Ignoramus27088 wrote:

After looking at HV resistors on ebay, I realized that I may have a
couple in my junk pile (pieces from a radar test set). Will check
tonight. There are probably 5 kV rated, but I could put 2 in series.

i

For the discharge resistor, leave your self some margin. If 5KV rated,
put three identical ones in series if you are testing at 9 to 10 KV.

What procedure are you proposing to non violently check the caps are
actually discharged? Personally I'd want to know they were fully
discharged (well past 99%) before handling them. Also does your plan
include checking the HV probe after use before relying on it to indicate
they are safe?

Insulation can be a problem, beware of surface leakage, all surfaces
need to be extremely clean and absolutely dry. I've used glass up to
about 35KV with a grounded guard ring (in case there is a flaw I haven't
spotted) with no trouble so if you have a large enough quartz glass tube
that should be suitable to hold the resistors. Some uncolored plastics
are also suitable for high voltage work. There is no way you'd get me
using wood unless it was freshly kiln dried then vacuum impregnated with
paraffin wax. Corona discharge can also be a real problem. It
shouldn't be TOO bad at 10KV but you still want to be really carefull to
get nice smooth connections with no sharp edges or points.

High voltage har a really annoying way of finding the slightest
weakness or pinhole in any insulation and many TVs have had a fine
fireworks display from the side of the LOPT on my bench. Its a bit
inconvenient if one is just trying to get the TV powered up successfully
to decide if its condition is good enough to justify LOPT replacement
but with your setup it's potentially lethal. Its also important to
confirm the integrity of the grounding wires in your test circuit. I
left off the ground lead to the aquadag on a large screen TV by mistake
ONCE, (in 12 years) now I'm rather cautious. You goof up your grouding,
yoy'd better allready have got a good deal on a pine box . . .


Wild wacky and way out there idea!! Does anyone have any idea if a
suitable length of carbon core vehicle ignition cable would make a
satisfactory bleeder resistor? Iggy would be dumping 100 joules into
it, its got distributed resistance and sufficient insulation so the main
worry is can a maneagable length take the peak power?
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- &
[dot]=.
*Warning* SPAM TRAP set in header, Use email address in sig. if you must.