Re: Electrolytic capacitors

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"Chris Jones"
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** If electro caps are deteriorating and needing replacement  -  then it is
*odd  on* they are operating in a hot environment.  So 105 C types will
likely last much longer than the 85 C types.

Also be aware that the ESR of an electro goes DOWN when the cap gets hot  -
by a factor of up to 5 times !!!



........  Phil





Re: Electrolytic capacitors



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The point I was making is that the ESR of the 105 degree types was several
times larger than that of the 85 degree type from the same manufacturer,
when I measured it.  Therefore in some applications where ESR really
matters e.g. SMPS output, it is possible that after replacing the caps with
higher temperature types, the thing will not work as well as it would have
done if the 85 degree type had been used, and in the worst case, the 105
degree caps could heat up more than twice as much as the 85 degree type,
and could exceed 105 degrees in a situation where the 85 degree caps would
have stayed below 85 degrees C.  If people read the maximum ripple current
spec of the caps when they replace them then they wouldn't have this
problem, but I was just pointing out that the higher temperature caps are
not universally better, some thinking can be required.

Chris





Re: Electrolytic capacitors



"Chris Jones"

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 **  Shame you did not say  *that* before.

Kindly post the revalant info  -   ie cap maker,  ratings, physical size &
actual ESR readings.

 In many years of checking electros I have NOT come across anything like
your claim.



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**  You are making this all up as you go along.

 Electros are not operated at such high temps in SMPSs.




...........  Phil



Re: Electrolytic capacitors


On Mon, 13 Feb 2006 10:50:38 +1100, "Phil Allison"

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Phil the God and creator of all SMPS's on this would know.



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Re: Electrolytic capacitors



"The Real Andy"



 ** Shame Andy has run out of public toilets to troll.

  Maybe he will stalk the ones at the local primary next.





........  Phil





Re: Electrolytic capacitors


On Mon, 13 Feb 2006 20:29:24 +1100, "Phil Allison"

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You are a sad pathetic fuckwit Allison, when will you come up with
some new lines? The old ones are becoming a bit tired now.

Yawn...

Re: Electrolytic capacitors



"The Real Andy"



 ** Shame Andrew Pearson has run out of public toilets to troll.

 Maybe he will stalk the ones at the local Brisbane primary next.





........  Phil






Re: Electrolytic capacitors


On Tue, 14 Feb 2006 10:42:57 +1100, "Phil Allison"

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Shame Phli Allison the worn out uni reject roadie has run out of
lines.

Re: Time Wounds All Heels



"The Real Andy"

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**   You need some sleep.




........  Phil



Re: Time Wounds All Heels


On Wed, 15 Feb 2006 15:13:50 +1100, "Phil Allison"

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Your repetition is making me tired.



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Re: Electrolytic capacitors



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They were Nippon Chemi-con, though it was a while ago so I don't know the
part numbers.  The 105 degree ones were brown in colour and the 85 degree
ones were black.  The actual ESR readings have been long since forgotten,
but I just remember that in that particular case the 105 degree ones were
higher by a surprising amount, and that I should in future measure the ESR
before making any "clever" substitutions. Here is a catalogue from the same
manufacturer.
http://www.chemi-con.co.jp/pdf/catalog/al-e1001f/al-lead-e-051221.pdf
What is now clear to me is that there are so many different types in both
temperature ranges that it would not be surprising if there were some high
and low ESR grades in both ranges and therefore the possibility of me
finding high temperature ones that happen to be from a series which doesn't
have as good ESR as some of the low temperature grades.  The lesson that I
learnt was that I should measure the ESR and not assume any temperature
range are always better.

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Fair enough.

Well I have never seen it happen so yes if you like, but certainly a
capacitor with high ESR could be heated quite a bit when subjected to a few
amps of ripple current.

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Hopefully not, in a good design, but then I probably wouldn't be trying to
fix it if it had been designed properly.

Chris

Re: Electrolytic capacitors



"Chris Jones"
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 **   Nor falsely assume that temp grade and ESR go hand in hand.



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 **  Shame how the ESR falls as the electrolyte heats up.



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**  You got a diploma in Pure and Applied Guesswork ???

     Or still working on that.



........   Phil







Re: Electrolytic capacitors



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No, if I can measure the ESR instead then it is indeed better not to assume
anything about it.

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It's not a shame, it's quite handy really, but if the ESR were lower in the
first place then it wouldn't have to heat up.


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yes.



Re: Electrolytic capacitors


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a lot depends on what frequency the ESR is measured at. It varies
significantly with frequency. Michael Gaspari wrote a great paper in IEE
trans. Industry applications, vol.41 no.6 nov/dec 2005, pp1430-1435.

his cap model is:

---[Ro]---[R1]---+----[R2]----+----[C1]----
                  |            |
                  +----[C2]----+

R0 = resistance of foil, tabs & terminals
R1 = resistance of electrolyte
R2 = dielectric loss resistance
C1 = terminal capacitance
C2 = dielectric loss capacitance


R2 and C2 give a large variation in ESR with frequency. typically the
effect of R2,C2 peters out above 10kHz, so you can take the ESR at
100kHz as the combined value of R0 and R1. this can be seen from the
ripple current multiplier tables a decent cap data sheet has.

R0+R1 = ESR @ 100kHz

R2 = ESR @ 100Hz - (Ro + R1)

and pick C2 to get the right values for ESRs in the 100H - 10kHz range

the reason the ripple current varies with temperature is the loss in the
cap is kept constant (for a given lifetime) so lower ESR means more
current. you can thus translate a ripple-current multiplier table (eg
see LXZ cap datasheet in linked PDF) into an ESR multiplier.

ESR_multiplier = 1/(ripple_multiplier)^2

the LXZ table for 220uF - 560uF caps is:

120Hz    1kHz    10kHz    100kHz
0.5    0.85    0.94    1.00

so the ESR multiplier is:

4    1.4    1.13    1


these caps have 4x the ESR at 100Hz. hardly surprising, they are
designed for smps, so have low ESR at 100kHz.


ESR variation with temperature is due to the increased conductivity of
the electrolyte.

R1(T) = R1o*exp[(To-Tcore)/E]

R1o = ESR at temperature To

E = temperature sensitivity factor

R1 is usually 5x Ro, and you can calculate E from the two ESR
measurements (-10C, 20C) for a given cap family.


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Cheers
Terry

Re: Electrolytic capacitors



"Terry Given"

(snip drivel)


**  Terry is one of those studious guys who wrote brilliant answers to every
exam questions  he faced -   but was then marked 1 or 2 out of 10 for them.

Because what Terry wrote did NOT answer the question as posed.

No insight.

At all.



........   Phil




Re: Electrolytic capacitors


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Phil said it, so it must be true.

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:)

Well done Phil, not a single piece of invective.

Cheers
Terry

Re: Electrolytic capacitors



"Terry Given"

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**  ROTFLMAO   !!!!!!


  It's a lay down mezzanine.




........  Phil







Re: Electrolytic capacitors



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[snip]
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Thanks, I found that interesting.
Chris

Re: Electrolytic capacitors


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no worries. I should have given a summary though: its pretty darned
important to know what frequency ESR is measured at. Also caps designed
for large amounts of 100/120Hz ripple are different from those designed
for HF ripple - and tend not to specify ESR at all, just ripple current,
DF and lifetime.

what frequency does the ESR meter use? is there an on-line schematic?

M.G. also gives the real guts on lifetime calcs too, but they are
transcendental so no closed-form solution. but if you know enough to
look at a nichicon or nippon chemi-con catalogue, you've probably come
across their lifetime calcs.

he has a very interesting plot of the effect of line impedance on cap
lifetime - in a standard diode-cap recitifer, the line impedance
directly controls the peak current, and hence lifetime.

Of course in practise most cap lifetime problems arise because the
"designer" did one or more of the following:

1) used the wrong part - eg cheesy DSE caps instead of LXZs etc.
2) beat it to death, usually by ignoring (or being unaware of) ripple
current. dont forget a smps mains cap sees 100/120Hz *and* HF ripple
current.
3) cooked the damned thing, by placing it next to something very hot

I was involved once in the design review of a small toshiba AC motor
controller - IIRC 1/2HP. It was far, far cheaper than our offering, so
we bought one and reverse-engineered it. The first thing we noticed was
the tiny DC bus cap, which wouldnt last long at all. Buried deep in the
manual, in small print, was the requirement to replace it every year :)
Oh, we fired it up, slammed it into current limit, and it never tripped
- just went bang 5 minutes later. Our one would operate continuously
into a dead short. cheap usually means nasty.

Cheers
Terry

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