DIYbanter - Safely testing 22 kV capacitors

On Thu, 30 Mar 2006 19:19:12 GMT, Ignoramus27088
Gave us:

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.

On Fri, 31 Mar 2006 10:17:49 GMT, Roy L Fuchs wrote:
On Thu, 30 Mar 2006 19:19:12 GMT, Ignoramus27088
Gave us:

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?

Yes, although I will probably keep one for myself.

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.

Yes, you are right, it is indeed not easy. Thank you for your post, I
saved it for future reference.

i