Hi Peter,
Good circuit !
However I have a couple of questions:


1.
I presume the FET (Q2) will need a heatsink, as it will
dissipate approximately 12W when discharging at 1 Amp ?

2.
R9 should be 470 ohm, not 470 K

Cheers, John G.

"Peter Nyffeler" wrote in
message ...
| In article
, "Roger
Druce" wrote:
| Perhaps someone out in r.a.s land may be able to point me
in the direction
| of a commercial piece of equipment which would perform
the following task.
|
| I would like to be able to charge up a 12 volt (nominal)
gell cell battery
| and then plug it into a piece of equipment to check its
total AmpHour
| capacity during discharge at some constant rate current
(say the "10 hour"
| rate or the "20 hour" rate). All this towards assessing
whether the battery
| has proven useful capacity and life left in it, or has it
reached its
| discard date?
|
| The equipment would show the delivered amp-hours up to
the point at which
| the voltage has fallen to a nominated end voltage.
|
| I realise that you can do it in a way with a light globe
to discharge the
| battery and then time the length the light holds up
glowing brightly. This
| is all too primative for this day and age, and there
ought to be some piece
| of equipment available for the task.
|
| Or some circuit from an electronics hobby magazine??
|
| Thanks in antcipation.
| Roger Druce
|
| I built one myself.
| You find the schematic at
http://www.ppc.ethz.ch/~peny/sf/ah_test.html
|
| Peter Nyffeler
| Tel P 01 363 62 42, Tel G 01 632 43 60, Fax G 01 632 10 21