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 300KV Cockroft Walton multiplier
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| Mates |
 Sat Feb 16 2008, 11:53AM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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I‘m starting a new HV project...
For my future experiments I need 300KV DC power source and here is the try to get it for low costs…
It is classical CW multiplier, based on ignition coil 50KV at 6 KHz. In fact it is just next step after the doubler which I presented here  recently. The caps are home made disassembled from my old Marx generator which I’m actually trying to replace.
The diodes are stacks of 1N4007 , probably the cheapest diodes you can get (I bought 1000pc for 20$) dipped in cooking oil. So theoretically I can rectify 1milion volts… 
Here is a test run - two stages. Spark gap is 15cm, probably I can go much widther. The sparking rate is approx. 15 per second and sound is really loud  . I plan at least 8 stages in the future so hopefully I’ll send more exiting picture soon…
I’ll have to think a lot how to design the 8 stages into a compact device (probaly everythnig will end up inside an oil bath). Any suggestion regarding this would be great. And of course any question and comments are welcomed…
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| Spedy |
| Sun Feb 17 2008, 12:02PM |
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Registered Member #964
Joined: Tue Aug 21 2007, 07:39PM
Location: Stockton, CA
Posts: 134
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Wow, that's amazing. Though I can;t see that lighter sitting in spark gap going to well lol. 300kv is alot, don't you get enough corona to fill a bunch of 2 liter bottles?
Either way, congrats. so far the only hv thingy I've gotten to work is a kit that makes like 1/2-1" sparks... lol.
How much time did you spend trying to make this thing work? So far I can;t even make a camera-flash inverter based CW multiplier work..
Anyway, hope you eventualy manage the big 1mill! Be sure to post pictures when you do! lol
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| Mates |
| Sun Feb 17 2008, 04:34PM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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Spedy wrote ...
300kv is alot, don't you get enough corona to fill a bunch of 2 liter bottles?
You do not understand it well, 300KV is the aim which is still far away. My guess is, that with those 2 stages my final tension is little bit above 100KV. Corona does not seem to be a problem. You can check the darker picture...
Spedy wrote ...
How much time did you spend trying to make this thing work?
This project is glued of parts of my older ones. Thus, completing this thing was a quick action. Only soldering the diodes is PITA work.
Today I've made another stage with new caps which are 30% less capacitance. I plan to reduce the capacitance gradually with each next stage. I placed everything on a plastic board so it is much more compact now. With the test run I scared to death a friend of mine  I'll send new pictures tomorrow 
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| Shaun |
| Sun Feb 17 2008, 09:11PM |
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Registered Member #690
Joined: Mon May 07 2007, 10:47PM
Location: New Jersey, USA
Posts: 616
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You should really use a limiting resistor, since every time you directly short that you discharge the capacitor string through the 1A rated 1N4007s. Seems you've had no problems so far, but once you get up to higher stored energy it could be bad news for those diodes. |
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| Mates |
| Mon Feb 18 2008, 06:26AM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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Shaun wrote ...
You should really use a limiting resistor, since every time you directly short that you discharge the capacitor string through the 1A rated 1N4007s. Seems you've had no problems so far, but once you get up to higher stored energy it could be bad news for those diodes.
That's actually very good point Shaun. This is exactly the reason why I'm discussing the whole project here. Any design flaws you people notice are thankfully accepted. I didn't realize that this is not a Marx and amp peak must be really big in the diodes during discharge (It must be a good luck and gods support they are still alive  ). I will use 1Mohm resistor made of 10pc of 100K/2W high voltage resistors all dipped in oil. I've been using them for my Marx and I know for sure that 3 of them in series can stand 60KV. I'm very curios how the sparks will look like with this type of limiter...
Thanks...
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| Spedy |
| Mon Feb 18 2008, 12:01PM |
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Registered Member #964
Joined: Tue Aug 21 2007, 07:39PM
Location: Stockton, CA
Posts: 134
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Ah, I see. a 300kv goal is pretty high by my standards lol.
I can understand how those diode chains can be a pain, I've burned myself numerous times trying to make a little tiny CW where all the components hardly have any leads at all >.<
Hey, what circuit are you using for the iggy coil? 50kv ac from an iggy seems kinda insane to me... |
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| Mates |
| Tue Feb 19 2008, 05:01PM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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Here is my latest progress. I made the whole device more compact and added one more stage. I also built the HV resistor as you can see on the picture.
However, despite I’m still far away from my aim I already have to deal with serious problems. The resistors works only if the spark gap is below 22cm. If I make larger gap the initial few sparks are not resistor limited (the electricity finds somehow way around). I also noticed that I have flashovers between the connection points within the device in case the spark gap is more than 26cm. This means I’ll have to built the final device differently with greater spacing or/and placing it inside an oil bath  . I’m sending at least some sparks pictures limited by the resistor. The HV terminals are 22cm apart…
and one more picture here |
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| Kizmo |
| Thu Feb 21 2008, 04:27AM |
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Registered Member #599
Joined: Thu Mar 22 2007, 02:40PM
Location: Northern Finland, Rovaniemi
Posts: 446
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That is *really* impressive!
..You made me buy 3000pcs of 1N4007s from ebay :D (1k for me, rest are for my friend) |
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| Uzzors2k |
| Fri Feb 22 2008, 01:27AM |
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Registered Member #95
Joined: Thu Feb 09 2006, 10:57AM
Location: Asker, Norway
Posts: 1298
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That's excellent Mates! I like how you used nothing but common components and household junk. Good job and keep it up! |
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| thermite |
| Fri Feb 22 2008, 09:46PM |
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Banned on 02/27/2008
Registered Member #1326
Joined: Sun Feb 17 2008, 05:19PM
Location:
Posts: 49
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I think the voltage multiplier is not called walton and cockroft.
Walton and cockroft is identical to Marx.
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| Dave Marshall |
| Fri Feb 22 2008, 10:07PM |
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Joined: Thu Feb 02 2006, 08:22AM
Location: Meadville, PA
Posts: 587
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Actually thermite, a Marx generator is very specifically a spark gap switched multiplier. A Cockroft Walton is a diode switched multiplier.
The CW multiplier is capable of continuous generation of high voltage (dependant of course on the load, and with a very high ripple) where the Marx can only generate very distinct pulses of high voltage with a comparably high off time.
Further discussion of this difference should be taken to another thread.
Dave |
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| Mates |
| Sat Feb 23 2008, 03:49PM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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I I performed some design changes. I placed the caps from the other side of the board to keep them far away from the diode connections. I also made a new HV resistor which holds.
I started checking the main corona losses. And I immediately found what was sparking inside the device last time. One cap had a failure and was side-sparking over (funny thing is that this was a completely new cap, which I’ve made recently. Old caps disassembled from my old Marx are still fine despite the corona stress).
I changed the cap and checked the corona once more. It is not so bad. You have to realize that the picture is taken at iso 800 and exposition is 10s.
Next I started with increasing the spark gap distance. At 25cm the spark was accidentally attracted by my metal cupboard. I store all my electronics over there so I’m curious whether I destroyed something 
After I moved the table 25cm sparks are running without any problems. Main corona losses are detectable only at connections of the resistor.
However, I have another big problem. During the last run I noticed that something is sparking also in my main 220V plug-in. The sparking even continue 1-2 seconds after I stop the CW – shit what should I do now. Where on earth is this HV sparking inside the plug-in coming from???? 
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| teslacoolguy |
| Sat Feb 23 2008, 03:56PM |
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Registered Member #1107
Joined: Thu Nov 08 2007, 04:09PM
Location:
Posts: 792
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very nice work, now what is the approximate repetition of those sparks? |
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| Mates |
| Sat Feb 23 2008, 04:03PM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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teslacoolguy wrote ...
very nice work, now what is the approximate repetition of those sparks?
I would say around 10-15 per second. But, I can easily increase the power of the ignition coil driver... |
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| Mates |
| Mon Feb 25 2008, 05:50PM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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I increased the power of the iggy driver by 30%. I played with increasing the distance of the spark gap. I reached 30cm and two of my caps started side spark over . I'll have to replace them a probably play more with the design of gluing the sides together. The side spark-over is a stupid problem - the weakest point which limits the rating of the caps.
Here are the latest pictures…
30 cm sparks front view
The back view and the side sparking cap... |
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| Tesladownunder |
| Tue Feb 26 2008, 08:54AM |
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Joined: Thu Feb 02 2006, 03:45AM
Location: Bunbury, Australia
Posts: 1435
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Good stuff.
When designing HV you need to account for spacing things 3 times as far apart if there is a surface connecting eg like a cap or diode string. Surface tracking is why this ignition coil sparking 3 inches, has a 9 inch tracking spark.
TDU
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| Mates |
| Tue Feb 26 2008, 10:38AM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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Tesladownunder wrote ...
When designing HV you need to account for spacing things 3 times as far apart if there is a surface connecting eg like a cap or diode string. Surface tracking is why this ignition coil sparking 3 inches, has a 9 inch tracking spark.
Isn’t it the surface tracking problem mainly of the AC? I never experienced bigger problems with DC discharges (usually 20% larger distance than free air is enough).
The cap side sparking which I referred about is not due the surface tracking problem. My cap was not capable to stand the electric stress and it breaked down around the sides (the dielectric layer there was not very good because is based on amateur gluing with high temperature).
BTW: In case you want to get rid of the surface tracking of your coil just dip it inside a cooking oil (like I did). It is a cheap non-toxic solution which works.
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| ramses |
| Tue Feb 26 2008, 12:35PM |
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Registered Member #1208
Joined: Thu Jan 03 2008, 11:30AM
Location: Chesterland, OH
Posts: 154
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he might be referring to the edge of the foil, which is very sharp, even though you can't cut yourself. |
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| Mates |
| Sat Mar 01 2008, 03:50PM |
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Registered Member #1025
Joined: Sun Sep 23 2007, 02:53PM
Location: Czech Rep.
Posts: 566
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OK, I hope it is not starting to be boring. I redesigned the caps, so finally they do not spark over. The trick is in gluing the sides really properly. (I also tried oil and wax - both failed). Now I run easilly 35cm sparks (still litle bit afraid to go for longer distance of the spark gap). Moreover, sometimes happens like you can see on the second picture that the electricity finds a way around the resistor. It always makes a laud bang and the total length of the track is over 50cm!. Luckily the diodes do not complain 
I'll add other stages soon...
So enjoy the last pictures
Corona analysis...
Here is the case when the electricity finded the way around the 1Mohm resistor
and litle bit of art
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