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Registered Member #1548
Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61
I want to make a high voltage power supply for the laser I am building. I am going for 12-15kV or more, as well as 30ma or more. I had a setup using a flyback (from about 1980), being driven by a single 2n3055. I had an input voltage of 25.2 volts. The flyback arced over after a few minutes of operation. I have decided that I would like to go for another source. I was thinking an Ignition Coil, or an oil burner ignition transformer. Those both seem like readily available transformers. I have tried looking for info on both of these, and I still don't feel like I have a full understanding of them. Do these need certain driver circuits? Somewhere I read that they had used the ZVS Driver with an ignition coil, and got great results. I have also read that they will run off of mains. I'm not really sure, and it would be appreciated if someone could clarify and point me in the right direction here. Also, for the laser it needs to be continuous operation, so it can't be pulsed. If anyone has any insight for my situation please provide me with it. If you have any questions about my laser construction, or have any knowledge of the power requirements, please share. Thank you for your time.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Since you need large amounts of power, a flyback or ignition coil isn't going to cut it for any period of time. Your best bet would be to go with a NST (the new solid state ones would work well for this applcation).
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
how much power is your tube rated for? I saw a lower power tube once built using a CW multiplier (just a couple stages, so current drop was not TOO low, but I would think a MOT with a couple of stages would have sufficient voltage and current for a small-medium power tube, at least that is my suggestion)
Registered Member #1548
Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61
That's the thing. Everything in my setup is home-built. Nothing is pre-fabricated, so I will probably have to go with the NST just to make it easier. My tube is 48 inches in length with a 970mm active medium.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
what is the pressure? The pressure of the gas can determine the conductivity, and overall power requirements and limitations... is your gas going to be pure CO2 or is it going to be diluted? an NST may be too much power for a homebuilt tube, but maybe not, it all depends... but gas pressure and size are the main components... just curious, what coolant are you using?
Registered Member #1548
Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61
My pump at the moment only pumps down the tube to about 25 in of hg. The gas mixture is: 75% Helium 15%Nitrogen 10%CO2
The gas is premixed by my local industrial gas supplier. Electrode spacing is a little under a meter. The diameter of the plasma tube is 10mm. The tube is water cooled, I have a pump cycle water through a cooling jacket. My tube is moderately large for an average home-built tube. I have thought about using alcohol and dry ice once I get the laser working well.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
25 in Hg and one meter spacing seems a little high, but it is doable... ig you want to test the tube at this pressure, you will need the NST, but I don't know if 12-15kV will do that for sure... what you might try to do (since these tubes are DC anyways) is get an NST around 8kV and use the CW multiplier (this will make it DC and multiply the voltage, and since the change in voltage and current is proportional, there is no loss in power from the NST!).. I would put in three stages (four seems like overkill) and use a variac and slowly start to build up... you should be able to notice when you have reached the stopping point (at least from what I have read... I have built supplies for these, but never a tube.)
Registered Member #1548
Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61
Okay. I am going to get a new pump when I get some cash (so who knows how long that will be ). I may have a lead on a 15kV 30mA NST. Would I want to buy this or would I want to get a lower one? I don't see the problem with more voltage. Perhaps then I could only use one or two stages in the CW. A quick question about the diodes i use. They're high voltage diodes that are rated for 10mA. Do I need to get new diodes for the new amount of current that would be flowing through?
P.S. How much is a variac and where can I get one? I have always wanted one...
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
variacs can vary on prices, ebay sometimes has good deals... maybe a step down transformer to start (if you get some with taps on the output, that will work for adjustments... if you have AC output wall-warts I use those sometimes, and radioshack has some AC ones with variable output and the 15Kv should be fine, just start with two stages in the CW and at those ratings you should get around 450W max which is a lot, especially for a homebuilt laser... and also ebay has NSTs very cheap if you cant get something to vary the power... maybe someone here has something, have you asked in the sale and trade forum? also, you may look into restoring a molecular vacuum pump found for cheap (that is what I see many people do)... or there is another method... this involves using plenty of "getter" material, and using a bunch of that to suck away the air and isolate it from the chamber... look into the amateur scientist sections as they have many details...
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Building a CO2 Laser power supply
). I may have a lead on a 15kV 30mA NST. Would I want to buy this or would I want to get a lower one? I don't see the problem with more voltage. Perhaps then I could only use one or two stages in the CW. A quick question about the diodes i use. They're high voltage diodes that are rated for 10mA. Do I need to get new diodes for the new amount of current that would be flowing through?