Re: Proper sparkgap for a small coil design

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Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


At this power level, for best performance, it's a requirement that you run a
rotary type spark gap.  I would use a small 11 inch dia. rotor on a 1/2 HP
motor with 12 electrodes on a 10 inch dia.  Motor speed could be DC type
motor with the actual rotor on a separate pillow block mounting arrangement
(McMaster-Carr) and a 5/8 inch dia. shaft (also McMaster-Carr).  The surplus
DC motors used on treadmills work great for this --- at 8,000 RPM they have
a 3/4 HP rating.

Setup the pulleys to produce a max of 550 breaks/sec (pps).  Also, avoid
solid state motor controllers with this setup --- they tend to lock on full
speed with all the RF.  I use a 7.5 Amp variac with a 25 Amp rectifier block
and a few large filter caps (50-100 uF) for smooth motor operation.

This will give you very good performance.

Hope you can make it to our Teslathon --- we are running our large coil on
this exact setup only with a 16 inch dia. rotor.

Best regards,

Dr. Resonance
 >
 > And what would you say to a two MOT with doubler producing around 11 kV
 > at several hundred mA feeding 47 nF MMC powering a 3.5" coil?  My 5 gap
 > copper pipe gap does not cope well with the heat.
 >
 > Cheers, Chris (NZ)
 >