Capacitors in PSU are dangerous?

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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?



"w_tom" <w_tom1@hotmail.com> wrote in message
news:4081D418.993D1AEA@hotmail.com...
> Power supply operating in either 120 VAC or 230 VAC still
> charges capacitors up to 320 volts. Anyone with minimal
> knowledge of power supplies knows this. One should never
> post without first learning basic power supply functions.
>
> Properly posted was that power supplies will have bleed off
> resistors on those capacitors. However I have seen power
> supplies missing this resistor. In one, the resistor failed.
> In another, the resistor was missing. Always use a screw
> driver to short out those capacitors before working on a power
> supply.
>
> Computer power supplies can hurt you. Now for something
> even more dangerous. For the same reason (electrolytic
> capacitor), a microwave oven will kill. If that microwave's
> bleed off resistor is missing or failed, well, microwave
> repairmen have been killed by that missing resistor. Yes -
> capacitors inside a power supply can harm humans - despite
> posts to the contrary.
>
> How a PC (switching) power supply works: AC mains is
> converted to 320 VDC. Then 320 VDC is converted to AC and put
> through a tiny transformer. Transformer so small and light
> because of how DC is converted to AC. AC voltage output from
> transformer converted again back to DC, filtered, monitored,
> and then output.
>
> half_pint wrote:
> > "Regal" <stua_NOTTHISBITsmith@yahoo.co.uk> wrote in message
> > news:Xns94CCAAEC4846D628D1@208.42.66.156...
> >> I read on some website that the capacitors in a PC's PSU can hold a
> >> charge for long after they have been switched off and that the
> >> charge could be fatal.
> >>
> >> Is this really so? Surely that is exaggerating?
> >
> > I don't think that is true, certaintly not if the PSU has a
> > transformer. The capacitors are on the output side and so I see
> > no reason why they be charged to more than 12V.
> >
> > So no more dangerous than touching both terminals on a car battery.
> >
> > However some power supplies may be of a different design and not
> > use a transformer to step down the voltage.
> > I don't know how PC PSU's work for sure but I assume they use
> > a transfromer.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

"kony" <spam@spam.com> wrote in message
news:q2l380970c4m0gdncaj3l2k0hp8q2a841d@4ax.com...
> On Sun, 18 Apr 2004 00:07:18 +0100, "half_pint"
> <esboella.nospam@yahoo.com> wrote:
>
>
> >> if a faster processor needing extra power was installed (say, it
> >> needs an extra 30 W) then would that noticeably reduce the life of
> >> the power supply?
> >
> >Actually.... thinking about it..... it may well *increase* the life of
the
> >power supply if the extra load meant the capacitor was not always
> >fully charged.
> >What is more likely is your PC would not work and may well have
> >mysterious reboots (like mine does sometimes) because the
> >required output voltage cannot be met at peak demand.
> >
> >The lower the charge on the capacitor the longer it life will be
> >IIRC.
> >
>
> The short answer is, no.

Well your considerable longer answer than mine appears to disagree with
you.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

I think that is the problem in most electrical circuits, everything is,
unsurprisingly wired togeather!! (A part from the bit that failed
open circuit of course!).
I knew when I returned my £40 stereo system that that would not
even attempt a repair and just send me a new one, so I spent £8
posting it back so they could bin it! I imagine hf radio circuits are
harder to work on than PSU's too.
You can buy a bog standard PSU for £14 and it probably costs
less than half that to manufacture, obviously you can pay a pile more
if you are that way inclined.


"w_tom" <w_tom1@hotmail.com> wrote in message
news:4081D864.B34D591C@hotmail.com...
> Most power supplies are difficult to diagnosis because they
> use feedback loops. In a feedback loop, everything looks
> defective when only one part has failed.
>
> In one power supply, out of frustration that supply was
> winning, I once took the shotgun approach. Removed and tested
> every component. Got down to the last few parts when I
> discovered an open pull up resistor. Did not even know what
> that resistor was doing until I replaced it and monitored. Its
> only purpose, to my surprise, was to kick start the circuit
> only on power up. Just another reason why power supplies are
> so difficult to repair. Some components even have unexpected
> surprise functions - as well as located in feedback loops.
>
> A little thing called floating ground. Don't understand it
> and vaporize test leads. Many good reasons why they seal up
> those power supplies. Power supplies are not so simple.
>
> half_pint wrote:
> > Well I don't know I am sure a visual inspection would reveal a lot
> > of faults. Maybe the PSU's you had in mind are a bit more complicated
> > than the type I was thinking of.. Surely you could test many things
> > using a lot lower voltage?
> > Anyway isn't it more economical just to bin it and put a new PSU in?
> > When I sent my faulty stereo for repair they just sent me a new one!!
> > ( The new one also had developed a fault within a few weeks, but
> > cleaning the cd lens appears to have fixed it.).
> > Both units manufactured by Bush care of Powerhouse. :O) who
> > incidently went bankrupt voiding my 12 month 'guarantee'.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

On Sun, 18 Apr 2004 02:59:30 +0100, "half_pint"
<esboella.nospam@yahoo.com> wrote:


>You can buy a bog standard PSU for £14 and it probably costs
>less than half that to manufacture, obviously you can pay a pile more
>if you are that way inclined.

Ah, but the whole reason why the first unit failed may easily be that it
was constructed for "half that". A good power supply may run a decade, a
cheap one may die in a few months and take other parts down with it.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

kony <spam@spam.com> wrote in message news:<9kr3805l4fau49au1eejhm01ml75fhf2j4@4ax.com>...
> On Sun, 18 Apr 2004 02:59:30 +0100, "half_pint"
> <esboella.nospam@yahoo.com> wrote:
>
>
> >You can buy a bog standard PSU for £14 and it probably costs
> >less than half that to manufacture, obviously you can pay a pile more
> >if you are that way inclined.
>
> Ah, but the whole reason why the first unit failed may easily be that it
> was constructed for "half that". A good power supply may run a decade, a
> cheap one may die in a few months and take other parts down with it.

When i was a kid i bought a pair of scissors from a stationery store.
I don't remember my age but i might've been in elementary school. I
remember that i absent-mindedly tested them by seeing if they can cut
through a black wire that ran across my field of vision, i must've
been engaged in some imaginary game with myself where the wire stood
for something, the wire happened to be the mains cable and i got such
shock that adults who were in the living room, i was in another room,
heard it and came over.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

half_pint <esboella.nospam@yahoo.com> wrote:
<snip>
| Well I don't know I am sure a visual inspection would reveal a lot
| of faults. Maybe the PSU's you had in mind are a bit more complicated
| than the type I was thinking of.. Surely you could test many things
| using a lot
| lower voltage?
| Anyway isn't it more economical just to bin it and put a new PSU in?
| When I sent my faulty stereo for repair they just sent me a new one!!
| ( The new one also had developed a fault within a few weeks, but
| cleaning the cd lens appears to have fixed it.).
| Both units manufactured by Bush care of Powerhouse. :O) who
| incidently went bankrupt voiding my 12 month 'guarantee'.

Visual inspection might reveal a swollen capacitor, charred resistor or
transformer gone into meltdown but that's about it. Semiconductors tend to
look the same whether they are working or wrecked. If you find somethig like
a charred resistor, then something has made that happen - just replacing it
probably won't fix the problem, just let you see it again.It is nigh-on
impossible to properly check-out an electronic circuit without making some
voltage and current measurements, and with AC examining waveforms. If the
unit isn't powered then there's nothing to measure.
But please do explain how your unpowered diagnosis works. Let's use the
condition of an open-ciruit diode or rectifier as an example. I'm looking
forward to learning.
As regards cost, well, most of us treat our own time which we spend on our
'little projects' as essentially free - so if I spend the odd hour fixing a
broken PSU then it hasn't actually hit me in the wallet. Fair enough,
though, it would probably cost more to pay someone else to fix a PSU then
buy a new one. Of course, if your interest lies with 'vintage' machines,
then you might have no option but to fix what you've got. My oldest machines
are almost thirty years old.
Given that we are having this conversation in 'homebuilt computer'
newsgroups, then I think we can presume that a 'hobbyist' approach
prevails - reasonable technical knowledge, some basic tools, willingness to
learn, a desire to actually 'do' things rather than have things done by
others and a certain enthusiasm to communicate with others on the subject.
N'est ce pas ?
Kevin.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

kony <spam@spam.com> wrote:
| On Sun, 18 Apr 2004 02:59:30 +0100, "half_pint"
| <esboella.nospam@yahoo.com> wrote:
|
|
|| You can buy a bog standard PSU for £14 and it probably costs
|| less than half that to manufacture, obviously you can pay a pile more
|| if you are that way inclined.
|
| Ah, but the whole reason why the first unit failed may easily be that
| it was constructed for "half that". A good power supply may run a
| decade, a cheap one may die in a few months and take other parts down
| with it.

Oddly enough, I normally find that the cheaper parts - the ones you buy
because 'they'll have to do for now untill I can get something better' -
have a habit of outlasting expensive ones. This is obviously sod's law in
practise ! You can spend years waiting for super-cheap PSU, which you had
to buy after finding your wallet has a leak, to give up the ghost - but it
doesn't. You are really looking forward to buying a nice new shiny
gold-plated dual-fan 600w job, but you can't justify it because the nasty
cheap little tin box just won't die.
This works the other way, of course. You spend what seems like a lifetime
getting enough dosh together to build a machine which really needs a
top-notch PSU so you just have to go out and buy one. You put it all
together and get about one day's use out of it before it's as dead as a dodo
and smells funny. Those two big fans and gold-plated finish don't look quite
so clever now, do they ? In desperation you dig the old tin box out of the
pile of old parts it got 'retired' to when its former PC got too obselete to
be usefull. You reluctantly screw it into that nice expensive aluminium case
you bought for the new system, and gently lay the gold-plated dual-fan
invalid on a protective cloth on the workbench. Of course, the posh new
machine works perfectly with the old cheapo tin box PSU.
Does this happen to everyone else, or is it just me ?
Kevin.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

Mike Henley <mnhenley@msn.com> wrote:
| When i was a kid i bought a pair of scissors from a stationery store.
| I don't remember my age but i might've been in elementary school. I
| remember that i absent-mindedly tested them by seeing if they can cut
| through a black wire that ran across my field of vision, i must've
| been engaged in some imaginary game with myself where the wire stood
| for something, the wire happened to be the mains cable and i got such
| shock that adults who were in the living room, i was in another room,
| heard it and came over.

Yeah - I've met kids like that. :-(
Sandwiches in the VCR, dish-washing detergent in the washing machine, cling
film over the toilet, cat in the microwave. local anaesthic cream on the
condoms. . . . .

 

[gb]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

w_tom <w_tom1@hotmail.com> wrote in message
news:4081D418.993D1AEA@hotmail.com...
> Power supply operating in either 120 VAC or 230 VAC still
> charges capacitors up to 320 volts. Anyone with minimal
> knowledge of power supplies knows this. One should never
> post without first learning basic power supply functions.
>
> Properly posted was that power supplies will have bleed off
> resistors on those capacitors. However I have seen power
> supplies missing this resistor. In one, the resistor failed.
> In another, the resistor was missing. Always use a screw
> driver to short out those capacitors before working on a power
> supply.
>

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?

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

On Sun, 18 Apr 2004 09:58:37 +0000 (UTC), "Kevin Lawton"
<kepla@btinternet.com> wrote:


>Oddly enough, I normally find that the cheaper parts - the ones you buy
>because 'they'll have to do for now untill I can get something better' -
>have a habit of outlasting expensive ones. This is obviously sod's law in
>practise ! You can spend years waiting for super-cheap PSU, which you had
>to buy after finding your wallet has a leak, to give up the ghost - but it
>doesn't. You are really looking forward to buying a nice new shiny
>gold-plated dual-fan 600w job, but you can't justify it because the nasty
>cheap little tin box just won't die.
>This works the other way, of course. You spend what seems like a lifetime
>getting enough dosh together to build a machine which really needs a
>top-notch PSU so you just have to go out and buy one. You put it all
>together and get about one day's use out of it before it's as dead as a dodo
>and smells funny. Those two big fans and gold-plated finish don't look quite
>so clever now, do they ? In desperation you dig the old tin box out of the
>pile of old parts it got 'retired' to when its former PC got too obselete to
>be usefull. You reluctantly screw it into that nice expensive aluminium case
>you bought for the new system, and gently lay the gold-plated dual-fan
>invalid on a protective cloth on the workbench. Of course, the posh new
>machine works perfectly with the old cheapo tin box PSU.
>Does this happen to everyone else, or is it just me ?
>Kevin.

It almost sounds like you're assuming cosmetic eye-candy or price mean
quality, or perhaps considering only a single specimen or two...
spot-failures do happen. Unfortunately it seems many power supplies now
have median (if that) parts inside a very pretty casing.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt (More info?)

Frank le Spikkin <zaq@invalid.jp> wrote:
| "Kevin Lawton" <kepla@btinternet.com> wrote in
| news:c5sg00$ekd$1@sparta.btinternet.com:
|
|| 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.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

half_pint <esboella.nospam@yahoo.com> 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 ah heck when you try to get out of the car and forget
you're wearing one !

 

[ken]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

On Sat, 17 Apr 2004 23:38:57 +0100, "half_pint"
<esboella.nospam@yahoo.com> wrote:

> Presumably it depends when you remove it from the AC supply on
> how much of a shock you get. If you are lucky you might not
> get any shock at all. Unlucky if you get the full 110V.
> Or 240 in the UK. Who uses 110V?

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

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

"beav AT wn DoT com DoT au" <"beav AT wn DoT com DoT au"> wrote in message
news:408336e7@quokka.wn.com.au...
> 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

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

On Mon, 19 Apr 2004 04:10:27 +0100, "half_pint"
<esboella.nospam@yahoo.com> 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

 

[ken]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

On Sun, 18 Apr 2004 15:29:18 +0100, Michael Salem <a$-b$1@ms3.org.uk>
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.

 

[ken]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

On Sun, 18 Apr 2004 15:29:18 +0100, Michael Salem <a$-b$1@ms3.org.uk>
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.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

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.

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

"kony" wrote:
> 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.


What about the reverse leakage current in the rectifier? Doesn't
that amount to a bleeder resistor?

*TimDaniels*

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

Timothy Daniels wrote:

> > 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.
>
> What about the reverse leakage current in the rectifier? Doesn't
> that amount to a bleeder resistor?

Current path would be...???

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

Conor wrote:

> Too true. Thats why you can stick your fingers in the HT lead hole in
> the top of a monitor tube and just get an arm jolting belt. Sure its up
> to 20,000 V but theres not alot of current.

Err.. right..

You first!

 

[Guest]

Archived from groups: alt.comp.hardware,alt.comp.hardware.pc-homebuilt,uk.comp.homebuilt,alt.comp.hardware.homebuilt (More info?)

"kony" <spam@spam.com> wrote in message
news:q8s6809ia53gtj6nrg39rqkqlbrtqb6c45@4ax.com...
> On Mon, 19 Apr 2004 04:10:27 +0100, "half_pint"
> <esboella.nospam@yahoo.com> 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.

Don't be so condesending.

>
>
> >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.

Its two seperated conductors, you obviously no idea about electronics.

>
>
> >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

You don't have a clue do you?
Try inceasing your vocabulary to that of a 5 year old.