Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Watch that PIV
Date: Feb 01, 10:29 am
Poster: Richard Hull

On Feb 01, 10:29 am, Richard Hull wrote:


A number of us make our own power supplies. Be advised that the gas load variation on fusors can have a voltmeter reading of 18kv and should the chamber flash or quench, the instantaneous voltage can soar to exceed the PIV rating of your diodes.

The above hap;pened here this weekend as I was approaching 20KV. The system flashed and quenched and immmediately my voltage plunge to 2 KV and stayed there. I initially thought I had arced an insulator internal to the chamber, but on close examination, one of my 2 20KV piv silicon rectifiers was hot and, therefore, shorted.

This is not a problem for me as I had several spares, but those who don't have such spares would be well advised to stay at least 6 KV below the top PIV rating of your diodes or put in higher PIV units before venturing upward in voltage and power.

Three common microwave oven diodes in series are theoretically bale to handle 26kv PIV. It is wise to place a 100meg 2 watt special HV resistor across each one to equalize there voltages.

Resistors needed for high voltage work are special and very pricey if purchased new. Check surplus catalogs and ham fests. Every now and then some really good buys come up.

Richard Hull