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Third Light
Listers:
There's been a flurry of coiling activity since my last post (second
light), namely:
construction of a new MMC using the UK Bulk buy spec caps consisting of
3 strings of 30 0.047uf caps. Total capacitance is 4.7 nF. Should
survive the 25KV for a while!
2 new toroids made from aluminium shower extraction ducting 100mm
diameter. One is about 10" major diameter (centre line), the other is
16" major diameter. These were made by bending the un-streched tubing
around an MDF former with Aluminium positioners screwed around the edge.
Bad Ascii art follows
Side View
)=========(
Plan view is beyond my child like ability with ASCII art, but there's 12
of the )( things around the circumference. The two ends of the ducting
are glued on the end faces with contact adhesive and then secured by
copper wire "stitching". To finally secure, hot glue was applied to the
seam.
I also made a RQ air blast cooled gap. From 6" reinforced PVC pipe
scrounged from Sharpe and Fisher. Free. 24 x 3" long x 22mm diameter
copper pipes as
electrodes with a series of holes drilled in parallel with each gap. gap
spacing varies between 1mm and 3mm to allow for experimentation (OK
poor measurement). The electrodes are screwed in rather than glued so
they can be removed and cleaned.
Took apart a spare hoover and put the blower inside the tube so air is
forced thru the gaps. Endplates of 1/4" MDF.
This is way cool. makes a whistling noise like small jet when it fires
up.
A new control panel was made from an upturned stacking bin from B&Q -
the spiritual home of the coiler. This houses two variacs, one used as a
series ballast for the transformer and one as a voltage control for the
tranny. It also contains a filter circuit and a switch. The reason for
this change was twofold. With the previous setup, my variac was mainly a
device for turning electricity into smoke. My slightly larger new variac
and the introduction of a current limiting inductor is an attempt to
rectify this. The other reason was to increase the distance between me
and the coil in the unlikely event that my sparks would increase to more
than the puny 2 feet so far.
Other changes to my setup include the removal of the girls technology of
filter caps and series chokes. The chokes were a bit silly as they were
about 30 turns of wire in series with each leg of the HV supply to the
gap. Caps had to go due to gap re-design.
Phew. Anyway, now to the good bit. I've just fired up with the smaller
toroid and the 4.7 nF Cap. If people remember my second light post I was
getting 2 footers with my 12 x 2 toroid and a 10nF MMC tapped at about 9
turns.
With this setup I need to tap out at 24 (count 'em) turns for tune.
Suffice to say that I'm glad I moved the control panel away from the
coil. I'm now pushing Five footers, glorious branching streamers comin'
atcha. I initially experienced intermittent firing without the forced
air in the gap, this disappeared when I ran the blower. Nice. What
wasn't so nice was the puff of Dioxin laden burning PVC smoke that
stopped my fun. I think a bit of PVC swarf got caught between a gap and
oxidised. I've now cleaned up the gaps and ready to run again tomorrow
night :-)
I guess the bottom line is that *high* voltage Trans (25KV) = low
current = small cap = higher inductance primary = less gap loss
therefore higher o/p. For my coil this seems to be the optimum design.
Looking forward to Saturday's UK Winter High Voltage Halloween event.
Cheers
Steve Crawshaw
"Better Living Through Coiling"
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