High voltage power supply (DC) current limiter?

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RobertTubbs
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High voltage power supply (DC) current limiter?

Post by RobertTubbs »

Howdy all, this is my second post so far. I would like to thank those of you who gave me some great advice on my previous vacuum chamber, I'm now working on getting a new stainless steel vacuum chamber fabricated for me as a result. So on to business, I have a high voltage DC power supply rated at 60kV 2mA max, it goes up by (6) 10kV increments. Question is, will I need a current limiter so that the fusor doesn't suddenly draw a wanton amount of amperage and just fry my power supply? I've seen some rather interesting and improvised current limiters built on this site, even noticed one fellow used a glass of water. If I do use a current limiter, what kind would be advisable, assuming my power supply even needs one.

(I realize the amperage is a little low, but from what I understand about this PSU, which aint much, I suspect it will still work for a demo fusor, and maybe even the real thing.)

Below is a link to where I got my power supply.
http://www.unitednuclear.com/hvsupply.htm

RT
Wilfried Heil
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Re: High voltage power supply (DC) current limiter?

Post by Wilfried Heil »

What does United Nuclear say about the flashover/short circuit protection of their power supply?
RobertTubbs
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Re: High voltage power supply (DC) current limiter?

Post by RobertTubbs »

"This is an all electronic/solid-state power supply that outputs high voltage (unfiltered) DC from about 10Kv to over 60 Kv in 10Kv increments. " -Unitednuclear.com

As far as the website goes that's it, the manual will be here in a day or so, they might have something more to work with in there.

RT
Dan Tibbets
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Re: High voltage power supply (DC) current limiter?

Post by Dan Tibbets »

Without knowing the innards of the power supply, I'm guessing it has a high order voltage multiplier. The 2 mA rating might be an open circuit condition- no load with the lowest voltage setting. With a load, even a small load like in a fusor with a very low vacuum and a small grid, the mA may not come close to the rated mA, and the voltage may drop through the floor.
See R. Hull's article on Neon sign transformer ratings (any voltage multipliers would worson the tradoffs) and look up voltage multipliers.
http://www.geocities.com/CapeCanaveral/ ... 2/hv2.html
http://www.kronjaeger.com/hv/
http://www.play-hookey.com/ac_theory/ps ... liers.html

More than a few stages results in profound voltage drops with more than tiny current loads. You may be better off sticking with the lower voltage settings- less multiplier stages.



That being said, there is a member that reported the achievement of measurable silver activation with a power supply rated at 1 mA (or was it 5mA?) and 20 kV.


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Carl Willis
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Re: High voltage power supply (DC) current limiter?

Post by Carl Willis »

The short answer is that this is not suitable for a fusor.

These are "solid-state" (triac-switched, rather than mechanically-interrupted) line-operated induction coils. Induction coils deliver a high-frequency-rich pulsed DC (waveform depending some on the load and the drive circuit). 60 kV may be the peak voltage, but not the average. 2 mA is likewise almost certainly not the average current that the coil can sustain.

Further complicating matters is that induction coils are often center-tapped, or if not explicitly tapped, at least intended not to have their midpoint at high potential or the endpoints at high potential relative to ground for long periods. Many of these are cheap Chinese construction, and if you take them apart, you find just two bobbins inside the can, set up for balanced HV output, with the midpoint leads just loose inside the can right next to the core bundle. Fusors with grounded metal chambers are not likely to present a Chinese coil with a load it can handle for very long!

You can do a lot with an induction coil, though. X-ray tubes run just fine (modern dental tube filaments will operate on two "D" batteries so the cathode can be isolated from ground).

-Carl
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RobertTubbs
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Re: High voltage power supply (DC) current limiter?

Post by RobertTubbs »

Much obliged Dan, for those links, good information on current limiters (and how to Macgyver afew.) Also, if what you said is the case, then it sounds like a x-ray transformer/neon sign transformer would be better suited for the job. (an xray transformer perhaps a little more potent than I would actually need for my first/second power supply.) In regards to my present power supply you stated that if it does indeed work off of voltage multipliers, any load put on the circuit would cause the amperage to drop dramatically. And not to make a stupid comment but would that be a suffeciant current limiter in it self?

P.S. I originally posted this message afew seconds after Carl said this power supply was a no go for a fusor.....so let me toss in another question here, will this ni-hao power supply at least work for a demo fusor? Or will it just go ape when I ground it and win me a darwin award?

RT
RobertTubbs
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Re: High voltage power supply (DC) current limiter?

Post by RobertTubbs »

Well....It would seem I have a new power supply for my x-ray tubes! ^_^

RT
Dan Tibbets
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Re: High voltage power supply (DC) current limiter?

Post by Dan Tibbets »

"...circuit would cause the amperage to drop dramatically. And not to make a stupid comment but would that be a suffeciant current limiter in it self?"

Short answer- I don't know.

2 mA ( probably at the lowest voltage setting- each doubling of the voltage cuts the current in half) is realitively benign from a health stand point. But if it shorted out and damaged the electronics, there could be possible exposure to high currents from the A/C plug(?) It may also be a fire hazard if there is no fuse. And , while I think I understand the basics of transformers, inverters give me a headache. As CW said the current / voltage may be fairly intermittent. I have an 'electronic' oil ignition transformer rated at 18.5 kV, 45 mA and 87 Watts. It does not come close to this (actually 1/2 of this since it is center taped like NST's) unless it is an open circuit. Even with a voltage drop to ~ 1000 V it only puts out ~25 mA. When I took pictures with exposures shorter than ~ 1/60th of a second I often had a dark frame- no glow discharge. This confused me since it is susposed to be operating at 20,000 Htz. Once I hooked it up to an ocilloscope I found that it would put out a burst of perhaps 10 voltage spikes(presumably at 20,000 htz), then nothing till the next A/C cycle (~ 60 Htz). In any case, without a current limiting resister I have managed to burn up several diodes, due to arcs, anominolus glow discharge, grimlins, etc.

And, your power supply will probably work for a demo fusor(?). I can get a modest glow well below 1000 volts, and less than 1 mA. This assumes your vacuum is not too good. Neon sign transformers (even the 15 kV ones) and oil burner transformers are marginal at best for measurable neutron production because they are current limited and center taped. X- ray transformers are the way to go for the commited Fusor. Microwave transformers (MOT) will work with a voltage multiplier because they are not current limited and have plenty of power. They are more dangerous, but then so are X-ray transformers. If you are a scavenger and want to build your own power supply you can sometimes find used microwave ovens cheap ( need the old, and heavy transformer version; not the newer, lighter inverter based ovens). Also, you get a capaciter, diode and some short lengths of high voltage wire in the bargen. A second MOT can serve as a current limiter. Two ovens provides most of what you need to make a one stage voltage miltiplier circuit (~ 6 kV and over a hundred mA, which is plenty for additional multiplier stages, not to mention heart stopping power). Also, a 'Variac' is almost essential if your power supply allows it.

And, finally, if you haven't already done so, brouse through the links on the right side of the home page. Lots of usefull information has been contributed by various members.

Dan Tibbets
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Chris Bradley
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Re: High voltage power supply (DC) current limiter?

Post by Chris Bradley »

Please see

viewtopic.php?f=2&t=971#p3878

and also note that if you had entered "unitednuclear.com" or "unitednuclear" into the search engine, then you'd have found several entries.

Use SEARCH. It's for searching for stuff!



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RobertTubbs
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Re: High voltage power supply (DC) current limiter?

Post by RobertTubbs »

Thank you Chris, If only your cited threads had all the information that I was looking for, which was kindly provided by the folks right above me.

---------

In any event I'll take a look around locally and hunt for an x-ray/neon sign transformer. However, as we speak there are some on ebay for fairly cheap. It's not a time critical thing, I was curious what I could do with what I had on hand. From what I've gathered the power supply could POSSIBLY work for a demo fusor however Carl made an important point that it may be a hazard if I attempt to ground it like that. So I will probably not even try to do that and wait until I have something a little more appropriate for the job at hand. Again I would like to thank you folks for the very helpful input given.

RT
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Chris Bradley
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Re: High voltage power supply (DC) current limiter?

Post by Chris Bradley »

If you find a pre-existing thread but it doesn't answer your question, then add to that one, even if it is years old. That way all the relevant information on a topic hangs together and it just helps keep things in good order.

There are many threads now on the usage and wiring arrangements of all manner of transformers, but unfortunately they are scattered and surely can be difficult to find. All the more reason for trying to tie these things up. So do a thorough search and your perseverance will likely bring rewards.

Good luck, and always think 'safety'.
Wilfried Heil
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Re: High voltage power supply (DC) current limiter?

Post by Wilfried Heil »

This power supply is made to look like an old vibrating reed induction coil, the time proven standard for historic x-ray tubes. It probably has some form of Oudin coil in it, or perhaps a TV derived high voltage transformer.

Since you are getting it anyway, maybe you could have a look inside and post some images.

Some information on many variants of such coils can be found here:

http://www.coe.ufrj.br/~acmq/tesla/mres4.html
http://www.coe.ufrj.br/~acmq/tesla/tefp.html

You might like the other pages of Antonio C. M. de Queiroz too, as he has built or restored a collection of absolutely fantastic electrostatic generators.
RobertTubbs
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Re: High voltage power supply (DC) current limiter?

Post by RobertTubbs »

Okay so going back and actually tinkering with the little fella, it turns out these things are indeed little voltage multiplier stacks drivin by wimpy lil transformers. They are cheap chinese made power supplies as Carl has pointed out.

On the positive side of things, these power supplies do produce that oh so wonderful plasma, but not a whole hell of alot. I'll include three pictures, one of the power supply next to a NST, one of the "ni hao's" plasma and one of a NST plasma.

--------

Lesson: Unless you are like me in that you get your jollies from shoving 60,000 volts into old TV tubes, this probably isn't a good investment.

RT
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