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Re: AC-rating for MMC caps // EMMC vs the GTL-WIMAs

Hi Stefan,



>>How high is the factor Udc/Uac for the caps you mentioned? There
>>are types where it is pretty low (1000Vdc/600Vac) and where this 
>>should be no problem as the peak voltage (850Vpeak) is nearly the 
>>rated dc voltage (1000Vdc). The caps the GSTCs ('German Speaking 
>>Tesla Coilers) ordered are 6kVdc/700Vac and therefore there is a BIG
>>difference!

>We build hundreds of types of switching power supplies and use 
>hundreds of different WIMA types.  I will run a search through the
>failure analysis files for the word "WIMA" and see what I come up 
>with.  I remember one problem two years ago but that was our fault 
>where a part was overheated...  WIMAs are regarded as being very 
>reliable and tough parts.

Just to follow up.

	The only cases of WIMAs failing was when they were overheated due to
excessive current.  I did find one application where we ran them at over
20C ambient!  In this case, we used the 1600 volt version which is far over
the needed voltage.  Apparently, if you run a high voltage cap with much
lower voltage, you can push more than the rated current through them
safely.  WIMA examined and approved this application.  I would be cautious
about taking that too far because the exact waveforms and such were
examined very carefully to be sure it would be reliable (personally, it
still worries me).  Like I said, the "normal" capacitor ratings given in
data sheets have many exceptions...

	Everything so far looks like MMC caps should be every bit as reliable as
any other Tesla cap.  In fact, I would not be surprised if they are much
more reliable.  Just as we can push the specs on them to save money, we
could just as easily spend more money for very high reliability.  The fact
that we can get so much information on them and easily test them as we need
really gives them an advantage over any other type.  Also they can be built
up into almost any value/voltage we need with ease.  They can also be made
so the strings can be selected to give a wide range of values.  I am
planning on using them exclusively from now on...

Cheers,

	Terry