Re: primary/mmc stuff

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

Hi Michael,

At 11:48 PM 7/31/00 -0700, you wrote: 

>
> Hello everyone,
>  
> As some of you already know, I'm organizing a bulk MMC buy next week. I was
> wondering what the consequences of not having bleeder resistors is? Does it
> cause the cap to fail? Greg Hunters MMC failed and he didn't have bleeders...
> This is the only failed MMC case I can think of other than ones caused by
> direct strikes from their TC. 


Bleeder resistors, at like a penny each, are just a darn good idea!  They
prevent the caps from unbalanced charging and bleed the caps down when power is
removed which has save a number of rear ends :-))

>
> Also, Is it true that you can rate an MMC by it's max DC voltage for your
> transformer? We're going to be getting 1600 v -at- .047uF polypropylene caps,
> and I was thinking of putting 10 or 12 in a string. What's the minimum I can
> get by with to save $$$?


The maximum voltage from a transformer is typically the RMS voltage times
1.414...  So a 15kV transformer's peak voltage is 21.213kV.  It has been shown
that an MMC cap can easily be used at it's DC, rather than AC, voltage.  So you
can use 21213/1600 = 13.25 caps, or 14, 1600 volt caps with a 15kV transformer
quite safely (My EMMC uses 10 :-)).  

>
>  
> I've decided on a flat spiral made of copper tubing for my primary. I would
> have gone with a more "novel" design approach but i wanted to have a shining
> example of a modern TC.  I'm sick of messing with flashovers and
> overcoupling...


The good ol' flat primary is something that really can't go wrong...

>
> I got a lexan cutting board from my local Big-K (K-Mart) for $8 which I will
> use as primary supports. I'm planning on making one as seen here:
>
> <http://www.fwpd-dot-net/dona/tesla/primary.htm>http://www.fwpd-dot-net/dona/tesla
> /primary.htm 
> Only, i'm not going to paint mine and it will be on a plywood table. 
> How far does the strike rail have to be before the primary arcs to it?  I'm
> thinking only an inch and a half... Does that sound acceptable?


Yes.  The strike rail stands out well to the fields and should attract the arcs
well.  However, don't be afraid of making the coil higher so that strikes to
the rail are not an issue.  

>
> How, exactly, would one mount these supports other than screws? I was
> thinking of cutting little blocks of HDPE and gluing them to the side of the
> supports and then using nylon bolts to hold them down... Just a thought.


Tyewraps and lashing them with nylon cord have worded for me.  I use nylon
screws on my latest coil:
http://users.better-dot-org/tfritz/newcoil/

Cheers,

        Terry

>
> Thanks,
>  
>         -Michael
>