High Voltage Supply

[mia_rupani]

Hiya! I'm very new to this fusor forum so sorry if my questions seem a little obvious!

I know that the voltage required to put into the fusor is around 40-50kV, and post speaking to electrical engineers they told me that the transformer and rectifier I needed costs about half a million pounds and that I'd need to rent an entire plot of land to build a small substation, but I've seen youtube videos of people doing it in their back sheds!
Is there any more financially viable way of getting this big of a voltage without having to buy a huge transformer?!

Thanks,
Mia

[Rex Allers]

The engineers' advice you got is either clueless or focused on the point of view of commercial power distribution. You don't need megawatts of power for the kind of fusor made by amateurs here.

For a real fusing fusor (not demo version) I think your target of 40-50 kV is reasonable.

The other thing you need from the supply is its current capability. For that you probably want a minimum of 10 mA. It will be easier with 20 mA or more.

Another way to look at the supply is it's output power maximum. A simple formula...
P = I x E = current x voltage ; where P in watts, I in amps, E in volts

A just barely adaquate supply for detectable fusion might be 30 kV at 10 mA or 300 watts output. I think most who have successfully done fusion have supplies capable of 400 or more watts, eg. 40 kV at 10 mA. An easier operation would be, say 800 watts or 40 kV at 20 mA.

One of the more common supplies that have been successfully used are x-ray transformers with a custom built rectifier and a variac to adjust the input voltage and thus HV output voltage. The current required depends on the loading from the plasma but this type of supply should be able to provide 20 mA or more.

The other common option is to find a commercial HV supply that produces negative HV and in the ranges just mentioned. Two main vendors of this type are Spellman and Glassman.

Neither of the supply options are very easy to find at this time. The x-ray transformers were a bit easier to find, say, 20 yrs ago. The commercial ones are available if you are willing to spend a lot of money.

Here are three forum FAQs with good information:

#2 FAQ - Current needed in a fusor.
Post by Richard Hull » Tue Feb 25, 2014 6:46 pm
viewtopic.php?f=29&t=9171#p62349

#3 FAQ - Voltages needed in a fusor
Post by Richard Hull » Thu Nov 17, 2011 4:04 pm
viewtopic.php?f=29&t=4843#p27681

FAQ - X-ray transformers
Post by Richard Hull » Wed Dec 04, 2013 8:14 pm
viewtopic.php?f=29&t=8972#p61515



***** Note to all Newbies here *****
You should spend a few days reading the Posts in the FAQ sections of this forum

A recent link I posted on using the FAQs
"Re: Total newbie"
Post by Rex Allers » Fri Dec 14, 2018
viewtopic.php?f=46&t=12555&p=81504#p81504


And one on searching
Re: viewing port material?
Post by Rex Allers » Sun Mar 03, 2019 3:19 am
viewtopic.php?f=46&t=12682#p82553

[mia_rupani]

Hiya!

Thank you so much for your advice and the links you sent - it was so helpful!

After reading some other forums, I think we have decided that maybe building a demo fusor and running it around 20kV would be a better idea for the type of project we want to do in school. We did some more research and found that an ignition coil (found in most motor bikes I think) can step up our voltage straight to 20kV from 20V and seem very inexpensive online! Do you think this sound feasible?

Thank you so much again!
Mia

[Rex Allers]

No. Ignition coils are not what you want. The links I provided talk about both voltage and current. You are focusing only on voltage but even that misses a lot about trying to use an ignition coil.

Ignition coils are designed to make very short pulses of high voltage. The ignition circuit of a vehicle puts the battery voltage across the primary coil for a short period to store magnetic energy in the coil core. Then this input voltage is quickly switched off. The magnetic field trys to collapse and in the process creates a quick high voltage pulse on the secondary.

You don't just apply a voltage and get high voltage out. Some circuit must switch the input voltage as a minimum requirement.

Here's a link to someone who did use ignition coils as a HV supply that also could make a bit of current.
http://www.neon-john.com/Nuke/X-ray/HEI ... driver.htm

The circuit switches power into the coil primaries at a fast rate making the output more continuous than their intended application.

The circuit makes high voltage, maybe enough to drive a demo fusor, but -- there are many bad or dangerous aspects.

- The parts to build the circuits are probably going to cost a good bit more than the coils.
- This is not a project for an electronics novice.
- Mains voltage is not isolated making it dangerous even without the high voltage output.
- The switching circuit is non-trivial for a beginner.
- The voltage and power being switched into the primary of the coils is much more than they are designed for.
- The coils need to be in oil for insulation and heat dissipation

So I think you should avoid this idea.

---
On these forums, there has been some discussion about using precipitation HV supplies. Finn Hammer made a lot of great posts here but hasn't been around for a while.

Finn did some testing and measurements on one of these supplies and suggested they might be OK for a demo fusor. Here's a link
"Test of Chinese Precipitator Supply"
Post by Finn Hammer » Tue Nov 14, 2017 3:07 am
viewtopic.php?f=11&t=11992&p=77912&hili ... tor#p77912

These supplies are still on ebay
https://www.ebay.com/itm/High-Voltage-E ... SwKJZbIeao
or
https://www.ebay.com/itm/High-Voltage-E ... SwYihb0V8s

Sounds interesting but as far as I know, no one here has ever posted about making plasma with one of these. Good luck if you want to try going this way. We would like to hear about someone really trying one.

For those of us here in USA these supplies want input voltage of minimum 180 VAC (spec 180V-250V) so not ok for our default of 115-120 VAC wall sockets.