Pretty Light Fusor V2

For posts specifically relating to fusor design, construction, and operation.
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

Doesn't the gauge need calibration though? An analog input is simple enough I thought I saw that it all needs to be calibrated. That gauge I did see an arduino build here for though so maybe I'll get that, couldn't find any around that price so thank you very much for finding that one.
User avatar
Liam David
Posts: 543
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: Pretty Light Fusor V2

Post by Liam David »

I think you're mixing up two things here: (1) gauge calibration and (2) conversion from analog output to pressure.

The gauge calibration is how accurately the gauge measures pressure. It will drift over time but is usually not enough to be worried about. You might see a factor 2 difference in measured versus actual pressure, ignoring gas-type-dependent sensors for the moment. This may seem significant, and in some applications it is, but your case it is not. As long as both sensor elements are functioning, I would not worry about the calibration of a 901p, especially for your first go at things.

The conversion from analog measurement value to pressure is always given in the manual. Details for the 901p can be found on page 27 of the manual. An Arduino could easily measure the analog output signal, do the math, and then display the pressure to an LCD, for example, or send it to a computer for display.

I would do some more searching before pulling the trigger on the gauge I linked. It's an ok deal, but bear in mind that it has a VCR fitting.
JoeBallantyne
Posts: 345
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: Pretty Light Fusor V2

Post by JoeBallantyne »

The gauge Liam linked to is an RS485 gauge with a two wire connection. That will likely be more complicated to get working than one of the RS232 3 wire connection gauges. Per the manual, if the second digit in the device model number is a 2, it is RS485, if it is a 1, then it is RS232. Something like a 11030 or 11040 or 21030 or 21040 is more like what you want. First two digits of 11 or 21 should be the least difficult to get connected to, both electrically, and vacuum wise.

You might offer this guy https://www.ebay.com/itm/196169055522 $40 each for 2 or 3, and hope that one of the DB15 connectors is repairable/useable. He might not take $40, but I would be surprised if he doesn't take $50. I would start at $40. Unless you want to ask him for devices with electrical connectors (DB15) that are not obviously mashed. In which case I would offer him $50 each for 2.

Joe.
User avatar
Liam David
Posts: 543
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: Pretty Light Fusor V2

Post by Liam David »

Thanks for the additional info Joe.

Ebay is all about waiting for a good deal to pop up. The 901p selection seems to be mediocre right now. I'm sure good deals on other gauges exist, with some effort in searching.
User avatar
Dennis P Brown
Posts: 3229
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Pretty Light Fusor V2

Post by Dennis P Brown »

If the price of a low end vacuum gauge is a deal breaker, how will you handle neutron detection? Or the power supply? A fusor, even using a good bit of DIY and lucky e-bay finds will dwarf the cost of a simple vacuum gauge. If your just playing with a small plasma device I get it. But do consider what your goals are - currently, you made a plasma. Will just a vacuum gauge get you where you want to be?
User avatar
Richard Hull
Moderator
Posts: 15071
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Pretty Light Fusor V2

Post by Richard Hull »

The answer to Denniss last question is NO! The vacuum gauge that is useful in fusor use is the tiniest tip of the fusion iceberg bobbing above a future sea of cash. the power supply and sufficient neutron detection capability tower over the cost of any vacuum gauge.

Baby steps will get anyone there on a low budget over a longer period of time. A good vacuum gauge is essential, sure, but just a beginning.

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
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

Thank you all so much for the many responses, I am currently in the process of trying to find a hamfest/flea near me that would have a gauge, just in case.

In response to Dennis, I am not currently looking to get into measuring and putting Deuterium in it just yet. For now this is just a display piece to show off the plasma that can facilitate fusion (although as stated I'm not quite there and have MANY upgrades), not actually doing any fusion, hence the name of the thread "Pretty Light Fusor", that is all it is, a pretty light (for now).

Also thank you for the correction Liam I most definitely misunderstood something I read. Since that is the case this is a lot easier than I expected and could probably do this with any (good) gauge since I have done so much stuff arduinos for projects I have lost count, and from what little I have looked at the manual it seems as simple as doing a map for the analog voltage to the units I would need. Sending the serial commands may be a bit tricky but I may be able to bit bang it on arduino.
User avatar
Taylor Romain
Posts: 26
Joined: Mon Oct 03, 2022 5:20 pm
Real name: Taylor Romain

Re: Pretty Light Fusor V2

Post by Taylor Romain »

While the FAQ suggests starting with a Thermocouple gauge, based on my experience, I've found the Edwards Pirani Gauge to be an excellent choice for beginners. It's relatively straightforward to interface with and doesn't require back EMF diodes (although they are optional), unlike the inverted magnetron, which can generate high voltages/current when turned off without an EMF diode. Additionally, it's capable of measuring down to the levels necessary for a foreline gauge or a demo fusor. The one I purchased off eBay was 75$ and functions as intended. If you can afford it, I found one on eBay taken from a mass spectrometer. It seems to be in good condition, of course, take it with a grain of salt. Depending on your build, you will need an adapter from NW16 to KW25.

https://www.ebay.com/itm/285601580063?c ... uwQAvD_BwE
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

Hey all long time no speak, I've been preparing to exhibit at Open Sauce so it's been busy. I've made some important upgrades and am trying to find the right fitting to adapt the MKS 901p vcr 4 fitting to the 1/4 NPT ones of my flanges. Can anyone tell me if this is the right kind of adapter?
JoeBallantyne
Posts: 345
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: Pretty Light Fusor V2

Post by JoeBallantyne »

No. It's not. You need a VCR to NPT adapter. But why? NPT SUCKS! Want vacuum leaks? Use NPT.

What you need is a KF based chamber and then you could use a VCR to KF adapter. That would not leak. You will need to buy a metal VCR gasket to connect that 901p you bought. You didn't take my advice about which model number 901p to get. VCR works great but it does require one time use metal gaskets which are not cheap for what they are. (I'm not too much a fan of paying $2 to $4 each for tiny little pieces of one time use metal...)

Joe.
JoeBallantyne
Posts: 345
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: Pretty Light Fusor V2

Post by JoeBallantyne »

You need to do some research on VCR connections and how they work.

Joe.
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

Thanks for the advice Joe. The only reason I am going NPT is because KF fittings are too big for my fusor, also they would end up being threaded anyway since I don't have a welder to weld the fittings on, on top of the fact they are way too expensive for what I am doing, again this project is just a demo. If you look at my original post you can see the CAD of my fusor and the space I am working with. As for the VCR fitting I will look for an MKS 901p with a KF fitting instead and get a KF to NPT adaptor.
User avatar
Liam David
Posts: 543
Joined: Sat Jan 25, 2014 5:30 pm
Real name: Liam David
Location: PPPL

Re: Pretty Light Fusor V2

Post by Liam David »

Since you have to stick with NPT, go with whichever (VCR or KF) is cheapest given your situation and parts in-hand. You also mentioned clearance concerns. Since you already have a 901p with VCR, it's probably best to get a VCR to NPT adapter and a VCR gasket or two. Once you join the VCR fittings, there's no reason to ever take them apart as long as you disassemble things via the NPT. Don't bother with McMaster for VCR fittings. Always check Ebay: https://www.ebay.com/itm/226122206660
JoeBallantyne
Posts: 345
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: Pretty Light Fusor V2

Post by JoeBallantyne »

Thanks Liam for finding the right part.

Aidan - you should buy the ebay part Liam linked to. That is the correct adapter. You will also need to buy at least 1 1/4" VCR metal gasket to use for the connection between the adapter and your 901p.

Something like these:

https://www.ebay.com/itm/355375902889

Note that another option here, would be to get a 1/4 NPT to KF16 or KF25 adapter, and then go all KF/VCR from there.

That way you would only have 1 NPT connection in your system (the fewer the better) that went straight into your fusor. If you get that one leak free, you are OK.

Other benefit of that, is that over time you could add additional KF parts, and build a fusion capable fusor.

My bet is that for the amount of money you spent building the MAKE magazine fusor, you could have gotten most of what you need for a KF based neutron capable fusor.

The core part for an inexpensive KF based fusor is either a KF50 to KF16 reducing cross or a KF50 to KF25 reducing cross. You can get them on e-bay for about $45 shipped.

https://www.ebay.com/itm/394680512034

I bought a couple each of the KF50 to KF25 and the KF50 to KF16 crosses from the above vendor, and 3 out of 4 of the parts were pretty much perfect. One of the KF25 faces on one of the crosses had some scratches, and I asked them to ship a replacement for that one. These parts are brand new, so should be perfect. This vendor shipped my crosses with plastic covers on all the KF flange faces, so that is good. It drastically reduces the likelihood of damage to the flanges during shipping and while not in use. The single flange that was damaged, was clearly damaged during the manufacturing process, as it had circular scratches that had been made by some sort of power tool.

Joe.
Last edited by JoeBallantyne on Sun May 05, 2024 5:50 pm, edited 2 times in total.
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

Thank you both for the very helpful responses, I'll go ahead and get that adaptor you suggested. The only question I have is relating to the gasket, I see that there are three types of gaskets and I was wondering if one was better, there are gaskets with retaining rings for pretty much the same price as ones without. Is there any reason to get the one without the retaining ring over the one with it? The retaining ring seems like it would make installation easier right? Also I don't have the MKS 901p yet, it's just that the best one I found that seems in working order and is a good price is VCR 4.
JoeBallantyne
Posts: 345
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: Pretty Light Fusor V2

Post by JoeBallantyne »

If you didn't buy the MKS 901p yet, then I would suggest just like I did before that you get a 901p with a KF flange. Typical model numbers start with 11 or 21 - ie: 11030, 11040, 21030, 21040. There was one that sold just a week ago for $51. I know, because I was the only other bidder at $50.

Do an ebay search for "MKS901p 11030" and see what pops. Or MKS901p 11040, or MKS901p 21, or MKS901p 11.

Then get a KF to NPT adapter - which are also on ebay and cost about $10 each. Then screw the 1/4 NPT KF adapter into your fusor using PTFE tape, and use all KF after that.

If you add a KF tee, you can connect both your vacuum gauge and your vacuum pump to the tee, and connect the other end to the KF to NPT adapter which goes to your chamber.

KF is really nice because ALL of the parts are reusable. Nothing is one time use. The seals are o-rings, and can be reused as many times as you want. Plus if the o-ring is shot, they are cheap, standard sized, and easy to replace.

KF is the closest thing to Legos the vacuum world has.

Joe.
Last edited by JoeBallantyne on Sun May 05, 2024 6:09 pm, edited 1 time in total.
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

Apart from this one which I'm not sure I would like to take my chances with, there are no KF fitting 901p's under $110, hence why I am leaning to the other one with VCR.
Daniel Harrer
Posts: 16
Joined: Fri Aug 18, 2023 11:01 am
Real name: Daniel Harrer

Re: Pretty Light Fusor V2

Post by Daniel Harrer »

You earlier dismissed Pirani gauges as too expensive, but I cannot see why. A used TPR 260/270/280 on eBay can easily be found for around 100 bucks and from my experience (3 bought so far) they work without issues. A controller can be made from an arduino nano and a basic 24V power supply (1W should suffice) at very low cost.

And I agree with Joe that you should definitely aim for KF flanges. Easy to use, relatively cheap, and very vacuum-tight. If you must use NPT / BSP / JIT or such then I strongly recommend to use some paste-like sealant such as Hylomar Blue. They are not intended for high vacuum but in my experience they work for typical fusor vacuum needs and unlike other seals actually didn't leak heavily.
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

Just got my MKS901p and hooked it up. I made a very janky version of Finn Hammers controller for it, but it works so... The one worry I have is relating to high voltage, is there any protection I should consider to make sure the gauge doesn't get fried? Is it ok to have it powered through a wall wart or should I use a battery to isolate it?
Attachments
20240516_194211.jpg
20240516_194253.jpg
User avatar
Dennis P Brown
Posts: 3229
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Pretty Light Fusor V2

Post by Dennis P Brown »

That problem can be partly solved - add a protective metal screen that is grounded via contact with the surrounding metal components/walls. This will help prevent any stray high voltage plasma from reaching the device electronics. This works well for my TC gauge head. I place the screen across the detector's port adapter.

Aside: that thread adapter I see isn't very good for vacuum work. Definitely add teflon tape - that can still leak too but is vastly better than metal on metal sealing.
JoeBallantyne
Posts: 345
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: Pretty Light Fusor V2

Post by JoeBallantyne »

Using a wall wart for power should be fine. There are KF centering rings with a metal screen built in that you can get if you are worried about protecting the gauge from plasma or arcs. Not sure how good of an electrical connection they get by default with the rest of the system when they are used, because most of the pressure of the connection is on the o-ring which is typically non-conductive. It might be possible to get conductive o-rings, but the simplest solution at least for now, is just use the gauge with the HV off. At this point you are still just trying to accurately measure the pressure in your chamber, which from the pictures we know was much too high.

Once you get all the leaks out of your chamber (which by the way may prove to be impossible - given that you built the MAKE mag chamber) then you can worry about protecting the gauge from HV/plasma.

If you get the pressure low enough (like 10-20 microns or less) in the chamber before raising your voltage, in my experience the plasma automatically stays inside the center of the cathode, and so you don't have to worry about protecting the vacuum gauge from plasma.

Nice job wiring up and programming that digital display for the 901p. How are you boosting the voltage for the 901p?

Put it on your chamber using PTFE (teflon) plumbers tape, or better using the suggested liquid sealant that is vacuum safe, pull a vacuum on the chamber and see how low a vacuum you can pull on your system. Be warned that if you just use PTFE tape, you must wrap it very tightly, and use at least 8-10 wraps especially if you are using the stock Home Depot plumbers tape as it is very thin. It still may leak at that NPT joint if you just use tape.

Joe.
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

So for the circuit I'm actually just putting 9v into it, no boosting, I'll just use a 9v wall wart. Any recommendations for a metal screen? Like how dense it should be? Considering how far the gauge is from the grid do I really need the mesh, if I'm understanding correctly I just need to make sure the gauge section is grounded right?
JoeBallantyne
Posts: 345
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: Pretty Light Fusor V2

Post by JoeBallantyne »

You should just ground your whole chamber. Then the gauge section will automatically be grounded along with everything else.

Attach a good ground directly to one of the bolts holding your chamber together. Verify with an ohm meter that the connection is good. (You should get a zero ohm reading between ground and all of the metal that is part of your chamber including the connected KF fittings.)

I have never used one of those KF centering rings with mesh/perforated metal in them, and have not had a problem. I think that is likely overkill, as long as you only turn up the voltage on your setup AFTER it is pumped down.

If you crank up the voltage when the pressure is high, then all bets are off. I've seen videos where people have made plasmas all the way down the vacuum tubing to their pump. (They likely also didn't ground their chamber properly...)

Joe.
Last edited by JoeBallantyne on Fri May 17, 2024 1:43 pm, edited 1 time in total.
JoeBallantyne
Posts: 345
Joined: Tue Jul 20, 2010 4:08 pm
Real name: Joe Ballantyne
Location: Redmond, WA

Re: Pretty Light Fusor V2

Post by JoeBallantyne »

On a NEMA 5-15R three prong polarized receptacle (a standard United States wall socket - one of the vertical slots is longer than the other), two of the connections go straight to ground. IF the NEMA 5-15R receptacle is wired correctly, both the circular and the larger slot should go to ground. The smaller slot is hot - so is nominally at 120 RMS AC volts. That is the one that can give you a nasty shock, and fry things that aren't expecting to get hit with 120V AC.

BUT, sometimes wall sockets are wired incorrectly, and the larger slot, which SHOULD be ground, is HOT instead, and the smaller slot is actually ground.

You can verify that the socket is wired correctly by switching your multimeter to measure AC on a range of 150V or more, and measuring the voltage between each pair of openings in the wall socket. You should read 0V between the larger slot and the circular one, and about 120V between the smaller slot and each of the other two. Be CAREFUL when making this measurement to not get shocked. Don't touch the metal leads on the multimeter probes while they are inserted into the wall socket...

IF and ONLY IF you get a zero volt reading between the circular ground and the larger slot, you can then also switch your multimeter to measure resistance, and verify that there is 0 ohms between those same two connections. Do NOT try to measure ohms between connections that read 120V, or you will almost surely fry your multimeter. You have been warned.

Joe.
Last edited by JoeBallantyne on Fri May 17, 2024 1:48 pm, edited 1 time in total.
Aidan_Lee-Calamera
Posts: 24
Joined: Tue Feb 20, 2024 5:33 pm
Real name: Aidan Lee-Calamera

Re: Pretty Light Fusor V2

Post by Aidan_Lee-Calamera »

Ok, I'll make absolutely sure the gauge section is grounded. The flanges are already grounded to the case of the NST which is a direct ground so no worries there, just have to make sure there's a good connection to the gauge.
Post Reply

Return to “Fusor Construction & Operation (& FAQs)”