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Posted to rec.crafts.metalworking,sci.electronics.design
oldjag
 
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Default Safely testing 22 kV capacitors


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.

Ignoramus27088 wrote:
Got myself some capacitors for $10 apiece.

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=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...tem=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.

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

i