RE: MMC vs Maxwell comparison

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

Original poster: "Oxandale, Terry by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Toxandale-at-spp-dot-org>

My experience has been comparable, but with some differences. I used the GE
3000vdc caps (12/string) .1mf/cap for a total of 33nf (4 strings). This was
compared to the Maxwell 35nf caps recently being sold on ebay (I have tried
several of them with the same performance from all of them during a
checkout). Anyway, spark length and appearance were unchanged (6 foot
discharge at a particular input). The main difference was the warming of the
Maxwell cap verses the unchanged temperature of the MMC. I feel the
temperature stability of the MMC is in part due to the fact that I chose to
use more (read excessive) caps per string, for the expressed purpose of then
needing more strings (per given total capacitance), which would then reduce
the current/string.

(Un)Terry

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, February 20, 2002 9:03 PM
To: tesla-at-pupman-dot-com
Subject: MMC vs Maxwell comparison


Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<FutureT-at-aol-dot-com>

Hello all,

I finally built an MMC using thirty RS Arcotronics 0.047uF, 1500VDC
caps.  I used three strings, each with 10 caps, and the total combo 
measures 0.0142uF.  I placed two one-half watt 10Meg resistors in 
series across each cap.  These MMC's are reported to be the good type,
and have the desireable polypropylene dielectric.  These are
yellow and tubular, but I don't have the specs handy.  These are the
type used by Richie Burnett and Alan Sharpe in England.  I believe
that Malcolm is using the same type also.  The number on the 
package is 114-474.

I did the test using my new TT-32 TC which gives 33" sparks using a 
0.0164uF Maxwell cap, and a 9/25 NST with sync gap.  I decided to
replace the Maxwell with a different Maxwell measuring 0.0147uF, 
to make the comparison with the MMC more comparable.  After 
retuning, this gave the same 33" spark.  I adjusted the coil to be 32" 
from the wall, and the sparks hit the wall about every 10 seconds 
or so.  Then I replaced the 0.0147uF Maxwell with the MMC, and 
tried retuning and rephasing slightly for best spark output.  It turned
out that the same tune point and phase point seemed adequate for
both capacitors.  I couldn't find any spark length advantage by 
changing the tuning as I switched capacitors.  I did however do the
tests for each cap with a variety of tune and phase positions.
The spark was similar, but was slightly weaker using the MMC, 
and hit the wall only about every 20 seconds or less.  The MMC 
got somewhat warm within a couple of minutes of intermittent run
time.  As a verification, I re-installed the Maxwell, and the sparks
were again stronger than the MMC sparks.  I was somewhat 
surprised that the MMC sparks were weaker, because I really 
didn't expect to be able to see any difference in spark length.  
I was also surprised by how quickly the MMC's heated up.

Next, I moved the coil 1/4" closer to the wall, and this caused the 
MMC sparks to hit the wall as often as the Maxwell sparks.  This
suggests that the Maxwell sparks are about 1/4" longer than the
MMC sparks.  I don't know if other MMC brands would perform any 
differently.  It may seem difficult to detect a 1/4" difference in spark
length, but the MMC consistently underperformed the Maxwell
through all the test runs.

Despite this difference (less than 1% in spark length), I find the 
MMC's to be convenient, small and lightweight, flexible, and low
priced for small coils, and the performance is close to the Maxwells. 
Therefore the MMC's are a good choice for many coilers. 

Measuring spark lengths to within less than 1% is difficult, so 
perhaps other folks will do their own comparisons of this sort 
and report their results.  I reported the full specs of this Tesla
coil a couple of weeks ago.

Cheers,
John