Re: MMC vs Maxwell comparison

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi John,

On 20 Feb 2002, at 20:03, Tesla list wrote:

> 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.

Sorry I have to ask: what is the primary iductance?

Thanks,
Malcolm