Re: OHVM HV Breakdown Test, Plastic Use Warning

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

Original poster: "Malcolm Watts by way of Terry Fritz <teslalist-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Dave,

On 6 May 2003, at 19:44, Tesla list wrote:

 > Original poster: "David Sharpe by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>
 >
 > All
 > I ran a full power HV breakdown test of my OHVM high voltage
 > divider.  It is basically a 8.5" x 10" PCB with TVSS and load
 > resistors integrally mounted, suspended upside down on a 3/8"
 > Lexan top.  The entire assembly sits inside an 'O'-ringed
 > 10" wide x 12" long x 2" thick UHMW PE enclosure that 1-1/2"
 > of material has been milled out.  Top is held in place using (38)
 > 1/4"-20 x 2" long nylon pan head screws on top and hex nuts in
 > counter bored holes from bottom.  Enclosure was filled using
 > 60 oz (3 bottles) of Wal-Mart brand baby oil.
 >
 > Unit successfully operated for 5 minutes at 24kV (~35kV peak).
 > I then ramped voltage by rewiring PT's primaries in series to
 > parallel.  I then ramped voltage up to 40kV rms (~56kV peak;
 > 8.08V rms out).  No overheating, no corona in a darkened room,
 > and no partial discharge picked up on AM radio  (  :^)))  ).
 > Now its time for final assembly and end to end calibration.
 >
 > Although slightly off this topic, a piece of advice for those of
 > you out there using Polycarbonate (Lexan) for components or
 > assemblies.  DO NOT allow fast evaporation liquids (canned
 > air, defluxing compounds, fast evaporation aromatics) to
 > contact the Lexan.  My first cover plate cracked between
 > 3 holes when I used flux remover on OHVM divider board!
 > It appears to be a thermal shock phenomenon, that will cause
 > cracks to propagate through the Lexan; IDK if this problem
 > is possible with other plastics commonly used (ABS, Plexiglas
 > [Acrylic/Perspex]).  Surprised the hel.. out of me, and set
 > my completion date back a week...  :^C

Acrylic/plexi tubing goes craze(y) with just about any type of
solvent. I haven't seen it with sheeting so it may be a function of
stress caused by the inner surface being smaller than the outer.

Regards,
malcolm


 > Up loaded two new files showing test setup for 2.4kV and
 > the oil divider final subassembly. Files are at:
 >
 > http://hot-streamer-dot-com/dave
 >
 >     OHVM 2_4kV HV divider test setup.jpg
 > 2.4kV powered setup to determine Rdivide ratio
 >
 >     OHVM Oil Jacket Rdivider.jpg
 > Divider nework assembly completed (including oil), ready for use.
 >
 > Corrected error seen at 60Hz <<1%.
 >
 > Regards
 > Dave Sharpe, TCBOR/HEAS
 > Chesterfield, VA. USA
 >
 >
 >