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Get your kicks (out of) polishing toroids
Hello All,
Today I had a rather interesting experience. I had just finished
soldering my corona shield together. I built this out of 3/4"
soft copper (hard as heck to bend into a 15" perfect circle)
and some 9/16" hard copper for the spokes. It looks like a
marine type steering wheel. After filing away the excess
solder, I decided to polish it to remove sharp edges that
might lead to corona (okay, okay, Iīm a stickler for good
looks!!). So I stuck a buffing wheel into my Walker-Turner
drill press and started polishing away. After a few seconds
of polishing I accidently got my head near the drill press
top (steel case) and got ZAPPED!!. Believe me, I sure was
surprised. I immediately stopped polishing and stopped the
drill. I kept hoping "Please not the drill press" (being
defective, I mean) Anyway, I whipped out my DMM and
started measuring. Nothing!! Everything was normal. I
couldnīt have believed it anyway, since my shop is fused
and has a ground (and neutral) fault interrupter that kicks
out if >30mA flow, where they shouldnīt. So I started
polishing again and..... yep, the same thing happend (only
this time it was my finger, which wasnīt as "surprising" as
to my forehead. I could repeat this at will. Very amusing
(once you get used to it). What happend? Well, during the
polishing action I was charging my 10pF cap (the corona
shield). The longest spark I got was about 5/8" long.
Interestingly enough the charge would "stay around" for
at least 10 seconds. The second interesting thing was it
wasnīt even a super dry day (air humidty was ~35%).
So, even though I usually hate polishing things (lots of
work!!) I really got a kick out of it (sorry, but I COULD
NOT resist that pun) this time.
Coiler greets from germany,
Reinhard