Re: GE 42L series caps Good or Bad??

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Steve,

At 12:02 AM 9/14/2002 -0500, you wrote:
>Hi,
>
>I would say BAD IDEA for the .22uf at 1200v.  But for some reason, my large 
>.68uf caps, are still running strong!!  I ran the large coil tonight with 
>15/120 PSU and only 1 string of 24, and it ran great. I probably only have 
>about 5 minutes of time on the caps, but thats better than the .33uf that 
>started boiling in about 45 seconds!  I will try putting some new caps in 
>their place, and see what happens.  IF they fail again, i will use the caps 
>for my GMHEIC record thing that Terry set.  Im sure they will last the small 
>1200v pulse every few seconds.  Im planning on twins, and a limited 15" 
>spark :)  Let the coils live for awhile.
>
>Terry, here is my question.  If there is no sign of heating, will these caps 
>likely last?  I ran in intervals of about 10 seconds, on and off for about 
>an hour.  I felt the body, and ends of every cap.  They were all cold!!  Im 
>still getting 5 footers to the ground.  I will be trying out my new sucker 
>gap (like gary lau's).  The epoxy was drying tonight, so i still had my RQ 
>gap.

If we are talking RMS currents and general resistance heating, cold is
great.  But Ipeak with metalized caps is just like a fuse.  A little less
current and you are fine, a little too much and it blows. 

>
>I think i will invest in a few more of the .68uf 1200v GE caps, but im 
>staying away from anything else on the 42l's.  Why get more???  Well, im now 
>1 short (i took one apart), and if one blows i will be able to replace it.I 
>actually have enough caps for 2 strings of 24, but that is way too big i 
>guess.  I can even have 2 cap banks on hand so that if i blow a cap, i can 
>easily sub in another bank.  So ill probably get another 5 or 10.  Please 
>dont follow in my foot steps!  Stick with the panasonic or CD caps.  Im not 
>sure why the 3000v caps i had lasted soo long (42l's).  Maybe they used the 
>foil with the metalized film.  So im still confident in my large caps at the 
>moment, they are taking a beating, and dont mind it.

Scott may have hit on the fact that "fatter" caps have a whole lot more end
contact area which is the "weak spot" in metalized caps.  Twice the area,
twice the current.  Fat caps may be able to handle far higher currents than
skinny caps...  That may be the key.  

>
>Terry, could it be that these caps are better because of all of that extra 
>surface at the end caps? The .68uf are much larger than the .33 that i sent 
>you.  But still im running 2X + the amount of power through them.  Well, ill 
>try to get a lot more run time in on it to test the reliability of the caps 
>(at least short term).  So is it possible that, if there is no heat build 
>up, that maybe the caps will last??  Im guessing no heat= no damage.  Or are 
>these caps destined to pop?

I am starting to think of full metalized caps as fuses....  Just hoping we
can find their "rating" and stay below it.  Many people have had great luck
with "fat" GE caps.  So there is much hope ;-)  Fat caps and their great
end cap contact area directly fights this end cap blowout problem in
metalized caps. 

Cheers,

	Terry


>
>Steve Ward.
>