On Mon, 7 Sep 2026 19:33:35 +0100, chrisq <syseng@gfsys.co.uk> wrote:But a resistor plus an inductor could give a critically damped decay, which would be quite a bit faster. I don't know enough about the circuit to be prepared to try to work out how much inductance you'd need, and you clearly can't be bothered.
On 9/7/26 16:18, john larkin wrote:It's a 1500 amp laser driver.Suppose we have a box with some big caps inside, for example 0.2>
farads that run at about 200 volts. When AC power is off, we want to
discharge them for several reasons.
>
Putting, say, a 1K resistor across them dissipates 40 watts and has a
200 second time constant. It will take many tau before the voltage
gets low enough for people to poke around inside.
>
The ideal discharger would be a constant-current or even better a
constant-power load, all the way down to zero volts. It would be dumb,
not switched by some decision circuit or anything fancy like that.
>
And of course we need several LEDs as warnings that the thing is hot.
>
What sort of design needs 0.2 Farad cap, at 200 volts ?. If you are
working at that level, put in a cheap relay and a rated heatsink
wirewound resistor to dump the energy, when the power goes off.
Cheap, and lossless as well. Motor drive inverters often have
big resistors to brake the motor.
>
>John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
The input to our box is DC, from an external power supply.
I do want a circuit that's foolproof, that always discharges the caps
but doen't often go up in flames.
A resistor makes an exponential decay which could be a very long time
to get down to safe levels.
I thought the group might like a circuit design problem once in aBut you don't do circuit design, and this sort of question makes it obvious why you don't.
while, a break from politics.
--
Bill Sloman, Sydney
| Date | Sujet | # | Auteur | |
| 7 Sep 26 |  discharging caps | 165 | john larkin | |
| 7 Sep 26 |  Re: discharging caps | 7 | Simon Simple | |
| 7 Sep 26 |   Re: discharging caps | 6 | john larkin | |
| 7 Sep 26 |   Re: discharging caps | 1 | Simon Simple | |
| 8 Sep 26 | Re: discharging caps | 4 | legg | |
| 8 Sep 26 | Re: discharging caps | 1 | john larkin | |
| 8 Sep 26 | Re: discharging caps | 2 | Phil Hobbs | |
| 8 Sep 26 | Re: discharging caps | 1 | john larkin | |
| 7 Sep 26 | Re: discharging caps | 12 | ehsjr | |
| 7 Sep 26 | Re: discharging caps | 11 | john larkin | |
| 7 Sep 26 | Re: discharging caps | 2 | Liz Tuddenham | |
| 7 Sep 26 | Re: discharging caps | 1 | john larkin | |
| 8 Sep 26 | Re: discharging caps | 8 | Jan Panteltje | |
| 8 Sep 26 | Re: discharging caps | 7 | john larkin | |
| 8 Sep 26 | Re: discharging caps | 6 | Jan Panteltje | |
| 8 Sep 26 | Re: discharging caps | 5 | john larkin | |
| 9 Sep 26 | Re: discharging caps | 4 | Jan Panteltje | |
| 11 Sep 26 | Re: discharging caps | 3 | Simon Simple | |
| 11 Sep 26 | Re: discharging caps | 1 | Jan Panteltje | |
| 11 Sep 26 | Re: discharging caps | 1 | Phil Hobbs | |
| 7 Sep 26 | Re: discharging caps | 2 | Bill Sloman | |
| 7 Sep 26 | Re: discharging caps | 1 | john larkin | |
| 7 Sep 26 | Re: discharging caps | 89 | chrisq | |
| 7 Sep 26 | Re: discharging caps | 86 | john larkin | |
| 8 Sep 26 | Re: discharging caps | 62 | Bill Sloman | |
| 8 Sep 26 | Re: discharging caps | 4 | john larkin | |
| 8 Sep 26 | Re: discharging caps | 3 | Bill Sloman | |
| 8 Sep 26 | Re: discharging caps | 2 | john larkin | |
| 9 Sep 26 | Re: discharging caps | 1 | Bill Sloman | |
| 8 Sep 26 | Re: discharging caps | 57 | john larkin | |
| 8 Sep 26 | Re: discharging caps | 56 | Bill Sloman | |
| 8 Sep 26 | Re: discharging caps | 55 | john larkin | |
| 9 Sep 26 | Re: discharging caps | 54 | Bill Sloman | |
| 9 Sep 26 | Re: discharging caps | 53 | piglet | |
| 9 Sep 26 | Re: discharging caps | 52 | john larkin | |
| 9 Sep 26 | Re: discharging caps | 1 | Bill Sloman | |
| 9 Sep 26 | Re: discharging caps | 50 | Jeroen Belleman | |
| 9 Sep 26 | Re: discharging caps | 9 | Bill Sloman | |
| 9 Sep 26 | Re: discharging caps | 6 | john larkin | |
| 9 Sep 26 | Re: discharging caps | 5 | Bill Sloman | |
| 9 Sep 26 | Re: discharging caps | 4 | john larkin | |
| 10 Sep 26 | Re: discharging caps | 3 | Bill Sloman | |
| 10 Sep 26 | Re: discharging caps | 2 | john larkin | |
| 10 Sep 26 | Re: discharging caps | 1 | Bill Sloman | |
| 9 Sep 26 | Re: discharging caps | 2 | chrisq | |
| 9 Sep 26 | Re: discharging caps | 1 | Bill Sloman | |
| 9 Sep 26 | Re: discharging caps | 40 | Bill Sloman | |
| 9 Sep 26 | Re: discharging caps | 37 | Jeroen Belleman | |
| 10 Sep 26 | Re: discharging caps | 36 | Bill Sloman | |
| 13 Sep01:27 | Re: discharging caps | 35 | Waldek Hebisch | |
| 13 Sep01:38 | Re: discharging caps | 20 | Lane W | |
| 13 Sep04:11 | Re: discharging caps | 19 | Waldek Hebisch | |
| 13 Sep15:50 | Re: discharging caps | 18 | john larkin | |
| 13 Sep16:14 | Re: discharging caps | 3 | Lane W | |
| 13 Sep17:18 | Re: discharging caps | 2 | Bill Sloman | |
| 13 Sep17:28 | Re: discharging caps | 1 | Lane W | |
| 13 Sep16:28 | Re: discharging caps | 14 | Bill Sloman | |
| 13 Sep20:03 | Re: discharging caps | 13 | john larkin | |
| 13 Sep23:54 | Re: discharging caps | 9 | Simon Simple | |
| 14 Sep01:12 | Re: discharging caps | 8 | john larkin | |
| 14 Sep07:05 | Re: discharging caps | 7 | Bill Sloman | |
| 14 Sep16:21 | Re: discharging caps | 6 | john larkin | |
| 15 Sep09:28 | Re: discharging caps | 5 | Bill Sloman | |
| 15 Sep18:23 | Re: discharging caps | 4 | john larkin | |
| 16 Sep09:39 | Re: discharging caps | 3 | Bill Sloman | |
| 16 Sep11:21 | Re: discharging caps | 2 | john larkin | |
| 16 Sep12:16 | Re: discharging caps | 1 | Bill Sloman | |
| 14 Sep06:59 | Re: discharging caps | 3 | Bill Sloman | |
| 14 Sep16:22 | Re: discharging caps | 2 | john larkin | |
| 15 Sep09:31 | Re: discharging caps | 1 | Bill Sloman | |
| 13 Sep01:59 | Re: discharging caps | 3 | john larkin | |
| 13 Sep05:21 | Re: discharging caps | 1 | wmartin | |
| 13 Sep07:27 | Re: discharging caps | 1 | Bill Sloman | |
| 13 Sep07:24 | Re: discharging caps | 11 | Bill Sloman | |
| 13 Sep14:36 | Re: discharging caps | 10 | Waldek Hebisch | |
| 13 Sep17:05 | Re: discharging caps | 9 | Bill Sloman | |
| 13 Sep19:40 | Re: discharging caps | 8 | John R Walliker | |
| 13 Sep20:08 | Re: discharging caps | 4 | john larkin | |
| 14 Sep07:18 | Re: discharging caps | 3 | Bill Sloman | |
| 14 Sep16:24 | Re: discharging caps | 2 | john larkin | |
| 15 Sep09:36 | Re: discharging caps | 1 | Bill Sloman | |
| 14 Sep07:11 | Re: discharging caps | 3 | Bill Sloman | |
| 14 Sep16:56 | Re: discharging caps | 2 | john larkin | |
| 15 Sep09:50 | Re: discharging caps | 1 | Bill Sloman | |
| 10 Sep 26 | Re: discharging caps | 2 | john larkin | |
| 10 Sep 26 | Re: discharging caps | 1 | Bill Sloman | |
| 8 Sep 26 | Re: discharging caps | 14 | chrisq | |
| 8 Sep 26 | Re: discharging caps | 1 | chrisq | |
| 8 Sep 26 | Re: discharging caps | 12 | john larkin | |
| 8 Sep 26 | Re: discharging caps | 3 | chrisq | |
| 8 Sep 26 | Re: discharging caps | 2 | chrisq | |
| 9 Sep 26 | Re: discharging caps | 1 | john larkin | |
| 8 Sep 26 | Re: discharging caps | 5 | Bill Sloman | |
| 8 Sep 26 | Re: discharging caps | 4 | john larkin | |
| 9 Sep 26 | Re: discharging caps | 3 | Bill Sloman | |
| 9 Sep 26 | Re: discharging caps | 2 | john larkin | |
| 9 Sep 26 | Re: discharging caps | 1 | Bill Sloman | |
| 8 Sep 26 | Re: discharging caps | 1 | Bill Sloman | |
| 14 Sep17:44 | Re: discharging caps | 2 | Buzz McCool | |
| 14 Sep18:15 | Re: discharging caps | 1 | john larkin | |
| 11 Sep 26 | Re: discharging caps | 3 | Bill Sloman | |
| 17 Sep08:19 | Re: discharging caps | 6 | Cydrome Leader | |
| 8 Sep 26 | Re: discharging caps | 2 | Jan Panteltje | |
| 7 Sep 26 | Re: discharging caps | 20 | Lasse Langwadt | |
| 8 Sep 26 | Re: discharging caps | 1 | legg | |
| 9 Sep 26 | Re: discharging caps | 1 | Jeremiah Jones | |
| 9 Sep 26 | Re: discharging caps | 17 | someone | |
| 9 Sep 26 | Re: discharging caps | 6 | Joerg | |
| 13 Sep19:52 | Re: discharging caps | 9 | legg |
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