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TANK CAPACITOR BURN IN

 * Carbons Sent to: Esondrmn-at-aol-dot-com

 
 > From: Esondrmn-at-aol-dot-com
 > To: richard.quick-at-slug-dot-org
 > Subject: Tank capacitor burn in

 > Richard,

 ES> Last night I was burning in my recently completed .02mfd     
 ES> rolled tank capacitors as suggested in the Keelynet          
 ES> capacitor file.  I used a 12kv, 60ma neon transformer and    
 ES> conected each transformer output to one capacitor, connected 
 ES> the other two capacitor terminals together and connected     
 ES> this point to the transformer center tap (case).  I ran the
 ES> transformer on a variac at about 50%.  Each capacitor should 
 ES> have had about 3kv across it.  The transformer got extremely 
 ES> hot.  I had a large fan blowing on it after about 2 hours.   
 ES> I ran it for 4 hours total. The transformer was so hot you   
 ES> could not hold your hand on it.  A small amount of oil       
 ES> (melted tar I bet) actually seeped out of the bottom of
 ES> the transformer.  

Oww! Brutal! Where did you read about this method of breaking in
tank circuit capacitors? I don't think I would ever be caught
dead advocating something like this. Please let me know where you
heard this and we can try to snuff the file, or at least the 
section you referred to, before someone else cooks a neon.

 ES> I thought the neons were current self limiting and they      
 ES> would not burn up under load.  Am I missing something?  Is   
 ES> there a better way to do this? Thanks,  Ed Sonderman

Let me try to explain. The neon will hold up fine to a dead
short, but hooking a pulse discharging capacitor across a neon
secondary is a far cry from shorting one out. The capacitor is
taking a charge for 1/120 of a second, and when the polarity of
the secondary on the neon reverses there would be quite a current
flow: not from the current limited neon mind you, but from a
fully charged cap discharging into the neon's secondary winding.

The way to break in homemade capacitors is to hook a small coil 
up to them and operate the coil at no more than 50% of the normal
voltage. By small coil I mean something like a four inch diameter
secondary, by normal voltage I mean 1/2 of the normal input
voltage of the neon powering the small coil. I run the coil with
a duty cycle of 1-3 minutes firing with 10 - 15 minutes rest. I
do this a couple of hours a day for a couple of days, then let
the cap(s) rest one day. I finish the initial break-in with one
more day of intermittent work with a duty cycle of 3-5 minutes
firing, 15 minutes off. 

With this method the input energy is properly consumed, and the
capacitor is allowed to settle in gradually in a pulsed circuit.
The pulsing of the cap at low power is much more effective at
bubbling out air than the "static" break in you attempted. It is
the firing of the spark gap that really vibrates the capacitor
and settles in the plates and dielectric while forcing out air.
Just don't run the voltage up until all of the air is gone. It
really takes about 6 months of firing and sitting before homemade
capacitors may be considered fully broken in. You should check
the oil level occasionally during this period.

Richard Quick
... If all else fails... Throw another megavolt across it!
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