Safely testing 22 kV capacitors

[Dave Hinz]

Just for reference, the energy stored in that cap at 22 kV is
approximately 242 joules. About as much as small caliber rifle
bullet.

And, about the starting energy for a defibrillation sequence. Get that
sucker in the wrong point in your waveform, and you're _staying_ dead.

 

[Ignoramus6399]

I have a bunch of 1N4007 diodes (1000v rated). If I put, say, 20 of
them in series, would that be sufficient to rectify 9,000 VAC safely?
I have read some articles discussing that since leakage amps are not
identical, that I need to put resistors in parallel with them. If so,
these need to also be 1kV rated resistors, right?

If not, would anyone have a suggestion for a 30 mA rectifier for 9
kVAC?

thanks

i

 

[Jon Elson]

Ian, would you or anyone have any idea if what I have is HV resistors?


They are blue, about 3 inches long, and are marked VICTOREEN MOX-3 12
MEG.

Yup, that's the cream of the crop! I can't give you ratings off the
top of my head, but a few of them in series should definitely handle
10 KV.

Jon

 

[Ignoramus6399]

Yup, that's the cream of the crop! I can't give you ratings off the
top of my head, but a few of them in series should definitely handle
10 KV.

Cool. They came from a radar test set. It actually had a 5kV DC power
supply (xfmr plus bridge rectifier), but, alas, I sold the
rectifier.

i

 

[Jon Elson]

If you want to test them closer to their actual rating, you could charge two
caps to 9kv each, and then hook them in series across a single, giving you
18 kv. Doing it all with broomsticks, of course. For discharge, you could
point a steam hose in their vicinity. Again, with a long stick, and from a
good distance.

I would start by inventing remotely operated aligator clips.

Connecting differently charged caps like these together with wires
will end up with no wires and much noise. And, any resistance, from
just the wires themselves to high value resistors will burn off half the
energy transferred (if the wires live long enough to complete the
energy transfer.)

And, if you have a 0.5 uF cap charged to 18 KV, and connect it to
a discharged 1 uF cap, you would expect the final voltage to be
2.25 KV, I think, due to the smaller cap value (2 1 uF caps in series)
charging the 1 uF, and the loss of energy on transfer. This is a
standard exam problem.

Jon

 

[Jon Elson]

Know anyone with a small Van DeGraf generator you could borrow? One of
those could probably charge up those caps slowly enough for you to watch
the voltage rise on the meter, and you could turn it off when you got to
20 KV.

Big Van DeGraf machines produce microamps! Charging a uF to 20,000 V
at one uA will take 20,000 seconds. And, that's one of those 6 foot
tall jobs with a 6" wide belt.

Jon

 

[Ecnerwal]

At the olde ion beam lab, we used pvc or fiberglass handles, not wood.
Wood would be a poor choice. And a resistor (a big honking 50W resistor,
which the Lab's EE assured inquiring minds WOULD NOT be surviving a full
discharge - this is a safety tool used to approach supposedly discharged
capacitors and be damn sure that they are discharged before you touch
them, not a device to discharge them through, other than that last few
hundred volts which is more than enough to kill you...) Speaking of
which, you never want to store these things without having them shorted,
solidly. A HV capacitor which is just sitting around can collect a
lethal mount of static. If they did not come to you pre-shorted, someone
was not behaving responsibly at fermilab.

It's been a few decades, so I don't recall the precise size of the banks
involved, but even the little bitty ones made a bang of unholy
proportions, and spewed a fine dose of X-rays around the discharge area
as well. Nobody but nobody got anywhere near the things when they were
charged, and they lived in tanks full of transformer oil to keep the
terminals from arcing over in the air. The big one (many capacitors)
sounded a bit like dropping a V-8 engine from 3 stories, and vaporized
the electrodes every time it was fired.

If the capacitors are oil-filled, and they probably are, you need to
verify (or make the seller verify) that they are free of PCBs, or you
are in for a world of trouble disposing of them in any way. They should
not have sold them if they were, but you need to be sure.

In short, you really do not want to test these to anywhere near their
capacity. Your HV supply is not suitable, and if it was, you'd be
looking at a world of hurt without investing a few thousand in test
gear. You could test them in a low-voltage RC circuit, I suppose, but
for all actual purposes which they might be used, it's not very relevant.

 

[John Larkin]

Got myself some capacitors for $10 apiece.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7603382621

The specs are 22 kV, 1 uF, discharge capacitor. See

http://igor.chudov.com/tmp/cap.jpg

The seller was wrong in describing them as 22 VOLT capacitors. They
are 22 KILO volt capacitors. (the seller is Fermilab).

They are similar to this one:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7598631638

but have twice more capacitance.

Anyway, here is my question. I have a 9 kV DC power supply. (a
Franceformer). How can I safely test these caps before selling
them. At 22 kV, they can store about as much energy as a .22 bullet,
according to my calculations.

It would be less at 9 kV, but still, obviously, very deadly.

Certainly unpleasant, in the ballpark of a defrib.

So. What is a safe way to charge them, verify that they hold the
charge, and then DIScharge them at 9 kV.

Well, you need a HV supply: neon sign xfmr + HV doubler, or a
flyback/rectifier from a color TV set. Read it on a DVM with a HV
probe, and then just leave the probe on there until it's mostly
drained, and kill the last few hundred volts with a resistor.

No big deal.

But if it was a 22KV cap, and it behaves like a 1 uF cap at low
voltages, it's very likely fine to sell.

John

 

[Ignoramus6399]

At the olde ion beam lab, we used pvc or fiberglass handles, not wood.
Wood would be a poor choice. And a resistor (a big honking 50W resistor,
which the Lab's EE assured inquiring minds WOULD NOT be surviving a full
discharge - this is a safety tool used to approach supposedly discharged
capacitors and be damn sure that they are discharged before you touch
them, not a device to discharge them through, other than that last few
hundred volts which is more than enough to kill you...) Speaking of
which, you never want to store these things without having them shorted,
solidly. A HV capacitor which is just sitting around can collect a
lethal mount of static. If they did not come to you pre-shorted, someone
was not behaving responsibly at fermilab.

Thank you. I will pick them up on Tuesday early morning, I believe
that they are all shorted.

Well, here's a picture of the data plate, courteously emailed to me by
the seller:

http://igor.chudov.com/tmp/cap.jpg

Do you thikn that it has PCBs?

In short, you really do not want to test these to anywhere near their
capacity. Your HV supply is not suitable, and if it was, you'd be
looking at a world of hurt without investing a few thousand in test
gear. You could test them in a low-voltage RC circuit, I suppose, but
for all actual purposes which they might be used, it's not very relevant.

Thanks... I will think about this...

i

 

[Mike Henry]

Got myself some capacitors for $10 apiece.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7603382621

The specs are 22 kV, 1 uF, discharge capacitor. See

http://igor.chudov.com/tmp/cap.jpg

The seller was wrong in describing them as 22 VOLT capacitors. They
are 22 KILO volt capacitors. (the seller is Fermilab).

Are you sure that Fermilab is the actual seller? Based on what I know of
DOE labs, it's not very likely that they would be selling direct on Ebay or
even to the public at large.

<snip>

 

[DoN. Nichols]

On 30 Mar 2006 19:43:34 GMT, Dave Hinz <[email protected]> wrote:

[ ... ]

I think that I do not have a 22kV rated probe, no.

Without one, you are SOL -- unless you get other things made for
the purpose.

Take a look at eBay auction 7603726273. This is an
electrostatic voltmeter. It draws *zero* current. The range is set by
pulling out or pushing in the small knob on the end of that long
insulator sticking out the back. I can't get this particular auction to
show me the other images, so I can't see what the scales really are.
Some recent eBay auctions lock up Opera with weird JavaScript.

O.K. Using Mozilla, it looks as though it will go up to 30KV
full scale, if I am reading that label on the back properly.

Here is another -- 7605561926

What is it about the sellers of these which keeps them from
posting the voltage scales? But these are both dirt cheap for what they
are.

You can perform an interesting experiment with one of these and
a variable capacitor of the sort used for tuning old AM radios. Set it
up with the sections fully meshed (maximum capacitance), and connect it
to the meter. Momentarily touch a source of voltage enough to get some
deflection on the scale. Now rotate the shaft of the capacitor (which
is grounded to the frame, and you will see the voltage swing *way* up,
as the number of electrons used to charge it interact with the
capacitance changing.

I am aware that I cannot built a divider with regular resistors, and
high voltage resistors might be hard to come by.

Especially ones which you can *trust*. Generally, the skin oils
from handling will produce a leakage path significantly lower than the
highest value resistors. I have seen some as high as 2.5 terra Ohms. A
spiral carbon film deposited on a ceramic body, and covered with a
transparent shrink-on plastic sleeve.

Well ... the discharge route is best done with a large value
resistor, attached to the end of about an 18" clear PlexiGlass rod.
From the end attached to the rod (drill and tap the rod for a screw),
run a wire off to ground. Pick about five 22 MegOhm 2W resistors in
series -- solder with short leads so it is fairly stiff, and touch this
to the capacitor's terminal. This will put about 4W in each resistor at
the full 21 KV. Too much for the resistor long term, but probably
enough for the purposes. Make sure that the lead from the rod is *well*
grounded. And observe the voltage on a meter as it discharges.

I think that I can easily test them at low voltage with a capacitor
testing function of my multimeter.
Yes.

Would testing them ALSO at HV be worthwhile?

Well ... it is possible for them to have failure modes which
will only appear at high voltage, and your purchasers will probably
expect them to work at their rated voltage.

Thanks Dave, yes, I am very apprehensive of HV.

That is wise.

I've been bitten by as much as 60 KV, but not at high current.

My worst one was actually at 2KV -- but *lots* of current --
from a 100 uF bank of capacitors.

Enjoy,
DoN.

 

[DoN. Nichols]

Well, here's a picture of the data plate, courteously emailed to me by
the seller:

http://igor.chudov.com/tmp/cap.jpg

Maxwell Labs caps are really nice quality pulse discharge
capacitors.

Do you thikn that it has PCBs?

Hmm ... It says "impregnant MIPB" which sounds like something
different from PCBs. You might check whether they are still in
business, and ask them.

And these *might* actually surivive a dead-short discharge --
but it is still kinder to them to not do that.

Enjoy,
DoN.

 

[Ignoramus6399]

On 30 Mar 2006 19:43:34 GMT, Dave Hinz <[email protected]> wrote:

[ ... ]

I think that I do not have a 22kV rated probe, no.

Without one, you are SOL -- unless you get other things made for
the purpose.

Take a look at eBay auction 7603726273. This is an
electrostatic voltmeter. It draws *zero* current. The range is set by
pulling out or pushing in the small knob on the end of that long
insulator sticking out the back. I can't get this particular auction to
show me the other images, so I can't see what the scales really are.
Some recent eBay auctions lock up Opera with weird JavaScript.

O.K. Using Mozilla, it looks as though it will go up to 30KV
full scale, if I am reading that label on the back properly.

Here is another -- 7605561926

What is it about the sellers of these which keeps them from
posting the voltage scales? But these are both dirt cheap for what they
are.

You can perform an interesting experiment with one of these and
a variable capacitor of the sort used for tuning old AM radios. Set it
up with the sections fully meshed (maximum capacitance), and connect it
to the meter. Momentarily touch a source of voltage enough to get some
deflection on the scale. Now rotate the shaft of the capacitor (which
is grounded to the frame, and you will see the voltage swing *way* up,
as the number of electrons used to charge it interact with the
capacitance changing.

I am aware that I cannot built a divider with regular resistors, and
high voltage resistors might be hard to come by.

Especially ones which you can *trust*. Generally, the skin oils
from handling will produce a leakage path significantly lower than the
highest value resistors. I have seen some as high as 2.5 terra Ohms. A
spiral carbon film deposited on a ceramic body, and covered with a
transparent shrink-on plastic sleeve.

Well ... the discharge route is best done with a large value
resistor, attached to the end of about an 18" clear PlexiGlass rod.
From the end attached to the rod (drill and tap the rod for a screw),
run a wire off to ground. Pick about five 22 MegOhm 2W resistors in
series -- solder with short leads so it is fairly stiff, and touch this
to the capacitor's terminal. This will put about 4W in each resistor at
the full 21 KV. Too much for the resistor long term, but probably
enough for the purposes. Make sure that the lead from the rod is *well*
grounded. And observe the voltage on a meter as it discharges.

I think that I can easily test them at low voltage with a capacitor
testing function of my multimeter.
Yes.

Would testing them ALSO at HV be worthwhile?

Well ... it is possible for them to have failure modes which
will only appear at high voltage, and your purchasers will probably
expect them to work at their rated voltage.

Thanks Dave, yes, I am very apprehensive of HV.

That is wise.

I've been bitten by as much as 60 KV, but not at high current.

My worst one was actually at 2KV -- but *lots* of current --
from a 100 uF bank of capacitors.

DoN, thanks a lot. I will buy a HV probe, the advantage of which is
that it can also help me discharge the caps. When I try them, I will
let you know. I have a plexiglass rod of some sort (from a hospital
dumpster), I will try to test it with a megohm meter and see if it is
suitable.

i

 

[oldjag]

If you have a high voltage probe, the load from the probe itself may be
suffcient to discharge the 1 uf caps if you are patient. Charge the
cap to only a few hundred volts then put the probe on and see how fast
the cap discharges from only the probes load. If this procedes fast
enough, you can estimate how long it should take to discharge from a
higher test voltage. This has the advantage of requiring no other
equipment besides the HV probe. Make sure you read the instructions on
how your HV probe is supposed to be used, especially if it requires a
separate meter/scope. The meter may need to have a certain minimal
input impeadence for the probe to read correctly! I still have a bank
of 3 150 mfd oil filled 10KV caps that I used to discharge thru a air
gap into a coil for magnetic forming of thin sheet. They weigh about
75 lbs each. They fortunatly have built in bleeder resistors. Don't
know what kind oil they use...could be PCB I guess.
Don't dead short your caps from full voltage unless you know they are
designed to handle it. Some caps are not designed to handle the current
from such an event and might be damaged.

 

[James Waldby]

I have a bunch of 1N4007 diodes (1000v rated). If I put, say, 20 of
them in series, would that be sufficient to rectify 9,000 VAC safely?
I have read some articles discussing that since leakage amps are not
identical, that I need to put resistors in parallel with them. If so,
these need to also be 1kV rated resistors, right?

If not, would anyone have a suggestion for a 30 mA rectifier for 9
kVAC?

According to http://www.pupman.com/listarchives/1998/August/msg00143.html
"Use a MOT diode: typically they are 9kV 450mA and very cheap."
Apparently MOT means microwave oven transformer. Note, the 9kV RMS
AC of your Franceformer presumably peaks at about 13kV, so you would
need a variac on its input if using a single 9 kV diode. Also see
http://www.pupman.com/listarchives/1998/August/msg00309.html in same
thread, which implies that obvious tubes like 1B3 won't handle 30 mA.

-jiw

 

[Tim Williams]

I have a bunch of 1N4007 diodes (1000v rated). If I put, say, 20 of
them in series, would that be sufficient to rectify 9,000 VAC safely?

Nah- 9kVAC is 12.7kV peak, call it 15kV peak. The rectifier has to stand
off full voltage on the backswing, so you need 30kV diodes, minimum. 40 or
50kV would be even nicer.

If you make a doubler (which uses diodes of the same rating, but produces
twice the output voltage) you can test the capacitors at a bit over rated
voltage (maybe 26kVDC, 118% of ratings). All the caps I've bought are rated
for 150 or 200% of rated voltage for some time, though that doesn't mean
these are.

If you bring up the voltage slowly, through a resistor or variac perhaps,
you can monitor it (assuming you get a voltage probe) and stop right at 22kV
or so.

I have read some articles discussing that since leakage amps are not
identical, that I need to put resistors in parallel with them. If so,
these need to also be 1kV rated resistors, right?

Yeah, but conversely, I recall reading an article which stated that modern
diodes are avalanche rated, meaning that if the voltage across one diode
increases to say, rated PIV, current starts going up (it looks like a really
high voltage zener diode), pulling it back into balance.

Capacitors across the diodes were also recommended, but today's diodes are
more rugged to pulse and avalanche conditions (we've come a long way from
"top hat" diodes!) so this isn't necessary either.

If not, would anyone have a suggestion for a 30 mA rectifier for 9
kVAC?

Could rip the diodes out of a few TV sets/monitors. Or use the flybacks
themselves, LOL.

Tim

 

[Robert Latest]

["Followup-To:" header set to sci.electronics.design.]
On 30 Mar 2006 19:43:34 GMT,

They're not PCB-era, are
they? Because if they are, you just inherited someone else's problem.

It says "Impregnant: MIPB". That's monoisopropyl biphenyl which doesn't
seem to contain halogenes (PCB is polychlorinated biphenyl).

robert

 

[Robert Latest]

["Followup-To:" header set to sci.electronics.design.]
On Thu, 30 Mar 2006 21:44:08 -0600,

Connecting differently charged caps like these together with wires
will end up with no wires and much noise.

A great aphorism!

robert

 

[Roy L. Fuchs]

Anyway, here is my question. I have a 9 kV DC power supply. (a
Franceformer). How can I safely test these caps before selling
them.

You bought them just to resell them?

Ok, we will use ONE cap as an example.

A: You do not need to charge the cap up very far, voltage wise, to
test/verify the value of the cap.

B: If you wish to test it for leakage, you need a voltage that is
closer to the max rated value than your 9kV supply. Do you have an
old PC CRT monitor or a TV laying around? The anode voltage of those
devices are typically pretty high, and you can look the model up to
see exactly what each particular one operates at.

C: You need a high quality high voltage probe to do what you are
asking.

At 22 kV, they can store about as much energy as a .22 bullet,
according to my calculations.

I am not sure about your choice of comparative mechanisms, but you
shouldn't use these old caps at 22kV. Even when they were new.

One does NOT operate a cap AT its rated voltage (at least, it isn't
considered "proper"). They are ALWAYS placed into designs where the
applied voltage will never exceed about 70% of the maximum rated
voltage. This is true for ALL capacitors actually. Some should even
be designed in at only 50% of the expected voltage, meaning that one
should use a cap at half its rated voltage in such a case.

For testing, however, with caps that old, I would go no higher than
90% rated voltage.

It would be less at 9 kV, but still, obviously, very deadly.

This is a strange remark. I am not sure that we should be giving you
further assistance after seeing this.

So. What is a safe way to charge them, verify that they hold the
charge, and then DIScharge them at 9 kV.

The test is very simple, but the procedures are what are strict, and
somewhat difficult, and the parts requisite to construct a safe test
circumstance may be outside your budget.

If you think that your declaration that "they have been tested"
would change their value somehow, you are likely wrong. HV caps are
NOT all that easy to test, and your declaration is likely to be taken
with a grain of salt by anyone knowledgeable in HV settings.

The test:

Procedural rules.

1: YOU WILL NOT EVER work on or make changes to a live setup.
You only get to break this rule once.

2: Making "big fun" arc discharges is a bad thing for the caps, and
you supplies, and basically just not a good practice.

3: Ideally, you should have a bird cage or other large metal cage
around these test setups, and you should energize the circuits from a
distance of several feet.


Parts requisites:

A: A high quality HV probe. 40kV is typical for the level you are
at.

B: Twenty to twenty-five feet of 30kV TV anode wire, or better
quality "soft" 40kV HV wire, solid ignition wire, or hard teflon HV
hook up wire at 30kV or 40kV or even 60kV insulation strength.

C: A ten-pack or two of standard medium sized alligator clips with
the rubber sheaths.

D: A good Digital Multimeter with at least 4.5" digits.

E: Four 5" diameter pyrex dishes at about 1.5 to 2" tall.

F: About one quart of good, clean transformer oil.

G: Twenty-five ten Meg Ohm ten watt resistors at 5kV or 10kV voltage
rating (for Capacitance Value test load and Quick Discharge Wand).

H: A good anode supply at 20kV set point (use probe to set) (for HV
leak test at max voltage charge).

I: A simple, lower voltage supply (300V-500V) (for Capacitance Value
test)

J: A 3 or 4 foot length of dry wooden broomstick handle (for Quick
Discharge Wand)

K: A 2 foot length of solid #12 or #10 bus or house wire (unsheathed).

L: Some string (2 feet?) for tieing the resistor "wad" together.

M: The biggest cheap teflon cutting board you can find. (18x24, 20x30
whatever the biggest you can get is).

N: A couple or few four ounce sticks of modeling clay.

O: A stopwatch or timer capable watch.

The pre-prep:

A: Cut 4 24" lengths of the HV wire, and strip and tin both ends
carefully at a quarter inch length. If it TV anode wire, it will
likely already be fully tinned.

B: Attach (install the boots first) two alligator clips to the ends
of each wire. These are your HV test jumpers.

C: Take a short piece of the #12 wire, and make a pencil diameter
(inside) loop with a two inch tail on it. Sharpen a point on the tail
(not needle sharp, just taper it down on the end, it can even be
rounded on the point after that. A good x-acto knife will cut copper
a bit (enough for this). Bend the loop over 90 degrees. This
attaches under your HV probe's end point (unscrew it, then
re-tighten).

D: Take two of the Ten Meg Ohm resistors, and snip the lead on one
end of each at 3/8". Lay the two short cut ends together, and solder
them in "lap joint" fashion. Use a shear to cut the leads )on your
wire stripper, not cinch type snips (side cutters or diagonal
cutters). Shear cut the remaining ends at approximately 1", and use
some of the string to tie each resistor of the pair at the tip of the
broomstick handle. Two strings per resistor at their end caps (just
inside). Take an eight inch segment of the #12 inch wire, wrap two to
four turns of it around the end of the broom stick handle, and leave a
two inch length pointing off the end of it, or cut it to that length.
Lay the 1 inch resistor lead from the top resistor (closest to stick
end) along the coil of large copper wire, and solder it. Wrap the
resistors and coil with electrical tape to keep them from shifting.
Cover all four string ties, and the center node, and the end coil with
a few to several wraps at each location, leaving to remaining resistor
lead accessible. Attach one end of an eight foot length of the HV
wire to the exposed resistor lead, solder the connection, and tape
down about five inches of the HV wire to the top of the stick. You
can even zig zag it to remove pull stresses from the lead attachment.
Tape it down with several wraps, and include the remaining solder node
you just made. This should result in a stick with the last ten or so
inches taped up, and a point sticking off the end. Add an alligator
clip to the remaining end of the free flying seven foot segment of th
HV wire. This is your Safety/Quick Discharge Wand.

E: Place the cutting board on your test bench. Keep the pyrex dishes
handy as well as the transformer oil, and clay.

The set-ups:

Capacitance Value Test:

Cutting board components will be the cap under test, the probe, the
meter, one HV jumper, one pyrex dish, the medium voltage power supply
and the timer. Optional components are one or more of the load
resistors, requiring two additional HV jumpers, and one additional
pyrex dish.

The long, slow, high statistical reliability test simply uses the
probe to load the cap, and the timer to test for the discharge rate.
The probe tip, and HV jumper end go into the dish, and the leads get
held down to the cutting board by a clump of clay. Oil covers exposed
leads in the tray, and the probe rear end can be held elevated by a
empty paper towel roll tube cut to length to fit the angle that points
the probe tip down into the pyrex dish. The probe should always be in
place when energizing the test circuit/setup. Never use the probe on
live gear in "free hand" mode.

The HV jumper lead that attaches to the HV side of the cap can
remain bare, just like the cap node already is (as pictured). The
Grounded side of the cap gets a lead to the MV supply ground, as well
as the ground lead from the HV Probe (very important). The MV supply
positive lead will also go to the cap's HV node. The banana jack
probe leads go into the meter, typically set on the 10 volt range.
Again, make sure the ground lead of the HV probe is grounded to the
low side of the cap. The probe is typically 1V per 1kV. They are
generally 1 Gig Ohm loads, or that is what you should get.
You can calculate the discharge rate for a 1G Ohm load at a given
voltage on a given cap value. You can then charge the cap with the MV
supply, read the voltage on the meter, the remove th MV source lead,
and time the discharge period to verify the cap value.

The alternative would be to fashion a set of the load resistors in
series, tie the bundle together, immerse it in a second pyrex dish
with transformer oil in it. Attach the HV jumper from the cap to one
end, and from the other end to the grounded side of the test setup.
Attach the remaining HV jumper to the HV cap output node, and to the
HV Probe dish. This presents your load resistor as well as the HV
probe's loading value to the cap. Charge it up, and time the new,
quicker discharge rate, calculate cap value. Test(s) complete.
Always ensure that meter reads zero volts before touching any setups.
A good practice is to take the discharge wand, and attach the lead
clip to ground, and touch the pointed barb to the immersed node in the
pyrex dish for a few seconds.


High Voltage Max Charged Leak Test:

Need: One dish, probe, meter, HV supply (danger)

Test: Without cap, attach ground lead of probe to ground side of HV
supply. Attach high side of supply to probe tip in oil bath. Turn on
meter. Turn on HV Supply, and set output to 20kV. Turn off supply.
Ensure that meter reads zero volts before touching anything, or use
the discharge wand to ensure that there are no charges hanging around.
Place the cap on the cutting board, and attach the ground lead from
the HV supply to it. Attach the HV supply output lead to the cap HV
node. Attach the HV jumper from the probe dish to the cap's HV node.
Make sure that the HV probe ground lead is attached to the HV Supply
ground lead. Turn on meter. Turn on HV supply (use single hand/hand
in pocket techniques). Read meter. If cap is bad it may arc
internally, but will discharge into the HV probe load at a much higher
rate than expected. Use wand to discharge after testing, and always
reattach shorting jumper that ALL of these caps should have on them
(remove them of course during testing)This test isn't 100% definitive
or ideal.

Testing to only 9kV will not allow you to declare that "they have
been tested" with any validity if that is your goal, since as you say,
you are selling them.

See... it isn't as easy as it appears.

 

[Roy L. Fuchs]

They're not PCB-era, are
they? Because if they are, you just inherited someone else's problem.

You obviously didn't look at the auction page very well.