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Re: [TCML] Testing HVdiodes


The HV diode modules contain strings of ordinary diodes in series inside. If you have an 80 KV model, you would have at a minimum (80) 1KV individual diodes in series inside, and perhaps more, if the maker added them as a safety factor.

Each individual diode would have a typical forward voltage drop of 400 - 600 millivolts, depending on temperature, so you would have to apply a minimum of 32 - 48 volts to begin seeing conduction in the forward direction.

I would hook the diodes to a DC power supply capable of delivering 100 - 150 volts, through a 1K ohm current limiting resistor and a DC milliammeter. As you increase the voltage to a point above where the diodes all start to conduct, you will register the onset of current flow through the string on your milliammeter. That will prove that the diodes are working in the forward direction.

To test the reverse blocking capability of the string is a bit more challenging. No diodes are perfect, and they all leak a few microamps in the reverse direction. To test the reverse blocking capability of the diodes, you would have to have an 80 KV or more DC supply, a big 10 megohm Tiger Stripe power resistor (not easy to find) and a meter reading in microamps. You would ramp up the applied voltage in the reverse direction, and see how many microamps pass in the reverse direction as the applied voltage approaches the rated working voltages.

_Note that in this setup, you must not touch any component of the test rig, including the meter, when it is energized._

From the reverse current at rated voltage, and your computer voltage drop across each diode in the string, you could compute the power dissipated in the reverse direction, and see how it compares with the specs for individual diodes when reverse biased. In general, diodes, don't like to dissipate a whole lot of power in the reverse direction before they start to fail.

To simplify, if the diodes have a reasonable voltage drop when forward biased, and appear to be open circuit when reverse biased, then you can probably assume that they are satisfactory for your HV application.



On 8/12/2014 10:21 PM, mddeming--- via Tesla wrote:
Hi All,

I recently picked up a couple of diodes (5" black plastic rectangular rods) rated 200 ma @ 80 KV. A standard diode checker doesn't seem to work with ones this big. Is there an easy way to test them before they go in the circuit?

Matt D.

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