Re: MMC Testing vs equations (plus MMC bulk update)

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

On 30 Aug 00, at 8:18, Tesla list wrote:

> Original poster: "acmnovak" <acmnovak-at-msn-dot-com> 
> 
> Greetings,
> Earlier today, I went through Terry's MMC power handling calculations. I
made a
> few mistakes at first, but I think I got it right... finally. The capacitors
> are the ones in the latest bulk buy. They are rated 2000vdc (700vac) .068uF
> with a lead spacing of 27.5mm... I plan on using 13 in each string,
> Do these results look typical of a well made mmc?
> Ecap=.08872 Joules Per Bang
> Rcap=.02029 Ohms Internal Resistance
> Wo=.07152 Watts Per Capacitor
> To=2.86085 degrees celcius
> Life Expectancy of ~555 Hours
> Does that all add up?

Too lazy to do the calcs on that one but I have a couple of 
comments on the other things mentioned.......
  
> Wouldn't the bleeder resistors play a role in any of these equations? 
> How do you know how long the cap will last? I'm sure I can't time it down to
> the hour. I usually keep runtime down to 1-2 mins at most. I don't know how
> anyone could kill a cap by using it for 555 hours. BTW- Is that time
> continuous, or intermittent operation?
>  
> Also, I tested a cap to destruction earlier today. It took about 1 minute of
> run time at 4kV firing voltage to kill it.  Before that, I ran it at 2kV for
> 3-5 minutes with no heating....Using Terry's equations, shouldn't it last
over
> 40 hours at 2kVac to kill it?  

It probably depends on whether any recovery from mild heating 
is allowed. Terry?

> Upon autopsey, I found that every layer had been punctured. There were two
> dissimilar burned holes all the way through the cap on opposite sides...
Ouch. 
> When it failed, all I heard was a quiet little snap. No cracks in the
> potting...
> Don't failed MMC caps usually just explode?

No. I love them for exactly that reason :)  Mind you, I've 
never killed one. I just take great solace in knowing their 
not stuffed to the brim with potentially volatile substances 
like oil.

Regards,
Malcolm