RE: Rotary Spark Gap, the rpm's, and horsepower

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

Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

The RPM determine how many electrode "presentations", or alignments occur 
per second.  If you're looking for a synchronous gap, you'll want 120 per 
second.  1800 and 3600 RPM synchronous motors achieve this using 4 or 2 
rotating electrodes, respectively.

The required HP rating of the motor is only determined by the mass of the 
rotating disk plus electrodes.  Larger coils switch higher currents, and 
need beefier electrodes, which tend to be heavier.  A heavier disk assembly 
needs more HP if the motor is synchronous.  If a disk assembly is too heavy 
for a given sync motor, it won't be able to spin up speed.  If an 
asynchronous motor is used, the HP is less critical; a heavier disk will 
just take longer to accelerate up to speed, not a problem.

IMHO, folks often seem to over-design async gap motors.  I can't believe 
that 1-2 HP is necessary just to spin a disk, unless it's truly massive 
like the Electrum project.

For your 1/20 HP motor, you first need to confirm that it's 
synchronous.  If so, I would recommend a Terry Blake "propeller" gap 
design, as it has minimal HP requirements and is very simple to 
construct.  See  http://www.tb3-dot-com/tesla/sparkgaps/index.html.  A 6" disk 
would probably be OK, but it would have to be relatively thin stock with 
none-too-massive electrodes.

Regards, Gary Lau
MA, USA


 >I will be making a RSG, but I don't quite understand the significance of
 >motor RPM's and horsepower in the design.  Is it better to have more or
 >less RPM's and horsepower?  I have a whole bunch of 1/20 HP, 3600 RPM
 >motors from film projectors.  Would one of these be suitable for an RSG
 >with like a 6" disc?  I see that most of the professional RSG's have huge
 >motors attached (1/4, 1/2, or 1 HP), but the RPM's are usually only like
 >1800.  Why is it necessary to have so much power and so little RPM's?
 >
 >Many thanks,
 >Jack