[Amps] Construction of Light-Weight Wide High Voltage Range High-Pot Testers With Excellent Voltage Resolution

[Paul Marbourg]

Dear Colleagues,

I built a hi-pot tester about five years ago using components purchased from
a company called:

http://www.emcohighvoltage.com/

They manufacture a wide range of solid state "cubes" and supporting voltage
dividers that can easily generate a very wide range of DC high voltage.

The unit I built can range from a starting 2,300 VDC up to over 20,000 VDC @
100 uA.  It weights all of about 4 pounds and uses a 10 turn pot to give
excellent voltage resolution.  This particular design uses a DC to DC
converter cube smaller than the size of a 1/4 pound of butter and uses a
voltage divider on the high voltage side to allow the use of a high
impedance VOM (I use my Fluke 77) to read the output voltage/1000.  The
DC/DC converter and voltage divider are both standard Emco products.  I
built a small full wave rectifier DC supply to feed the cube.  I have a 50
uA analog meter to monitor current flow.  This assembly works like a dream.
The hardest part of the whole project was finding dropping resistors of
sufficient breakdown voltage rating.  A friend supplied me with some old
resistors scavenged out of an old TV fly-back transformer supply.  The
tester has been invaluable for testing components like vacuum variable
capacitors and vacuum relays.

Emco was very willing to sell their products to a ham.  They may ask for a
copy of your ham license, however, as there are security concerns associated
with this type of device (they are used in commercial taser products etc.).

I highly recommend this approach to building a light weight, bullet proof
high pot tester for ham applications.  I probably spent something around
$150.00 to finish this project (not counting the cost of my old Fluke 77
VOM).

In particular, check out their models:

DX150: 12 VDC in and 2.5 to 15 kV DC out @100 uA

DX200: 12 VDC in and 3 to 20 kV DC out @ 75 uA

DX250: 12 VDC in and 4 to 25 kV DC out @ 75 uA

These units are quite reasonably priced for the dollar conscious ham like
me.

For the voltage division to enable the use of my Fluke 77 meter with this
system, I used the Emco V1G miniature voltage divider product.

This is a sweet set up.  Keep in mind when testing vacuum capacitors that
most Jennings capacitors are voltage rated with 60 Hz AC HV.  When using HV
DC to test Jennings vacuum capacitors, they recommend using only 60% of the
rated 60 Hz AC high voltage.

The Emco high-pot tester works VERY well to flash over (or "tinct") vacuum
capacitors which have grown "fingers" of copper between the plates.  Be very
careful not to overdue this treatment or the capacitor will be ruined.
Also, most vacuum relays are rated @ full VDC, not 60 Hz AC.

73,

Paul WN7T