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'[EE] Capacitor Temperature Ratings'
2007\04\13@112110 by Sean Breheny

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Hi all,

Can anyone tell me exactly what the temperature rating for aluminum
electrolytic caps means? When the datasheet says 105 deg C max, which
of the following (if any) does this mean:

a) the capacitor will operate within specs (including max ripple
current) when the ambient temp is 105 deg C (so the case could
actually be 20 to 30 deg C hotter)

b) the capacitor will operate within specs when the case is 105 deg C
(so the ambient may need to be 20 to 30 deg C cooler if running at max
ripple current)

c) the capacitor will operate within specs when the maximum internal
temperature (hot spot) is 105 deg C (very difficult to determine
without more data from the manufacturer)

Thanks,

Sean

2007\04\13@131624 by David VanHorn

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On 4/13/07, Sean Breheny <spam_OUTshb7TakeThisOuTspamcornell.edu> wrote:
> Hi all,
>
> Can anyone tell me exactly what the temperature rating for aluminum
> electrolytic caps means? When the datasheet says 105 deg C max, which
> of the following (if any) does this mean:

The lifetime (typically 2000 hours) is specified at this temperature,
and within all other ratings. Each 10C below that temperature doubles
the life, more or less.

2007\04\13@131654 by Vasile Surducan

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Sean,
Fortunately I don't understand your english so I'm blessed... :)

If you expect from your capacitor to filter the max ripple current as
well at 20C and at 105C you are very optimistic.

b) is the most plausible

My advice (based on 20 years of reading datasheets very carefully and
many times testing some parameters from datasheet):

NEVER EVER believe entirely the producer datasheet, any producer will
be. The producer is a humble human being. The datasheet writer also.
And the user too.

On 4/13/07, Sean Breheny <.....shb7KILLspamspam@spam@cornell.edu> wrote:
{Quote hidden}

> -

2007\04\13@134731 by Peter P.

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Vasile Surducan <piclist9 <at> gmail.com> writes:

> b) is the most plausible

And also, the internal resistance changes with temperature. Usually higher
temperature = lower internal resistance (because the electrolyte's conductivity
increases faster than the lead resistivity). However, a new in spec capacitor
will perform as per the datasheet over temperature. Another parameter to pay
attention to is self resonant frequency. This can be in range for many smpsus.
The result can be very bad.

> NEVER EVER believe entirely the producer datasheet, any producer will
> be. The producer is a humble human being. The datasheet writer also.
> And the user too.

Oh, so you mean datasheets are like game quiz forms where the user must guess
which parameters are grossly exaggerated (250A peak in TO220 Mosfet), impossible
to achieve in normal operation (Vpor = Vss) etc etc and win a pat on the back
from oneself ? Hmm, I have seen that before somewhere. But where ?

Peter P.


2007\04\14@182710 by Florian Voelzke

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For a better understanding of the temperature specs of electrolytic caps
I recommend looking at some high power high voltage cap datasheets.
There you usually find graphs with useful live versus ripple current and
temperature and more. Evene if your cap datasheet does not have this
info, it gives you a general clue how the different parameters work
together. And be careful how the manufactor specifies the temperature
value! Is it body temp, surface or ambient? How is ambient defined and
so on...

One quick example:
Look at the B43511 series from epcos

Regards,
Florian

Sean Breheny wrote:
{Quote hidden}

2007\04\14@192838 by Sean Breheny

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Thanks to all who responded.

Florian got to the heart of my question: does the temp spec refer to
capacitor case temp or ambient temp. The particular caps I was using
are Panasonic FC series. Maybe I am blind but I couldn't find any
definition in that datasheet of where the temperature was to be
measured.

I've seen higher-end cap datasheets but they usually go into a lot
more detail (which is good), but still doesn't tell me how Panasonic
chose to spec their temp data.

Actually, I discovered this morning that I don't need nearly as much
capacitance in this circuit (high current motor drive) as I had
thought, so it looks like I can get rid of the electrolytics and just
use many MLCC chip caps (which I already had present in the design,
sprikled about the PCB  to take the fast current edges from the FET
switching). If I simply double the quantity of these little caps, I
will be able to eliminate the electrolytics and save a lot of board
space, too. The MLCC chip caps are rated for something like 3 A rms
ripple each(since their ESR is so low), so they should be able to
handle the current (in the neighborhood of 80 to 90A rms) when spread
over the large number (more than 100).

Thanks,

Sean


On 4/14/07, Florian Voelzke <fvoelzkespamKILLspamgmx.de> wrote:
{Quote hidden}

> -

2007\04\15@190211 by Paul Hutchinson

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> -----Original Message-----
> From: .....piclist-bouncesKILLspamspam.....mit.edu On Behalf Of Sean Breheny
> Sent: Saturday, April 14, 2007 7:29 PM
>
> Thanks to all who responded.
>
> Florian got to the heart of my question: does the temp spec refer to
> capacitor case temp or ambient temp. The particular caps I was using
> are Panasonic FC series. Maybe I am blind but I couldn't find any
> definition in that datasheet of where the temperature was to be
> measured.

I believe IEC standard 60384 defines operating temperature as ambient
temperature for capacitor specification sheets. IME, most of the major
component manufactures follow IEC standards for definitions of parameters.

Paul

2007\04\16@093533 by Russell McMahon

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flavicon
face
>> ... does the temp spec refer to
>> capacitor case temp or ambient temp. The particular caps I was
>> using
>> are Panasonic FC series. Maybe I am blind but I couldn't find any
>> definition in that datasheet of where the temperature was to be
>> measured.

> I believe IEC standard 60384 defines operating temperature as
> ambient
> temperature for capacitor specification sheets. IME, most of the
> major
> component manufactures follow IEC standards for definitions of
> parameters.

I'd be wary of that.
What is of interest is the internal capacitor temperature.
Where ambient and core temperatures are similar it doesn't matter too
much which you spec.

For eg high ripple currents the cote temperature can rise
substantially AND temperature rise appears to be a key factor in
setting acceptable ripple current.

Capacitors can have life times extended by adding heat sinks.

All of which suggests that core temperature is the spec that is specd.


       Russell


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