Why NOT laser power supplies?

[lanewaddell]

Hey all,

The general sentiment on the forum is that you need a super big old school transformer to make this work (the more pcbs the better your Fusor works : ) )

In fact, there is a whole FAQ post devoted to saying that laser power supplies and percipitator supplies will not work.

However, I've found several commonly available (and cheap) laser power supplies that I have confirmed are available with negative polarity with specs at 30-40 ma and 48 kv.

Why can't we use these? It would certainly lower the entry point if we could find cheaper power supplies in the modern era.

An example:

https://lightobject.com/150w-180w-pwm-l ... co2-tube/

Also, I've seen several posts claiming very good results in the 7 ma range including in excess of 1e6 n/s. Do we really need to be aiming for 30 ma + for smaller fusors?

[JoeBallantyne]

Lane, I just made an extensive set of posts about building an inexpensive fusor using a precipitator supply, and proving that you CAN do fusion with it.

Was it easy to do fusion with the precipitator supply and a spark plug feedthrough? No. Did the precipitator supply impose some significant limitations on the system? Yes.

But you CAN do fusion with a precipitator supply. Finn Hammer and Mark Rowley showed that a LONG time ago. Mark even did activation using a precipitator supply. (60kV)

Do you HAVE to use a 150+ pound line frequency x-ray transformer behemoth in order to do fusion. NO!

NO. NO. NO. NO.

In fact at this point, I would say that more people have probably done fusion using something OTHER than an x-ray supply, than those who have used a variac driven line frequency x-ray supply.

Will big, HEAVY, oil filled, line frequency, old school, 100kV+ 300mA x-ray transformers work? Of course they will. But they are certainly NOT required.

Will a laser supply work? Maybe. It depends on how exactly the supply functions. If it will put out 300W continuous, at -30kV and 10mA, for hours on end, and it has reasonable voltage and current regulation, and will reduce the voltage instead of shutting off if there is a dramatic change in load resistance (ie: when the plasma lights off), then it should work just fine for fusion. Can you determine all of that from reading specs from a website - well, not really.

Why don't you just start out using a precipitator supply?

They are cheap. You can do fusion with them if you are careful. You can always upgrade to something better later. They work really well for a demo air plasma fusor. Just run them at their minimum kV output, and raise the pressure in the fusor until the plasma lights off.

We're talking about $100 more or less, depending on what output voltage you go with. (30kV or 40kV)

Just buy one (or two) already.

Joe.

[lanewaddell]

Joe this is excellent.

Thank you so much!

I think I am going to follow your exact advice. I'll try a percipitator supply or a laser power supply and see what I get and then upgrade if needed.

I agree that you should be able to do some degree of fusion with this. If I get any fusion and it is paltry after everything I can do to optimize it I will consider an upgrade (maybe by then I would have sold my old house and be able to afford it : ). )

Ill be sure to let you guys know what luck I have.

[Rich Gorski]

Lane,

Take Joe's advice and look for something other than a laser PSU. Although a laser power supply has sufficient voltage and current I think the main problem for a fusor is that they are designed for a fixed HV output voltage near the laser tube operating point. There might be a small range of HV adjustment but for a fusor you will want to start out at a few kV and slowly increase as you discover how your fusor behaves. I don't think you will want to slam on a fusor suddenly and right up to 30kV. The precipitator supplies can go down to a few kV output and as high as 30 to 60kV.

Rich G.

[lanewaddell]

Thanks Rich

Looking at percipitator supplies I can only find the very sketchy looking Chinese eBay version.

Do you know of any semi-reliable companies or places to buy these?

[JoeBallantyne]

The sketchy Chinese ones on eBay are what everyone here at fusor.net have used.

Myself included.

They work just fine despite their "sketchiness".

Bite the bullet and buy some sketch. I put a link to the one I used in my posts about the low cost fusor. (It is fully exposed and does NOT come in any kind of enclosure. I have NO experience with the enclosed ones. I don't think Finn or Mark used an enclosed one either.)

I bought 3 40kV supplies, and the first two worked just fine. (I did kill the first one eventually.) I haven't needed to use #3 yet, but I expect it will work just fine also.

Joe.

[Richard Hull]

Take the above advice seriously as you will never find one of the old x-ray systems today that can handle 2KW crazy loadings with ease. I was lucky and got my monster system free back in the 90's just to haul it away. Truly indestructible,heavy, brutish. Worked without a burp since 1999, still there today up to 45kv @ 50ma continuous, but I never take it over 20ma. I may be the only fusioneer with such a supply but I am damned glad I have it.

Today, virtually everyone uses solid state switcher supplies of moderate voltage output and voltage multipliers or switchers that output up to the full voltage desired. Most of these need careful attention if using voltage multipliers. (some electronic savvy).

As noted, newbies might buy a minimum of 2 of such chi-com wonders as in getting them to work satisfactorily will usually wind up with the first one killed. A backup and lessons learned, hopefully, will see the second one brought to success. These are the future that is here now!

A $3000 HV supply by a top maker of HV supplies 0-30kv @10ma was so well protected that the VCU physics department on their fusor had it shut down every time the fusor tried to light off its plasma. They had to install 250k ohm high watt resistors in the HV line to get it to light off and then get the current and gas pressure stable. They used a HV relay to kick out the 200k resistor to a 40k ohm resistor to run their fusor. The supply was beautiful and superbly metered, but as delivered, would not work a fusor without special external modifications.

Again, as noted modern HV professional supplies are made more for a well defined, stable load related to both voltage and current. The fusor is not such a load.

Enjoy you adventure into cobbling together your high voltage and crazy variable current loading power supply.

Richard Hull

[lanewaddell]

Thanks other Rich,

So considering the comment regarding the laser supply.

My understanding is this is essentially a flyback transformer source. I doubt I'd have the kind of control as one of the optimal systems, but I wonder if I can control voltage enough using a variac on the 120vac input to ease it to lighting.

Once lit and stable unfortunately voltage would be slaved to current setting which I suspect would make me choose between a higher voltage and lower pressure.

If anyone has a more suitable recommendation (manufacturer and model) for a percipitator or other supply with solid voltage control characteristics that would be appreciated!

[Rex Allers]

Perhaps something educational in these links.

FAQ - Mark Rowley on the 30 & 60 kV precipitator supplies
viewtopic.php?p=88916#p88916
Fri Sep 11, 2020 4:51 pm

Precipitator HV Supply Hacking
viewtopic.php?t=12919#p83944
Rex Allers
Wed Aug 21, 2019 6:17 pm

Fusion Success with Precipitator Power Supply
http://www.fusor.net/board/viewtopic.ph ... 98&p=83788
Mark Rowley
Mon Jul 22, 2019 3:57 pm

Test of Chinese Precipitator Supply
http://www.fusor.net/board/viewtopic.ph ... 92&p=77912
Finn Hammer
Tue Nov 14, 2017 3:07 am

[Rex Allers]

Oops, I forgot to mention

Joe Ballantyne fusor V2. (Low cost fusor.)
viewtopic.php?p=102218#p102218
Wed May 22, 2024 5:53 pm

[lanewaddell]

Hey Mr. Rex,

Thank you much for that index!

From what I read, you can have these little guys be negative or positive polarity depending on how you ground them. Can you explain that part in more details?

Is there any stranded energy concern? Do you do anything to discharge these when you are done?

Thanks!

[JoeBallantyne]

There are two wires coming out of the precipitator supply. One red, and one black. Both of those wires are HV insulated wires. The red wire is at a positive potential relative to the black wire. (At least on every supply I have used so far.)

These wires are connected to the secondary windings of the transformers on the power supply, and so are floating relative to the 220V input fed to the supply. Note that there is NO ground connection anywhere on the precipitator supply. You connect the two input terminals directly to 220-240V. Which in the USA means that both of the supply lines are HOT.

If you want a negative potential supply, then you ground the red HV wire, and connect the black HV wire to your HV feedthrough.

If you want a positive potential supply, then you ground the black HV wire, and connect the red HV wire to your HV feedthrough.

If you are building a standard glow discharge fusor, then your feedthrough is connected to your cathode, which needs to be at a negative potential relative to the grounded shell of your fusor.

Therefore, you ground the red wire, by connecting it to the grounded shell of the fusor, and you connect the black wire to your HV feedthrough.

To discharge the output, you simply UNPLUG the precipitator from the power lines that feed it, and you then wait. For 60 seconds or so. In my experience the HV discharges a few seconds after the supply is disconnected from power. Waiting 60 seconds or so is a wise conservative measure to take, before messing with any of the HV output connections.

I don't understand why you keep asking extraordinarily basic questions that are answered ad nauseum in the FAQs.

Have you purchased anything for your fusor yet? Any vacuum parts? A precipitator supply?

I find it a little strange that for some reason it seems that you want to pay Chinese prices to get parts from non Chinese suppliers.

It doesn't work that way. You want to buy stuff that is not expensive, then you buy it from China.

The expensive stuff that in your words comes from "semi-reliable companies" was most likely also made in China, and was simply marked up by a factor of 5 or more by your "semi-reliable" middleman.

The one thing middlemen do VERY reliably, is mark up the goods they got from someone else.

IMO a lot of the stuff you can buy on eBay directly from China, is actually very good quality stuff.

But then again, I've bit the bullet, and actually bought some.

Have you?

Joe.