Laser Power supply drops in mA

Hello everyone!

I’m running into some problems with my lasercutter last week. The power output seems to vary randomly during a cut out of nowhere.

I performed a test shot with 95% power. This should be around 21mA.

A test shot (about 10s) gives me to following situations:

  1. Perfectly on 21mA (no issues)
  2. Starts on 21mA and drops to 6mA
  3. Starts on 6mA and jumps to 21mA
  4. Starts on 6mA and jumps to 21mA and jumps back to 6mA

The things ive checked:

  • I havent changed settings i can recal.
  • on 95% the ruida controller outputs nealy 5v (so this should be good)
  • output of digital psu screen matches with my anolog meter.

Machine specs:

90 watt co2 tube
150 watt power supply (adjusted to output a maximum of 22mA at 100%)
ruida controller
runs deionized water

Im kinda lost at the moment. Does someone have an idea?

Did you adjust this via the lps? Sounds like you did, since it’s a hefty lps for the size of tube.

When you set this, use 50% power and the mA meter to set it at 50% of the current you want. Keeps you from long times with max power when it’s not needed.

22mA seems very low to me. My 50 watt came with a test that showed a max of 21mA. I set my 50% level to 10.5mA. I run mine mostly engraving, but I’ve done my share of cutting at 18mA.

The description indicates a failing tube to be, but I hope not. I’d check the TEM state to ensure you are resonating at TEM0…

A faulty cathode connection can cause issues. Check the HV and but mostly the ground path…

Good luck


Thanks for the reply!

Yes the power is adjusted on the LPU. Via the tiny hole on the side.

It’s a Cloudray CR90 tube with a maximum mA of 25mA. So 21mA at 90% seems oké to me :slight_smile:

The tube has less than 10 hours of running time on it, so I don’t suspect the tube just yet. It always has been cooled and never been over the 25mA.

What is TEM state? And how to check it?

I will check the cathode connections tomorrow and see if I have arcing somewhere on the cabling. The behavior is just so random…

I was mentioning that my 50 watt tube max is 21mA and your 95 watt is 25mA… doesn’t sound right.?

The link I sent you shows the beam, usually from mirror 1 (m1).

Put a target at m1 and make a brown mark, not a hole. In TEM0 state, the beam has a normal Gaussian power distribution, darker in the center, getting lighter as it move outward.

Compare it to the patters in the post and post it here…

You can ‘drag and drop’ a photo onto the reply window and it will upload it or use the upload icon download-icon-background

I would think it has to be the lps or tube, assuming good mechanical connections.


This is the result of a test shot at 25%

I’ve upped the power on de lpu from 21mA to 25mA @ 100%. I haven’t seen the drop during my tests.

Maybe the lpu didn’t like the output setting to be so low.

I will continue testing and update it here.

Most machines will lase down to about 10% power, but that falls off as they get older, I understand.

Can’t tell anything about the ‘spot’ as it’s way too ‘burnt’… need to pulse lower power so there is just a brown spot. That allows you to see the actual Gaussian power distribution and the resonance.

Odd that there is a ‘non’ burned area on the left. What are you using for a material?


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