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Re: ?? About MMCCalc

Hi J.B.,

	You have found the problem a number of people are having.  In the old days
everyone just found the resonant caps size and thought that was best.
However, we now know there are other, perhaps better, cap sizes out there.
I just posted a note with some equations on this subject but let's see what
we come up with in your case...  

At 02:50 AM 02/19/2000 +0000, you wrote:
>
>Hello Coilers:
>
>I just downloaded and ran the new MMCCalc program....it sure has the old
>calculator number crunching beat!
>
>I've a few questions about sizing an MMC for my coil.  Here is the data
>from WinTesla:
>
>Transformer: 3 OBITs, 10 KV -at- 69 mA.
>Cap/Trans Z match: 0.0186 uF.
>Prim. turns: 14
>Sec. Res. Freq: 379 kHz. (with toroid)
>
>1) If I want to go LTR, how much bigger than 0.0186 uF. do I have to go?

Using my new formula:

0.92 x ( Vo x Io - L ) / ( BPS x Vo^2 ) = C

I will guess L at about 10% (69 watts) and we always like to run LTR coils
at 120BPS here in 60Hz land.

0.92 x ( 10000 x 0.069 - 69 ) / ( 120 x 10000^2 ) = 47.6nF

So that is around the biggest cap you need.  Your voltage is low and your
current is high so you can charge a fairly big cap.

Going to MMCCalc:

MMC Calculator  Ver. 1.1  2/15/2000  Terry Fritz
Firing voltage =  14100 
Fo =  379000 
Break rate =  120 
Cap value =  5.6E-08 
Strings   Caps/String   Total Value   Temperature   Cost
  5         6            46.67         9.47          43.50  Safe
  6         7            48.00         6.95          60.90  Safe
  7         8            49.00         5.32          81.20  Safe
  8         9            49.78         4.21         104.40  Very Safe
  9        11            45.82         2.82         143.55  Very Safe
 10        12            46.67         2.37         174.00  Very Safe

That 7x8 looks good but maybe the 8x9 would give a little more voltage
headroom.  That would give you 8 strings of 6.22nF each so you would have a
cap that would be very adjustable.  With three strings, you get your
18.66nF cap.  Neat isn't it!!  You can then keep adding strings until your
coil performance decreases.  Then you can build a rotary sync gap and add
more strings...

>2) With 14 available prim. turns, small cap-many turns or big cap-few turns?

Since cap size in LTR coils is pretty well set in concrete, the decision is
made.  With MMCs you want to make it so you can select individual strings
to get many values so you can adjust it to what you want but still have the
capacitance needed for every situation.

>3) My gap is 7 segment RQ fan quenched.  Is break rate 120 BPS for this gap?

See my other post.  If the cap is large, it will be 120BPS  With a smaller
cap you may charge to a higher BPS.

>
>Now all I have to do is find a source for the caps.  I wish the exchange
>rate was more favourable, as I'd go for some that Terry has...oh, well!!

Can't help much with that expensive border...  I only have 146 caps left at
the moment.  Maybe after the credit card recovers, I'll need another
thousand ;-))

Cheers,

	Terry

>
>
>73, Weazle, VE3EAR/VE3WZL
>
>Listening: 147.030+ and 442.075+
>E-mail:    weazle-at-hurontel.on.ca
>           or ve3ear-at-rac.ca
>Web site:  www.hurontel.on.ca/~weazle
>