Understanding current draw on a fusor
Posted: Sun Feb 19, 2017 7:02 pm
So, without doing enough research on the subject, I thought a fusor didn't actually draw much electrical power and rather the light and heat produced inside of the jar was a result of the power produced by the fusion reaction occurring. With this in mind, since I already have a vacuum pump and high voltage test equipment on hand (I have access to either a 75 kV DC or 150 kV DC hipot through my job) I thought I could achieve this task relatively cheaply.
I work in the electric utility industry and in my experience, vacuum is a good insulator, it is better than air. Some low and medium voltage circuit breakers have the interrupting contacts in vacuum bottles because of this. With that knowledge, I intuitively thought there would be almost no load on the fusor. So I built my fusor and tested the resistance between the inner sphere and outer with no vacuum using a Megohmmeter (megger) and I had about 300,000 Megohms @ 15kV, very good! As soon as I applied a vacuum the resistance went down and the load increased! The needle indicating resistance pinged out low and the voltage dropped to 1000V. So, I decided to use a hipot instead this time, also used for testing purposes, but has a higher VA. The hipot it trips out at 7 microamperes, and I could only get about 2000V before I reached that level. At that voltage I had some arcing inside and small amount of purple corona?
I can't wrap my head around it. What is going on inside that chamber that makes it want to draw more power when it has a vacuum instead of less?
Any suggestions for a power supplies? Would using a 15kV 60mA NST and a voltage doubling circuit be a good choice? Furthermore, NSTs with ratings like that, does that mean it can produce a continuous 60mA at 15kV?
What VA rating should the transformer supplying a fusor have? And roughly how much current would you expect on the secondary (high voltage side) of the power supply at 30kV?
I work in the electric utility industry and in my experience, vacuum is a good insulator, it is better than air. Some low and medium voltage circuit breakers have the interrupting contacts in vacuum bottles because of this. With that knowledge, I intuitively thought there would be almost no load on the fusor. So I built my fusor and tested the resistance between the inner sphere and outer with no vacuum using a Megohmmeter (megger) and I had about 300,000 Megohms @ 15kV, very good! As soon as I applied a vacuum the resistance went down and the load increased! The needle indicating resistance pinged out low and the voltage dropped to 1000V. So, I decided to use a hipot instead this time, also used for testing purposes, but has a higher VA. The hipot it trips out at 7 microamperes, and I could only get about 2000V before I reached that level. At that voltage I had some arcing inside and small amount of purple corona?
I can't wrap my head around it. What is going on inside that chamber that makes it want to draw more power when it has a vacuum instead of less?
Any suggestions for a power supplies? Would using a 15kV 60mA NST and a voltage doubling circuit be a good choice? Furthermore, NSTs with ratings like that, does that mean it can produce a continuous 60mA at 15kV?
What VA rating should the transformer supplying a fusor have? And roughly how much current would you expect on the secondary (high voltage side) of the power supply at 30kV?