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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Please comment if you see a better way of doing things!
This is my first project thread post! I intend to show how I build/enclose resistors and resistive HV dividers. And then show how I have made measurements of HV. Let's get going!
The basic components, made by Vishay/Dale. ROX150 200M FKLBS -- 200Mohms, 11kV resistors
"FKLBS" suffix is defined as : -- Tolerance +-1% -- TCo, 100ppm -- leads are Tin/Pb, Lacer -- Solid Body, Axial, AL2O3
They are definately inductive.)(they are inductive but it seems to not cause any problems.)
If you absolutley positively have to have plastics joined for critical purpose and function, then this PMMA is the best epoxy ever!!!
components for case, terminal and resistor. --Notice the hole in the all thread stud. solder filled. --The all thread is 1.6" long, 10-24, steel. --Endcap is 3/4", PVC.
All pieces disassembled for cleaning. --all pieces cleaned with acetone, flux, dirt, and ink on PVC washed away. --Zig-zags in the leads keep the resistor and its leads near center. --notice the flats, filed into the endcaps, a flat place for the nut and washer to live.
Dry fit of all but the tube, checking form, fit, and function. --Acetone is used to de-gloss the PVC just before epoxing. --Acetone also sensitizes the PVC.
Measurment and cutting of the tube body. --Tube itself if 4.17" long. --The two blue lines are 0.800" from each end. --PVC pipe is 3/4" schedule 40. rated for 480 PSI I think.
Epoxied the left most side. --you could use normal PVC solvent glue to attach the endcaps, but you would need epoxy the hole.
Vertical ready for dielectric fluid. --cleaned with compressed air, for de-particle.
Vertical, filled with extra light olive oil. --Olive oil was chosen because of all food oils it changes its electrcal properties the least when exposed to copper/tin. --Olive oil has a Dielectric strength similar to other oils, 300-500 volts/mil, i use the 300v/mil number. --Olive oil is most resistent to oxidation changes. --Olive oil is the most expensive, so use it wisely! --Less then 5% of volume was headspace, dry air was prepared.
Yet again.
Final device, yay! --this device does work as intended --the oil mass keeps the 100ppm Tco from changing fast, more thermally stable then if only expose to air.
IMPROVEMENTS! : (Updated on 12/17/2010)
This is again the basic design, all-thread rod (10-24), soldered to leads.
Here's the lesson learned from the previous attempt: The Problem: -- When filled with oil, then pressing the cap on caused oil pressure to rise, eventually bursting through the all-thread/epoxy endcap. The solution: --I put the whole thing together with epoxy, and without oil. Then after the epoxy setup I drilled and tapped a 1/4-20 screw hole, then filled the body tube with oil. With proper headspace the hole was sealed with a nylon threaded set screw.
Next, the area was cleaned with Acetone. More epoxy prepared and a curved PVC "cap-patch" was put over that nylon screw. Presto! liquid tight!
The labels are temporary. I will make better ones with my laser printer, then laminate them.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I bought 5 of those same resistors. I figured since 2 other forum members (you and Radhoo) had them, why not! I will use 5 in series for a 50Kv meter for X-rays.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...
Nice work, Patrick.
TY!
Arcstarter wrote ...
I bought 5 of those same resistors. I figured since 2 other forum members (you and Radhoo) had them, why not! I will use 5 in series for a 50Kv meter for X-rays.
Keep up the good work!
Remember that these are inductive but at a few uA maybe this does not matter. Caddock makes better resistors, but they are hard to have made for one peson, though Caddock spent several hours on the phone with me, knowing I was only a student not a corp. Caddock is top notch.
I was hoping to put two ressistors in "anti-series" to cancel out the inductance entirely.
radhoo wrote ...
hope we can get some good results if we do this together.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I've used 1G 40kV Russian resistors as R1 in simple divide-and-measure strings, but the ones I have are scattered over plus minus 5% and sometimes worse, so it's always meant measuring their resistance individually, and then calculating the value of R2 to preserve the 1000:1 ratio.
Whether this extra time and trouble is worthwhile or not I have no way of knowing, and am slightly sceptical about G-ohm measurements, because there are so many potential leakage paths shunting the main resistor.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Patrick wrote ...
Proud Mary wrote ...
Nice work, Patrick.
TY!
Arcstarter wrote ...
I bought 5 of those same resistors. I figured since 2 other forum members (you and Radhoo) had them, why not! I will use 5 in series for a 50Kv meter for X-rays.
Keep up the good work!
Remember that these are inductive but at a few uA maybe this does not matter. Caddock makes better resistors, but they are hard to have made for one peson, though Caddock spent several hours on the phone with me, knowing I was only a student not a corp. Caddock is top notch.
I was hoping to put two ressistors in "anti-series" to cancel out the inductance entirely.
radhoo wrote ...
hope we can get some good results if we do this together.
Yeah I would like to collaborate.
Does the inductance really matter with CW DC measurements? This would be used with an LOPT and X-ray tube (or whatever tube i torture into making me some X-rays) load.
Here is a stupid question that i am far too embarrassed about to post my own thread, but, i have a 50mv full scale deflection analog meter... What does that mean for current? Is it 50ma full scale deflection, or does the voltage really have nothing to do with current without a shunt resistance? If it was a 50ua meter i could just series the 5 resistors for a 50kv meter. Not like it matters, but it came with a 50mv @ 500 amp shunt.
I have never had an analog meter before, and apparently i need to be spoon fed.
I guess i will just use a 1.1M resistor and a 10M internal impedance DMM with manual ranging in parallel for the measuring resistance. Proud Mary suggested that one, so i am inclined to think that would work better than anything else i could come up with .
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Proud Mary wrote ...
I've used 1G 40kV Russian resistors as R1 in simple divide-and-measure strings, but the ones I have are scattered over plus minus 5% and sometimes worse, so it's always meant measuring their resistance individually, and then calculating the value of R2 to preserve the 1000:1 ratio.
yep, I do the same. but my meter tops out at 100Mohms.
Proud Mary wrote ...
Whether this extra time and trouble is worthwhile or not I have no way of knowing, and am slightly sceptical about G-ohm measurements, because there are so many potential leakage paths shunting the main resistor.
YES, YES, I too am suspicious of Giga- and Tera- ohm devices/measurements, for the same reason. most of the North Star/Tektronix/others, use 200M to 800M for 80kV or less, only when they measure above 100kV do i start to see 1.6Gohm dividers. And yes such a small current, can be influenced by any bogus sources-like radio waves.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Sounds about right... 400Mohm it is! That is fine, 125uA, 6.25 watts shared between 2 5 watt resistors... And that means more current so less false readings. Sound fair enough? I can use the other 3 for something else.
EDIT: Well, these resistors are rated for only 11kv, so 22kv would be the rating of the seriesed resistors. That is half of 50kv . But it takes 31.7kv to reach the rated dissipation, so does that mean that putting the resistor under oil would allow them to see much higher voltage? I was hoping to do this without oil, but it's fine if i do need it.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Arcstarter wrote ...
Sounds about right... 400Mohm it is! That is fine, 125uA, 6.25 watts shared between 2 5 watt resistors... And that means more current so less false readings. Sound fair enough? I can use the other 3 for something else.
Yes, I was thinking 400M too! But I measure AC @10 kHz so I want to put one with its resistence path CW, and the other CCW, in series thus canceling the inductance.
Arcstarter wrote ...
EDIT: Well, these resistors are rated for only 11kv, so 22kv would be the rating of the seriesed resistors. That is half of 50kv . But it takes 31.7kv to reach the rated dissipation, so does that mean that putting the resistor under oil would allow them to see much higher voltage? I was hoping to do this without oil, but it's fine if i do need it.
I dont know, but I was told by Caddock via phone, that thier resistors are rated for the qouted number of Vmax, or heat (temp) dissipated, which ever comes first, so above a certain voltage you are V limited, below that number you are heat limited. But why not call them?
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HV Resistors for HV measurement....
I figured since 2 other forum members (you and Radhoo) had them, why not! I will use 5 in series for a 50Kv meter for X-rays.
. But it takes 31.7kv to reach the rated dissipation, so does that mean that putting the resistor under oil would allow them to see much higher voltage? I was hoping to do this without oil, but it's fine if i do need it.