Building a CO2 Laser power supply
Doubl3 Helix, Mon Jun 16 2008, 11:07PMI 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.
Re: Building a CO2 Laser power supply
..., Mon Jun 16 2008, 11:31PM
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).
..., Mon Jun 16 2008, 11:31PM
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).
Re: Building a CO2 Laser power supply
Doubl3 Helix, Tue Jun 17 2008, 12:08AM
So, where would be my best bet for for getting one of these? How much should I expect to spend? Also, are they usually internally ballasted?
Doubl3 Helix, Tue Jun 17 2008, 12:08AM
So, where would be my best bet for for getting one of these? How much should I expect to spend? Also, are they usually internally ballasted?
Re: Building a CO2 Laser power supply
Hon1nbo, Tue Jun 17 2008, 01:08AM
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)
Hon1nbo, Tue Jun 17 2008, 01:08AM
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)
Re: Building a CO2 Laser power supply
Doubl3 Helix, Tue Jun 17 2008, 01:48AM
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.
Doubl3 Helix, Tue Jun 17 2008, 01:48AM
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.
Re: Building a CO2 Laser power supply
Hon1nbo, Tue Jun 17 2008, 02:02AM
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?
Hon1nbo, Tue Jun 17 2008, 02:02AM
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?
Re: Building a CO2 Laser power supply
Doubl3 Helix, Tue Jun 17 2008, 02:35AM
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.
Doubl3 Helix, Tue Jun 17 2008, 02:35AM
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.
Re: Building a CO2 Laser power supply
Hon1nbo, Tue Jun 17 2008, 12:32PM
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.)
Hon1nbo, Tue Jun 17 2008, 12:32PM
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.)
Re: Building a CO2 Laser power supply
Doubl3 Helix, Tue Jun 17 2008, 03:08PM
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...
Doubl3 Helix, Tue Jun 17 2008, 03:08PM
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...
Re: Building a CO2 Laser power supply
Hon1nbo, Tue Jun 17 2008, 04:57PM
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...
Hon1nbo, Tue Jun 17 2008, 04:57PM
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...
Re: Building a CO2 Laser power supply
Firefox, Tue Jun 17 2008, 07:00PM
If you are having trouble with the pump, you can use old CRT monitors as vacuum reservoirs and use a punch to put a tiny hole in it, then seal a hose over it to suck out the air in your tube.
Also with a CW, Mates has a nice thread on his homemade one here. He was hoping to get up to 300kV, but I don't know if he ever did.
Firefox, Tue Jun 17 2008, 07:00PM
If you are having trouble with the pump, you can use old CRT monitors as vacuum reservoirs and use a punch to put a tiny hole in it, then seal a hose over it to suck out the air in your tube.
Also with a CW, Mates has a nice thread on his homemade one here. He was hoping to get up to 300kV, but I don't know if he ever did.
Re: Building a CO2 Laser power supply
RickR, Tue Jun 17 2008, 07:32PM
A little off-topic, but if the availability of a vacuum pump is a problem, a sorption pump might work for you. It looks "relatively" simple to implement ( http://www.sas.org/E-Bulletin/2001-12-07/features2/features.html ) and it can evacuate a 1 liter volume down to 10 millitorr in about 20 minutes. In addition, there's not a lot to wear out (other than having to replenish liquid nitrogen).
Rick
RickR, Tue Jun 17 2008, 07:32PM
A little off-topic, but if the availability of a vacuum pump is a problem, a sorption pump might work for you. It looks "relatively" simple to implement ( http://www.sas.org/E-Bulletin/2001-12-07/features2/features.html ) and it can evacuate a 1 liter volume down to 10 millitorr in about 20 minutes. In addition, there's not a lot to wear out (other than having to replenish liquid nitrogen).
Rick
Re: Building a CO2 Laser power supply
Doubl3 Helix, Tue Jun 17 2008, 08:45PM
The CRT method for the vacuum is an okay idea, except for the fact that my laser gas is constantly flowing. So, I would need a mechanical pump. Right now I am using a compressor salvaged from a window air conditioner. I went to all of my local shops asking for fridge compressors, and none of them had any spares . Also, RickR, that might work, except the source of liquid nitrogen. It would probably be more economical in the long run just to buy a good vacuum pump. I am going to start building a two stage CW soon, so I will take a look at that thread.
Doubl3 Helix, Tue Jun 17 2008, 08:45PM
The CRT method for the vacuum is an okay idea, except for the fact that my laser gas is constantly flowing. So, I would need a mechanical pump. Right now I am using a compressor salvaged from a window air conditioner. I went to all of my local shops asking for fridge compressors, and none of them had any spares
. Also, RickR, that might work, except the source of liquid nitrogen. It would probably be more economical in the long run just to buy a good vacuum pump. I am going to start building a two stage CW soon, so I will take a look at that thread.Re: Building a CO2 Laser power supply
jpsmith123, Wed Jun 18 2008, 11:56AM
You can get a mechanical pump (two stage rotary vane type) rather cheaply on ebay. Since what you're doing doesn't require a high volume throughput, you can use a small pump, which you can get for 100 - 120 dollars or so, and even cheaper if you get a used or "refurbished" pump.
BTW, with regard to a sorption pump, as someone suggested, notwithstanding the problem of somehow achieving continuous pumping (if yours will be a slow-flow laser), a sorption pump based on molecular sieve adsorbent probably won't work well in your application as it will trap CO2 more effectively than N2 and He (it may not trap He at all) thus it will significantly change the composition of your gas mixture as it pumps.
jpsmith123, Wed Jun 18 2008, 11:56AM
You can get a mechanical pump (two stage rotary vane type) rather cheaply on ebay. Since what you're doing doesn't require a high volume throughput, you can use a small pump, which you can get for 100 - 120 dollars or so, and even cheaper if you get a used or "refurbished" pump.
BTW, with regard to a sorption pump, as someone suggested, notwithstanding the problem of somehow achieving continuous pumping (if yours will be a slow-flow laser), a sorption pump based on molecular sieve adsorbent probably won't work well in your application as it will trap CO2 more effectively than N2 and He (it may not trap He at all) thus it will significantly change the composition of your gas mixture as it pumps.
Re: Building a CO2 Laser power supply
Doubl3 Helix, Wed Jun 18 2008, 02:21PM
Yeah, I was thinking about using this pump, once I get some money. That should be enough for most of my vacuuming needs.
Doubl3 Helix, Wed Jun 18 2008, 02:21PM
Yeah, I was thinking about using this pump, once I get some money. That should be enough for most of my vacuuming needs.
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