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How do I make a 10kv mains powered cascade?

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Zack

Sun Feb 20 2011, 09:46PM

Registered Member #3624 Joined: Mon Jan 17 2011, 01:08AM
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Posts: 25

I've tried plasmana's marx power supply on instructables, but all I got were bright fat sparks every 2 seconds or so. They were 400VDC/250VAC 0.1uf caps, and although I was able to power the cascade with a flash unit, I got fat 2cm sparks every 5 seconds, not a constant output. I used 30 caps with 1n4007 diodes. Do you guys have any suggestions? Maybe lower the capacitance?

Dr. ISOTOP

Sun Feb 20 2011, 10:09PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Are you trying multiply mains to 10KV? Not going to work; with 30 stages at 60 hz, as soon as you draw current the voltage drop will be tremendous.

Zack

Sun Feb 20 2011, 10:13PM

Registered Member #3624 Joined: Mon Jan 17 2011, 01:08AM
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That's all right if 10kv isn't possible; would 4kv work? I'd buy new caps anyway, considering that the original ones blew up when I tried connecting them to a homemade inverter.

Dr. ISOTOP

Sun Feb 20 2011, 11:58PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Use a transformer - two MOTs in series work well. So does a doubled MOT.
Be warned that MOTs output lethal amounts of current.

Adam Munich

Mon Feb 21 2011, 08:59AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
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A rectified and smoothed 7.5kV NST will give you approximately 10.6kVDC at 30mA. Is this close enough?

James

Mon Feb 21 2011, 09:19AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Jeez, don't play with MOTs unless you *really* know what you're doing. They are extremely dangerous. A NST is a good idea, still dangerous but not nearly as much so. As others have said, getting several kV from 50/60Hz mains from a multiplier will be difficult. Do you have a particular need in mind or do you just want to play with arcs? Flyback transformers are still the easiest way to get nice arcs for almost no money.

Zack

Mon Feb 21 2011, 08:00PM

Registered Member #3624 Joined: Mon Jan 17 2011, 01:08AM
Location:
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I want to make something very small. I saw sam barros' high voltage generator on powerlabs, but I don't think he is all that truthful with how "simple" some of his projects are. I have used flybacks, but they're all dc, pretty bulky, and I don't currently have the right parts to make a driver. Also, I'd like to make a cascade because I haven't done it before.

I want to have this as a high voltage plug-in power supply. I can run a small cascade of 250VDC 10nf caps by taking a mains transformer and repeatedly touching the leads in reverse. But I need a constant output. NSTs are too expensive, and I'm terrified of MOTs.

Dr. ISOTOP

Mon Feb 21 2011, 08:09PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

If you want multiple KV's, you *will* need a transformer. You cannot draw appreciable current from a 60 Hz multiplier and maintain a reasonable voltage.
Example:
(I'm from the US, so I will assume 120V mains)
Let's say we want 10KV nominal. Let's further assume that we will allow a 1KV drop, and we want to draw 30 mA - so our final output will be 9KV/30mA, a good, respectable NST-level output.
To get our 10KV, we will need 42 stages.
The voltage drop of a CW multiplier is 2*I*n^3/(3*f*C), for large n.
Setting this equal to 1000, and using mains frequency (60 hz), I = 30mA, n=42, we find that C = 0.0265F, or roughly 26500 uF; i.e. the stage capacitance has to be 26500 uF@240V. An expensive capacitor...

James

Mon Feb 21 2011, 08:20PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Wind a small transformer on a salvaged ferrite and drive it with a Royer oscillator. Surely you can find a couple of NPN transistors and resistors? Use about 20 turns center tapped on the primary, 10 turns center tapped as the feedback winding and 100-300 turns on the secondary. Feed that to your cascade and with a 12V input you should get some decent current on the output.

I have seen mains powered cascades that would run a small HeNe laser tube from 240V, I think the output was around 1500V at a couple of mA so you can get arcs, but you won't get very much power at line frequency, it's just not possible to do without big bulky expensive components. That's why most modern power supplies are high frequency.

Scrounge around for a few old CRT monitors or TV sets. They are a treasure trove of components to harvest. Modern LCD monitors have some good parts too, the inverters for the CCFL tubes will produce a few kV and the tubes themselves are pretty cool too.

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