Film capacitor as power-supply filter

[Phil Allison]

Winfield Hill wrote:

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

Phil Allison wrote...

You can make a 100nF Green Cap smoke and explode with a
40W bench amplifier and a series inductor of a few mH
operating at resonance.

Good cheap fun.


The caps can easily have Q in excess of 1000. I have
made inductors with Q that high, with litz wire, etc.,
but most are much lower. But even Q=100 can potentially
turn 35 volts into over 3.5 kV.

** My inductor was large, air cored, 5.6mH and with 0.8ohms series R.

To ensuequick death needs about 250VAC at resonance = 7.7 kHz.

However, high Zout of the amplifier is a severe Q limitation.

** Ordinary SS power amp with output Z of about 0.25 ohms.

After solving
that, you have to deal with high resonate circulating
currents, and power dissipation in the inductors. If
your capacitor goes first, that can save the inductor.

** Think you are over thinking this.

This scheme is most useful when driving piezo elements,
where power injected into the coupled medium limits the
Q and maximum voltage. E.g., my acoustic oceangraphic
instruments in the 80s, and sonoluminescence experiments
in the 90s, looking for the supposed neutrons, hahaha.

** I was just having innocent fun destroying Greencaps and a number of X2 rated polyester mains caps. 3kV ceramics stood up quite well.

Needed to knew the limits cos of the high AC voltages on the primary side of valve output transformers.

Can reach 5kV rel to chassis under certain conditions.

But audio just simple shit.


..... Phil

 

[Phil Allison]

John Larkin wrote:

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

** I have a TO3 lateral MOSFET with a neat, round hole in the top of the lid.

Not the only example I have seen.

Just below the hole is the top of the drain pin, somewhat burnt.


The springy source wire bond strap would sometimes fly off the chip
and hit the top of the can. Bipolars did that too.

** Really?

Hitachi TO3 lateral mosfets have thin, aluminium drain wires that act as fuses under chip failure conditions.

The resulting metal vapour can initiate an arc from drain pin to the lid above that continues, backed up by a hefty 110VDC supply.

A neat, round hole forms and enlarges to a few mm diameter before self extinguishing.

The cute things is the amplfifer normally keeps going afterwards with the remaining good mosfets.

Audio is simple shit.



...... Phil

 

[Phil Allison]

jla...@highlandsniptechnology.com wrote:

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

Design something that works. Post it here.



** How to get rid of 10 pounds of ugly fat ?

Cut your head off.



** That one went over JL's head like a Scud missile ....

That was a corny attempt at humor whan I was a kid. Maybe it has
recently propagated to Australia.

** JL has still missed the point of my juxtaposition.

Maybe it was too pointed ....


( snip pile of worthless JL drivel and trumpet blowing )

FYI to all:

Fraid I am not one bit interested in ANY of JLs nonsense replies to my serious complaints.

There are none so blind as those who will not see.

Then there are people like JL.



...... Phil

 

[Phil Allison]

John Larkin wrote:

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

Besides the damaged MJs, I got any number of Motorola fakes from well known outlets about that same time - mostly MJ15003/4 types from Dick Smith Electronics, remember the Aussie helicopter aviator ?


Dick Smith invented the Coa Thanger car antenna.

** Not true at all.

Was already invented and named by radio hams ( we call them "amateurs" ) before Dick mentioned them in one of his catalogues.

The correct name is "co-tanger", a pun on "co-linear".

There was a Dick Smith retail store in Silicon Valley, but it didn't
last long. It had a lot of salesmen and cheap parts and no customers.

** Be like selling ice blocks to Eskimos.



...... Phil

 

[Phil Allison]

jla...@highlandsniptechnology.com wrote:

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

Bill Sloman wrote:

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

Nobody is going to treat Phil Allison as a beginner.


** Happens here daily by Win, John and Phil H.

The Three Stooges.


He's not complaining about not having his hand held,
but rather the absence of proper documentation.

** Not complaining about anything like that.

Just the ingenuous nature of JLs malicious trap request.


He may be asking a bit much. Proper documentation is bulky.


** Have you *never* seen a published project in a magazine or on line ?

Ones I did for EA magazine consisted of 2 to 3 thousand words, colour pics, a PCB pattern and component layout, specifications list, block diagrams and of course a full schematic with parts list and where to get any oddball parts.

A prototype had to be supplied too, so the mag's staff could see that it worked and take their own pics.

Enough info was needed for a hobbyist and others to build one and for parts dealers to make up kits. The cost of such had to be less than any similar commercial offering - a major hurdle.

One was forbidden to use exotic, hard to get parts or expect builders to own more than a DMM.

The article had to interesting reading in it own right, to help sell the magazine when sitting on seller stands.

I seriously doubt any the Three Stooges would have a clue how to do the same.


Win and Phil both author books (everybody should have both) and do
proprietary designs that they can't publish.

** Blah, blah, blah,

JL has no idea he is posting worthless responses.

Concertos for solo trumpet, his own and now others.

I already 100% KNOW how The Three Stooges behave here

= appallingly !!!


Not one word of JL's narcissistic drivel can undo that.




...... Phil

 

[Phil Allison]

Winfield Hill wrote:
---------------------

The series inductor Q will be determined by its esr
in series with the amplifier's Zout. A high Q leads
to high resonant recirculating currents. Most amps
have low Zout, but 70-volt PA outputs are often not.

** Ummmm - where did the 70V PA amp come from ??

I know my initials are "PA" but that cannot be it.

Three Stooges logic ?

Make any mad assumption you feel like and post it as fact ?


FYI to all:

the good thing about writing text books is that you do not have to put up with being contradicted or having your mistakes pointed out in real time.

In fact, you can pretty much get away with murder.

At Sydney Uni in the early 70s, we used the still popular text

"Fundamentals of Physics " by US team Halliday and Resnick.

It was chock full of mistakes, particularly in the test questions.

About 50% of the published answers were wrong - the smarter students ( 18 year olds) were able to point out the exact logical & math errors that had led to the wrong answers.

Of course, this paled into insignificance in comparison to the absurd level of mistakes found in notes and black board math supplied by lecturers - most of them PhD students.

No complaints from undergrad students were possible nor errors ever corrected.

And I was doing the special " Honours Physics " course.

Not very honourable.


..... Phil

 

[Phil Allison]

John Shithead is a Dumb Cunt wrote

Nobody is going to treat Phil Allison as a beginner.


** Happens here daily by Win, John and Phil H.

The Three Stooges.


He's not complaining about not having his hand held,
but rather the absence of proper documentation.

** Not complaining about anything like that.

Just the ingenuous nature of JLs malicious trap request.


He may be asking a bit much. Proper documentation is bulky.


** Have you *never* seen a published project in a magazine or on line ?

Ones I did for EA magazine consisted of 2 to 3 thousand words, colour pics, a PCB pattern and component layout, specifications list, block diagrams and of course a full schematic with parts list and where to get any oddball parts.

A prototype had to be supplied too, so the mag's staff could see that it worked and take their own pics.

Enough info was needed for a hobbyist and others to build one and for parts dealers to make up kits. The cost of such had to be less than any similar commercial offering - a major hurdle.

One was forbidden to use exotic, hard to get parts or expect builders to own more than a DMM.

The article had to interesting reading in it own right, to help sell the magazine when sitting on seller stands.

I seriously doubt any the Three Stooges would have a clue how to do the same.


And I doubt you would have a clue how to write a book similar to "The
Art of Electronics" as has been done by one of the Three Stooges.

** What an absurd remark.

If you don't like this group, go find another.

** Nah, this is a public forum and should not be dominated by arrogant bullies.

Otherwise, shut up.

** Go fuck your mother.

( might well be a redundant idea )



.... Phil

 

[Phil Allison]

Winfield Hill wrote:

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

Phil Allison wrote...

https://au.mouser.com/ProductDetail/KEMET/C4AQCBW5200A3FJ?qs=sGAEpiMZZMv1cc3ydrPrF95ZAHiPXMKgQ3r3TgzZkS816veTKZI9aw%3D%3D


That's a good find. Rather large: 20x42x40mm high.

** Needs no more PCB space than pair of 47uF, 450V electros.

Cheaper as well.


..... Phil

 

On Mon, 21 Oct 2019 13:27:38 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

jla...@highlandsniptechnology.com wrote:

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


Design something that works. Post it here.



** How to get rid of 10 pounds of ugly fat ?

Cut your head off.



** That one went over JL's head like a Scud missile ....

That was a corny attempt at humor whan I was a kid. Maybe it has
recently propagated to Australia.


** JL has still missed the point of my juxtaposition.

Maybe it was too pointed ....


( snip pile of worthless JL drivel and trumpet blowing )

FYI to all:

Fraid I am not one bit interested in ANY of JLs nonsense replies to my serious complaints.

There are none so blind as those who will not see.

Then there are people like JL.



..... Phil

Please post those links to stuff you have designed and I (apparently)
snipped.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[whit3rd]

On Sunday, October 20, 2019 at 11:13:27 AM UTC-4, jla...@highlandsniptechnology.com wrote:

Conservation of energy says that the explosion won't liberate more
joules than I pushed into the cap. None of my bench supplies can
deliver explosive amounts of energy in any reasonable time.

Yeah, but... real HV capacitors need a shorting chain EVERY time.
An uplugged genset can resonate with wall wiring, and melted shorting
chain is the best way to find out about that sort of thing...

 

[Bill Sloman]

On Tuesday, October 22, 2019 at 2:04:19 AM UTC+11, jla...@highlandsniptechnology.com wrote:

On Sun, 20 Oct 2019 21:25:06 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

jla...@highlandsniptechnology.com wrote:

<snip>

** LOL - hand drawn fragments of ideas are not "designs".

They are ideas, which is what electronoc designers start with when
they are brainstorming. Fragments can be evolved or rejected or
trigger other, sometimes very different ideas.

Which is to say, they aren't designs.

Brainstorming is a group of people having fun with ideas. You couldn't
do it. You are angry and hostile and want everything to be a Heathkit
manual. Some people poison brainstorming, and poison all stages of
electronic design.

Egomaniacs like John Larkin don't make good brainstormers - they tend to hog the discussion. They don't notice that they are doing this.

You asked for a "DESIGN" - fuckhead.

Published DESIGNS contain all the things I mentioned and more.

What project have you had published and been paid for?

I just manufacture them and sell them. I do post some ideas and
schematics and pictures of actual products here, when I think it would
be helpful and not harm my business.

What I've seen hasn't been impressive, and most of it had been around for so long that it didn't actually count as helpful.

Care to post a link?

You *maliciously* snipped all reference to the ones I had published.

Must have missed them. Please repost the links.

Egomaniacs don't tend to notice other peoples contributions.

and scores of photos of real stuff I've designed,

** Again, no-one can sensibly judge a design from a pic of some a PCB.

and scores of Spice sims.

** Nothing faintly like a "design".

Sims are all 99% worthless.

Good grief, that's an interesting statement. Do you ever run Spice?

Others have posted, freely given away, as many.

** But no complete designs one could sensibly construct.

Again, buy a kit if you want to build something without having to
understand it.

Have you seen Win's HV amps, or
Phil Hobbs low-noise circuits, posted recently?


** Spice listing are NOT designs.

I think they are.

They are circuit diagrams, and - as such - can incorporate elements that illustrate how a particular design could work.

The map is not the territory, but Spice simulations - in expert hands - can illustrate the territory in some detail.

Parasitic elements - lead inductances, stray capacitances, interwinding capacitances in transformers - do need to be kept in mind, even if they can often be ignored.

Win's HV lab amp looks like a nightmare.

It's not my schematic style, but it's original, correct, and it works.

I prefer to waste more paper, spread things across less-populated
sheets. That leaves more room for scribbles on the bench.

But can make it difficult to extract the big picture.

Plus, the complete nonsense he posted about a on-line design that was in fact NOT mine was absurd. I shot it to pieces and so he ignored me.

Possibly you re-discovered something. That happens a lot.

What's that got to do with anything?

Wot an utter ass.

Not a bit, but your shrieking and swearing does sometimes put people
off. Why do you do that? It can't make you any happier.

Some people are very complacent. It can take a certain amount of verbal violence to get them to register that they are being disagreed with.

John Larkin expects a non-stop stream of praise, and fells insulted if he doesn't get it.

I don't furnish detailed "justifications";

** Cos you haven't got nay.

My stuff works and people buy it, and keep buying it. Do you contend
that I don't understand it? That's silly.

(Well, OK, sometimes I don't understand it. I'm just an engineer.)

Engineering is about understanding what you put together. You have just confessed to being a tinkerer.

The reasoning behind a design decision is usually non obvious to outsiders and crucial - cos it may be very good or very bad. A simple fact JLs raging ASD and pig arrogance prevents him from knowing.

The fool has no credible theory of thought - you see.

Some, or a lot, of what I do is instinct.

Instincts are preprogrammed by evolution. Transistors haven't been around for long enough for this to work.

Quite a lot of human cognition occurs in the sub-conscious. Anybody who has woken up with the realisation that a particular circuit won't work will be aware of that.

The fact that you weren't conscious of the processing going on doesn't make it instinctive.

Once you have worked out that something isn't going to work you have an obligation to work out why it isn't going to work, so that you can explain it to other people.

Sorry. The solution space
for even a modest electronic design is way too large to be searched by
any canned procedure. It requires most of a brain to be working as a
quantum computer, encompassing a lot of possibilities in parallel.

Twaddle. Or - to be more specific - one of Roger Penrose's less plausible speculations.

> That concept annoys a lot of people who want everything to be just so.

It annoys even more people who don't like gratuitous and unhelpful nonsense..

Sorry.

"Theory of thought" is exactly what I don't want.

It undercuts your favourite sort of pretentious drivel.

I assume that competent
engineers can look at a schematic and figure out what's going on, and
improve any idea that they want to.

** That barking mad idea is exactly what I am saying is 100% WRONG !!

I can see the problem here. You want every circuit concept to be
explained in detail, with values, like in some old HP manual.

Mostly it doesn't have to be explained in detail, but not every picture is worth a thousand words, and some written text can save a lot of barking up the wrong tree.

> Sorry.

If only he knew enough to realise what he was apologising for.

There's a least one paper on man-machine interaction that spells out the way engineers aren't conscious of what they are doing.

The prize example was an instrument designed by a left-handed engineer that right-handers found very difficult to use. For some reason, left-handers - like me - are less inconvenienced by the choices that right-handers make (probably because being right-handed seems to be frequently a consequence of brain-editing that doesn't seem to happen in left-handers, who are essentially the half of the ambidextrous population who got into the habit of using their left hand more often).

The more substantial comment was about error-recovery - engineers knew what the machine was doing, and knew how to get it to recover after they had done something wrong.

Naive users had a harder time because the engineers didn't write the error recovery procedures into the manual - they didn't realise that they had to spell them out.

--
Bill Sloman, Sydney

 

[Phil Allison]

jla...@highlandsniptechnology.com wrote:

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

Please post those links to stuff you have designed and I (apparently)
snipped.

** JL thinks he is above the rules of usenet posting, all the time.

One of which says to always post UNDER the words you wish to comment on,

so do invent words and claim another posted them.

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

FYI to all:

As a matter of fact, all my Australian magazine projects ( 8 of them ) were available for perusal on line and download until about two weeks ago.

Then this happened:

https://americanradiohistory.com/Radio_and_Hobbies.htm


As Forrest Gump said ....



..... Phil

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

On Mon, 21 Oct 2019 07:57:11 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

The issue was series strings of electrolytic caps, where the total
supply voltage is more than the rated voltage of the caps. Film caps
can blow up in that situation. What do lytics do?

Answer: their IV curves make them safely self-equalize.

How does self-equalization work, and why does the I-V curve have to be
exponential?

The cap with more voltage across it would conduct way more current,
which would integrate to lower voltage on itself and more on others.
The end result is obviously equal currents, but *less* current than
there would be if the voltages were evenly distributed in the string.

When you first apply voltage across the cap, the current decays
exponentially. So both caps may have a high current, but they both decay
quickly.

The best test would be to find two caps with different leakage current.

Put them in series, apply voltage, and plot the voltage at the junction.

This could be done with a digital scope.

Betcha they don't equalize.

 

On Tue, 22 Oct 2019 07:15:45 -0000 (UTC), Steve Wilson <no@spam.com>
wrote:

jlarkin@highlandsniptechnology.com wrote:

On Mon, 21 Oct 2019 07:57:11 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

The issue was series strings of electrolytic caps, where the total
supply voltage is more than the rated voltage of the caps. Film caps
can blow up in that situation. What do lytics do?

Answer: their IV curves make them safely self-equalize.

How does self-equalization work, and why does the I-V curve have to be
exponential?

The cap with more voltage across it would conduct way more current,
which would integrate to lower voltage on itself and more on others.
The end result is obviously equal currents, but *less* current than
there would be if the voltages were evenly distributed in the string.

When you first apply voltage across the cap, the current decays
exponentially.

Not exponentially, because the cap leakage is nonlinear.

So both caps may have a high current, but they both decay
quickly.

If voltage is applied quickly, the voltage across each cap is inverse
on C.

As the leakage time constants lick in, the voltage redistributes into
the minimum-current situation. It might take hours to mostly settle
down, or maybe days.

The best test would be to find two caps with different leakage current.

Put them in series, apply voltage, and plot the voltage at the junction.

This could be done with a digital scope.

Betcha they don't equalize.

Of course they don't equalize to equal voltage. They do magically find
the voltage distribution that minimizes the leakage current.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Tue, 22 Oct 2019 18:00:15 -0000 (UTC), Steve Wilson <no@spam.com>
wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 22 Oct 2019 07:15:45 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

On Mon, 21 Oct 2019 07:57:11 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

The issue was series strings of electrolytic caps, where the total
supply voltage is more than the rated voltage of the caps. Film caps
can blow up in that situation. What do lytics do?

Answer: their IV curves make them safely self-equalize.

How does self-equalization work, and why does the I-V curve have to be
exponential?

The cap with more voltage across it would conduct way more current,
which would integrate to lower voltage on itself and more on others.
The end result is obviously equal currents, but *less* current than
there would be if the voltages were evenly distributed in the string.

When you first apply voltage across the cap, the current decays
exponentially.

Not exponentially, because the cap leakage is nonlinear.


So both caps may have a high current, but they both decay quickly.

If voltage is applied quickly, the voltage across each cap is inverse
on C.

As the leakage time constants lick in, the voltage redistributes into
the minimum-current situation. It might take hours to mostly settle
down, or maybe days.


The best test would be to find two caps with different leakage current.

Put them in series, apply voltage, and plot the voltage at the junction.

This could be done with a digital scope.

Betcha they don't equalize.

Of course they don't equalize to equal voltage. They do magically find
the voltage distribution that minimizes the leakage current.

Does that voltage distribution mean that one capacitor may have a voltage
that exceeds its rating?

Possibly, but since the current is low, it does no harm.

Current damages electrolytic caps. As noted, the string current is
lower than it would be if the cap voltages were forced equal.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

On Tue, 22 Oct 2019 07:15:45 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

On Mon, 21 Oct 2019 07:57:11 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

The issue was series strings of electrolytic caps, where the total
supply voltage is more than the rated voltage of the caps. Film caps
can blow up in that situation. What do lytics do?

Answer: their IV curves make them safely self-equalize.

How does self-equalization work, and why does the I-V curve have to be
exponential?

The cap with more voltage across it would conduct way more current,
which would integrate to lower voltage on itself and more on others.
The end result is obviously equal currents, but *less* current than
there would be if the voltages were evenly distributed in the string.

When you first apply voltage across the cap, the current decays
exponentially.

Not exponentially, because the cap leakage is nonlinear.


So both caps may have a high current, but they both decay quickly.

If voltage is applied quickly, the voltage across each cap is inverse
on C.

As the leakage time constants lick in, the voltage redistributes into
the minimum-current situation. It might take hours to mostly settle
down, or maybe days.


The best test would be to find two caps with different leakage current.

Put them in series, apply voltage, and plot the voltage at the junction.

This could be done with a digital scope.

Betcha they don't equalize.

Of course they don't equalize to equal voltage. They do magically find
the voltage distribution that minimizes the leakage current.

Does that voltage distribution mean that one capacitor may have a voltage
that exceeds its rating?

 

[Bill Sloman]

On Wednesday, October 23, 2019 at 5:21:17 AM UTC+11, John Larkin wrote:

On Tue, 22 Oct 2019 18:00:15 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 22 Oct 2019 07:15:45 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

On Mon, 21 Oct 2019 07:57:11 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

The issue was series strings of electrolytic caps, where the total
supply voltage is more than the rated voltage of the caps. Film caps
can blow up in that situation. What do lytics do?

Answer: their IV curves make them safely self-equalize.

How does self-equalization work, and why does the I-V curve have to be
exponential?

The cap with more voltage across it would conduct way more current,
which would integrate to lower voltage on itself and more on others.
The end result is obviously equal currents, but *less* current than
there would be if the voltages were evenly distributed in the string.

When you first apply voltage across the cap, the current decays
exponentially.

Not exponentially, because the cap leakage is nonlinear.

The capacitance leakage current is a non-linear function of what?

What Steve Wilson was observing was that it was a non-linear function of time at constant voltage - specifically an exponential function of time.

John Larkin seems to be saying that the time dependence wouldn't be exponential because the leakage current is a non-linear function of something else.

Since he hasn't specified what the something else might be - he probably had voltage in mind - he's just being confused rather than saying anything that might have been useful.

So both caps may have a high current, but they both decay quickly.

If voltage is applied quickly, the voltage across each cap is inverse
on C.

As the leakage time constants lick in, the voltage redistributes into
the minimum-current situation. It might take hours to mostly settle
down, or maybe days.


The best test would be to find two caps with different leakage current.

Put them in series, apply voltage, and plot the voltage at the junction.

This could be done with a digital scope.

Betcha they don't equalize.

Of course they don't equalize to equal voltage. They do magically find
the voltage distribution that minimizes the leakage current.

Does that voltage distribution mean that one capacitor may have a voltage
that exceeds its rating?

Possibly, but since the current is low, it does no harm.

Voltage stress is what ruptures the layer of aluminium oxide that forms the dielectric in an electrolytic capacitor.

Once this has broken down, all bets are off.

Current damages electrolytic caps. As noted, the string current is
lower than it would be if the cap voltages were forced equal.

There's no requirement that current damages each capacitor in the same way.

--
Bill Sloman, Sydney

 

[Steve Wilson]

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

On Tue, 22 Oct 2019 18:00:15 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

On Tue, 22 Oct 2019 07:15:45 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

On Mon, 21 Oct 2019 07:57:11 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

jlarkin@highlandsniptechnology.com wrote:

The issue was series strings of electrolytic caps, where the total
supply voltage is more than the rated voltage of the caps. Film
caps can blow up in that situation. What do lytics do?

Answer: their IV curves make them safely self-equalize.

How does self-equalization work, and why does the I-V curve have to
be exponential?

The cap with more voltage across it would conduct way more current,
which would integrate to lower voltage on itself and more on others.
The end result is obviously equal currents, but *less* current than
there would be if the voltages were evenly distributed in the
string.

When you first apply voltage across the cap, the current decays
exponentially.

Not exponentially, because the cap leakage is nonlinear.

So both caps may have a high current, but they both decay quickly.

If voltage is applied quickly, the voltage across each cap is inverse
on C.

As the leakage time constants lick in, the voltage redistributes into
the minimum-current situation. It might take hours to mostly settle
down, or maybe days.

The best test would be to find two caps with different leakage
current.

Put them in series, apply voltage, and plot the voltage at the
junction.

This could be done with a digital scope.

Betcha they don't equalize.

Of course they don't equalize to equal voltage. They do magically find
the voltage distribution that minimizes the leakage current.

Does that voltage distribution mean that one capacitor may have a
voltage that exceeds its rating?

Possibly, but since the current is low, it does no harm.

Current damages electrolytic caps. As noted, the string current is
lower than it would be if the cap voltages were forced equal.

Allowing the capacitor to exceed the rated working voltage is not a
suitable engineering goal.

You can use your method. I'll stick with the industry standard bleeder
resistors where the bleed current is 10 times the maximum capacitor
leakage spec

A typical spec is

I = 0.01CV or 3uA, whichever is greater

Where
I : Max. leakage current (uA) at 20C after 2 minutes
C : Nominal capacitance (uF)
V : Rated voltage (V)

The leakage current is measured at 20C by applying the rated voltage to
the capacitor through a series resistor of 1000 Ohms. The leakage current
is the value 2 minutes after the capacitor has reached the rated voltage.

This test requires the capacitor to be already properly formed.

Example for a 1000uf, 450V capacitor

I = 0.01 CV = 0.01 * 1000 * 450 = 4,500 uA

So the bleeder current should be 45mA, or

R = 450 / 45e-3 = 10,000 Ohms

The bleeder dissipation is

P = 45e-3 * 450 = 20.25 Watts for each resistor.

In addition to supplying a known voltage across the capacitor, this also
provides a means of discharging the capacitors, which your method ignores.

The bleeder time constant is

RC = 10,000 * 1000e-6 = 10 seconds.

So the capacitor voltage should be reduced to a safe level one minute
after power off.

Your method would allow a dangerous or lethal voltage to remain on the
capacitor for an unknown amount of time. That is hardly an example of good
engineering.

 

[Phil Allison]

Steve Wilson wrote:

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

Your method would allow a dangerous or lethal voltage to remain on the
capacitor for an unknown amount of time. That is hardly an example of good
engineering.

** With most tube gear, the tubes themselves drain all the electros after switch off - thy do keep on working for quite a while with no supply to the heaters.

It is only those amplifiers with standby by switches that allow this to happen
- however the correct procedure is to turn off the AC first.



...... Phil

 

[Winfield Hill]

Steve Wilson wrote...

A typical spec is
I = 0.01CV or 3uA, whichever is greater

Where
I : Max. leakage current (uA) at 20C after 2 minutes
C : Nominal capacitance (uF)
V : Rated voltage (V)

That's a common, but horrible formula, especially if
the units aren't stated. Should be farads and amps.

Example for a 1000uf, 450V capacitor
I = 0.01 CV = 0.01 * 1000 * 450 = 4,500 uA
So the bleeder current should be 45mA, or
R = 450 / 45e-3 = 10,000 Ohms

The bleeder dissipation is
P = 45e-3 * 450 = 20.25 Watts for each resistor.

Wasting 40W in a pair of bleeder resistors is not an
attractive situation, leading one to change the "rule".

I routinely make HV supplies, with big caps for high
pulse output currents, but with a maximum dissipation
of under 10W. Wouldn't want to waste more than 4W.

The bleeder time constant is
RC = 10,000 * 1000e-6 = 10 seconds.

So the capacitor voltage should be reduced to a safe
level one minute after power off.

I designed a fairly simple HV discharge circuit, that
works automatically when the operating voltages are
removed, fully discharges the HV in under 5 seconds.


--
Thanks,
- Win