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Re: Spark Gap Construction Questions
:
> >Original Poster: Chris Tominkson <internetinbox-at-yahoo-dot-com>
> >
> >I recently went to "Twin City Surplus", in Reno and bought some stuff
> >for a spark gap. I got a medium sized AC motor, it has nothing on it
> >to tell anthing about it, and a 3.75" AC fan. The fan says 7200 RPM,
> >220 volt. When I hooked up the motor, it ran fine, when I hooked up
> >the fan, it was spinning VERY slow, like 30 RPM.
> >
> >Does anybody know what could be wrong? If its relevant, it says "Use
> >with external Capaciter" on the outside, and gives a value, which I
> >can't remember.
>
Almost certainly a PSC (split phase) motor. There are two windings, the
main winding (which will be about 9 ohms DC resistance) and the other an
auxiliary winding (probably around 50 ohms DC resistance). Often, the main
winding is split into two halves to allow dual voltage operation. The real
problem is that you need to know the size of the cap to make it work. Is
there any manufacturer information on the motor? If so, you can probably
call the mfr ( with about a half dozen phone calls to get to the right
person), and get the hookup diagram and cap value.
The PSC motors I used a lot of had 5 wires coming out, winding common (
main A bottom end and Aux bottom), Aux winding top, Main A top end, Main B
bottom End, Main B top End. For 110 use, Main A and Main B were connected
in parallel, for 220, Main A and Main B were connected in series. The cap
was always connected betwen Main A top and Aux top (in 220 mode, the main
winding acts as an autotransformer so the aux winding always works at
110V).
In any case, you can try with about 10 uF, 380V motor run cap and see what
happens. Feed the motor through a 100W light bulb in series (to limit the
current if all else fails). Make sure the cap is a motor RUN cap.. Motor
Start caps (which are more common, and much cheaper) are designed to only
take the current for a few seconds while the motor starts up.