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Re: Fw: CD 942 failure tonight
Original poster: Esondrmn-at-aol-dot-com
In a message dated 2/28/04 5:53:04 PM Pacific Standard Time,
>Copnsidering the recent MMC debate, I figured that I would share this
>evening's run. This is a first fire, and tuning was done at partial variac
>setting. Volt and amp meters are not in yet, so I can't give any real
>numbers. Also, SRSG was set using a flourescent bulb, as I am still
>waiting on my motor run caps for John's phase controller.
>Here are the specs:
>Topload: 4x24 Soon to have an additional 4x36 on top of it.
>Secondary: 4.5 OD PVC with 36" of heavy build #24, 1481 turns. Plan on an
>8" with an 8 by 36 toroid in the future.
>Primary: .25 Cu tubing, .25 between turns, 16 turns total, seems happiest
>tapped at 6 and 5/8 turns.
>Safety across RSG: Set at .5"
>NST safety gap: 5/8"
>Capacitor bank: 4 strings of 9, total of .0667, per MMC chart.
>After rough tuning and ramping up variac, I heard one cap blow. Black soot
>and a hole about a quarter inch deep. Soldered up a new one, and ramped
>variac up to 120 volts. Sparks about 4 feet, and gap won't fire until
>variac is above 60%. After that it will fire all the way down to about a
>quarter turn on the variac. Checked rotary, and there is no follow around
>with the gap arc. She fires right on electrode alignment, so I am assuming
>that phase is pretty close. Started it up again, and tried to fine
>tune. A half turn either way from the tap point of turn 6 5/8 and
>performance diminishes. Put tap back at this point and fed the trans the
>full 120 volts. I stopped things again to check everything out. First I
>checked the variac, an ancient Ohmite, to see if it was getting warm. It's
>only rated for 10 amps, and I made a new brush out of a piece of brass due
>to no access to new parts. Everything looks good and runs cool. The lash
>up wiring to the coil primary is 14 gauge, and it is hot to the touch, and
>the primary is warm. Will go to #8 for final set up. Looked at cap bank,
>and the new cap looked like a piece of popcorn that had just popped, black
>and all. The one on the next string over was bulging like you know what,
>but no black stuff. I can see the foil, however.
>Why is this happening? I am not going to re-fire the system until the last
>portion of the tank wiring is replaced with #8, PFC caps and meters
>installed, phase controller up and running, and new toroid installed. I've
>put lots of work into this thing, including welding up a nice stand for the
>controller, gap, trans and cap assembly, and want to get to the bottom of
>this cap problem. Any thoughts?
Perhaps the rotary is not firing at the correct phase angle. I did run
mine with the trial and error system of rotating the motor in the
cradle. It was difficult to find the correct spot. After building John's
phase control system, things are much easier. I now use synch rotary gaps
on both coils with the phase control system. The variacs are marked at the
120 bps mark which is where I usually run them. I run the gap up to speed
with the varic set at zero, then set it to the 120 bps mark, then apply
about 50% power to the coil, re-adjust the phase control, go up to 100 %
power and fine tune the phase control.
I am not sure that running with the firing angle misaligned will cause
blown caps but I know the firing is erratic. I see that you do have a
safety gap across the rotar gap, which is a good thing. Is the secondary
grounded? I did not run the numbers but it sounds like the primary /
secondary tuning is ok.