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Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Second attempt at typing this out, I got a bluescreen last time (think I might have a bad stick of RAM).
Anyway, yes the spark gaps played a big part in getting it to work. That faint noise when there is no output for me turned out to be one of the spark gaps firing prematurely and discharging all of the other caps. Look at the spark gaps really closely and see if one of them has a small arc across it.
@Physics Junkie My gaps are around 1.5mm's each, with both electrodes pointing at each other rather than vertical like a jacobs ladder which is what I originally had them like.
I think having them pointed at each other is normally avoided with some of the bigger/higher input voltage marx's, but at lower voltages they seem to help "encourage" the gaps to fire.
I ran into a slight problem with R2 going open circuit after a few test fires. Not sure if that is becuase its too low wattage or if I simply got a dud, but it is in the path of the HV return for the marx. After replacing it with a higher wattage one and by-passing it from the HV return it has been fine.
By bypassing it I mean using an external resistor or no resistor at all (haven't had any problems so far in doing that).
Video of it running, I'm only putting around 2kV in so the final output is not at its greatest potential (pun intended).
I should note that I am not using the HV multiplier board since I live in 240v land and have no variac. The Marx is connected directly to a small inverter that gives around 1.5-2kv, can't be sure for certain though since I have no "official" way to measure it.
I have also bypassed the 4.7Mohm resistor for the time being with a smaller one since I am using a lower charging voltage.
Also checked the multiplier board and found C16 to indeed be isolated from the diodes and C14, so its defiantly a mistake in manufacturing.
Registered Member #3450
Joined: Sun Nov 28 2010, 05:01AM
Location:
Posts: 61
I got mine in the mail today. It is a very nice looking kit.
After correcting the missing trace between C14 and C16 I got a few sparks before it quit. I had the lights off and noticed some corona coming from R2 on the Marx board. R2 failed open. I jumpered R2 out, now I only get a 1/2 inch spark about every 5 seconds.
Is the consensus on the spark gaps to face the pointed ends of the cap leads together?
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Physics Junkie wrote ...
Very nice Alex! I did notice several premature fires though. You might be able to get away with a more distance on the gaps perhaps?
Thanks. I did play around with the spark gaps quite a bit and have come to the conclusion that my charging voltage is just too low for any larger spark gaps. If one of them was too large then non of them would fire, or the one with the smallest gap would fire and a continuous arc would form.
Edit: I think it might just be the effect of the camera's rolling shutter (CMOS sensor), sparks taking place between frames etc.
I am going to make a regulated power supply for this at some point, since the capacitors are rated at 6kV each I am thinking of aiming for the 4.5-5kV mark to leave for some headroom. I was thinking of using a UC384x + feedback loop of some sort to shut the supply down on short circuit or over voltage.
Polonium210 wrote ...
I got mine in the mail today. It is a very nice looking kit.
After correcting the missing trace between C14 and C16 I got a few sparks before it quit. I had the lights off and noticed some corona coming from R2 on the Marx board. R2 failed open. I jumpered R2 out, now I only get a 1/2 inch spark about every 5 seconds.
Is the consensus on the spark gaps to face the pointed ends of the cap leads together?
I had the exact same thing on mine, R2 went open circuit after a few runs and I recall there being some arcing around that area before it failed. What I suggest is replacing it with another 1Mohm resistor and then soldering a wire directly to the capacitor leg after R2 for your HV return, bypassing the resistor from the HV return path.
If you wanted to then limit the discharge current use a much smaller higher wattage resistor of about a few 10k, any higher than this and the discharge arc is too faint to see in a moderately lit room (if arcs are your primary goal, for other applications it might be fine).
Also try bypassing the large charging resistor with a much smaller one, the 4.7Mohm is overkill and really slows down the burst rate. I put a 150k in parallel with the charging resistor on mine, this was for 1.5-2kV charging voltage so you might want to use something like 200-300k for the multiplier board.
BTW How much current does the whole set-up draw when the multiplier board is used? I just did some calculations and @ 60hz the capacitive reactance of a 100nF capacitor is 26.526 Kilohms.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Excellent, thanks for posting the video. I'm so glad you got such great results. Spark gaps were trickier than i originally thought! I did manage to get mine running today although i used an old portable HV DC supply that we had lying around.
Lots of good advice you guys posted - i will dive into all of that tomorrow and respond more! Keep up the good work.
I'm thinking for the final kit to actually use the brass nuts as someone had recommended. Might be a better way of controlling the spark gap distances. And they could be installed using an included shim.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
EasternVoltageResearch wrote ...
I'm thinking for the final kit to actually use the brass nuts as someone had recommended. Might be a better way of controlling the spark gap distances. And they could be installed using an included shim.
That is a good idea, the idea behind that to discourage premature sparks as well as reduce corona losses by using a 'curved like' surface as the spark gap electrode. Unfortunately I haven't had much success with the curved spark gaps, and as Alex pointed out, they seem to rely on the encouragement to fire by making the lead sharp and pointed towards each other.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
EasternVoltageResearch wrote ...
Excellent, thanks for posting the video. I'm so glad you got such great results. Spark gaps were trickier than i originally thought! I did manage to get mine running today although i used an old portable HV DC supply that we had lying around.
Lots of good advice you guys posted - i will dive into all of that tomorrow and respond more! Keep up the good work.
I'm thinking for the final kit to actually use the brass nuts as someone had recommended. Might be a better way of controlling the spark gap distances. And they could be installed using an included shim.
Any possibility of some photos/short video of yours running? Obviously you wouldn't be able to upload to eastern voltage research's "official" youtube channel, but perhaps you could start a development channel of some sort for small clips like this.
@Houdini0118 and HB how are your marx generators coming along?
BTW I have started work on a switching charging supply for mine, although I am still thinking of a way to add a feedback loop on such a high voltage secondary. Don't want to go off topic here but could anyone point me to some app notes regarding high voltage control loops (SMPS stuff).
A potential devider + optoisolator should work I think, but I am just concerned about efficiency of such a divider.
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Obviously you wouldn't be able to upload to eastern voltage research's "official" youtube channel, but perhaps you could start a development channel of some sort for small clips like this.