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CO2 Power Supply Schematic Help

Sigurthr

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The tube isn't dead, it's still lasing a bit, don't do anything destructive! Not having a solid plasma channel in the bore is why the output is low. We don't know that there is anything structurally wrong with the tube at this point. Photos look OK unless I missed something.

The problem is that the water cooling is functioning as a low resistance path for the HV current. Increase that resistance (dramatically) and you will save the mirrors (and the tube as a whole). Personally I'd flush the tube with alcohol, blow it dry, and then use mineral oil (cheap grocery store stuff) for cooling. Run it that way and see how it performs. It should be like it was when dry, but without any of the overheating risks. From that point on, we can see true tube health, and delve into power supply concerns.
 

upaa27

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The tube isn't dead, it's still lasing a bit, don't do anything destructive! Not having a solid plasma channel in the bore is why the output is low. We don't know that there is anything structurally wrong with the tube at this point. Photos look OK unless I missed something.

The problem is that the water cooling is functioning as a low resistance path for the HV current. Increase that resistance (dramatically) and you will save the mirrors (and the tube as a whole). Personally I'd flush the tube with alcohol, blow it dry, and then use mineral oil (cheap grocery store stuff) for cooling. Run it that way and see how it performs. It should be like it was when dry, but without any of the overheating risks. From that point on, we can see true tube health, and delve into power supply concerns.
Ok. That a bit of a relief. The diodes should be coming in today and I will see if I can grab some mineral oil today or tomorrow.

Thanks again guys. :)
 

djQUAN

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Is it because of running the tube on AC? HV AC can pass through glass through capacitive coupling but it happens at high frequencies though.

Not really 100% sure as I don't have any experience with gas lasers but just putting it there :)
 

Sigurthr

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At 60Hz there's negligible capacitive coupling, but if this was running at tens of KHz it would be a concern for sure.
 

djQUAN

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I know the OP said something about using a NST to power it but there are both the old heavy transformer based and the lighter SMPS types. Not entirely sure about what voltage the SMPS types put out if they run the neon tubes at HF or 60Hz AC (I assume DC is not good for neon tubes so that is out).
 

upaa27

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I know the OP said something about using a NST to power it but there are both the old heavy transformer based and the lighter SMPS types. Not entirely sure about what voltage the SMPS types put out if they run the neon tubes at HF or 60Hz AC (I assume DC is not good for neon tubes so that is out).
Allanson SS1235ICH neon sign transformer This looks like the nst I salvaged but is rated at 30ma instead of 35.

I'm guessing it is a smps due to the size although I am not an expert.

EDIT: in the description of the nst I listed it says that it is HF. This could be creating some of the wierd discharges as you guys stated. I am going to rectify this asap as this doesn't look good
 
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Sigurthr

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Oh, I missed where you said you were using a SMPS (if you did)! Yeah, it's putting out HF so we're probably just seeing capacitive coupling to the reservoir gas. That would explain the plasma stream to the mirrors too, you can't use conductive coolant with a HF or RF powered CO2 tube. Better get yourself a gallon of mineral oil. Nice catch, dj!

Hmm, you keep mentioning diodes. What diodes did you order, EXACTLY? You can't use standard power diodes with HF or RF, they just plain don't work. You need FAST diodes (they are declared as such, it's not just a relative term of performance). Part number please. Earlier in the thread we assumed you were using a standard iron core 60Hz transformer, big old heavy clunker.
 

upaa27

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Oh, I missed where you said you were using a SMPS (if you did)! Yeah, it's putting out HF so we're probably just seeing capacitive coupling to the reservoir gas. That would explain the plasma stream to the mirrors too, you can't use conductive coolant with a HF or RF powered CO2 tube. Better get yourself a gallon of mineral oil. Nice catch, dj!

Hmm, you keep mentioning diodes. What diodes did you order, EXACTLY? You can't use standard power diodes with HF or RF, they just plain don't work. You need FAST diodes (they are declared as such, it's not just a relative term of performance). Part number please. Earlier in the thread we assumed you were using a standard iron core 60Hz transformer, big old heavy clunker.
I never actually specified the type of transformer as I did not reall know that NSTs had multiple types. I just looked up the stuff when Quan mentioned it.

For diodes I was thinking of using 2 2CL2FMs with a voltage multiplying corcuit using the 2200 pf caps that I already have due to the frequency being able to sustain the caps.

Would this fix the problems?
 

Sigurthr

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Ya, those diode look good actually. 100nS Trr (rule of thumb frequency max of 1MHz, rated for 15pF at 1Mhz too). Yep, those diodes and a smoothing cap would do the job well to rectify (haha) the HF problem.

I wouldn't make a multiplier out of it though, multipliers divide the current by the same factor they multiply the voltage by. What's the current rating for the tube? Your NST is only 35mA, so even a doubler would cut it to ~17mA. Only make it a doubler if it fails to ignite the tube (being HF right now the ignition potential is drastically lowered, so it is possible that even doubled it may not strike).
 

upaa27

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Ya, those diode look good actually. 100nS Trr (rule of thumb frequency max of 1MHz, rated for 15pF at 1Mhz too). Yep, those diodes and a smoothing cap would do the job well to rectify (haha) the HF problem.

I wouldn't make a multiplier out of it though, multipliers divide the current by the same factor they multiply the voltage by. What's the current rating for the tube? Your NST is only 35mA, so even a doubler would cut it to ~17mA. Only make it a doubler if it fails to ignite the tube (being HF right now the ignition potential is drastically lowered, so it is possible that even doubled it may not strike).
Tube is 22ma rated. As for the viltage multiplier... I will attempt to ignite it with a single cap and diodes if it fails I will try the voltage multiplier. I that fails(Which it probably will lol) I will use the zvs flyback. :p
 

Sigurthr

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Let us know the results before you go and try ZVS, please. Oh and mind you, depending on driver, supply capacity, turns ratio, and lots of other factors, ZVS units can pump out waaay more than 22mA. I have one on my shelf that does 640mA secondary current.
 

upaa27

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Let us know the results before you go and try ZVS, please. Oh and mind you, depending on driver, supply capacity, turns ratio, and lots of other factors, ZVS units can pump out waaay more than 22mA. I have one on my shelf that does 640mA secondary current.
Will do. That's quite a bit of current from the zvs. I will put in really low voltage so that I can multimeter it.

Thanks again. I have learned a lot about some gas laser problems and it has generated a lot of interest in the gas laser field for me.

:thanks:
 
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I would be very careful about connecting a
multimeter directly to the output at any
input voltage. I screwed up a nice
multimeter once that way before I knew what
I was doing. It MUST BE in current mode
and properly set up. A safer way would be
to measure the voltage drop across a 1k
resistor in series with the tube. It would
read 1V/mA and pass 1.225W @ 35mA. That
might affect the measurement, so maybe a
10Ω or 1Ω would be better.

Maybe Sig will tell us how he measured that
640mA. :thinking:
 

Cyparagon

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Ammeters are perfectly fine to use with high voltage. There is ideally no voltage across an ammeter, so the meter is in no danger from over-voltage, only from over-current, which won't happen from a NST. It is unsafe to touch if it's on the high side of the load, but if it's just before ground there is no danger at all. It's certainly safer than physically probing a shunt.

I have an ammeter permanently wired to my CO2 tube, and it's never given me problems.
 

Sigurthr

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^^ As Cyparagon said. I used a 1-Ohm precision shunt between load and HV return, measured by an isolated (battery run) DMM. The voltage across the DMM terminals was thus only 640mV. If it had not been a DC flyback but rather an AC one I could have used my 100:1 precision-burdened 1V/A current transformer and oscope too. In that situation (AC flyback) a CT and oscope would have been preferable as the induced and capacitively coupled HF/RF (that flows parallel to the meter inputs) would have precluded the use of a DMM, as most aren't rated for HF. I do have a good DMM rated for up to 6MHz, but I wouldn't chance it on a HV device, so an analog meter would have been needed.
 

upaa27

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Ok. I will pick up an am emoter then. For a ballast resistor can I use a 1k resistor?
 




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