Re: new coil specs
Sorry for thge lateness of my reply, Stan, but I've been a litle busy
lately. I don't know if someone lese has already answered your questions,
but, here's my spiel: (snipped from some other replies of mine. I've told
a fair No. of people how to do this)
this is a description of what an AC-synchronous motor does:
The rotor becomes 'locked' into the rotating magnetic field, the movement
of which is directly controlled by the mains frequency. In that the
rotation always matches the line frequency, so the rotor will always be
in the exact same spot for any given point of the 60 sine wave.
Manufactured AC-sync motors are rare and expensive, you can modify normal
You need to look for a medium to low hp AC induction motor.. mine was
labled 'split phase induction motor' and had an original speed of
1725rpm, and the modification locked this to 1800rpm. It was a 1/3hp,
others have used 1/4, 1/2, 3/4, 1+ or anything around there succesfully.
To check out a prospective motor:
The key ID is the fact that the rotor will have no windings on it, and no
commutator. These motors tend to be quiet in operation. Look for motors
larger than 1/3 hp. Since in the conversion, a good deal of that hp will
And the modification:
After removing the rotor, there will be a fairly large, regular
cylndrical section that is normally in close proximity to the coils
withing the motor case. This is what needs to have four "flats" machined
into it. I used a mill to cut them, but a lot of people have used hand
files, disk sanders, and anything thier imagination says will work. The
material is mostly aluminum, so it will be easy to machine. four flats,
evenly spaced around the curved surface of the cylinder, should be cut
about 1/16" to 1/8" in depth. This means that four lengthwise flat
sections will be filed into the rotor, with 1/16" to 1/8" of material
removed. light colored bands of metal will be seen at an angle after the
top payer of the rotor is filed off. Try not to cut completely through
any of them.
After you perform the modification, a good way to test whether it is
spinning in sych in with a non-phosphorus containing neon sign. It will
produce 120 pulses of light per second, and if you draw two thick black
lines perpendicular to each other accross a disk face attched to the
motor, the lines will appear to stand still. I've done this with neon
lights, mercury vapor tubes, and diodes powered with an unfiltered
I used a 1/3 hp salient pole induction motor, and it is working fine with
a 6" rotor.
On Thu, 28 Oct 1999 22:39:22 -0600 Tesla List <tesla-at-pupman-dot-com> writes:
> Original Poster: Stan <sdarling-at-columbus.rr-dot-com>
> Hello all, I'm getting the urge to build another coil, which of
> means I have questions!
> My major question is what is the relationship of sec. diameter to
> spark length and b) the input power needed? In my case I'm deciding
> between 6" and 8" PVC. Right now I have only one 12/60 NST but plan
> getting more soon. I have MMC capability between 5 nF and 30 nF.
> Finally, I would like to start building a S-RSG. Does anyone have
> step-by-step info on how to do this? I am a complete newbie when it
> comes to this aspect. My understanding is that you need a special
> motor, and that you need to modify it to operate syncronously. What
> kind of special motor, and how to modify it, I am clueless! :( I've
> gathered that this mofication can be very tricky and time consuming.
> there a motor that can be purchased to avoid having to do this?
> I'm sorry if I'm reasking recent questions!
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