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Re: Rotary gaps (sync) (fwd)





---------- Forwarded message ----------
Date: Sat, 1 Aug 1998 09:30:27 EDT
From: FutureT-at-aol-dot-com
To: tesla-at-pupman-dot-com
Subject: Re: Rotary gaps (sync)

In a message dated 98-07-31 22:01:48 EDT, you write:

<< 
>     I did some thinking about making a rotor gap for the
> MOT transformers that I'm going to use for another coil.
> I was thinging that i'd make a sync rotor so that I could
> you it on a noen for tests too. Does it just have to break
> 120 times a sec to be sync? I figured I could make a 
> gap with a 1200 rmp motor and have 6 electrodes on the
> disk. Does the diameter of the disk really matter? For this
> forst test rotor I plan on just using some bolts on a motor
> I have. I don't know the speed of this motor but I plan on
> getting a heafy DC motor or a .5 hp AC motor. Anyone
> let me know what you think about this. Thanks

Shaun, all,

A sync-rotary gap requires a synchronous motor that runs at exactly
the correct speed, and is locked to the line frequency.
A regular AC induction motor, or a DC motor won't give the correct
speed.  An induction motor can be modified to make it synchronous,
by grinding flats on the armature.  Procedures are in the list archives.

Some provision must be made to adjust the timing or phase of the 
rotor gaps relative to the incoming AC sine wave phase.  This can be
done by rotating the motor or the gap assembly, or by rotating the
rotor on the motor shaft.  Adjust for strongest sparks at full power.

Yes, 120 BPS is the usual approach.  The rotor diameter doesn't
matter too much, but if it's too small, the dwell times may be too
long, and the electrodes may be too close together.  Larger rotors
require better balancing and stronger rotor materials for safety.

It's especially important in sync gap systems to use the proper
sized tank capacitor.  In a static gap or non-sync rotary system,
one can simply raise the break rate to compensate for a too-small
capacitor, to a degree.  This option is not available in a sync-gap
system, unless of course you physically add more electrodes to
the rotor for a higher break-rate, (I've experimented with this idea,
but consider it not worth the trouble).  If you want or need a high
break rate, it's easier and probably just as good to use a non-sync
gap, or static gap.

Sync-gap systems seem capable of superior performance, but only
if the coil is carefully designed to optimize performance at the 120
BPS break rate.

John Freau
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