[glavey]

I recently bought one of the very common k40 laser cutters with a 40w c02 laser tube on ebay. The listing states the maximum current for the laser tube is 22mA, but that seems rather high judging by the fact that many of 40w laser tubes for sale on the internet have a maximum of between 12 and 16mA.

I asked the seller I bought from what the maximum current of the tube should be, and as can be expected, some translation error between english and chinese occured and I was told to not run at more than 5 to 10 amps. HA! I guess I have to rely on myself to find answers and forget asking the seller anything.

[glavey]

Anyone? If you don't know what a safe limit would be, but you own a 40w tube, could you list what you use as your limit?

I realize that all tubes are made different and will have different current limits, I'll just use it as an average over all of the 40w tube specs I've found across the internet.

[abyss]

Look at this as sample:
SP 35W CO2 Sealed Laser Tube for Small K40 laser engraving machine

Keep in mind higher power (= mA) cause laser tube life shorter.

[cinematic2]

For the first time I see seller`s info to be truth.
700mm long chinese laser is up to 32-34W. Not 40W as they usualy claim.

I completely do not understand glavey`s problem with the current.
You can not OVER curent your laser.
Laser will take only as much as it`s construction and condition will let.
Lowering current makes laser work with lower power.

[TehPepper]

You can not OVER curent your laser.
Laser will take only as much as it`s construction and condition will let.
Lowering current makes laser work with lower power.

It is certainly possible to drive more current through a tube than is good for it. Good here being defined as long tube life.

Tube current is related to the voltage supplied to the tube. The greater the voltage, the greater the current.

[cinematic2]

It is certainly possible to drive more current through a tube than is good for it.

No, it is not because laser takes from PSU as much as it can. And you may only limit it using potentiometer or PWM. There is no way to overcurrent laser as long as you use appropriate PSU.

Tube current is related to the voltage supplied to the tube. The greater the voltage, the greater the current.

You talking worst bul****s ever heard.
Current is a current, voltage is a voltage. Higher voltages does not make current higher.
DC lasers ARE NOT DRIVEN WITH VOLTAGE BUT CURRENT. VOLTAGE IS CONSTANT.
There are 2 levels of voltage supplied to DC excited laser (laser, not any f... tube). Ignition voltage and working voltage.
For instance for 700mm long laser it may be: ignition 20kV, working voltage 16kV. That is all. No any other voltage for the one kind of laser.

[TehPepper]

Well this

No, it is not because laser takes from PSU as much as it can. And you may only limit it using potentiometer or PWM. There is no way to overcurrent laser as long as you use appropriate PSU.

Seems to clarify this

Laser will take only as much as it`s construction and condition will let.

So laser tubes do indeed have a negative resistance characteristic which I was unware of when I made my first post. So yes, the laser PSU must carefully limit the current being drawn by the tube.

Gas Discharge Tubes - Introduction

Though, I will argue the how "appropriate" the power supplies shipped with cheap lasers are. My original cheap laser PSU and it's replacement were not limiting the current to a safe level for my tube. "100%" with one of them would have to been close to double the rated operation current of the tube. Given that I think glavey's concerns are perfectly justified. If any calibration is done at all I'm sure it would be done so that your getting the advertised "40 watts" from what is actually a 30 watt laser tube.

[jfong]

I recently bought one of the very common k40 laser cutters with a 40w c02 laser tube on ebay. The listing states the maximum current for the laser tube is 22mA, but that seems rather high judging by the fact that many of 40w laser tubes for sale on the internet have a maximum of between 12 and 16mA.

I asked the seller I bought from what the maximum current of the tube should be, and as can be expected, some translation error between english and chinese occured and I was told to not run at more than 5 to 10 amps. HA! I guess I have to rely on myself to find answers and forget asking the seller anything.

I have a K40 and multiple posts around the net says 15-16ma is the max you should run the tube if you want it to last.

[PanLino]

Hello guys. I have a k40 type laser machine and this issue with the amperage was a little tricky. My machine is the one with the +/- percentage of power control panel so you never know what current is passing through.Thankfully I was ready for it and installed an Ampere-meter in the middle of the cathode-psu wire. After talking with the supplier and searching around , i came up with some conclusions that make sense to me. First of all those 30w-40w 700mm tubes that come with the machine have mostly 15mA(??) max current. Of course you cant work with this current all the time because the tube will die pretty soon.So, a safe setting is a max 10-12mA . You can go up to 15mA but dont get used to it. Second thing is that if there's no documentation about the tested max amperage of a tube, we can never be sure. Start at the minimum amperage your machine is able to shoot and go up so you can test and set your tasks each time. Try to make your job with the minimum amperage(power) needed if you want to keep alive your tube for longer period. Some people push the power to the limit so they can cut thicker materials. Big mistake. Check mirrors/lens(clean and aligned), get air assist and you will do the work