Re: Condenser Products Caps and max BPS??

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Hi Dave (and welcome back!),

Condenser Products (CP) has always advised keeping these caps in a
horizontal position and rotating them periodically. Because the
cylindrical container doesn't allow for much internal expansion, CP
purposely leaves an air bubble in their pulse capacitors in order to
provide a bit of resilience when the cap heats up. CP was also one of
the few capacitor manufacturers to make "Tesla Coil" pulse caps and to
"derate them" in KVAC instead of only spec'ing KVDC. 

The relatively thin copper strips (or tabs) that internally
interconnected the chain of capacitor modules were apparently a source
of manufacturing difficulty for CP - if the solder interconnections were
not sufficiently robust, or the RMS current was too high, hot spots or
arcing could develop, apparently leading to capacitor failures.
Sometimes these failures could be quite spectacular, since the "stiff"
cylindrical containers didn't have much give, and these caps sometimes
failed explosively, blowing one end off, spewing hot oil everywhere, and
often disgorging one or more of the capacitor modules. Sort of like what
happens with a Glassmike, but without the glass shards. At least four
coilers on this list have had this happen to them while running their
coils. 

While testing a different CP model in my system for a friend
(TC253-34-300, 0.025 -at- 20 kVAC) it suddenly blew with a load POP and a
yellowish flame. There was absolutely no warning, and no change in coil
behavior immediately before the event. Some pictures of the capacitor
afterwards can be seen at:
  http://www.aquila-dot-net/berthickman/frames/cap1x.jpg
and
  http://www.aquila-dot-net/berthickman/frames/cap6x.jpg

This cap was then sent back to CP for failure mode analysis, where they
determined that the cap (and 24 other like it from a "group buy" by many
folks on this list) had a latent manufacturing defect. These were later
replaced under warranty by CP. Since your caps are a different model and
they have survived use with a pig successfully, I'd simply put them in a
plastic container (to catch pieces and oil "just in case") and continue
to use them. Try to lower RMS tank current by using a higher inductance
primary. I wouldn't be overly concerned with higher break rates with
these precautions.  

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
"Electromagically" Shrunken Coins!
http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Dave Hartwick by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>
> 
> I've got 2 Condenser Products, TC503-34-300 0.05 mfd 20,000 VAC capacitors
> (300$ each iirc). Purchased about 7 years ago, these units were designed
> specifically for coil duty.
> 
> They've not been used in 5+ years and have been sitting in the same
> horizontal position. Concerned about oil penetration after such extended
> none-use, I talked to CP. Engineer Gene said to rotate them occasionally and
> then bring the voltage up slowly. Sounds logical. Do you guys have any
> experience with this?
> 
> Most interestingly, he told me that those caps are rated for a max break
> rate of 120 BPS. I was not told this at the time of purchase. The problem is
> that I had been using an air-blast gap and the break rate was/is unknown to
> me. Gene suggested that the caps very well may have been compromised because
> of possible excessively high break rates, as much as 4-5 cycle for that type
> gap.
> 
> I wonder if this is the case? They were only fired for a total of maybe 20
> minutes at about 3 KVA (5KVA 14.4 kV pole pig). I noticed no deterioration
> in performance, but he suggested that any excessive internal
> heating--related to the "Tab" configuration connecting multiple internal
> series caps--could have resulted in damage that may not show up until one
> fails catastrophically and explodes.
> 
> The 2 caps were run in balanced series config at < 100 KHz, the coil
> producing about 5' sparks. Not very efficient for 3 KVA, at least measured
> against the current Coiling state-of-the-art.
> 
> So what do you guys think of this potential damage problem? The only thing I
> can do is try them again with a great deal of care. I guess I'll have to
> encase them in a blast proof container of some sort. My hunch is that Gene's
> caution was a bit overblown, but who knows?
> 
> I really thought these caps were supposed to be quite durable. They really
> should have included literature specifically stating the operational
> limitations, don't you think? Maybe I'll just go back to polyethylene salt
> water caps, which surprisingly seemed to work nearly as well.
> Dave Hartwick
> Chambersburg, PA