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failure of the low-ESR electrolytic capacitor in second winding

S

Simon

Jan 1, 1970
0
I met a big problem that the DC-DC converter circuit failure happend
frequently

I use UC3843B to control the Planar TRf 101 transformer to provide
multiply DC output;

and almost every failure has the same feature:

The failure on the low-ESR electrolytic capacitor at the second wiring
of the transformer;

it's kind of Low-ESR electrolytic capacitor, 1000uf/10V (ESR=0.07
ohm).

The UC3843B working at 100KHZ.


Is there anybody met that problem before?

What's the possible reason to lead to the failure?


Some body may say because of the high temperature, but it happends on
the product even working in less than 30 cent degree ambient operation
temperature.
 
E

Eeyore

Jan 1, 1970
0
Simon said:
I met a big problem that the DC-DC converter circuit failure happend
frequently

I use UC3843B to control the Planar TRf 101 transformer to provide
multiply DC output;

and almost every failure has the same feature:

The failure on the low-ESR electrolytic capacitor at the second wiring
of the transformer;

HOW does it fail ? Does it explode ?

it's kind of Low-ESR electrolytic capacitor, 1000uf/10V (ESR=0.07
ohm).

The UC3843B working at 100KHZ.

Is there anybody met that problem before?

What's the possible reason to lead to the failure?

Some body may say because of the high temperature, but it happends on
the product even working in less than 30 cent degree ambient operation
temperature.

What converter configuration ? e.g. flyback ?

What's the ripple current rating of the capacitor ?

What's the load current ?

Graham
 
F

Frithiof Andreas Jensen

Jan 1, 1970
0
What's the possible reason to lead to the failure?

1) Cooking it - either by wave soldering or by overload. There is an RMS
ripple current rating for these things - and at the max rated operating
temperature, normally specified as 80 deg.C., the expected lifetime will be
something like 2000 hours so maybe they are performing as designed!!

2) Overvoltage/Cooking due to resonance between the capacitor and the
wiring/transformer; low ESR is sometimes bad. I have blown some solid
polymer to hell on that.
 
J

Jamie

Jan 1, 1970
0
Simon said:
I met a big problem that the DC-DC converter circuit failure happend
frequently

I use UC3843B to control the Planar TRf 101 transformer to provide
multiply DC output;

and almost every failure has the same feature:

The failure on the low-ESR electrolytic capacitor at the second wiring
of the transformer;

it's kind of Low-ESR electrolytic capacitor, 1000uf/10V (ESR=0.07
ohm).

The UC3843B working at 100KHZ.


Is there anybody met that problem before?

What's the possible reason to lead to the failure?


Some body may say because of the high temperature, but it happends on
the product even working in less than 30 cent degree ambient operation
temperature.
you didn't say what type of failure?, So I'll assume a short.

Is it possible you're having periodic over voltage spikes on
the secondary side? This could happen for example if the cap
was already at a full charge near it's 10 volt limit then for
what ever reason, the switcher got unstable and caused a much
higher voltage to appear on the output? Because the cap is already
saturated, there isn't much to hold back that short pulse.
I suppose a cap being new might be able to hold off on this for
a bit.
Maybe you should try some TVS diodes closely matched to the
voltage of your cap on the output.

I've seen many low voltage caps that can handle only and no
more than what it states for the package. Could it be you have
some closely rated caps?
Have you performed a leakage test on the caps you're using?
 
P

Phil Allison

Jan 1, 1970
0
"Simon"
I met a big problem that the DC-DC converter circuit failure happend
frequently

I use UC3843B to control the Planar TRf 101 transformer to provide
multiply DC output;

and almost every failure has the same feature:


** But you don't say what kind of failure it is.


If the cap is blown apart - it's overvoltage.

If the cap has oozed electrolyte - it's the fault of the maker.

If the cap has gone high ESR after thousands of hours - it's getting too
hot.



....... Phil
 
S

Simon

Jan 1, 1970
0
The failure: The capacitor swollen a bit after just less than 1 or 2
month operation in Semi industry machine, while it is designed for
5000 hours

The capacitor type: HITANO EXR Low-ESR electrolytic capacitor 1000uf/
10V (0.08ohm, 1040 mA ripple current 105 Centi degree, 100KHZ)

The DC-DC converter mode: Flyback mode (UC3843B + Planar transformer)

i think it can be convenient to paste the circuit here. but seems
Google group doens't support that.

Second winding of the transformer: the failure happend at C105, C107


____VCC feedback to UC3843B

|
|-------|----|
----|------------|----------------------------|----------------------|-----------
inductor --------------|------------
----------|----------- CC
| | | + | C105 + |
C107
+| +|
| |----|>----| == 1000uf/10V ==1000uf/
10V == ==
100uf/10V
| D403 ER3B |
| |
100uf/10V |

|-------------------------------|----------------------------|--------------------------------------------------------------|---------------|--------|---
 
J

John Popelish

Jan 1, 1970
0
Simon said:
The failure: The capacitor swollen a bit after just less than 1 or 2
month operation in Semi industry machine, while it is designed for
5000 hours

The capacitor type: HITANO EXR Low-ESR electrolytic capacitor 1000uf/
10V (0.08ohm, 1040 mA ripple current 105 Centi degree, 100KHZ)

The DC-DC converter mode: Flyback mode (UC3843B + Planar transformer)

i think it can be convenient to paste the circuit here. but seems
Google group doens't support that.

Second winding of the transformer: the failure happend at C105, C107


____VCC feedback to UC3843B

|
|-------|----|
inductor --------------|------------
----------|----------- CC
| | | + | C105 + |
C107
+| +|
| |----|>----| == 1000uf/10V ==1000uf/
10V == ==
100uf/10V
| D403 ER3B |
| |
100uf/10V |

|-------------------------------|----------------------------|--------------------------------------------------------------|---------------|--------|---

Please try that again, using a fixed width (per character)
font, like Courier. No two proportional fonts are the same
but any fixed width font can be used to view any drawing
made with any other fixed width font.

You can select the fixed with font with the Options
selection in the dark gray thread title bar.

You can also copy and past this schematic into a fixed width
post and just correct the spacing, instead of starting from
scratch.
 
E

Eeyore

Jan 1, 1970
0
Simon said:
The failure: The capacitor swollen a bit after just less than 1 or 2
month operation in Semi industry machine, while it is designed for
5000 hours

The capacitor type: HITANO EXR Low-ESR electrolytic capacitor 1000uf/
10V (0.08ohm, 1040 mA ripple current 105 Centi degree, 100KHZ)

The DC-DC converter mode: Flyback mode (UC3843B + Planar transformer)

So, what's the LOAD current ?

And what's the ambient temperature *in which the capacitor operates* ? NOT the ambient temp of the surrounding room.

I expect you're exceeding the ripple current rating OR your capacitor supplier is a liar about the specification.

Try a PANASONIC or NICHICON capacitor and see if you still get the same problem.

Graham
 
E

Eeyore

Jan 1, 1970
0
Jamie said:
Because the cap is already
saturated, there isn't much to hold back that short pulse.

Bwahahahahahahaaaa ! Saturated capacitors is it now ?

What other nonsense do you plan to blow out of your ass today ?

Graham
 
P

Phil Allison

Jan 1, 1970
0
"Simon"
The failure: The capacitor swollen a bit after just less than 1 or 2
month operation in Semi industry machine, while it is designed for
5000 hours

The capacitor type: HITANO EXR Low-ESR electrolytic capacitor 1000uf/
10V (0.08ohm, 1040 mA ripple current 105 Centi degree, 100KHZ)



** Suspect you may be a victim of the infamous " capacitor plague".

Played absolute havoc with PC motherboards a few years back.

http://en.wikipedia.org/wiki/Capacitor_plague

A 1000uF, 10 volt, 105C, low ESR type is * smack in the middle* of the
problem category.

Buy a trusted brand - like Panasonic.



....... Phil
 
S

Simon

Jan 1, 1970
0
sorry, the circuit totally mess here.

the output of the sencond winding is: -Two ER3B pararell Diode -> Pi
filter, the left are two 1000uf/10V capacitors, the right are two
100uf/10V capacitors

The failure
happend on these two 1000uf/10V low-ESR capacitor




|
| ___Vcc_Feedback to UC3843
| ER3B |
|----|------|>---|-------|---------|-----|-----inductor
-----------------|------------|-----VCC
| | | + | + |
+ | + |
| |-----|>----| == ==
== ==
| |
| | |
| |
| | |
|-------------------------------------------------------------------------------------------
| 1000uf/10V 1000uf/10V 100uf/10f
100uf/10V
 
S

Simon

Jan 1, 1970
0
Thanks Phil,

i heard that story before, i hope we are not the victim of
that reason.

Otherwise, it will be a disaster for us. Although i
gradually got so many bad news from different customer ,

with the same failure features.

The capacitor swollen, and other related diode around the
PWM controller failed due to the bigger ESR just 1 to 2 month later.

I hope it is due to the customer wrong application, or even
our design. Since the customer will not accept the answer that we buy
poor quality capacitor


Really headache

Simon
 
F

Frithiof Andreas Jensen

Jan 1, 1970
0
Simon said:
The failure: The capacitor swollen a bit after just less than 1 or 2
month operation in Semi industry machine, while it is designed for
5000 hours

It's cooked - the electrolyte vaporises and the pressure flexes the can
which breaks the connection inside so it does not blow entirely apart.
Measure how hot it actually gets in the application. There are temperature
sensitive labels for that purpose.
The capacitor type: HITANO EXR Low-ESR electrolytic capacitor 1000uf/
10V (0.08ohm, 1040 mA ripple current 105 Centi degree, 100KHZ)

Check what the "105 Centi degree" rating actually means in Hours. It may
well be dying within the specified lifetime (because it is shite to begin
with) in which case it's your fault and not the manufacturers.

Like Phil says: Panasonic (or Nichion) are probably better. They *also* tend
to be specced at *85 centigrade* for a mere *2000-6000* Hours of lifetime!!!
The high temp rating of the Hitano component is suspekt IMO.
 
F

Frithiof Andreas Jensen

Jan 1, 1970
0
I hope it is due to the customer wrong application, or even
our design. Since the customer will not accept the answer that we buy
poor quality capacitor.

If they can't hande truth then lie!

What I also did in my younger years as part of design verification was to
cook the prototypes in an oven for a month or two at 105% rated load and
above rated max ambient temperature to see if I could force a failure and
how long it takes before the device failed - i.e. if it is consistent with
the reliability statistics, in which case we are good or Before which would
be a problem. Saves later grief and suffering!!

Every 10 degrees rise in operating temperature should halve the lifetime of
electrolytics f.ex. Which is why I go on about it - 'lytics are a chemically
programmed failure mechanism.
 
S

Spehro Pefhany

Jan 1, 1970
0
I met a big problem that the DC-DC converter circuit failure happend
frequently

I use UC3843B to control the Planar TRf 101 transformer to provide
multiply DC output;

and almost every failure has the same feature:

The failure on the low-ESR electrolytic capacitor at the second wiring
of the transformer;

it's kind of Low-ESR electrolytic capacitor, 1000uf/10V (ESR=0.07
ohm).

The UC3843B working at 100KHZ.


Is there anybody met that problem before?

What's the possible reason to lead to the failure?

You could have bad caps as others have described, but unlikely if they
have a recent date code. Of course if they were purchased surplus or
from a dubious dealer, it's more than likely the cause. Hitano does
not have a history of producing bad caps AFAICS.

What is your actual RMS ripple current?
Some body may say because of the high temperature, but it happends on
the product even working in less than 30 cent degree ambient operation
temperature.

That's the temperature inside, near the capacitor, including all the
self-heating of the electronics?

The Hitano EXR series caps are rated for 5,000 hours at 105°C so there
should not be failures as you describe unless you have a bad batch or
you are actually exceeding the ratings.

Keep in mind that 24/7 industrial operation will quickly exceed 5,000
hours (7 months) and you need to heavily derate the capacitors to get
reasonable life. If you are actually exceeding the RMS (I can't
emphasize the RMS enough) ripple current by, say, double or triple,
the electronics is running hot in a warm environment, and the customer
is running three shifts, this might be normal.


Best regards,
Spehro Pefhany
 
E

Eeyore

Jan 1, 1970
0
Spehro said:
Keep in mind that 24/7 industrial operation will quickly exceed 5,000
hours (7 months) and you need to heavily derate the capacitors to get
reasonable life. If you are actually exceeding the RMS (I can't
emphasize the RMS enough) ripple current

Let me re-emphasize.

The RIPPLE current is NOT the same as the AVERAGE current. It is MORE.

Graham
 
F

Fred Bloggs

Jan 1, 1970
0
Eeyore said:
Spehro Pefhany wrote:




Let me re-emphasize.

The RIPPLE current is NOT the same as the AVERAGE current. It is MORE.

Graham

I would say so, since "average" capacitor current is zero:) Funny
seeing you read the book to Spehro too.
 
W

Winfield

Jan 1, 1970
0
Simon said:
the output of the second winding is: -Two ER3B parallel
Diode -> Pi filter, the left are two 1000uf/10V capacitors,
the right are two 100uf/10V capacitors

The failure happens on these two 1000uf/10V low-ESR capacitor

I edited the drawing, is this right?

| ___Vcc_Feedback to UC3843
| ER3B |
|--o--|>|---o---o-------o-o-- inductor --o--------o-----VCC
| | | + | + | + | + |
| '--|>|---' _|_ _|_ _|_ _|_
| --- --- --- ---
| | | | |
|---------------o-------o----------------o--------o-----
| 1000uf/10V 1000uf/10V 100uf/10f 100uf/10V

What's your Vcc voltage and load current? What's your
measured output-voltage ripple on the 1000uF caps?
What's the uc3843 output-switching frequency, 50kHz?
Can you tell us the cap's manufacturer and part number?
Wait, I see, HITANO EXR Low-ESR 1000uf, 10V (0.08ohm,
1040 mA ripple current 105 Centi degree, 100KHZ).

The ripple current in each 1000uF capacitor is equal to
half your load current; compare this to the datasheet's
ratings. (If the rating is for 120Hz, you can multiply
this value by about 1.3, for use at 50 to 100kHz.)

A ripple-current rating for a good 1000uF 10V cap,
like nichicon's PW series, is 1.0A. This would limit
your supply to well under 2 amps, say 0.75 to 1.0A max.
Note, a 50kHz smps running at 0.5A per 1000uF cap,
would have 10mV of 50kHz dV/dt = I/C ripple voltage,
plus more from the cap's esr, 32mV across 65 milliohms
for the PW part, or 42mV total, which is a lot. Your
L-C output filter makes me wonder if your capacitor's
voltage ripple isn't rather high? Hmm, the HITANO EXR
cap has 76m esr compared to 65m for the nichicon part.

If your ripple voltage is too high, your best choice is
a larger capacitor: higher value or voltage rating, or
both, to lower the esr and increase the ripple-current
rating. If this isn't possible, you can try increasing
the 3843's operating frequency to reduce the capacitor's
dV/dt ripple voltage, which may help reduce its stress.

Phil's suggestion of a bad electrolyte is sadly a real
possibility. But this scene has been most common with
inexpensive substitutes for premium-grade conductive
polymer or organic-semiconductor high-conductivity-
electrolyte capacitors, like Sanyo's OS-CON types.
It's more likely you're just over-stressing your caps.

To test this idea, remove some "good" capacitors from
power supplies that have not yet failed, but that have
experienced a known stressful operating life so far.
Measure the capacitor's esr at 100kHz, etc., looking
for a significant increase compared to new capacitors.
If you have a supply with one failed capacitor and can
remove and test the other, that'd be an opportunity to
find one going bad before it self destructs. I measure
capacitors with an hp 4192A impedance meter, purchased
on eBay for $3k. That's what capacitor manufacturer's
use. But you may be able to get by with a Dick Smith
Electronics ESR meter. I bought mine from Canada,
let us know if you need help finding one.
 
E

Eeyore

Jan 1, 1970
0
Fred said:
I would say so, since "average" capacitor current is zero:)

Who said anything about average CAPACITOR current ?

Funny seeing you read the book to Spehro too.

Piss off. I was re-inforcing what he said and if you bother to check the thread
I was the FIRST to mention ripple current not Spehro.

Graham.
 
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