Capacitors in PSU are dangerous?

Frank le Spikkin wrote:
| "Kevin Lawton" wrote in
| :
|
|| Just need to find a virgin in time for the next full moon -
|| anyone got one they can spare ?
||
|
| http://www.annwiddecombemp.com/

No dount you are technically correct !
Given her stance on fox-hunting, do you think that she'd be up for it ?
Might not be too keen on all that blood.
I guess that to keep things in proportion I could sacrifice a turkey instead
of a black cockerel. :-)
Kevin.

half_pint wrote:
| Well I didt make it clear that not all transformers work in the
| same way, and that I was unsure how a PC PSU worked
| (apart from the one I am rapidly rapidly)
|
| Anyway my post did draw out the actually design of a
| standard PC PSU, so far from being irresponsible it might
| have saved someones life - not least mine :O)
|
| I suppose you could argue that the design of most PSU's is
| inherently dangerous, not least for the repairman.
| ( that is what I will be using in court anyway).
|
| Maybe the familly of an electrocuted repair man could sue the
| manufacturer of the microwave?
|
| A blatent disregard of employee safety fueled by corporate greed
| in my book.
|
| A bit like a car manufacturer saying seat belts are too expensive to
| fit and regarded as an inconvienience by the consumer?

I have some old 1960's car sales brochures in which seat belts are listed as
optional extras.
Anyway, it's a real bugger when you try to get out of the car and forget
you're wearing one !

half_pint wrote about a comment of mine on his posting:

Hmmm... I don't think that is fair, I did qualify my statement (you snipped
that out though)...

My intention wasn't to criticise, flame, or argue with you, but to warn
off anyone who might be tempted into having a look into a PSU; I
wouldn't have made any comment if there hadn't been potential danger.

I don't see any point in discussing fairness, etc. -- this is Usenet,
not a court of law. If you'd like to reword my posting so that it
remains brief, maintains its focus ("this is dangerous -- don't do it"),
and is fair to you, please do so, and I will withdraw my original.

Best wishes,
--
Michael Salem

Ken wrote:

All Europe use 230V today. UK adapted from 240V to 230V
and the other countries from 220V to 230 volts.

Nobody ACTUALLY changed their voltage, at least initially.

UK voltage used to be 240V nominal, tolerance -6%, +6%. Actual voltage
was typically 240V.

After the change UK voltage was 230V nominal, tolerance -6% +10%. Actual
voltage was typically 240V.

Best wishes,
--
Michael Salem

GB wrote:
Absolutely agree on the safety aspects. The only downside is that if
there
is a significant charge left in the capacitor shorting it out may wreck it.
Anybody have an idea of how likely that is with a fully charged large
capacitor?

No idea (sorry) BUT someone earlier mentioned that they use a 240V 100w
light globe and leads to discharge caps before use. This may be a safer
way to go...

--
-Luke-
If cars had advanced at the same rate as Micr0$oft technology, they'd be
flying by now.
But who wants a car that crashes 8 times a day?
Registered Linux User #345134

"beav AT wn DoT com DoT au" "beav AT wn DoT com DoT au" wrote in message
...
GB wrote:
Absolutely agree on the safety aspects. The only downside is that if
there
is a significant charge left in the capacitor shorting it out may wreck
it.
Anybody have an idea of how likely that is with a fully charged large
capacitor?

No idea (sorry) BUT someone earlier mentioned that they use a 240V 100w
light globe and leads to discharge caps before use. This may be a safer
way to go...

I guess it depends on the internal resistance of the capacitor, which is
probably
pretty negligible ( I have never ever seen it on a circuit diagram).

Remember I=V/R and if the voltage on the cap is say 200V and the
resistance is (choose a number) say one ohm then you have a current
of 200 Amps!! even with 10 ohms you have 20 amps, probably enough to
melt the connecting wires on the cap, never mind the microscopicly thin
foild of its plates.
Of course the internal resistance may well be much lower, fractions of
an ohm, negligible, say its 0.01 ohms?
Thats a current of 20 *thousand* amps.

Maybe open up a cap and unwind it and try and measure the resistance
from one end of the 'foil' to the terminal. It will probably regisiter as
zero.

Thats an infinite current!!



--
-Luke-
If cars had advanced at the same rate as Micr0$oft technology, they'd be
flying by now.
But who wants a car that crashes 8 times a day?
Registered Linux User #345134

On Mon, 19 Apr 2004 04:10:27 +0100, "half_pint"
wrote:


I guess it depends on the internal resistance of the capacitor, which is
probably
pretty negligible ( I have never ever seen it on a circuit diagram).

Don't guess.


Remember I=V/R and if the voltage on the cap is say 200V and the
resistance is (choose a number) say one ohm then you have a current
of 200 Amps!! even with 10 ohms you have 20 amps, probably enough to
melt the connecting wires on the cap, never mind the microscopicly thin
foild of its plates.

No, think about what a cap IS in the first place, that is obviously wrong.


Of course the internal resistance may well be much lower, fractions of
an ohm, negligible, say its 0.01 ohms?
Thats a current of 20 *thousand* amps.

Maybe open up a cap and unwind it and try and measure the resistance
from one end of the 'foil' to the terminal. It will probably regisiter as
zero.

Thats an infinite current!!

no

On Sun, 18 Apr 2004 15:29:18 +0100, Michael Salem
wrote:

All Europe use 230V today. UK adapted from 240V to 230V
and the other countries from 220V to 230 volts.

Nobody ACTUALLY changed their voltage, at least initially.

Wrong. In Sweden we did change from 220V to 230V a long time ago.

On Sun, 18 Apr 2004 15:29:18 +0100, Michael Salem
wrote:

All Europe use 230V today. UK adapted from 240V to 230V
and the other countries from 220V to 230 volts.

Nobody ACTUALLY changed their voltage, at least initially.

In Sweden we did change from 220V to 230V a long time ago.
Yes I could measure that on my volt meter.
230.5V on all 3 phases and 400V between the phases 5 minutes ago.

On Thu, 15 Apr 2004 23:49:24 +0100, Tim Auton
tim.auton@uton.[groupSexWithoutTheY] wrote:

It's beyond overkill to advise waiting 24 hours. Even if you didn't know
what you were doing you should've known that there's another very obvious
way an ATX power supply drains besides the bleeder resistors.

I'm assuming the worst case - ie component failure, where the only
discharge of the caps is self-discharge. In that case though, 24 hours
may not be enough. Hmmm, I think we need some experimental data.


Tim

Well the data is a bit slow in coming but I did a sloppy test yesterday...

I took a board from a power supply, that is quite typical, the basic
filtering components between the AC socket and the rectifier, NOTHING
after the rectifier... no bleeder resistors, no further power supply
components at all beyond the rectifier By attaching the capacitor
directly to rectifier output we would have an absolute worst case
scenario, there is no way for the cap to drain slower than that no matter
what else had failed in a power supply.

Power-on, charged voltage of cap (Rubycon 680mF) was 158V.
Within a couple hours it had lost over half of it's charge, below 70V.
Nearly 8 hours later it was below 10V and right now, 14 hours later, is at
about 7.5V and draining so slowly that further measurement might better be
made in days rather than hours.

Given that this was only a single cap and that I now have a better idea of
time inteval for measurements, I may try another cap soon of higher
capacity.