There is a lot of confusion over what the maximum laser cutting power you should set your CO2 Glass laser tube in order to maximise the tubes lifespan.
What Do You Need to Determine Your Max Power %?
There is one item and one piece of information you need in order to accurately determine the maximum laser power % you can safely use. They are:
- A milliammeter connected in series with the laser tube ground wire, and
- The recommended Max Working Current (not the Maximum Current!) value
For example:
SPT specify a Maximum Working Current of 25mA on their T90W and T100W tubes. Yet they recommend to run at no more than 22mA for the T90W and 24mA for the T100W
RECI give the following advice:
Current: The detection current is 28mA. The max operating current must be controlled at 28mA or less. And the long-term operating current must be controlled at 26mA or below. Working life can reach 8,000 hours if the current is 24mA or less. All current above must be based on the actual current of the ammeter connected in series on the cathode line.
RECI Model W Model Instruction Manual – Section 3.5 Working Conditions
Yet RECI’s Recommended currents range from 22mA for the W1 tube (75W) and 28mA for the W6 (130W) and W8 (150W) tubes. So any time you go over 24mA on the higher powered tubes, you are likely to impact the life of the tube.
How to Determine Your Max % Laser Cutting Power
Assuming you have a milliammeter and the correct recommended max working current. All you need to do is run the laser at a number of different laser power % settings and determine where the recommended Max Working Current and Power % settings overlap. I.e. at what power % setting is the current at it’s recommended maximum working value.
For my SPT T50W laser, the max working power is 20mA and the recommended current is 18mA. This worked out as a maximum power value of 59%. Don’t be too concerned by what the value is, as I’ve seen values ranging from 50~95% for the same brand and power tube.
If you’re not able to reach the specified current, then it means your HV-PSU laser supply is not powerful enough for your laser tube. You can still run your laser machine, but you will not achieve the maximum power output from your tube. Please note: Running a laser tube with an underpowered HV-PSU can result in excessive stress on the power supply if run at it’s maximum output for an extended period of time.
By the way, increasing the the power % above this recommended max level does not necessarily give much of a boost in laser power output. Pushing the current above the manufacturers Max Working Current can in some cases give a lower laser power output. So it’s just not worth the risk of shortening the life of your laser tube.
What Do You Do With This Value?
If your laser machine is using a DSP (Digital Signal Processing) controller such as those from Ruida, then you will be able to modify the vendor settings of the controller through a software package. I.e. You can limit the maximum power % that the laser can run at. Even if someone tries to run at 99% power, the lasers output will be limited to that value specified in the vendor settings. In my case 59%.
Modifying the Vendor Settings in RDWorks
Click File(F) / Scroll Down and select Vendor Settings
Password page Pop up – Password is RD8888 / Click on the Laser Parameter
With the laser connected to your computer, click on Read. This reads the information from your laser controller. Now all you need to do is change the Max Power(%) to your Max power % (59 in my case) and click on Write to send the changes back to your laser controller.
Click Exit to return to the work screen.
Modifying the Vendor Settings in LightBurn
Click Edit / Scroll Down and select Machine Settings. Click on Read. This reads the information from your laser controller.
In the Property window, scroll down to the bottom, where you will see Vendor Settings. Click on Vendor Settings.
A Safety Warning will pop up, choose Yes to continue.
Scroll down to Laser Settings.
Now all you need to do is change the Laser 1 Maximum Power (%) to your Max power % (59 in my case) and click on Write to send the changes back to your laser controller.
Click OK to return to the work screen.
Conclusion on Setting Your Maximum CO2 laser cutting power %
Working out your Maximum Laser Cutting Power % is a simple test to make, and should be completed in just a few minutes. If you modify your Vendor Settings accordingly. it will stop you (and other users) from inadvertently over driving your laser tube and shortening it’s life. Potentially saving you 100’s of £$€ in replacement tube costs.
Please Note: You need to do this for every new tube you fit. Even if you replace your tube with the exact same model, there can be significant differences between tubes.
How to Fit A Milliammeter To Your Laser Cutter
People often get worried about adding a milliammeter to their laser cutter as they are afraid of the the high voltages (15kV +) associated with the laser power supply and laser tube.
However, the milliammeter is actually fitted in series to the laser tube ground wire, meaning there is a negligible voltage across the milliammeter. The drawing below shows just how simple a connection this can be:
The hardest part is usually cutting the hole for the milliammeter in the laser cutters chassis. If you have a higher specification Hi-voltage Laser PSU, you can now buy LCD Current meters that plug directly into the hi-voltage power supply without the need for any wiring. You still have to cut a hole for it of course.
It goes without saying, although I will have to say it. Do not work on the electrics of your machine while it is connected to the mains supply.
What Next?
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Disclaimer
Last updated April 25, 2024
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