconds!).

Eeek!

His hand made, computer matched, 36 cell battery pack was designed to
deliver power at a steady 2kW. After each run he drained the pack into a
string of light bulbs, while monitoring the individual cell voltages.

Yup, have done similar myself .. not these days though ..

Then individually discharged each cell down to 1V with an old moving
iron meter.

Mine is a suitably sized ww shunt restistor in a little ally box with
basic voltmeter calibrated in amps (10A FSD) fitted on the top. I
touch / hold that across each cell till I see it start to drop from
10A .. seems to work ok ;-)

Then finally fast charged using a combination of delta V and
temperature sensing. Nice boat (all carbon fibre etc weighed "nothing"),
serious 12 pole lekky motor etc. Alas I missed the entertainment the
following day when he demoed its performance and sank it! ;-)

Doh! ;-(

I only lost the lid off the cat when it back flipped at speed (Donald
Campell stylee). *Luckily* there were some lads swimming nearby who
fancied a challenge and recovered it for me! ;-)

All the best ..

T i m