# Circuit diagram for a power supply that outputs about 25kv

1. Jul 25, 2009

### wolram

Does any one have a circuit diagram for a power supply that outputs about 25kv at a few mA dc.
25kv is just a ball park figure it could be 22 or 30 kv, or even better adjustable from 22 to 30.
Input would be 230v ac
Thanks.

2. Jul 25, 2009

### Astronuc

Staff Emeritus
Re: 25kv@5mA

Basically you want an AC/DC converter from 230V(AC)/25kV(DC). Basically 110:1, or 80-130:1 if one is doing a range of voltages. I imagine one could use a tap on the low voltage side.

There are probably off the shelf power supplies that do that.

3. Jul 25, 2009

### Phrak

Re: 25kv@5mA

You might make do with a TV flyback transformer using a small 230VAC variac to adjust the voltage.

Depending on what you are doing, you might simply use the entire television plugged into a larger variac, complete with remote on/off switch It won't work if the flyback supply tries to regultage the output voltage back to nominal, though.

Last edited: Jul 25, 2009
4. Jul 25, 2009

### waht

Re: 25kv@5mA

TV flyback would be a good choice for the project, however the flybacks are designed to work at high frequencies. A 60 Hz input from the outlet will be absorbed by its core.

Luckily, flybacks have multiple primary windings needed to setup a relaxation type of oscillator using a transistor or two. Supply power is DC, so you need an AC/DC stage first.

The simplest way to adjust the output voltage is to vary the frequency because there is a relationship between the frequency and magnetic core power absorption. You can't change the frequency of the relaxation type of oscillator as you would have alter the primary windings, the solution would be a variable square wave oscillator driving the primary windings. Frequency 10 KHz to 20 KHz could do, depending on the core.

http://www.geocities.com/CapeCanaveral/Lab/5322/fly-drv2.gif

5. Jul 25, 2009

### Phrak

Re: 25kv@5mA

I expected someone might call me on this, good work. I was refering to the entire inverter + output rectifier. That'll teach me to use shorthand.

As Astronuc was talking about, it would be a lot easier for a one-off, to buy one, than build one.

As for a roll your own, you're schematic doesn't identify the core, the supplier of the core or the wind ratio or wire gauges to use. Gotta have them. What's the part number of the output rectifier? (Does he want DC or AC?)

I didn't find any suppliers of 25KV flyback inverters that would sell in quantities of one. Given that, I would scavange the supply from a television. The remaining problem with this approach is guestimating the voltage developed as evidenced by the size of the television screen and profile. Wolram would need a TV guy for that.

Last edited: Jul 25, 2009
6. Jul 25, 2009

### Phrak

Re: 25kv@5mA

Wolram. Do you want AC or DC output?

7. Jul 25, 2009

### TurtleMeister

Re: 25kv@5mA

Does it have to be 230v input? If not then my first choice would be the flyback also. It's much lighter and cheaper. And it will probably already have the HV rectifier with it.
http://members.misty.com/don/samflyhv.html

8. Jul 26, 2009

### vk6kro

9. Jul 26, 2009

### wolram

Re: 25kv@5mA

DC output, i intend to build an (ionic lifter), if i can buy a ready made PSU it will be better as i can use it for other projects.
Thanks for all the help guys.

10. Jul 26, 2009

### Phrak

Re: 25kv@5mA

OK, you might try digikey. You might also consider a neon sign light transformer, where you have to supply the rectifiers.

Last edited: Jul 26, 2009
11. Jul 26, 2009

### Staff: Mentor

Re: 25kv@5mA

Do you mean filter instead of lifter, woolie?

12. Jul 26, 2009

### negitron

Re: 25kv@5mA

No, I'm pretty sure he means one of these.

13. Jul 26, 2009

### waht

Re: 25kv@5mA

I built one these before with balsa wood and aluminum foil. For it to lift off you need more than 30 KV, and make the structre extremely light. I used a flyback transformer for the power supply, but had to over drive it up to 50 KV to increase the current. It worked for a while until the secondary winding arked and burned.

14. Jul 27, 2009

### Staff: Mentor

Re: 25kv@5mA

Huh, never seen that before. Thanks negitron.

15. Jul 27, 2009

### Staff: Mentor

Re: 25kv@5mA

So you're saying this is a pretty safe activity for this OP to be working on... :tongue2:

16. Jul 27, 2009

### vk6kro

Re: 25kv@5mA

They had this on Mythbusters a few months ago. It worked well.

It was supposedly an antigravity machine but probably works by generating an air flow downwards.

A van De Graaf generator or a Wimshurst machine could probably generate high voltages at enough current to make it work.

17. Jul 27, 2009

### negitron

Re: 25kv@5mA

Yep. The electric field ionizes air and accelerates the electrons upwards and the ions downwards; the latter having much greater mass than the former, almost all the thrust is upwards. Neat toy, but likely not practical for large-scale applications in the forseeable future.

18. Jul 27, 2009