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High Voltage Test Equipment




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From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
Sent:  Thursday, March 05, 1998 11:21 PM
To:  Tesla List
Subject:  Re: High Voltage Test Equipment

Jim,

At 07:11 PM 3/5/98 -0600, you wrote:
>
>----------
>From:  Homer Lea [SMTP:HomerLea-at-aol-dot-com]
>Sent:  Thursday, March 05, 1998 2:05 AM
>To:  tesla-at-pupman-dot-com
>Subject:  Re: High Voltage Test Equipment
>
>In a message dated 98-03-05 00:46:30 EST, you write:
>
>> From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
>>  Sent:  Wednesday, March 04, 1998 5:22 PM
>>  To:  Tesla List
>>  Subject:  Re: High Voltage Test Equipment
>>  
>>  Jim,
>>          Having just gone through the HV voltage divider design zoo with my
>>  equipment, I have one caution.  At 60Hz the long string of resistors will
>>  work fine.  However, if you wan't to measure voltage waveforms at say
>200KHz
>>  the frequency response will be bad.  I am now persuing vacuum molded epoxy
>>  encapsulation to get small size, reasonable power dissipation, and high
>>  frequency response.  Your oil bath should do the same just a little more
>>  "fluid" :-)  Do try to make it very compact.
>>  
>>          Terry
>>  
>  Terry:
>I just sent off new specs:
>-------------
>post script: I ended up getting 400 15meg resistors. They are small (1/8)
>watt. My plan is to string them in series, put them in a Tygon tube and fill
>with oil. I will coil up the tube so it isn't 20 feet long. I assume the
>inductive reactance will be zilch compared to the 6 billion ohms of resistors
>The resistors will be in series with a  50 or 100 ua meter connected through a
>full wave rectifier bridge. Does anyone know how much voltage I can put across
>each resistor?? I am hoping for at least 500 v each and dreaming of 1000 v.
>------------------
>A 20 foot tube it not small, even coiled up. Is that going to screw me up? My
>original thought was simply to measure the output voltage of coils rather than
>wave forms.
>jim heagy
>
>

Hi Jim,

        My latest voltage divider is 1 inch long!  I thing you and I will
have the length extremes covered :-))  1/8th watt surface mount resistors
are typically rated for 400V max.  However, in oil, I would push that to
4KV!  (I used to build the damn things).
        You will have a little trouble getting the resistor string in the
tubing but I can help there.  Using air (pressure or vacuum) blow (or suck)
a fuzzy string through the tubing.  Once through, you can pull the resistors
into the tube using the string and some TLC.
        I would use an op-amp circuit to amplify and rectify the signal from
the resistors.  Common bridge rectifiers have voltage drops and minimum
currents that might mess with your system. I would suggest 1N34 diodes
(Radio Shack 276-1123) if you use a rectifier.  They will give good
performance (I hope).  If the resitors are thick film surface mount types I
would use them in a straight line.  If not, talk to Jim Lux.  He knows much
more than I about this.
        I would not commit all the resistors to the first test.  6G ohms is
high for any voltage.  Fewer resistors may work better.  If you could
explain a little more about what you want to measure and how I could give
suggestions on this.
        It will be very interesting to see what you come up with and how it
works.  I have not heard of anyone actually trying this.  Much will be learned.

        Terry