Most of us experience this sooner or later, but if you experience it really close to where your machine was delivered, here is the two top reasons why your laser tube died.

1: Overpowering the tube

While the tubes are called 40w, they cannot really handle 40w and has a effective output of about 30-35 watts depending on tube quality.
This mostly happens on the digital versions of the K40, where the milliamp. output isnt visible, only a percentage of the power.
Theese machines cannot handle 100%, they cannot handle 90%, you will overpower your tube at 90%, thus lowering the life span drastically.
If you have a digital version, i suggest installing a 30mA amp meter.
Keep your tube below 18mA at all times to be safe. You can go up to 20-25 but the gain is very little and you are strangling your tube for every second doing it.

2: Overheating the tube

This is pretty common, not having a clue about the water temperature in your tank and just running the machine.
The laser tube works the best at 15-20c water temp, anything above will degrade your tube.
If you run at 23c your tube will not die tomorrow, but you may lower the expected life time by a couple of weeks or month. So for some its ok to run at 23c as they know they need a tube change later on.
There is also a link between using wrong coolant to unexpected tube malfunctions.
Read more about that in the watercooling article.

But if you want to use your tube the most, keep temperature around 20c.
Whats happening when the temperature is too high is the regenerative gases has harder to regenerate inside the tube wich lowers the power output with time.
There is a deeper scientific explanation, but i keep it simple and understandable for now 😉

Quick info: Never go beyond 18mA and keep water att 20c or lower 🙂

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12 thoughts on “Top 2 reasons why your laser tube dies”

  1. When you say the best temp is between 15 and 20 degrees , does that mean there is a loss of power when running the tube under 15 degrees? Was just wondering why this would be the case… cheers

    1. Lower temp will introduce condensation on the tube (dew point), that might cause arcing in a bad situation. You do not gain anything with having the coolant colder than 15 either, just bigger risk of cracking the tube if you get a hot-spot or a flush of hotter water.

  2. Bonjour HP Persson

    Pour Un Bon fonctionnement Laser CO2 100w

    Quelle Température ?? °c

    Quelle Puissance Max ?? mA

    Merci De Votre réponse

    1. It may be different between manufacturers, but above 20Celsius is not recommended. Some tubes, like RECI is made for 20-25C max. Max mA depends on the manufacturer, most 100W machines has 24KV output, max mA is then 28mA. If the output is 16KV, max output is 35-38mA – check with the seller for exact data.

  3. What is the recommended % of laser power for quality of clean rubber engraving for making a personal seal with complicated logo without causing damage to the CO2 laser tube?

    1. This is very different between machines, it depends on optical qualities, how good the machine is aligned and so on how much power you need. The best approach is to test it bit by bit, start at 20% and 150mm/s and see what you get – if its too light, lower the speed or increase power. But i would suggest installing a mA-meter, the %-meters are not very accurate, you are over-powering and damaging you tube already at 50-70%. A mA-meter will tell you the real power.

      1. So, 1 px/mm and 1 pass is enough or the best is 2 px/mm and 3 passes at the 25% power and 200 mm/s for the Kehui KH-3020 Laser Engraver to engrave a 40mm personal rubber stamp?

        1. Impossible to confirm or deny, even if you put two identical machines you have side-by-side, they will need different settings. You need to test it on the material you have. The machines are different and rubber stamp materials are different from different manufacturers, so the only way is to test it. I would go 1px/mm for everything.

  4. What are the symptoms of an overheat? Changing from TEM00 to TEM01? Or just a reduction in power?

    I had kink in the coolant line and the temps spiked to what I would imagine to be “catastrophic levels.” Something like 45C…

    The laser still fires and can still cut plywood to some extent, but nothing like when the beam was in TEM00.

    I guess I’m wondering if the change in the mode equates to loss in power or if the TEM01 mode distributes the power into the classic donut shape.

    Also, what is it that actually causes the change in mode? Does it have anything to do with the gas inside the tube, the optics inside the tube, or the physical shape/construction of the tube?

    1. Catastrophic failure often occurs with loss of coolant, overheating the tube and cracking some of the internal tubing so the coolant leaks out in the chamber around it – this often kills the tube completely right away.
      Overheating for a longer period of time – let´s say 40c water under 10hrs of runtime will show up as a lowered output or completely dead tube, there is so many parameters involved i can´t show a schematic of what will happen.

      When the laser is discharged the gasses are dissociated from Co2 to Co and O2 (there is more stages here but keeping it simple). The dissociation is quicker than the recombination if the gas mixture is not cooled, in our case, with water through the tube and if the water is hot or not there at all the recombination will slow down – and with time affect the output. This reaction is never 100% or 1:1 ratio, there is always a loss. Hot coolant, no coolant or overpowering the tube lowers this ratio – less Co2 to excite when discharging the laser – less Co and O2 (with Nitrogen, xenon and others) to recombine to Co2 again.

      45c for a short period, let´s say minutes should probably not kill the tube. I would suggest some “regeneration runs” – Low power, high cooling and let the recombination “work” for 10 min. Engraving or cutting for 10min at 14-16c coolant temp at maybe 5mA have shown better performance after similar issues.
      Also take a look at the end lens in the laser tube, when they overheat the glue tend to soften up and moving the outer part of the tube – this can give very strange beam shapes too.

      The TEM is not my area of best knowledge, i have a basic understanding of it but nothing to write home about.

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