Jay,Designing a high voltage divider for TC use is a decidedly non-trivial exercise.
Problem is that you are dealing with radio frequency currents. At high frequencies, you have to consider the capacitance and inductance of every component, not just the resistance. Every little carbon film resistor has a significant capacitance which lowers its apparent impedance, and there is equivalent inductance associated with the spiral resistor film which increases its impedance. You can get all kinds of interesting effects due to the parallel R, L, and C components of the impedance of an ordinary 1/4 watt carbon film resistor.
Precision measuring circuits start with non-inductive resistors, which are rare and tend to be expensive. Another approach is to use a capacitive divider. I have a Jennings capacitive HV divider made for RF measurements which is made with two specially designed glass vacuum caps, with a 1000:1 cap ratio, giving an approximately 1:1000 voltage division. However, the nameplate indicates that you have to figure in the capacitance of the coax lead to your oscilloscope, as well as the input impedance of the scope in order to accurately determine the voltage division ratio. Still, it's only rated to 20 kV.
The caps have an interesting electrode design apparently designed to minimize their inductance.
You would probably be better off starting with a pair of vacuum caps snagged off eBay or from a Hamfest. They will have better HV characteristics than a string of carbon film resistors, and their division ratio may be a little easier to determine. Still, building something that will work reliably with the 100s of kV associated with a TC discharge will be a difficult project.
HTH, Dave jhowson4@xxxxxxxxxxx wrote:
hey I was wondering if it was possible to make a voltage divider capable to measuring the voltage from a medium sized tesla coil...with resistors from say radio shack. i found some information online and everyone seemes to be using about 10 of those huge high power resistors. What if I used like a hundred normal resistors? since i can buy alot for really cheap from a friend. just wondering thanks, Jay Howson
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