Rotary cause failure ?
From: Thomas McGahee [SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: Wednesday, January 21, 1998 2:22 PM
To: Tesla List
Subject: Rotary cause failure ?
> Date: Wed, 21 Jan 1998 04:54:23 -0700
> From: dwight duncan <duncand-at-ccsalpha2.nrl.navy.mil>
> To: tesla-img-request-at-pupman-dot-com
> Hi All,
> Two days ago I fired up my 3 KW Tcoil and got some impressive results
> for being conservative. I had spent a few days re-building my supply and
> wanted to take it easy for a while using 1000 rpm on the rotary gap. Last
> night I took photo's of the unit and between frames increased the speed of
> the motor. After about 30 seconds at 2400 rpm one of my transformers
> again, died.
> The motor is non-synconus and I believe that is what lead to the
> transformers doom. Its is a 1/4 HP variable speed AC brush type motor that
> I acquired for free from someone that was throwing it out. It was the only
> motor I had available so I used it.
> My power supply configuration is as many people use with all of the Rf
> protection and safety gaps and line filters you can think of. I will give
> a brief description and maybe someone can let me know if the non-syncro
> motor was the real culprit.
> First off the line is a 30 amp line filter, switch and then into the
> primarys of two 5 KV, 300 ma tranies in series and one leg of each of the
> secondaries is grounded. From the two HV legs left they each go to one
> side of 30 KV, 3.9 nf caps who's other side is grounded. Next each leg
> goes through a 4.2 mH common mode choke(each side measured at that
> inductance value). Then to a saftey gap with each side on the high voltage
> and center post at ground. The safety gap was set so it would barely not
> fire when the HV was on and the rotary gap was not firing.
When you set these dual safety gaps with the rotary gap not firing
did you by any chance have the main capacitor connected? If so,
there is your error. The setting of a transformer safety gap should
be done with the capacitor out of the circuit. Otherwise you are
setting the gap wide enough for it not to fire even with full
resonant rise on your main cap!!!!
disconnect the main capacitor and open the main spark gap all the way
(or disconnect it during the setting of the safety gaps). Start the
safety gaps off too wide on purpose. Adjust each gap in a bit and then
apply power. Disconnect power and repeat adjustments until you can
finally get the safety gaps to just barely fire. This is the furthest
apart that you should ever set your safety gaps, because otherwise you
will be allowing to large a potential across the transformer. Pole
pigs are a different story. They have a transient voltage rating that is
several times the output voltage rating. But Neon sign transformers
and trannies like the H&R 5KV 300 ma transformers cannot take such
overvoltage at the HV terminals. I have several H&R 5KV 300 ma
trannies, but I have modified the placement of the inside winding
terminal so as to make them more robust.
Hope this helps.
Fr. Tom McGahee
> Now finally out
> to the tank which had the rotary gap in parallel with the supply.
> It all seems to be a sound design, and worked well at low gap speeds.
> The only thing that comes to mind is the gap motor being off sync of the
> line. Does anyone agree? Comments and questions are all welcome.
> One final note. As the gap speed increased the arc length increased
> and appeared to be almost a linear effect. This is a purely qualitative
> statement because I did not have time to make any measurements and it is
> well known that as input power is increased, so does arc length.
> Thanks all for any input.