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First light. Almost perfect and need some help

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Steve Ward

Mon Jan 29 2007, 06:10PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Be sure not to use your "good" meter. Go buy the cheap 5 dollar volt meter for this experiment. Ive blown up too many "good" meters (a nice wavetek once

) from using them around tesla coils and marx generators.

What is the gap spacing of your rotary? I always had to make my gap spacing at tight as possible for best performance from my old 15kV 100mA system. I think i usually kept the electrodes within 1/16", but closer if i could manage it. If you are using tungsten electrodes, be sure to have some sort of containment around the thing incase they collide and shear. My gap used a wimpy little synchronous motor that i accidentally stopped the rotor with my hand and didnt regret it *too* much

. So my gap was relatively harmless if the electrodes did collide. I was also running 1800RPM.

Anyway, i sorta suspect the GFI is acting funny. Either that or you have a power arc somewhere before the terry filter perhaps, and by turning the variac down you quench this arc allowing power to go back to the primary capacitor again.

Sulaiman

Mon Jan 29 2007, 06:58PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I find that moving-coil meters are the best around TCs and other eht-sparky-things.
Also has the advantage of no batteries required,
with the drawback that (say) 20 kV x 50 uA is 1W, ok for a TC but not lower power devices.

IamSmooth

Mon Jan 29 2007, 07:14PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

As far as my voltmeter that I will construct I will use a $5-10 simpson panel meter. I agree that using anything better puts it at risk of destruction.

My rotary gap is 1800rpm on 4" flywheel with 4 tungsten electrodes. They are about 1/16" of an inch. If I put them any closer I fear they will hit from thermal expansion during use.

I am hoping to find another nst 15kv/60ma without the gfi.

EDIT: Until I start swapping componets I won't know the real answer, but the person who sold me the bleeder resistor for my capacitor thinks the voltage tolerance is 30kv. this would coincide with the voltage the capacitors were probably seeing when they stopped working.

Hazmatt_(The Underdog)

Tue Jan 30 2007, 03:16AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

One thing I think bares mentioning is that on a non GFCI NST you have a true midpoint ground.

On a GFCI NST you do not have a true midpoint ground. The midpoint is raised about 60V above 0 because of the GFCI triggering circuit. You can test it if you like. The midpoint is plainly raised above case ground by a small ceramic support, and in the spec. sheet they explicitly tell you not to ground this to case ground.

IF you have the non GFCI NST (A) midpoint grounded to your Terry Filter, and you have GFCI NST (B) to a separate Terry Filter using its raised midpoint 'hot' grounded, A will cause a current loop with B if your grounds are shared.

IamSmooth

Tue Jan 30 2007, 04:24AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I don't have them both grounded to the filter. The midpoint of the filter literally goes to the ground. Each ground lug on the NST are connected to mains ground. I am in the works of getting a second no GFI unit.

Coronafix

Tue Jan 30 2007, 04:28AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

I'd like to bet on core saturation and phase shifting.
It only happens once you go up past a certain point,
and it doesn't reset until you bring the voltage back down to zero.
Is the current still high when it happens?

IamSmooth

Fri Feb 02 2007, 01:32PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

mistake...

IamSmooth

Mon Mar 05 2007, 12:41AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Problem solved: I disconnected the ground to the NSTs that I had in parallel. One is center balanced while the other is off by 60v (GFI unit). I also used a bleeder resistor on my capacitor with a voltage rating of 31KV instead of 15kv. These two changes now allow me to crank up the primary voltage to 120v without any problem.

Hazmatt_(The Underdog)

Mon Mar 05 2007, 01:11AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

heh, wha'd I say. Gotta be careful about your grounds.

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