Re: Polarized HV/ what's + and what's -

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Rieben" <drieben-at-midsouth.rr-dot-com> 

Hi Steve,

That's an excellent idea! I have the DVM plus I have a 1000:1
HV probe. I think the HV probe is rated for 40 kVDC so I
should be able to carefully ramp up the voltage to the x-ray
tranny and check out the polarity. If the polarity of the input
to the DVM is backwards, then the display will simply have
a (-) sign in front of the voltage readout. And yes, the rectifi-
ers are semiconductors, not tubes.

David
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, August 08, 2004 12:53 PM
Subject: Re: Polarized HV/ what's + and what's -


 > Original poster: "S&JY" <youngsters-at-konnections-dot-net>
 >
 > David,
 >
 > You should be able to directly measure the polarity with an ordinary
 > voltmeter on it highest DC scale (typically 1000 V).  You just have to
very
 > carefully ramp up the AC input until you get a meter indication.
 >
 > For better ramp-up control, you can run your variac into an AC arc welder,
 > MOT run backwards or large filament transformer and use the low voltage
 > output to more carefully run your X-ray power supply and have less chance
of
 > burning out your voltmeter.
 >
 > This only works if the HV diodes are semiconductors.  If they are tubes,
 > don't try this method!
 > --Steve Y.
 >
 > ----- Original Message -----
 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > To: <tesla-at-pupman-dot-com>
 > Sent: Saturday, August 07, 2004 9:34 AM
 > Subject: Polarized HV/ what's + and what's -
 >
 >
 >  > Original poster: "David Rieben" <drieben-at-midsouth.rr-dot-com>
 >  >
 >  > Hi all,
 >  >
 >  > I recently scored a pretty nice x-ray transformer. I think it's
 >  > rated around 150 kV -at- ~ 600 mA. I've already repaired a
 >  > carbon tracked phenolic rectifier mount twice. The new
 >  > phenolic mounting block also carbon tracked after the
 >  > first repair but so far the second repair has held up (keep-
 >  > ing my fingers crossed). Anyway, I'm wanting to keep
 >  > the rectifiers intact in this transformer since I'm wanting
 >  > this one as a very high DC voltage source. Since I have
 >  > it all back together after the last repair I really don't want
 >  > to dig into the oily mess again just to get a close look at
 >  > the diodes to determine the polarity of the HV outputs. I
 >  > have heard that one polarity tends to form corona easier
 >  > and actually arc further at a given voltage than the other.
 >  > I've noticed this phenomena from the output leads of this
 >  > transformer as I slowly ramp up the input voltage to it with
 >  > a big variac. Of course I'm also seriesing the variac's out-
 >  > put to it with a ballast assembly since x-ray trannies are
 >  > NOT current limited. Anyway, I was thinking that the ne-
 >  > gative terminal would be the one that would most likely
 >  > tend to more corona and arc further at a given voltage
 >  > but I simply can't remeber for sure. I think Antonio de
 >  > Quieros was talking about this once. Can anyone tell
 >  > me which polarity will form more corona and arc further
 >  > at a given DC voltage?
 >  >
 >  > Thanks,
 >  > David Rieben
 >  >
 >  >
 >  >
 >
 >