2Mev marx / Projects / Forums

Forums

4hv.org :: Forums :: Projects

« Previous topic | Next topic »

2Mev marx

previous 1 2 3 4 next

Move Thread

LAN_403

Conundrum

Fri Feb 26 2010, 08:31PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

maybe make "flat" resistor elements using BiPbSn alloy and carbon rods? :)

-A

teravolt

Mon Mar 08 2010, 06:12AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Hi all this has been quite a task to put to gether. I have decide to set up the small 44" section wich should be good for 800Kv at a 40Kv charge to see how it will behave before I build the rest. it weighs about 40-50 lbs. It is time to build the resistor assemblies and a flyback setup. It is pretty easy to build compared to something like a DRSSTC but time consuming for a marx with this many stages. any questions welcome.

klugesmith

Mon Mar 08 2010, 05:52PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Your craftsmanship is spectacular; thanks for sharing the pictures.

I have never worked with Marx banks, but see a possible weak point.
At less than 40 kV, you might get unwanted vertical sparks, even though the wire spacing is much greater than the intended spark gaps.
What counts is not the distance, it's the electric field strength at conductor surface. The wire lug connections have relatively sharp edges compared to the spherical surfaces of your spark gap electrodes.
It's also possible that corona discharge will bleed off charging current without making a big spark.

Good luck. Play safely.

teravolt

Tue Mar 09 2010, 05:44AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I have thought about the carona at the lugs and to charge I will use +20 and -20 wich should help. If I could find a circular shape to use as a field shaper that is ecinomical I would be happy to use it. suggestions are welcome. I found some nobs for cabinets for 5$ ea. wich would have been good for the spark gaps. The brass balls were freebies. Cirtanly if it flashes I will have to make some field shapers.

Steve Ward

Fri Mar 19 2010, 08:15PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

For my 10 stage marx using 100nF 60kV Maxwell caps i used 40k ohm charging resistors and it still takes about 30 seconds to charge.... good luck with your many megs of charging resistance! Id be surprised if you really manage to charge the whole thing to 40kV, the corona losses will draw too much current through the charging resistors limiting the maximum voltage for charging the top stages. The concept of using really high resistance (MEG ohms) for charging resistance probably comes from the hobby community because most of the MG's used tiny capacitors, and you need the right RC time constant to maintain the output voltage long enough to establish the arc (many uS for multi-foot sparks).

For brass balls i used:

Quite affordable. I used some 1" balls on my machine.

teravolt

Sat Mar 20 2010, 05:09AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

thanks for a reply to my thread, I have kind of done this on a budget, the caps and G-10 were freebies. The resistors I chose are a little high but I couldn't find any that would be cost effective at a lower resistance because I need about 102 to complete the stack. With a doorknob marx it may not be a problem because of the low capacitance so I don't know. I have finished a flyback power supply to start testing about 800kv of it. if worst comes to worst I will make some liquid resistors or inductors for the unit. To alleviate the corona I am going to charge it +20kv and -20kv and then unbalance it on the bottom to start the cascade. Thanks for the spark gap source if I have to use it I will. The other type of suto spark gap that I saw was a polished knobs for cabinets which are a perfect oval but they were 5$ ea. one last problem I have is weight the 800kv section feels like 50 to 60 lbs all ready. It may be about 150 lbs when I put the other 30 caps on top. The tall section will have to resized and sectioned to stack it. If it fires I will try to release a video. It certanly will need tinkering with that much voltage

Sat Mar 20 2010, 03:33PM

Registered Member #2372 Joined:
Location:
Posts: 62

Couldnt you just use brass acorn nuts for the spark gaps instead of balls? They are practically free from this website

teravolt

Sat Mar 20 2010, 06:22PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

yes you can use acorn nuts but the larger the radius
the larger the hold off on the electrode surface and a 3/4" acorn is hevy and costly. A acorn nut would be perfect for a doorknob marx or smaller. The brass balls that I am using were freebees from work and I have about a thousand of those. I think that the largest problem I will have is charge time with the resistors I have selected. stay tuned.

teravolt

Mon Mar 29 2010, 04:55AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hello all hears what happens when working on one project morfs into another. I am working on the power supply for the marx. what you see hear is a full wave cocroft walton voltage multiplier. I am using a mazilli circuit to drive 4, yes 4, flybacks 2 parallel pairs out of phase to create about 20kv at 250ma. The diodes are 15 1n4007's and the caps are 30 kv 500pf doornobs. Just to see if the leakage would be to much at the higher voltages I took thease two multipliers and combined them into one positive stack insted of the + and - 70kv you see hear to and still got a 7in spark. I hope add another neg stack this week to see if I can get over 300kv. hopefully I will get back to the marx this weekend but I am having to much fun with multipliers.

Steve Conner

Mon Mar 29 2010, 10:48AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Be careful arcing those things without current limiting resistors on their outputs. You could blow a bunch of diodes if not worse.

previous 1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob