Re: Hosfelt snubber caps

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Dave,

	We did a lot of work with the voltage ratings of MMCs.  These caps can
easily withstand the rated DC voltage as a peak AC voltage in Tesla coil
use.  So 7 caps at 3000 volts each will stand 21000 volts which is the peak
rating for a 15kV NST.  Many of us actually run them well beyond that
voltage rating with very few problems.  The caps are conservatively rated.
Being able to withstand twice their rated DC voltage is not uncommon.  

Film poly caps will also self heal.  When a blow through happens, they
happily heal themselves and keep on going.  It is not uncommon for a poly
film cap to take upwards of 100000 overvoltage events.  This is a far cry
from rolled and mica caps that are dead once they blow out.  I have seen
poly caps removed from normal service that have the dielectrics shot up
like Swiss cheese, yet they still continue to operate.

In the homemade rolled cap days, everyone designed the dielectrics to 3X
the voltage.  However, that is not at all necessary with commercial poly
film caps.  

Cheers,

	Terry


At 09:07 AM 9/9/00 -0400, you wrote:
>Hi,
>    I also have a large amount of those GE snubber caps, and it just caught
>my eye when Terry recommended to use 7 or more in series.  Is the 3000VDC
>rating really that reliable?,because that could allow me to greatly increase
>my MMC's capacity since they are set up for 10 strings of 14/string right
>now (when they could be set up for 20 strings of 7/string?).   right now I
>am assuming a safe rating of 1600VDC each.
>
>Thanks~Dave w
>
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Friday, September 08, 2000 8:47 PM
>Subject: Re: Hosfelt snubber caps
>
>
>> Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
>>
>> Hi David,
>>
>> Those big puppies will take like 15 amps RMS each!  Overheating them with
>> an NST is simply not an issue.  As long as you use at least 7 per string
>to
>> get the voltage, you will be perfectly safe.  If they screw down, you may
>> want to figure out a way to easily change them around to different values.
>>
>> DigiKey (www.digikey-dot-com) sells 10 Meg 1/2 watt resistors (10MH-ND) for
>> about two pennies each.  Use two in series across each of these big caps
>to
>> get the voltage standoff.
>>
>> Yours are the MMC caps the rest of us dream of ;-))
>>
>> Cheers,
>>
>> Terry
>>
>> At 06:24 PM 9/8/00 -0400, you wrote:
>> >Hi Terry, all,
>> >
>> >I was just letting everyone know that I finally broke down and
>> >ordered 60 of those 0.1 uFD, 3000 VDC snubber caps from Hos-
>> >felt today,that was discussed on this list a couple of months ago.
>> >I'm wanting to replace the current 0.018 uFD, 60 KVDC Chicago
>> >Condenser single unit cap that I am currently using in my 15/
>> >90 NST driven system as it seems very lossy and heats up in
>> >a short order after the coil is turned on. I am also wanting to re-
>> >do the primary and secondary coils for a more efficient design
>> >(I guess I am pretty much rebuilding the whole coil). Anyway,
>> >I have a few questions to place on the list regarding the use of
>> >these caps as an MMC.
>> >
>> >First, I was thinking of going w/ 4 strings of 15 (60 total) for a
>> >total value of 27nFD -at- 45 KVDC. This will be my 1st real at-
>> >tempt -at- a MMC cap and I was wondering if 4 strings of these
>> >would be enough to handle the current of a 15/90 NST bank?
>> >Without going into the mathematical equations, I figure on ~
>> >5 nF per 30 mA as resonant for NSTs. So, I am figuring 27 nF
>> >should make for a LTR cap setup for the 15/90 NST?
>> >
>> >Also, I was hoping someone could suggest a good source for
>> >1/2 or 1 watt, 10 meg bleeder resistors (preferably some local
>> >jobber like Radio Shack). Thanks in advance for your answers.
>> >
>> >Safe coiling,
>> >David R.
>> >
>>
>>
>>
>