Rotary cause failure ?
From: Esondrmn [SMTP:Esondrmn-at-aol-dot-com]
Sent: Thursday, January 22, 1998 4:58 PM
Subject: Re: Forwarded mail.... (fwd)
In a message dated 98-01-21 10:52:18 EST, you write:
<< 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
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. 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.
I use an asynch rotary also, on my 6.0" coil. It also performs better and
better as I crank up the rotary gap speed. The input current climbs, the
rotary speed is increasing audibly, the sparks are getting longer and fatter,
my heart rate is trying to keep up - and then something goes to hell. I am
using a pole pig and have never hurt it but I have lost a couple of caps.
I believe high rotor speeds just plain beat the system to death. I know it is
very hard on the tank capacitor but I am surprised it took out your 300 ma