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 🙂

Notify of
Inline Feedbacks
View all comments

I have a dual head Chinese laser, with 150 watt reci tubes, today laser 2 it not cutting through (3 mm Mdf ) amp gauge reads 6mA , laser 1 is fine and working well, im assuming it’s the tube failing, as they are both running off the same PSU.
Is there a way to test this first.

Helmut Schlechmair

My Laser has changed the beam spot from TEM00 to TEM01 , i have used the Laser with 0 degree water this Winter and after some jobs the beam is like a 8

Tracy M

Hello can u help me understand why my laser skips when powered above 3-5 ma. Is it losing power. The best is still slightly purple

Wayne Hooper

My laser tube failed on me, I’ve now replaced it and it fires on test. But for some reason I can’t connect to my laptop anymore. I’m running windows 8 with K40 whisperer. Any ideas?


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?


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?


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?

Christian Forasté

Bonjour HP Persson

Pour Un Bon fonctionnement Laser CO2 100w

Quelle Température ?? °c

Quelle Puissance Max ?? mA

Merci De Votre réponse

Christian Forasté

pour la réponse
HP Pression


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


Ok Thanks, I see your point. Will definitely keep that in mind.