You can't use an Ohmmeter to test high voltage rectifiers. You can use a
Megger or Hipot tester, which provides substantial high voltage applied to
the rectifier to monitor the breakdown voltage (apply reverse DC voltage,
crank it up and see when the rectifier avalanches into reverse conduction).
With a microwave oven rectifier, this would normally be in the 6kV-10kV
range. Unless you can apply that much bias, you have no idea if the
rectifier is good or not.
Usually, you can't even test to see if the diode junctions are intact using
only an Ohmmeter, because the Ohmmeters usually don't provide enough test
voltage to forward bias all those series junctions into conduction.
Assuming 0.6 to 1.0V per diode junction, and probably 10-15 junctions in
series per rectifier, it will take 6 to 15Vdc to make the junctions start
conducting in the forward direction. My Ohmmeters only deliver about 3Vdc,
not enough.
But, the "forward conduction" test isn't very meaningful, anyway. It just
shows there's a junction there, but not whether it's leaky or damaged.
WB2WIK/6
"Success is the ability to go from failure to failure with no loss of
enthusiasm." -Winston Churchill
> -----Original Message-----
> From: Gary Smith [SMTP:mandolinist@ameritech.net]
> Sent: Friday, March 14, 2003 7:56 AM
> To: Amps@contesting.com
> Subject: [Amps] reading 8-10kv with a digital multimeter?
>
> Hi all,
>
> Not quite related to amps exactly but I need a HV solution someone here
> might be
> able to help me with.
>
> I need to check diode integrity of some microwave oven diodes. I'm trying
> to build an
> two electrostatic type filters & need a + & - HV supply. I'm going to get
> the HV via a
> neon transformer rated at 6.3kv @ 30ma. I've obtained two hv diodes from
> microwaves put out to curb for pickup. The only device I have to check
> them is a
> Radio Shack digital multimeter cat # 22-812 & it will register a max of
> 1kv DC & 750V
> AC. I suspect the diodes are a string of diodes and aren't indicating
> anything when I
> test them with the ohm meter & "diode checking function" of the meter.
>
> I would like to use this multi-meter to tell me if the diodes are intact
> and would also
> like to observe the voltage characteristics when this project is under
> load. I don't
> have a high voltage probe & am thinking that I might be able to get a
> decent reading
> if I use a resistor in series with the probe.
>
> Might someone have a suggestion of what I can do from here to accomplish
> this?
>
> Thanks
>
> 73,
>
> Gary
> KA1J
>
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