Help with Feedthrough with No Known Max Volts

[River Marlowe]

Hey everyone,
I have been working on my demo fusor for a couple of months now but I have had some issues with getting a good HV feed through. After searching for a while, most standard ones were out of my price range, and making my own came with its own slew of problems. After being stuck on this for a while, I think I am ready to just bite the bullet and buy one. I went to eBay, as I have done for most of my parts so far, and came across about four different listings for feed-throughs that will fit my 2.75" cross. However, none of the sellers knew what the voltage rating was for these parts. So does anyone know if there is a way to go about finding this? I plan on running my demo fusor at 10kV. This sounds like a terrible idea but I figured I might as well ask: what would be the safety risks with simply hooking it up and slowly increasing the volts with a potentiometer until it reaches 10kV?

Here is the part I want to buy: https://www.ebay.com/itm/MDC-VACUUM-PRO ... SwIKNfj0Hs

Thank you
River Marlowe

[Richard Hull]

That might do for about 5kv-8 kv. Make an offer.

Richard Hull

[Mark Sato]

I don't know how good of an idea it is, but Ben Krasnow from the Applied Science Youtube channel used automotive sparkplugs as HV feedthroughs for his DIY SEM, which have worked for him.

[Joe Gayo]

Realize that it's only $95 new ...
https://mpfpi.com/shop/power-feedthroug ... 0113-1-cf/
(Note: The 12kV rating is only if used with a special silicone boot connector on the airside)

I would spring for the extra voltage at $210
https://mpfpi.com/shop/power-feedthroug ... 0234-5-cf/

[Joe Gayo]

Best Value:
https://www.ebay.com/itm/Metric-M14-x-1 ... 2480729252

Plus an oil burner spark plug

[Mark Rowley]

Agreed, spark plug should be fine.
I gotta laugh though, if you check the archives here you’ll see folks have been using spark plugs for demo fusors since day 1 (20+ years ago). Ben K probably got the idea from here or it’s just common sense simplicity.

Use the search function. There’s quite a few posts (spanning many years) about modifying a spark plug so it’ll support a grid stalk. There’s also details about what model of plug is best for this application.

Mark Rowley

[byron addams]

proberbly wouldnt be anny good for hogh vacuum ar ultra high vacuum. theraded fittings dont make a very good seal so its good practice not to use them. but if you dont have much money to spend on propper fitings it would proberbly work well enough.

[Joe Gayo]

@byron

Spark plugs are straight threads so they are sealed with a metal gasket or in the case of a fusor an o-ring making it a perfectly acceptable seal.

[Mark Sato]

Oh, cool! I might need to remember these KF to sparkplug thread adapters in the future.

[Mark Sato]

Sparkplugs for vacuum applications definitely seem like a DIY "hack" and something you would find used in a home setup, so it wouldn't surprise me if Ben got the idea from a community such as this forum.

[Joe Gayo]

@Mark Sato

Fusor.net asks that posters don't quote previous posts

[Mark Sato]

Noted. My previous two posts have been edited to meet forum guidelines.