R. Measures wrote:
>
> On Jan 17, 2006, at 8:53 AM, Steve Thompson wrote:
>
>>
>>
>> dick.knol@planet.nl wrote:
>>
>>> Rich Measures AG6K sells 450 WV 105ºC electrolytic caps for HT PSU use.
>>> (http://www.somis.org/Price-Info.html)
>>>
>>> Please note that contrary to crack, a 105ºC rating electrolytic cap
>>> cannot be obtained on every street corner. However, the 105ºC rating
>>> will result in a much longer servbice life in a hot HFF power amp
>>> environment.
>>
>> A while ago I looked at the ratings on Philips electrolytics, where you
>> can get physically identical capacitors, one family with 85C rating, the
>> other with 105C rating. For the same value, the ripple current ratings
>> were different, as were the lifetimes at the operating temperatures.
>>
>> I worked out the thermal resistance from the maximum allowed temperature
>> and I^R rating at 85C. Working backwards to 105C, I ended up with
>> exactly the ripple current specified for the 105C part. The different
>> lifetimes were related in just the same way. In other words, these
>> appeared to be absolutely indentical, just specified at different
>> operating temperatures. I don't know if there's any manufacturing
>> difference between 105 and 85C parts - but it would not surprise me if
>> they all come off the same conveyor and just had different part numbers
>> printed on them.
>
>
> The Matsushita low-ESR, high-ripple-I, 105º units we stock weigh in at
> about 80% more than similar-volume older 85ºC aluminum electrolytics.
> They are 3mm dia. by 50mm long and they weigh 90.2 grams
Doubtless thay have different specs. from those older ones.
There's nothing in the Panasonic TS family rated at 85C to compare with
the P11691. Considering a couple of others, both 560uF, 450V, same
physical size:
P11953 - 85C, 2000hrs, ripple current 2.82A, esr .355R
I^2*R=2.8W
P11820 - 105C, 2000hrs, ripple current 1.9A, esr .326R
I^2*R=1.2W
If you assume that they are the same part, just with different specs
applied then the figures give a thermal resistance of 12.5C/W (about
right for a can that size) and a maximum temperature of 120C, in line
with the 125C max specified by some manufacturers (Panasonic don't give
a figure). The data is consistent with the assumption.
The P11691 capacitors are very well rated - my point is that you can't
simply choose on the basis of a 105C rather than 85C label.
Steve
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