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HV Resistors for HV measurement....

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Pinky's Brain
Sun Dec 19 2010, 03:28AM
Pinky's Brain Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
Patrick wrote ...
The resistors are expensive/hard to find...
What's wrong with VR37 resistors? They can hold off 3.5 kV according to the sheet and cost only 12 bucks for 100 33M resistors at digikey.
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Patrick
Sun Dec 19 2010, 03:37AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
 		i thought the horizontal pieces in your drawing were the most significant areas. i normamlly just use a copper foil tube.
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Pinky's Brain
Sun Dec 19 2010, 04:02AM
Pinky's Brain Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
 		That is just if you want extra capacitance ... stray capacitance affects the capacitive part of the divider as well, the total capacitance of the divider has to overwhelm the stray capacitance. If you build say a 1 meter high one with 10 resistors you'd probably want 50+ pF per resistor, without the horizontal part you won't get there.

Also there is one potential problem ... at high frequency nearly the full voltage difference gets coupled to a small central part of the resistor (the shielding you have now has the same problem, at high frequency all the voltage is across the top of the resistor). You probably want a piece of wire in the middle with resistors above and below, also the centering has to be relatively precise or you will get errors in the cross over from resistive to capacitive division.
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Patrick
Sun Dec 19 2010, 04:23AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Pinky's Brain wrote ...

Patrick wrote ...
The resistors are expensive/hard to find...
What's wrong with VR37 resistors? They can hold off 3.5 kV according to the sheet and cost only 12 bucks for 100 33M resistors at digikey.
dam i wish someone would have told me about thosew awhile ago before i soldered together a 200 piece 10M resistor string!
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Patrick
Tue Feb 08 2011, 05:07AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
 		We all know HV resistors are like nuclear weapons, you can never have too many.



Here is my stock pile which will contribute to my other threads here on the forum.
1297141614 2431 FT102386 Sam 0346croppedtext

1297141614 2431 FT102386 Sam 0348croppedtext

1297141614 2431 FT102386 Sam 0350croppedtext



1297141614 2431 FT102386 Sam 0371croppedtext



1297141614 2431 FT102386 Sam 0375cropped
A 225kV, 3Gohm resistor string, from Del HV, (now Spelllman) C7817 unit.


1297141614 2431 FT102386 Sam 0378croppedbins
Storage !
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radhoo
Tue Feb 08 2011, 10:53AM
radhoo Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699
 		Those are some really nice components. I'm still using the blue ones/first pic. They are doing a decent job.
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Patrick
Tue Feb 08 2011, 05:38PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
radhoo wrote ...

Those are some really nice components. I'm still using the blue ones/first pic. They are doing a decent job.

TY! These will go towards oscillscope probes:

300M for 24kV, 2 Probes---> [ 80uA @ 30kV ]
400M for 30kV, 2 Probes---> [ 75uA @ 30kV ]
800M for 60kV, 2 Probes---> [ 75uA @ 60kV ]
1.40G for 100kV, 1 probe--> [ 71uA @ 100kV]

My lower current limit is 20uA (for good saturation of the DMM silicon A/D), my upper current limit is determined by power loss and heat gain.
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Proud Mary
Tue Feb 08 2011, 06:19PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
 		There are some parts that are so hard to get - at flea market prices, that is - that I just buy them on the likelihood of their being needed at some future date, and then forget that I have them and buy them all over again!

I found a box of Russian 1GΩ 40kV 10% in the back of a roll top desk, and can't think how they got there. But I'm glad that I have them all the same! smile

They're not half as nice as your Vishay 1%, though the 40kV rating is a strong case for using them.
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Patrick
Tue Feb 08 2011, 06:27PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...

There are some parts that are so hard to get - at flea market prices, that is - that I just buy them on the likelihood of their being needed at some future date, and then forget that I have them and buy them all over again!

I know how you feel! For what you see in the above 5 pics, I spent $130. amazed cheesey amazed cheesey

I also have some 25kV and 45kV, USSR made in 1980, tiger stripes that should be here in 2 days.
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Proud Mary
Wed Feb 09 2011, 12:20PM
Proud Mary Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...

Proud Mary wrote ...

There are some parts that are so hard to get - at flea market prices, that is - that I just buy them on the likelihood of their being needed at some future date, and then forget that I have them and buy them all over again!

I know how you feel! For what you see in the above 5 pics, I spent $130. amazed cheesey amazed cheesey

I also have some 25kV and 45kV, USSR made in 1980, tiger stripes that should be here in 2 days.


Steady yourself with a glass of brandy before looking at Farnell UK's list of 50kV resistors. The cheapest (or do I mean the least expensive?) - 220MΩ 1% 50kV - cost £50.27/US$80.73 each, whilst the most expensive - 5MΩ 10% 50W 50kV - be a mere snip at £259.58/US$416.88 - though in all fairness I should say that this price falls to £173.06 each if - when - you buy 10 or more...

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