"Blown up Sir!!" - OOPS....

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Richard Hull
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"Blown up Sir!!" - OOPS....

Post by Richard Hull » Sat Sep 29, 2018 4:08 am

The famous line from the movie "Stripes" might be my appropriate response when crowds at HEAS ask me what happened to my fusor.

While running up and conditioning fusor IV for HEAS, I have blown up the 42kv main supply. This supply has survived since it was first installed in 2004 in spite of my best efforts to kill it. Well, I finally killed it. Too much gas somehow ran into the system at 37kv on a run while I was taking notes. The current went nuts and I heard "click" and the breakers on the rack mounted Variac tripped. I could not even raise the primary voltage after reset to more than 20 VAC before it tried to draw 9 amps with no fusor load.

I pulled the transformer and diode/ballast assembly out of the oil in its tank. This took two hours to accomplish. It appears both secondaries read 37K ohms to ground (good!). The six 20kv semitech diodes do not read short ( wish they were, it would be an easy fix). They could still be broken down and check seemingly OK by an ohm-meter. More likely, the primary is shorted, it reads 1.8 ohms. I was hoping for 3-5 ohms, but this might still be OK. More testing needed but I am worn out. Back on it Saturday. I gotta' have a fusor to show. I will get this puppy up, but time grows short.

Next test will be to disconnect the diodes so nothing loads the secondaries. power up the xfmr and see if the problem is the transformer primary. If it powers up with no current draw, I am back to the diodes. That means a ray of hope.

More as I move into the issue.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

User avatar
Richard Hull
Site Admin
Posts: 10984
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: "Blown up Sir!!" - OOPS....

Post by Richard Hull » Sun Sep 30, 2018 8:48 am

After 14.5 man hours of work, all is well. Fusor IV is back in the biz of doing fusion. I am back on track to demo it at HEAS 2018 in 6 days.

It turns out that one of the two rectifier strings were blown. (three-20kv diodes in series.) The tank had 44 screws and nuts that had to be removed. Naturally, oil is a mess and drippings were everywhere no matter how much I tried to avoid it. With the repair completed, I just dropped the top cover with xfrmr, diodes and ballast back in the tank. I hooked up the metering and ran the supply up to 20kv with no real current draw. FIXED!!! I bolted everything back down and re-positioned the supply. Thank goodness the Xfmr is unharmed!

Next I hooked up the fusor and ran only the mechanical pump to get the system down to under 100 microns. I applied the power but inched it up slowly. SHORT!!! The fusor itself had an issue! I disconnected the supply and re-verified that it was not harmed. OK, it was not harmed as I did not turn the variac very far. at 3 kv I got a significant line current draw with the fusor connected.

I, next, pulled the conflat mounted insulator and grid stalk. This up-to-air would ruin all the two days of conditioning prior to the supply blowing up. My fusor had not been opened according to my log book since 2009. I attach images of this item. It turns out that some copper from some wire used to secure the grid in the post flashed and sputtered creating a path to the shell with a resistance of about 29 megohms. (measured with a Kiethley electrometer.) There was a lot of deposition over the last 9 years on the insulator, as you can see. I removed it with #800 grit paper wet with WD-40. The bulk of it came off within 1 minute. I finished with "mother's chrome polish", (auto stores). This fully removed what little was left and the alundum in the polish left a nice shine to the white BeO glazed insulator. ( made sure not to damage the glaze)

I cleaned it all up with acetone including both CF mating knife edges. I put in a new Cu gasket and bolted the item back in place. I started only the mechanical pump and the item slowly went to 100 microns and stayed there. I torqued the cap screws a tiny bit, all around, and instantly the gauge dropped to nearly 20 microns. I assumed this was sealed.

I reconnected the power supply and inched the power up to about 5kv with only a minimal draw on the line ammeter. the fusor was taking 26ma in glow mode and the grid was glowing a bit. Slowly, the current dropped and I ran the voltage up to 8kv and the current went up to 20ma. I kept this game up as the crud from opening was burning off and the shell was bombarded and heated a bit. The mechanical pump was down to 12 microns and went to 9 microns once the glow cleaning voltage was at 15kv @17ma. Totally fixed!

Finally, I turned on the diff pump and continued the glow cleaning until the pumps boiler got the jets going and it yanked the system down to 0.3 microns (3x10-4 torr). Note** I have a PID hooked to a thermister attached to the boiler on my diff pump. As the boiler reached about 85 Deg C. the foreline pressure really went up to nearly 50 microns, (Water and crap in the oil boiling out from the glow cleaning), As the boiler went over 100 deg C. the foreline pressure went back to about 12 microns.

I put in D2 to the pressure of 5-6 microns and was pleased to hit 100k n/s after about 20 minutes of timed 1 minute runs. This will improve with each new day's runs. This daily increase shows that my fusor seems to condition and bury D in the shell until, after 4 or 5 days of running, I have no trouble hitting the mega mark and beyond.

This can be a learning experience for many here in troubleshooting issues with a fusor that develops problems or is having issues right out of the chute.

Richard Hull
Attachments
Insulator (1).JPG
Full insulator and grid stalk with deposition
Insulator (2).JPG
Close up of the deposition This insulator was custom made by me using a naval BeO antenna bulk head insulator machined to mate to a custom machined 2.75
conflat. It can withstand 40kv+ in the fusor.
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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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