Spellman XLF mystery malfunction

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
Post Reply
Dan Knapp
Posts: 402
Joined: Wed Aug 06, 2008 8:34 am
Real name: Dan Knapp

Re: Spellman XLF mystery malfunction

Post by Dan Knapp »

12.7 ma at 1.7 kV through air at atmospheric pressure?
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

Re: Spellman XLF mystery malfunction

Post by John Futter »

Dan Actual current and voltage depend on many parameters
But our usual penning ion sources and anode layer sources typically run @ around 2kV 5mA anode to cathode under Vacuum.
On the bench in air raising voltage slowly breakdown @ 3kV and voltage falls to as per current limit to 1.2- 1.6kV 10-20mA.
It pays not to muck around for too long as the ozone production doesn't do the metal and insulating surfaces much good
Dan Knapp
Posts: 402
Joined: Wed Aug 06, 2008 8:34 am
Real name: Dan Knapp

Re: Spellman XLF mystery malfunction

Post by Dan Knapp »

John
Unless the air in New Zealand is significantly different than air in South Carolina, we seem to be having a miscommunication. You seem to be saying that an electrode at atmospheric pressure with -3 kV on it will show a discharge current of milliamps. I regularly operate apparatus with 15 kV on the atmosphere side of feedthroughs and see at most a few microamps leakage, most of which I believe is surface leakage rather than corona. Just to be sure I wasn’t missing something, I just put -3 kV on an exposed point (BNC center conductor) with a current meter that reads down to 1 microamp, and I see no discharge current in air. I don’t believe anyone is going to see much current drain at all with a power supply connected to an unevacuated spherical fusor.
With regard to your comment about testing ion sources at atmospheric pressure to check for shorts, I don’t see the relevance to the discussion at hand. In my prior life, I spent forty years working on ion sources and always checked for shorts at atmospheric pressure before evacuating the system. Are you talking about putting high voltage on the source at atmospheric pressure? (how high?) If so, and you say that you get milliamp currents from discharge in air at a few kV, how could you see a resistive short in the presence of milliamps of air breakdown current?
Please tell me what I’m missing here.

P.S. My lab is at 23 degrees, 58% relative humidity. Its very humid here, but I didn't think atmospheric moisture was a very good insulator.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Spellman XLF mystery malfunction

Post by Richard Hull »

Dan is spot on! After years in the Tesla coil business and working in real atmophere work with superb instrumentation, especially electrometers, micro amps are what one would expect in free air bleeds at high voltage in the 1-10kv range. Once highly visible corona occurs it can go up to a hundred micro amps, maybe.

A working load current of an electrostatic motor with a 100 gram rotor, spinning at 2300 rpm, at 20kv applied with noisy coronal hiss is on the order of 400 microamps here. I know, I have one and demo it regularly.

Milliamps?! If you measured milliamps, something is grossly wrong with your instrumentation or the supply.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

Re: Spellman XLF mystery malfunction

Post by John Futter »

Dan
please read what I wrote carefully all is there
and to find a resistive fault is easy as current flows before breakover.
However the worst kind of faults are the ones that are open circuit at low voltage and suddenly short before operating potential is reached
And our RH and temp range is very similar
Dan Knapp
Posts: 402
Joined: Wed Aug 06, 2008 8:34 am
Real name: Dan Knapp

Re: Spellman XLF mystery malfunction

Post by Dan Knapp »

John
I did reread your posts and had overlooked that you were talking about Penning and anode layer sources. That is a very different kettle of fish than a fusor. Both of these sources have a magnetic field that causes the electrons to take helical paths. You can of course get discharge at higher pressures and lower voltages in a magnetic field (increases path length of electrons and probability of ionization), but this has no relevance at all to a fusor.
Post Reply

Return to “High Voltage - Fusor Input Power (& FAQs)”