Getting -35Kv

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.

Getting -35Kv

Postby Robert Dwyer » Tue Dec 06, 2016 5:21 am

Hi,
The largest issue for me it seems, in the process of building the fusor, is figuring out how to get at least -35kv @ 20 milliamps, while being able to vary and measure the voltage and current. Now, I will admit right now before I go into everything, that I am young, and I am inexperienced in electricity, and I understand that this amount of power can potentially be very deadly. Now, through scrounging the forums and the FAQ's on the website, I have come to this conclusion and Idea for getting my power:

1.I want to build the power supply. I do not want to just go out and buy a couple thousand dollar unit to just plug in and hook up. I do not learn anything that way (and even if I wanted to do that, I couldn't afford to do it).

2. For simplicity, safety reasons, and reasons having to do with knowledge, I am really leaning away from wanting to use a voltage multiplier.

Due to these to reasons, my plan is to simply use a transformer, and vary the voltage with a variac. Originally I thought to get a variac capable of reaching about 350 volts, and hooking it up to a transformer with a turn ratio of 1:100. Of course, I ran into problems thinking about how I would actually acquire a transformer of that ratio (I have looked everywhere to no avail). I also need to make sure that even with that transformer I am able to get the amount of current that I want.

Anyways, I am asking for all of your advice on this situation. I have been looking at the forums and FAQ's for months, and this is the design that I came up with. I know this is the simple and dumbed down version, but I am asking for input.
Robert Dwyer
 
Posts: 30
Joined: Sun Sep 04, 2016 9:34 pm
Location: New Mexico
Real name: Robert Dwyer

Re: Getting -35Kv

Postby Robert Dwyer » Tue Dec 06, 2016 5:24 am

Also, I forgot to add,

The single largest thing confusing me about the high voltage, is getting he power supply "negative hot"
Robert Dwyer
 
Posts: 30
Joined: Sun Sep 04, 2016 9:34 pm
Location: New Mexico
Real name: Robert Dwyer

Re: Getting -35Kv

Postby Richard Hull » Tue Dec 06, 2016 6:32 am

Negative hot on any power supply is a snap and the absolutely easiest of all AC to DC power supply issues. It is a virtually irrelevant issue, it is so miniscule. It is well presented in the ancient FAQs in the this forum. Look them up.

The absolute best and most bullet proof Fusor supply is a self-built, variac controlled, single transformer, simple rectifier, no multiplier based supply. The snag......The transformer. ideally only the following items are needed.

1. A power cord
2. A power on-off switch
3. A variac of 1kw capacity
4. a. A transformer with a non-centertapped secondary of 25kv @ 25ma output and a simple bridge rectifier.
b. A transfromer with a center taped secondary capable of 60kv @ 25ma output and two individual diodes.
5. A suitable ballasting resistor for either 4a or 4b above
6. Suitable metering of output voltage and current.

That is all that is needed!

You can add a capacitor to the above, but I would not recommend it, based on personal experience.

Most here do not understand transformers at all. Power transformers all have a primary designed for a specific voltage input. The iron in that transformer is computed on the basis of magnetizing current for the specified AC input. The transformer turns ratio is effective and means something only up to the specified design voltage! Any attempt to take a power transfromer above its specified design primary voltage will cause the turns ratio to fail to perform as expected, as the core will saturate and no further increase in voltage can be had, period! You will draw a lot more power as the voltage is raised and beyond about 10% above the input rating no more voltage increase of any significance will be seen. Continuing to increase the voltage will blow a fuse and possibly damage the primary. Again, go much above the rated primary voltage and you are just heating iron!

There is no easy path to fusor power regardless of whether you go simple and bullet proof or high-tech, modern electronic switching with a multiplier.
You either luck onto a suitable transformer or a suitable modern electronic supply.

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: 10219
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Getting -35Kv

Postby Rich Feldman » Tue Dec 06, 2016 5:33 pm

Robert Dwyer wrote:... Originally I thought to get a variac capable of reaching about 350 volts, and hooking it up to a transformer with a turn ratio of 1:100. Of course, I ran into problems thinking about how I would actually acquire a transformer of that ratio (I have looked everywhere to no avail). ...

It is refreshing to see a beginner embrace, instead of dodge, the learning-about-electricity step.

All DC voltage sources have two terminals. Negative-hot just mean one that's running with its positive output connected to grounded stuff like the fusor, and thus safe to touch. Then only the negative output needs special insulation, and is unsafe to touch or even to get close to.

Regarding the transformer, you probably realize that the actual number of turns matters, not just the ratio. Otherwise step-up transformers would have one-turn primary windings. Magnetic saturation dictates the maximum number of volts you can get per turn. It's proportional to core area and operating frequency, and has nothing to do with load current. A 120 to 12,000 volt transformer (e.g. NST) would not work with 350 VAC input, it would instantly blow a fuse. Unless you increased the AC frequency to, say, 180 Hz. Then instead of core saturation, internal HV insulation failure would probably get you.

Here is one of my favorite tutorials on the topic: http://sound.whsites.net/xfmr.htm One site with formulas right up front, if you want to dive into numbers, is: http://www.eevblog.com/forum/projects/t ... s-in-here/

For 35 kV and no voltage multipliers, at mains frequency, the secondary windings have enormous turns counts and need special attention to insulation. Ready-made transformers of practical size are mostly those made for X-ray generators. Neon sign transformers are not made with high enough voltage to do the fusor job easily.
Richard Feldman
User avatar
Rich Feldman
 
Posts: 828
Joined: Mon Dec 21, 2009 11:59 pm
Location: Santa Clara County, CA, USA
Real name: Rich Feldman

Re: Getting -35Kv

Postby Robert Dwyer » Wed Dec 07, 2016 1:05 am

Thank you both for responding. This did help me a lot. Since it appears there is not an option left, I shall probably obtain myself an x-ray transformer, along with a variac. I take it for the x-ray transformer no special frequencies are needed right?
Robert Dwyer
 
Posts: 30
Joined: Sun Sep 04, 2016 9:34 pm
Location: New Mexico
Real name: Robert Dwyer

Re: Getting -35Kv

Postby Rich Feldman » Wed Dec 07, 2016 2:29 am

>> I take it for the x-ray transformer no special frequencies are needed right?

Well, uh, that depends on the XRT. There are plenty out there for 60 Hz, and an increasing number that need high frequency (more than 20 kHz).
Earlier in 2016 there was some chatter on fusor.net about one whose nameplate called for a 500 Hz inverter. Could be used at the not-so-special power frequency of 400 Hz, if derated to 80% voltage. Or 60 Hz at 12% of nominal voltages.

By the way, this thread should have been under New User Chat Are instead of Fusor Input Power.
See what it says near the top of the browser window, right below the FUSOR.NET banner?
Richard Feldman
User avatar
Rich Feldman
 
Posts: 828
Joined: Mon Dec 21, 2009 11:59 pm
Location: Santa Clara County, CA, USA
Real name: Rich Feldman

Re: Getting -35Kv

Postby Andrew Robinson » Tue Dec 13, 2016 2:03 am

Rich Feldman wrote:There are plenty out there for 60 Hz

Oh-really-Please.jpg

I find them becoming far more scarce as of late.
I can wire anything directly into anything! I'm the professor!
User avatar
Andrew Robinson
 
Posts: 619
Joined: Sun Aug 11, 2013 5:54 am
Location: Raleigh, North Carolina
Real name: Andrew Robinson

Re: Getting -35Kv

Postby Richard Hull » Wed Dec 14, 2016 4:22 pm

I cannot imagine a more difficult transformer quest than an old 60hz x-ray transformer. They are the prorverbial dodo bird and have mostly gone the way of all flesh. They will never-ever make-'em like that anymore. ( Why should they? Why would they?)

The only thing they had going for them was that they were virtually indestructable and could take a beating that modern gear has to auto-shutdown for due to the inherent delicacy of the replacement product.

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: 10219
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: Getting -35Kv

Postby Andrew Robinson » Wed Dec 14, 2016 6:49 pm

Ha, Richard had to get the last word in :)

Couldn't just leave it with my joke :)
I can wire anything directly into anything! I'm the professor!
User avatar
Andrew Robinson
 
Posts: 619
Joined: Sun Aug 11, 2013 5:54 am
Location: Raleigh, North Carolina
Real name: Andrew Robinson


Return to High Voltage - Fusor Input Power (& FAQs)

Who is online

Users browsing this forum: Yahoo [Bot] and 1 guest