Holy Moly -- Residual Electricity????

[krw]

Oh yes they do don't they In fact it's pretty much the opposite of
smoothing current.

Well that's true of bypass capacitors that're used near chips. But I
think it's fair to say the input capacitors in a power supply do
smooth current by removing mains voltage fluctuations, and thereby
preventing current fluctuations in the downstream load. And in fact
those are the ones that can hold their charge after switching off.

They don't "smooth" current at all. They "smooth" voltage by
storing/supplying current. They don't prevent current fluctuations
at all, indeed cause them in the attempt to maintain voltage.
Voltage across a capacitor can't change instantaneously, but the
current through one certainly can.

 

[Stuart]

It's a computer we are talking about.

May I just re-quote to you the text to which I replied?

---------------------------------------------------------------------

: A power supply in any electronic gizmo changes 110V (usually) AC to
: one or more voltages of DC, generally something like 5V - 20V, I
: think.
:
: Anyway, the voltage changing is done by a [snip transformer]
switching regulator.

------------------------------------------------------------------

Please note the word "any" in the statement:

"any electronic gizmo"

as used by Tim Slattery

Yes I've ben around long enough to know about Selenium rectifiers, Valve
rectifiers and mercury Arc rectifiers too!

Did you know Steel Tank mercury arc rectifiers used triggering to control
the output voltage just like an SCR or Triac?

;-)

--
Stuart Winsor

From is valid but subject to change without notice if it gets spammed.

For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk

 

[Androcles]

: In article <[email protected]>,
: > It's a computer we are talking about.
:
: May I just re-quote to you the text to which I replied?

No you may not, the record is plain enough.
If you quote part then quote all.

It's a computer we are talking about. We've had transformers
and bridge diodes since the dark ages but some people have
never evolved from their train set with its transformer, selenium
rectifier and rheostat.
http://www.theodoregray.com/PeriodicTable/Samples/034.10/s12s.JPG
http://img.alibaba.com/photo/51631125/Sliding_Rheostat_Specification.jpg
I was designing pulse width modulation controllers over 35 years ago,
the triac is older than that.

 

[Unknown]

The current on the output of a supply can vary by a considerable amount by
turning
devices attached to it on or off. Capacitors do not smooth current.

(e-mail address removed)> wrote in message

 

[Tony Harding]

: Gordon wrote:
: > : >> Capacitors.
: >>
: >
: >
: > capacitors usually discharge when the current is switched off - their
main
: > job is to smooth current, not to store volts....
: >
: >
:
: What utter crap.
:
: John.

Not only is it utter crap, the arrogant little prick gets bent out of
shape when you call him on it.

Thus the "arrogant" part of his moniker.

 

[Androcles]

: Androcles wrote:
: > : > : Gordon wrote:
: > : > : > : >> Capacitors.
: > : >>
: > : >
: > : >
: > : > capacitors usually discharge when the current is switched off -
their
: > main
: > : > job is to smooth current, not to store volts....
: > : >
: > : >
: > :
: > : What utter crap.
: > :
: > : John.
: >
: > Not only is it utter crap, the arrogant little prick gets bent out of
: > shape when you call him on it.
:
: Thus the "arrogant" part of his moniker.

Yes... I have no objection to someone being arrogant when
they know what they talking about, but all to often arrogance
and ignorance go hand in glove.


He who knows not and knows not that he knows not, he is a fool. Shun him.
He who knows not and knows that he knows not, he is a student. Teach him.
He who knows and knows not that he knows, he is a tool. Use him.
He who knows and knows that he knows, he is a sage. Follow him.


#define little_prick 1/sqrt[(arrogance^2)+(ignorance^2)]

(Androcles's inverse Pythagorean law)

 

[Michael A. Terrell]

Yes I've ben around long enough to know about Selenium rectifiers, Valve
rectifiers and mercury Arc rectifiers too!

How about copper rectifiers, and electrolytic rectifiers?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[M.I.5¾]

Is there some such concept as "residual electricity"???

There was a problem with a computer at work...it's a new Dell running
WinXP Pro...everything's fine, I go to lunch and come back to a blank
screen that won't wake up from power-save/sleep mode!! I do the
obvious and check connections, making sure they're secure and
whatnot. I turn off the computer and turn it back on a few times, to
no effect!

Tech Support suspects some kind of a "power management" issue --
whatever that is -- and suggests that I leave the system off for a few
minutes, literally, to let things "clear"...whatever that means. Sure
enough, however: it works!

So now I'm here asking, because Tech hasn't the time to puzzle over it
with me, WHAT HAPPENED??? And how come shutting off power for a few
seconds isn't comparable to leaving power off for a few
minutes????????????

Regardless of all the theories involving capacitors storing charge, the
power supply is shot (and it is most likely a faulty capacitor that is
responsible - that is one that is failing to store charge until it cools off
a bit).

 

[Androcles]

:
: : >
: > Is there some such concept as "residual electricity"???
: >
: > There was a problem with a computer at work...it's a new Dell running
: > WinXP Pro...everything's fine, I go to lunch and come back to a blank
: > screen that won't wake up from power-save/sleep mode!! I do the
: > obvious and check connections, making sure they're secure and
: > whatnot. I turn off the computer and turn it back on a few times, to
: > no effect!
: >
: > Tech Support suspects some kind of a "power management" issue --
: > whatever that is -- and suggests that I leave the system off for a few
: > minutes, literally, to let things "clear"...whatever that means. Sure
: > enough, however: it works!
: >
: > So now I'm here asking, because Tech hasn't the time to puzzle over it
: > with me, WHAT HAPPENED??? And how come shutting off power for a few
: > seconds isn't comparable to leaving power off for a few
: > minutes????????????
:
: Regardless of all the theories involving capacitors storing charge, the
: power supply is shot (and it is most likely a faulty capacitor that is
: responsible - that is one that is failing to store charge until it cools
off
: a bit).

Then when you swap out the PSU it turns out to be a problem
on the motherboard - Saudde's law.
Unless you changed out the motherboard first, in which case it was
the PSU - Murphy's law. And really, Tech doesn't have the time
to analyse it poking around with a voltmeter and staring at the
schematic when it only cost a few bucks to replace the module.
Gone are the days when you replaced a burnt out resistor
or an exploded capacitor in a TV, it's cheaper to buy a new TV
now.
As for computers, I've got three spare ... nothing wrong with them,
they are just too slow to bother with and who needs a 1 Gig
hard drive when you can get 320 Gig or whatever?

 

[Unknown]

What type of capacitor has to cool off before it accepts a charge?

 

[M.I.5¾]

What type of capacitor has to cool off before it accepts a charge?

A: A faulty one.

It is well a known problem particularly among certain types of electrolytic
capacitors. The usual problem is that the EPR (Effective parallel
resistance) of the capacitor falls alarmingly as it warms up rendering it
ineffective as a capacitor.

 

[Unknown]

How do you dream up all these ridiculous things?

A: A faulty one.

It is well a known problem particularly among certain types of
electrolytic capacitors. The usual problem is that the EPR (Effective
parallel resistance) of the capacitor falls alarmingly as it warms up
rendering it ineffective as a capacitor.

 

[Androcles]

Sounds like a short circuit to me. Perhaps he's connecting
them with the wrong polarity of the "certain type".

: How do you dream up all these ridiculous things?
: : >
: > : >> What type of capacitor has to cool off before it accepts a charge?
: >
: > A: A faulty one.
: >
: > It is well a known problem particularly among certain types of
: > electrolytic capacitors. The usual problem is that the EPR (Effective
: > parallel resistance) of the capacitor falls alarmingly as it warms up
: > rendering it ineffective as a capacitor.
: >
: >
: >
:
:

 

[Randy Poe]

Two charts of electrolytic capacitor failure modes. Check out
Table 2 here:
http://industrial.panasonic.com/www-data/pdf/ABA0000/ABA0000TE4.pdf

Operating at high temperature is shown to cause failure
by increase in leakage current.

or Figure 2.10 here:
http://etd.gatech.edu/theses/available/etd-04082007-083102/unrestricted/imam_afroz_m_200705_phd.pdf

Operating at high temperature is shown to cause failure
by loss of effective resistance (i.e. increased leakage).

- Randy

 

[Unknown]

What caused the high temperature?

How do you dream up all these ridiculous things?"M.I.5¾"

Two charts of electrolytic capacitor failure modes. Check out
Table 2 here:
http://industrial.panasonic.com/www-data/pdf/ABA0000/ABA0000TE4.pdf

Operating at high temperature is shown to cause failure
by increase in leakage current.

or Figure 2.10 here:
http://etd.gatech.edu/theses/available/etd-04082007-083102/unrestricted/imam_afroz_m_200705_phd.pdf

Operating at high temperature is shown to cause failure
by loss of effective resistance (i.e. increased leakage).

- Randy

 

[Randy Poe]

What caused the high temperature?

Being in a hot place.

- Randy

 

[Unknown]

Then the failure occurred BEFORE the capacitor went bad.

 

[Randy Poe]

Then the failure occurred BEFORE the capacitor went bad.

Um, what? You mean just the fact that I *try* to
operate a capacitor in a poorly air-conditioned room
implies it has failed?

Or do you mean that just the fact that the temperature
around my circuit board is above room temperature
implies that something has failed?

Or what?

- Randy

 

[RnR]

Being in a hot place.

- Randy

It would have to be pretty hot of at least above 120F tho I've seen
some hardware listed in the 140's F as maximum. My guess is the 2nd
applies here. Now the problem is what causes the high temperature to
begin with?? I have doubts about a bad fan but perhaps or maybe a
short circuit????

 

[Randy Poe]

It would have to be pretty hot of at least above 120F tho I've seen
some hardware listed in the 140's F as maximum. My guess is the 2nd
applies here. Now the problem is what causes the high temperature to
begin with?? I have doubts about a bad fan but perhaps or maybe a
short circuit????

This all seems incidental to the discussion. There was
doubt raised on the point that high temperatures could
cause failure of electrolytic capacitors. Let's say that
the high temperature is out of spec for the board. Let's
say that something else HAS failed. How does that
bear on the discussion of this failure mode for capacitors
exposed to high temperatures and whether or not it's
a "ridiculous thing" to say that high temperatures will cause
this effect on electrolytic capacitors?

- Randy