Re: [TCML] mmc cap protection by spark-gaps-any ideas?

["Mark Olson" <kc5gym@xxxxxxx>]

Snips and comments:

> .  Despite anything  
you can do, no two condensers are exactly the same. They each have a  
different internal resistance which means that when you connect a  
string of them across a voltage source, they will not have the same  
voltage across each condenser in the series 

$$$ The above statement is true without question.
 _______________________________________________
.  IT IS THERE TO PROTECT THE CAPACITOR AND NOT THE TECHNICIAN.   
The fact that resistor across the capacitor will discharge it is just  
a bonus but the fact that resistors fail is a fact of life.  

The high voltage was only 6000 volts d.c

Ray
_______________________________________________



Yes, for DC applications, like power supply filter caps in series, the
resistors certainly do help equalize the voltages across each cap.  Thus
they do add some protection to the caps.


$$$ The above statement is true without question.


But in TC usage, the voltage across the series strings of caps is RF,
changing polarity on the order of 100,000 times per second.  In this
situation, the RC time constant for a bleeder resistor across an MMC cap is
so large (seconds)in comparison to the roughly ten microsecond cycle time
that the resistors will do practically nothing to equalize the voltage
across the caps.

$$$ Have you ever known of a condenser discharging a-c of any frequency?
. 
I highly recommend adding resistors across caps in an MMC as one of several
human safety precautions.  Cap protection is achieved by using caps of all
the same type and having an ample voltage margin, e.g. run the caps at 1/2
or 1/3 of their DC ratings. 
--Steve Y.


 $$$ Not a bad idea, but I dont trust them...
.
Marko
KC5GYM

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