Re: high voltage probes

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Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 


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From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, September 28, 2003 9:57 AM
Subject: Re: high voltage probes


 > Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org>
 >
 > This sounds like a good idea.  I do have a 50's vintage tube scope that I
 > view as expendable.  I realize that "ground" is not really at ground
 > potential in a Marx.  I suppose I could make two and connect them to A and
 > B to make a poor-man's differential probe....  No, I do not have a UPS nor
 > access to one that is viewed as expendable.

Anyone doing serious HV work might consider lashing together an inexpensive
floating AC supply for just this sort of thing.  Go get a deepcycle battery
and one of those inexpensive 200-300W inverters.  <$100 all told, and yes,
fairly non-optimized for a number of reasons, but cheaper than your basic
battery operated scope. Sears has a selection of batteries.  I suppose one
could plug stuff into one of those transient suppressing plug strips
advertising $75,000 replacement guarantee, and work your way through their
mill when everything dies...



 >
 > Calibration is an issue, since I would rather like to figure out how a
32kV
 > rectifier was overvolted when only 20kV should have been across it.  We've
 > also lost two capacitors to what looks like overvoltage despite never
 > getting above about 65% of their voltage rating (22kV).

Calibration is fairly straightforward.  All you need is a suitable source to
calibrate from.  Most dividers are voltage independent.. that is, if you
build a 50:1 divider and calibrate it at 110V, it will work pretty much the
same at 11kV..


 >
 > Would a resistor divider with some 10Meg 1/4W resistors (I have plenty)
 > work in place of the HV probe?

Sure... string them together appropriately... Watch the power dissipation,
though...