Battery capacity checker

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

In article , "John Giddy" wrote:
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.

John you are right.

The FET needs a heatsink, as it works as a variable power resistor to provide
a constant discharge current
And R9 should have 470 ohm to turn on the monitor LED.

Thanks
Peter

Peter Nyffeler
Tel P 01 363 62 42, Tel G 01 632 43 60, Fax G 01 632 10 21

Another question on Peter Nyffeler's circuit:

I think the part number for the dual operational amplifier
is wrong. It should read "LM358" NOT "LM385". This last
item is a precision voltage reference, not an amplifier.

Cheers, John G.

"John Giddy" wrote in message
...
| 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
|