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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Houdini0118 wrote ...
Did you get the multiplier for running it off the mains working better as well?
Great question. For this and future marx generators, we are actually using a 0-6kVDC high voltage supply board we are designing. It will operate from 15VDC input and provide 0-6kVDC (variable) to charge up the marx generator.
We will still be investigating a better C-W multipler as well as a more cost effective solution to charging up the marx for the amateur with a smaller budget.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
EVR wrote ...
Great question. For this and future marx generators, we are actually using a 0-6kVDC high voltage supply board we are designing. It will operate from 15VDC input and provide 0-6kVDC (variable) to charge up the marx generator.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Update:
So I decided to revisit this project after putting it away when I blew some resistors. I sourced some larger high voltage resistors from CPC (Farnell without the £20 minimum order) and replaced all of the failed resistors on the board.
These resistors appear to be from the same series as the supplied ones but are higher wattage and rated for more voltage, they are YAGEO HHV-50JT-52-1M
This time I left some space between the resistors and PCB to try and discourage surface arcing. On the other side I cut the legs right at the board to help reduce corona loss.
Above: The new resistors compared to the old ones.
This got it working again but I still had problems with the spark gaps being too finicky, jitter and small continuous arcs forming across them. This was down to two things.
Pointed electrodes that I originally used to encourage sparking.
When I first received the board from EVR I used a measly charging voltage of about 1.5kV from a bug zapper for testing, with such a low voltage the pointed gaps helped to get the process going. But when I switched to a mini flyback/LOPT giving about 5-6kV the leakage at the gaps was enough for continuous arcs to form. This required a large amount of tweaking to get it to fire at a somewhat consistent rate, but even then it sometimes misfired.
The gaps did not have a direct line of sight with each other
Whilst doing some research on the shapes of spark gaps I came across the following from
The traditional Marx generator operating in air has all the gaps in a line with the electrodes operating horizontally opposed. This allows the UV from bottom gap to irradiate the upper gaps, reducing their jitter. Tests reported in Craggs and Meek showed that obstructing the UV led to greatly increased jitter in the bank output, which they attribute to the lack of UV irradiation on the upper gaps.
With this in mind I set about making some half decent spark gaps that were rounded with a direct line of sight from the first through to the last one for the UV light to travel unobstructed.
The electrodes are just pieces of solid wire with one end bent over in a loop, solder is then generously applied and the surface tension keeps it in there whilst it solidifies.
After doing all of that and tweaking the spacing of the gaps I can now get consistent jitter free sparks at a seemingly faster rate, so fast that I had to add a few more megohm in series with the 4.7Mohm ballast resistor. I guess the corona loading before was large enough to cause significant loss.
I still need to clean the flux residue from the board and some of the electrode legs could do with shortening to reduce parasitic inductance and improve overall neatness.
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