High Voltage Diodes

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: High Voltage Diodes
From: Tesla List <tesla-at-stic-dot-net>
Date: Mon, 2 Mar 1998 23:47:49 -0600
Approved: tesla-at-stic-dot-net


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From:  Thomas McGahee [SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent:  Sunday, March 01, 1998 5:30 AM
To:  Tesla List
Cc:  tank-at-magnolia-dot-net
Subject:  Re: High Voltage Diodes



> From:  RODERICK MAXWELL [SMTP:tank-at-magnolia-dot-net]
> Sent:  Saturday, February 28, 1998 12:15 PM
> To:  tesla-at-pupman-dot-com
> Subject:  High Voltage Diodes
> 
> I have four 15Kv-at-750ma microwave oven diodes that I plan on using in a
> Dc supply for my new tesla coil. When I test them with my ohm meter they
> all read infinite resistance even when I reverse the leads. Is this a
> property of high voltage rectifier diodes??? These are new diodes that
> have not even been used in a circuit yet. All of my experiance has been
> with the lower voltage variety. If anyone has used these type of diodes
> before, HELP!
> 
> 
> 
>                                   Frankensteins Helper
>                                           Max
> 
Max,
Many high voltage diodes are actually stacks of diodes inside a single case.
Each one of these will have a forward voltage drop of about .7 volts. Most
diode stacks in the size you have are composed of 1KV diode elements in series.
So I would guess that you have about .7x15 volts worth of diode drop. You would
have to apply a voltage greater than about 12 volts to get the stack to begin
conducting. 

I usually test such diode stacks by applying 120VAC to the diode assembly with
a
100K 1 watt resistor in series. Then I see if I get DC across the resistor. If
so, I assume the stack is OK. The resistor is just to supply a small load and
so I keep the value high so the power dissipation is low.

With really high voltage stacks like 100KV units you might have to apply
several
hundred volts to achieve conduction.

Hope this helps.
Fr. Tom McGahee