In order to charge up the capacitors to 10 kV I had to make my own power supply. The supply consists of a 0-140 Variable Transformer, a 120 to 14400 instrument transformer and rectifier circuit that feeds only the positive voltage peaks to the capacitor bank. The rectifier is a half-wave rectifier. I chose a half wave rectifier in order to keep everything as simple as possible.
This particular circuit is small enough that most of the component data prices, and performance values all fit on one page. The power board is layed out on a polyethylene board with plenty of spacing between components to avoid creepage breakdowns. The maximum potential across an air gap and the maximum creepage potential is 3 V/mil, this maximum occurs across the diodes. All other areas of the boards have lower potentials across any given area. The board is also fitted with a 0 to 0.5 Ampere meter circuit to measure charging current, and a circuit to measure voltage up to 10 kV. The large brown tubes at the top of the board are 1 kOhm wire wound resistors. The 5 blue rectangles at the left are the 5 MegaOhm resistors, each one is across a pair of high voltage diodes. The resistors on the right hand side serve as dissipation resistors and a means to draw a small current for the voltage meter. The capacitor bank has additional power dissipation resistors.
One of the capacitors was marked "Charged to -10kV" do not use. I believe all the caps came off the same bank of 30 or so, but only one was marked. Considering how old these caps are, and the fact the charging them 100% in the wrong polarity shortens their life considerably, they probably won't last long. However, I'm not going to be firing them too much, so I'll stay away, cross my fingers and have a fire extinguisher close by when I use them. I believe explosion is a common failure mode for these types of caps.
visitors since June 10th, 2005.
