Power drop

Hi Guys
Recently developed a power problems with my laser when cutting.
1st cut no problems 22mA 60W
2nd pass 16mA
3rd pass 9mA
When I test pulse the laser the mA is conisitant every time I pulse the test button.
Laser tube has been run for total 22hrs 8 min. engraving and cutting max mA 22.
Not sure if this is the B1 board the PSU or the K40 program?

Would appreciate any pointers.

Welcome @sundowner to this forum

Is this what is happening:

  • You run a job that has 3 passes programmed
  • The power, as indicated by your milliamp meter, all on its own reduces on every pass.
  • Yet if you hold the test button the current reads as expected for the pots power setting and does not reduce while holding the button.


  • We need to prove that the software is not changing the power on the fly. I have never seen this to be a problem.
  • Another possibility is that the LPS loses power over an extended time. Try holding the test button for an extended period while watching the laser current meter. See if the power stays constant. Be sure to have something under the head to absorb the beam so you do not start a fire.

I need to know what software you are using. That is included in the information requested below

The information requested below will help the community troubleshoot and fix your problem.
Please provide as much of it as you can.

Instructions for filling in the table(s) below:

  • For each table requested: Highlight the table in this post
  • Then click “quote”
  • A new post will open or for an open post text will be inserted which includes the formatting of the table in place
  • Just modify the text between the two (|) formatting characters, column to match your responses

---- Machine Information Table -----
Please fill in as much of this table as you can.

Select Y or N in the "Installed column. If that system is not installed (N) leave the rest of that row blank.

Subsystem Installed Manuf Model Link to info site
Machine model Y,N xxxxxxxxxx xxxxxxxxxx xxxxxxxxxx
Controller type Y,N xxxxxxxxxx xxxxxxxxxx xxxxxxxxxx
Control Software Y,N xxxxxxxxxx xxxxxxxxxx xxxxxxxxxx
Laser Power Supply Y,N xxxxxxxxxx xxxxxxxxxx xxxxxxxxxx
Moveable bed Y,N xxxxxxxxxx xxxxxxxxxx xxxxxxxxxx
Separate DC supply Y,N xxxxxxxxxx xxxxxxxxxx xxxxxxxxxx
Digital Control Panel Y,N
Laser current meter Y,N
Air assist Y,N
Interlocks Y,N
Distilled water coolant Y,N
Coolant Flow Sensor Y,N
Coolant Temp Sensor Y,N

You should check the temp and flow of your cooling water. The tube looses power if it gets too hot.


Thanks for yhat. I check water levels regularly. I have a chiller, flow meter, low water pressure switch and water temp sensor guage. Water temp constant 16 degrees C.


1 Like

Standard Chinese 60W 6040
Using a B1 board
K40 whisperer
Moveable bed
Digital Control Panel
Laser current mA meter
Air assist
Distilled water coolan
Coolant Flow Sensor



What about this??

A picture of your laser power supply showing the connectors please.

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I think I may have found the problem.
Cutting a 100mm dia. circle 60w 60% power setting 10mm/s
The laser starts to cut at 21mA after 3/4 of the circle the power drops 15mA
Second cut 15mA drops to 11 mA.
Did a test laser fire at this stage 11mA.
mAmmeter is connected in line between the return line of laser tube to laser supply.
I have checked all the cable connections no problems.

What are your thoughts?



I am confused.
You found what problem?

Do you have a DVM and do you know how to use it to measure voltage?

I am a retired electro mechanical engineer
I carried out a couple tests and found a drop across the laser Power supply Unit
A further test after a 1 hour showed the power output had returned to 21mA
The voltage to the PSU was a constant 240v
I then set up my multimeter to check the mAmps in the circuit and the mAmmeter after another hours rest same results

Eric, I am sorry I am having a difficult time (language?) understanding what your problem is?

Please try and answer all the questions I present to you.

What happens if you do this test?

test button held on for 30seconds no drop in current.

Connect a DVM
set to measure volts

  • lead on the LPS-IN pin.
  • lead on ground

Run the 100mm dia. circle job and see if:
Does the voltage on IN vary with the drop in current at the laser current meter.

If yes, Can you tell me how the voltage varies on IN.

Voltage is constant even when the current drops.

Ok, this means that the laser power is not being changed by the IN control of the LPS.

The other source must be the L pin

@Scorch do you have any thoughts on what could be causing this change in power?
It does not look like it is something weird with the supply which is why I checked the IN signal.
Does the M2 with whisperer still dither or does it control power in any way??

K40 Whisperer cannot control the power (it is strictly on/off).

During raster engrave it will look like there is a power drop on the ammeter because power is being turned on/off very quickly and the analog meter will smooth that switching so it looks like a lower power. Based on the discussion the problem is happening during cutting so raster engraving should not come into play here.

If I understand your answer: he is vector cutting meaning the beam should stay on and not see a drop in current on the meter?

In whisperer is there a programmatic difference between engraving and cutting? i.e. can the design file loaded in Whisperer in any way be causing this?

Nothing in K40 Whisperer would cause the current to drop during a vector cut or vector engrave operation.


@sundowner seen from above the change in current is not caused by “IN” nor likely by the software.

The only obvious thing left is the controller itself turning the L on/off for some period of time.

Please post a picture of your controller.

Then try this:

Thanks but first I must correct. I have a B1 controller not an M2.
Will that make a difference?

I do not think that B2 will make any difference.