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Measuring C, HV Resistors, etc.
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From: Steve Young [SMTP:youngs-at-konnections-dot-com]
Sent: Saturday, June 06, 1998 11:42 PM
To: Tesla List
Subject: Measuring C, HV Resistors, etc.
To all,
1) Every now and then, someone posts their need for inexpensive way to
measure C. A great source for all sorts of parts is Tech America. Their
catalog is available at Radio Shack, or you can get one via their website
at www.techam-dot-com. They sell a kit (part number 990-0043) for $13 which
lets one use a DVM to measure 2pf to 2 mf.
2) Occasionally, coilers indicate a need for HV resistors. If you don't
mind a lot of soldering, you can make your own very cheaply. Tech America
sells resistors for 100 for a dollar. Use 1/2 watt resistors which have a
rating of 350 volts. For example, suppose you have a 20,000 ohms per volt
meter which can measure 5 KV, but you want to measure up to 15 KV. Just
add 67 3 meg 1/2 watt resistors (200 meg) in series with the test lead and
presto, you have a 15 KV meter. Cost is 67 cents. The resistor string
will be good for at least 23 KV and can dissapate 20+ watts. Be sure to
arrange the ends of the resistor string so the HV doesn't flash over
possibly resulting in a fried meter. It would help to put the string in
oil to reduce corona and improve heat dissapation.
If you don't care about the exact value of the HV resistor, then another
easy solution is to use plastic tubing filled with tap water. Push wires
through plugs in the ends of the tube. Such resistors work great in a Marx
generator, for example. Just be sure the wires in the tube are at least a
few inches apart so they don't arc over and explode! Even though the
resistance is not very predictable, you can still make an accurate voltage
divider. For example, a hundred foot hose with a electrode pushed through
at the 1 foot spot would make a 100:1 voltage divider which could handle
many KV.
3) Tech America has just started carrying a line of Amidon toroidal cores.
Biggest ones are 2 inches O. D.
--Steve