source for good HV resistors?
YoshiEggz, Wed Feb 14 2007, 06:58PMI bought a bunch of doorknob caps rated at 40Kv each and built a makeshift marx generator with it. It works good but the resistors tend to break down near the end stages. I am starting with 5Kv from a NST and using six stages. my resistors are 1meg 2 watt carbon style.
Does anyone know a good source for resistors that will work in my application? I looked on Ebay and the glass "tiger-stripe" ones are very expensive and I think overkill for my application?
Re: source for good HV resistors?
J. Aaron Holmes, Wed Feb 14 2007, 08:21PM
I haven't built a marx before so I can't speak from experience, but there was talk in the not-too-distant past about using homebrew water resistors as well as black rubber for the resistors in a marx. The black rubber idea was pretty intriguing. A search of the archives would probably turn it up.
Another option would probably be to just stack the small carbon resistors, but use corona rings at the ends and in between sections to keep things from corona-ing to death. Maybe you're already doing that, though.
Regards,
Aaron, N7OE
J. Aaron Holmes, Wed Feb 14 2007, 08:21PM
I haven't built a marx before so I can't speak from experience, but there was talk in the not-too-distant past about using homebrew water resistors as well as black rubber for the resistors in a marx. The black rubber idea was pretty intriguing. A search of the archives would probably turn it up.
Another option would probably be to just stack the small carbon resistors, but use corona rings at the ends and in between sections to keep things from corona-ing to death. Maybe you're already doing that, though.
Regards,
Aaron, N7OE
Re: source for good HV resistors?
Marko, Wed Feb 14 2007, 08:29PM
I didn't try building a marx yet, but vulcanised rubber indeed seems to work quite well as a resistor and is easy to use.. just cut two strips and arrange the caps on it!
It may, although, have too high resistance per cm for our liking, so you may need to mount the 'electrodes' just few mm from each other. I didn't try it on a marx, so I don't know.
Marko, Wed Feb 14 2007, 08:29PM
The black rubber idea was pretty intriguing. A search of the archives would probably turn it up.
I didn't try building a marx yet, but vulcanised rubber indeed seems to work quite well as a resistor and is easy to use.. just cut two strips and arrange the caps on it!
It may, although, have too high resistance per cm for our liking, so you may need to mount the 'electrodes' just few mm from each other. I didn't try it on a marx, so I don't know.
Re: source for good HV resistors?
Nik, Wed Feb 14 2007, 08:47PM
I belive hot glue works to prevent flashover as long as you aren't going for good looks.
Nik, Wed Feb 14 2007, 08:47PM
I belive hot glue works to prevent flashover as long as you aren't going for good looks.
Re: source for good HV resistors?
..., Wed Feb 14 2007, 11:59PM
Hot glue should never be used for anything with an H or a V in the name. Trust me.
I have found silicone caulk to work pretty good. With my homewound flyback transformer I used OH transparencies and clear silicone to insulate it, nd haven't had a flashover even putting out 20kv at .5mhz
..., Wed Feb 14 2007, 11:59PM
Hot glue should never be used for anything with an H or a V in the name. Trust me.
I have found silicone caulk to work pretty good. With my homewound flyback transformer I used OH transparencies and clear silicone to insulate it, nd haven't had a flashover even putting out 20kv at .5mhz
Re: source for good HV resistors?
ShawnLG, Thu Feb 15 2007, 05:43AM
"Hot glue should never be used for anything with an H or a V in the name. Trust me."
What happens when you mix the two? I thought It would be a good potting agent. I have never used the stuff for HV.
ShawnLG, Thu Feb 15 2007, 05:43AM
"Hot glue should never be used for anything with an H or a V in the name. Trust me."
What happens when you mix the two? I thought It would be a good potting agent. I have never used the stuff for HV.
Re: source for good HV resistors?
..., Thu Feb 15 2007, 06:41AM
Well, it starts to conduct at a few kv, then it starts to boil... I suppose there is probably glue that doesn't conduct, but I haven't found it
I am not sure if it is just the capacitance of it and me using AC, but hot melt glue is not a good potting agent. I have completely killed operation of 3 things I built by using it
..., Thu Feb 15 2007, 06:41AM
Well, it starts to conduct at a few kv, then it starts to boil... I suppose there is probably glue that doesn't conduct, but I haven't found it
I am not sure if it is just the capacitance of it and me using AC, but hot melt glue is not a good potting agent. I have completely killed operation of 3 things I built by using it
Re: source for good HV resistors?
Electroholic, Thu Feb 15 2007, 06:47AM
the black rubber stuff has actually too low a resistance for marx applications.
as for my marx, im using 3 X 500k 2W metal film in series.
mines 20kv per stage btw.
Electroholic, Thu Feb 15 2007, 06:47AM
the black rubber stuff has actually too low a resistance for marx applications.
as for my marx, im using 3 X 500k 2W metal film in series.
mines 20kv per stage btw.
Re: source for good HV resistors?
Marko, Thu Feb 15 2007, 02:18PM
It depends heavily on rubber type and 'hardness' of vulcanisation. Some small rubber bands I have here measure few hundred kiloohms per centimeter, while some enforced black rubber 'tape' I couldn't measure at all, <2000 megaohms.
But it did conduct, although poorly, when I hooked an obit to it.
I guess it doesn't conduct until voltage is high enough to ''arc over'' between conductive particles in the strip, similary as ferrite.
Some 'surface tracking' could be seen at points where I stabbed the electrodes, so I don't know if it would be best for a marx.
I think it's better idea to find some lower resistance rubber and use longer strips if needed.
Marko, Thu Feb 15 2007, 02:18PM
the black rubber stuff has actually too low a resistance for marx applications.
It depends heavily on rubber type and 'hardness' of vulcanisation. Some small rubber bands I have here measure few hundred kiloohms per centimeter, while some enforced black rubber 'tape' I couldn't measure at all, <2000 megaohms.
But it did conduct, although poorly, when I hooked an obit to it.
I guess it doesn't conduct until voltage is high enough to ''arc over'' between conductive particles in the strip, similary as ferrite.
Some 'surface tracking' could be seen at points where I stabbed the electrodes, so I don't know if it would be best for a marx.
I think it's better idea to find some lower resistance rubber and use longer strips if needed.
Re: source for good HV resistors?
Self Defenestrate, Thu Feb 15 2007, 03:01PM
I was in the resistor challenge a while ago, and made a few resistors with water putty and graphite. They had horrible tolerances, and were fragile, but worked alright. These days I find it much easier to use 1/4w resistors in series(usually 100k, i have a reel of them) and put them in a length flexible pvc tube. Fill that up with oil, and seal the ends with some epoxy, and your set.
Self Defenestrate, Thu Feb 15 2007, 03:01PM
I was in the resistor challenge a while ago, and made a few resistors with water putty and graphite. They had horrible tolerances, and were fragile, but worked alright. These days I find it much easier to use 1/4w resistors in series(usually 100k, i have a reel of them) and put them in a length flexible pvc tube. Fill that up with oil, and seal the ends with some epoxy, and your set.
Re: source for good HV resistors?
Simon, Fri Feb 16 2007, 05:54AM
Simon, Fri Feb 16 2007, 05:54AM
Firkragg wrote ...
It depends heavily on rubber type and 'hardness' of vulcanisation. Some small rubber bands I have here measure few hundred kiloohms per centimeter, while some enforced black rubber 'tape' I couldn't measure at all, <2000 megaohms.
How are you measuring these resistances?It depends heavily on rubber type and 'hardness' of vulcanisation. Some small rubber bands I have here measure few hundred kiloohms per centimeter, while some enforced black rubber 'tape' I couldn't measure at all, <2000 megaohms.
Re: source for good HV resistors?
Marko, Fri Feb 16 2007, 12:51PM
I have a (relatively cheap) RC meter wich measures up to 2 gigaohms. It's slow but does measure high-resistance (>100 megaohm) carbon resistors pretty accurately.
And, it didn't work much at all on that piece of rubber. I found tha tit conducts only after I put some high voltage across it.
Marko, Fri Feb 16 2007, 12:51PM
How are you measuring these resistances?
I have a (relatively cheap) RC meter wich measures up to 2 gigaohms. It's slow but does measure high-resistance (>100 megaohm) carbon resistors pretty accurately.
And, it didn't work much at all on that piece of rubber. I found tha tit conducts only after I put some high voltage across it.
Re: source for good HV resistors?
Proud Mary, Tue Feb 20 2007, 04:39PM
Liquid resistors using aqueous copper copper sulphate or sodium thiosulphate solution are sometimes used in big very fast Marxes.
Designs typically involve a perspex tube with end plugs and disc electrodes. It's important to allow for a small amount of expansion of the electrolyte or the resistor will leak. Some designs use a small number of hollow polythene spherules which can be compressed when the electrolyte expands.
Resistance can be adjusted by altering the strength of the electrolyte, but resistances of more than a few hundred ohms become unwieldy.
On the plus side, liquid resistors have very low self-inductance, and can handle a great deal of power.
I have also seen them used as dump resistors - dummy loads - for discharging Marxes into, since they can readily be scaled up to handle high dissipation.
Proud Mary, Tue Feb 20 2007, 04:39PM
Liquid resistors using aqueous copper copper sulphate or sodium thiosulphate solution are sometimes used in big very fast Marxes.
Designs typically involve a perspex tube with end plugs and disc electrodes. It's important to allow for a small amount of expansion of the electrolyte or the resistor will leak. Some designs use a small number of hollow polythene spherules which can be compressed when the electrolyte expands.
Resistance can be adjusted by altering the strength of the electrolyte, but resistances of more than a few hundred ohms become unwieldy.
On the plus side, liquid resistors have very low self-inductance, and can handle a great deal of power.
I have also seen them used as dump resistors - dummy loads - for discharging Marxes into, since they can readily be scaled up to handle high dissipation.
Re: source for good HV resistors?
Sulaiman, Tue Feb 20 2007, 05:27PM
Would these
or these be useful ?
Sulaiman, Tue Feb 20 2007, 05:27PM
Would these
or these be useful ?Print this page