Hi Pot tester schematic

Posted on Feb 5, 2014

The design is based loosely on some ideas from K8CU and AG6K. However, I have simplified the circuit somewhat and used different components. The mechanical encapsulation is also different. I used LTspice to verify the tester before building it. The schematic is from the LTspice simulation (see below). I have also posted the simulation files so you

Hi Pot tester schematic
Click here to download the full size of the above Circuit.

can load them into your own LTspice simulator. The unit consists of a 700VA 12KV AC RMS output (nominal) center tapped neon sign transformer that I purchased on Ebay. The trafo was designed for less than 230V AC RMS nominal primary voltage. Therefore the transformer gives out a bit more than 12KV AC RMS when supplied from the 230V AC RMS mains in Norway. After the rectifier I get approx 17-18 KV DC. The transformer is simulated by a sine voltage source in LTSpice. The transformer is insulated from ground in the tester for safety reasons. The schematic shows a gnd connection but that is only to get the Spice 3F4 solver to accept the netlist. It is recommended to insulate your tester from ground if you build one. There is a variac (not drawn on the schematic) in front of the transformer and the input is current limited by two 100W light bulbs in parallel (bulbs not drawn on the schematic). The voltage metering circuit is a uA meter with a shunt resistor and the current measurement instrument is a std. 100uA instrument protected by back to back diodes (not drawn on the schematic). The instruments are at high potential so adequate protection must be implemented to prevent arcs to the operator. The device under test (DUT) is drawn. Note that a working tube has much higher resistance than 100 megs that is the load in the simulation. However this is placed as a load test for the simulation to check smoothing of the output...

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