On 12/09/2026 7:28 am, john larkin wrote:I'm sure you didn't mean that!On Fri, 11 Sep 2026 17:08:00 +0100, Simon SimpleOne of the more depressing things about electrolytic capacitors is the need to reform them by keeping the rated voltage across them for a day or so if they have been unused for a while.
<nothanks@nottoday.co.uk> wrote:
>On 10/09/2026 15:20, john larkin wrote:>
>
<xxxx>>2.4 KJ is about 16 firecrackers or five .45 cal bullets worth of bang.>
If I've done the sums right, that's a capacitor bank bigger than six
beer cans storing about the same energy as one AAA cell!
>People would notice if that were shorted.>
Yes, I used to operate capacitor banks of maybe 2-4 times that physical
size charged to 1kV and discharged via a spark gap through a marine
sparker for seismic work. Long time ago before H&S was a thing.
I got one of the giant caps. It says that it's 30,000 uF but it
measures 50,000. So we'll have 4000 joules with four in parallel at
200v.
>
I think it's normal for elecs to have more initial capacitance than
the nameplate value.
>
https://www.dropbox.com/scl/fi/apargzu733abcq6ww7w3b/30mF_250v.jpg? rlkey=00osgeyqpxceowgqf7l32mlnr&raw=1
The actual electrolyte is a layer of aluminium oxide on the electrode
surface, and that diffuses away slowly if the capacitor is stored uncharged. In extreme cases you have apply the reforming voltage through a big resistor because the thinned down layer can no longer stand off the rated voltage. With the big resistor you can measure the reforming current as the process proceeds.
Obviously the initial capacitance is higher than the rated capacitance. That may have contributed to your initial 50mF - a +50% tolerance only get you up to 45mF
I reformed a couple of electroltics many years ago when I bought some military surplus electrolytics for my home built hi-fi. I didn't bother to monitor the current.
| Date | Sujet | # | Auteur | |
| 7 Sep 26 |  discharging caps | 162 | 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 Sep11:54 | Re: discharging caps | 3 | Simon Simple | |
| 11 Sep12:01 | Re: discharging caps | 1 | Jan Panteltje | |
| 11 Sep14:59 | 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 | 87 | chrisq | |
| 7 Sep 26 | Re: discharging caps | 84 | 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 Sep07:23 | Re: discharging caps | 3 | Bill Sloman | |
| 17 Sep08:19 | Re: discharging caps | 4 | 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 | 8 | legg |
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