Fusor Forums

I have finished my demo and started running it today. Firstly I have a 12 kv 30 ma NST with a 7.5 amp variac with a metering system made by Richard for my system. On the vacuum side of it I have an Trivac 2.5E connected to a MicroTorr 11-D that is capable to reach <1 microns. Connected to the diffusion pump I have a right angle bellows type high vacuum valve with a 2.75 CF. I am unaware of what my HV feedthrough is rated at and most of my gear can be seen here : viewtopic.php?f=18&t=9241&p=62648#p62648

I have a problem with my system. When I run it the plasma only appears in the range 50-300 microns and I can only apply a max power of .3 kv according to my metering system and when the plasma disappears at <50 microns it says I am not applying any current. Here are some pictures of my best run so far and they are all taken at the exact same moment. Could it be the size of my chamber or my feedthrough? I have no idea, it may be a dumb problem that I have overlooked. Can someone please inform me what is happening and why.

Could I also be placed in the plasma club? Thank you.

That is a rotten vacuum you have there and the current should be max'd out. and the voltage down to almost nothing. This is normal. You are operating a neon bulb there and not a fusor. You should not try and run a fusor at all until you are well below 100 microns or the neon transformer will buckle. (Too much load and the transformer protects itself)

You have not got the current sensor resistor hooked up correctly for sure.

You do not hook ground directly to the fusor. You hook ground to the transformer case and all the power supply ground points to the case bolt as well as the shielded wire side of the current wire wound resistor board I supplied.

The only wire going to the outer grid or metal shell of the fusor should be the unshielded wire side for the wire wound current resistor board. In this manner, all power supply return current from the fusor must pass through the 1 ohm, high power, current sense resistor to ground and the meter reads this as the current through the fusor.

I think you have shorted out the current resistor by grounding the fusor body/outer grid. This will hurt nothing. It will just not allow the current meter to read.

Again make sure of all your connections. You might disconnect the fusor and take the variac up slowly and you should see the voltage rise. I assume you did all this before ever hooking the fusor to the system. The current meter will not read until you have the fusor connected and drawing current, of course. If the voltage meter doesn't rise then you have wired the voltmeter up wrong as well.

Richard Hull

I have hooked up the system like you told me to in the video, with the outer grid going to the floating nut and the ground wire from the plug going to the NST, with the resistor in-between them. The problem was my poorly made inner grid which was I made in a rush, I will fix it and report with information on my run, thank you for the information.

Does the high voltage read OK without the fusor hooked up? Make sure it does. It should.

Richard Hull

How do I test it?

Hi Charlie.

Can you find a local mentor who can help you
to understand the basics of voltage sources, electrical loads,
current in wires, and metering circuits?

What Richard wants to see is a measurement
when your power supply's negative output is disconnected from fusor,
but still connected to the high voltage metering circuit.
Do not change the positive (ground side) connections between power supply, fusor, and metering circuits (including the current sense resistor).
If in doubt, draw and post an accurate schematic diagram of how the electrical parts are connected.
https://learn.sparkfun.com/tutorials/vo ... viders/all

No, after almost a year of searching I cannot find a mentor.

When the NST is on and hooked up to the metering system it reads .3 kv

I am using a 12 kv 30 ma NST

charlie_mccartney wrote:When the NST is on and hooked up to the metering system it reads .3 kv

Something is very wrong, and dialog here is not a good way to find out what.
Part of the problem is that you don't seem to know enough about electricity to ask informed questions.
Set the fusor aside for a while, and pay attention to your power supply and metering gear.

Want to take some time to learn the basics, or would you rather skip that and move ahead with your fusor?
Assuming the former, the Internet makes self-teaching easier than it used to be.
Can you light up LEDs or light bulbs, or run a motor, with a battery?
Can you measure the voltage _and_ the current in those circuits, and understand the difference?
If the answer is no, here's one place to start reading: https://learn.sparkfun.com/tutorials/wh ... uit-basics

Regarding your immediate source of frustration, you can test the NST by attempting to draw arcs. Electrically attach one end of an insulated wire to the transformer case -- there's probably a screw for that purpose. Momentarily touch the other end to a HV output terminal, or to the junction of your rectifier diodes. Pull it away and see what happens. You could also try lighting a fluorescent lamp (be sure to bypass any built-in ballast) between any of those HV nodes and the transformer case.

For online support on this forum, it would help to see a schematic diagram of what seems not to work. Or a picture that shows all the wires. You don't need to show what's inside the box, just what you have connected outside the box. You can't usually expect helpers to spend more time answering than you spend asking. Good luck!

Attached is how the wiring must be made. It is a line drawing. It should be straight forward.

NOTE: the diagram below is for a special metering system that I made for Charlie with special connectors as seen. This is not a genral hookup method!!

Make absolutely sure of the direction of the diode banding. The banded ends must go to each HV knob and the other ends are the negative hot DC and go to the zig-zag devider board input and to the fusor grid This is the high voltage line.

The case of the transformer is ground and the braided shield side of the current wire resistor board goes to the bolt on the already AC grounded case. The other end of the current wire resistor board goes to the fusor shell or outer grid if you are in a bell jar.

Make sure the current board BNC cable goes to the current meter side and the zig-zag divider board BNC cable goes to the voltmeter side.

Is this exactly how you are hooked up. If so your connections are good.

Take Rich Feldmans advice. Be sure you can get good hot arcs off each transformer knob to a well insultaed wire connected to case ground. DO NOT HOLD THE WIRE! Use an insulated plastic stick taped to the bare wire end you are trying to arc off the knob. No matter how good the insulation, never hold a high tension wire in your hand to draw an arc...... even if it is connected to ground.

Richard Hull