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

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

Original poster: "Mccauley, Daniel H by way of Terry Fritz <teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>



Simply put:

1.  RPMs determine how many electrodes you need for a rotor, and ultimately
what the break-rate of your spark gap
will be.

2.  Horsepower is how "strong" the motor is defined.  This number will
determine just how large a rotor your motor
will be able to spin.

For example, if I have a 3600 RPM synchronous motor with 4 electrodes on my
rotor, I will have a break-rate of:

1800 Rev/Min * 1Min/60Sec * 4 = 120 BPS.  This is the correct speed and
number of electrodes for 60Hz synchronous
spark gap operation.  So when tuned properly (either mechanically or
electrically), the spark gap will "fire" at every AC peak, both negative and
positive.

1/4, 1/2 and 1Hp motors are way overkill for all but the largest rotors.  I
think a lot of people who have these large motors only have them due to
availability of the motors except for the ones with very large and heavy
rotors that require the power.
Someone wants to build a SRSG, and already has a grinder motor in the
basement, so might as well use that.

http://www.spacecatlighting-dot-com/teslacoil10.htm

The link above is my first spark gap ever.  (Yes, i did skip the static gap
completely in my learning path)
I'm using a 1/25HP, 1800 RPM hysteresis synchronous motor and it works
beautifully with power to spare.  Whats a
hysteresis synchronous motor you ask?  Well, in layman's terms, a hysteresis
motor may not start up in the same position
everytime you run it.  Therefore, you need to tune it every time you use it.
For me its not a problem, but some might rather use a true salient pole
synchronous motor.

Hope this helps.

The Captain


 > First of all, I'd like to say thank you to all of you who answered my
 > previous posting about splicing two secondary coil wires
 > together.  I will
 > be cutting my 4 foot secondary in half, and I guess I'll be
 > making another
 > tesla coil with it soon!  Many thanks, you'all saved me from disaster.
 >
 > 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
 >
 >