Laser amp drop during single cut job

I have OM Tech 100W laser. I am running a cut file that take 1hr 15 min to run. The power supply mA is 27 at the beginning of the job but drops to 18 mA by the end of the job. The job performance drops of time. Power supply only has about 50 hours on it. After about 20 minutes I can start a new cut job and have the same experience begins at 27mA and drops to 18 mA by the end. Is this a normal expectation?

How does the laser tube cooling water temperature behave during those cuts? If it’s steadily rising beyond 20 °C, then what you’re seeing is the tube output dropping as the gases overheat.

If you’re using a radiator, rather than a refrigerated cooler, that might explain what’s going on as the water temperature gradually returns to room temperature before you start the next job.

If you’re using a refrigerated cooler, then it’s not big enough for the amount of power the tube dumps into the water. This can happen as the refrigerant slowly leaks out over the course of years: it used to work fine and now it doesn’t.

Edit: If the water temperature is good, then you’re likely looking at an overheating power supply. It should have a fan to keep it cool, so check for adequate air flow through the electronics bay and make sure there’s no fuzz accumulated on the supply’s vents.

Thank you for your response! I do have a refrigerated cooler (CW5200) but it does bump up to 21.5- 22 degrees by the end of the cut. I live an the desert southwest and it is tough to keep the water temp down when it’s 100 degrees or more outside. I do have window AC unit but the laser is the furthest away from it.
I don’t think there is a fan located in the power supply area of the cabinet. I will check and add one if not. Thanks again.

That ought not make much difference in the tube output.

My OMTech had a uselessly noisy fan that I replaced with a blower:

Much better airflow with much less noise!

Sometimes fans just die, so make sure the blades on the fan in the power supply still go round and round …

I put a new fan in the cabinet aimed at the power supply which helped keep the amp from dropping below 22. However, I paused a cut job and when I resumed the cut the amp meter dropped to 6 mA and stayed there. I assume the the power supply finally just failed… would you agree?

That horse has plumb wore out!

Assuming your shop runs at comfortable shirt-sleeve conditions, then the power supply isn’t working correctly at “normal” temperatures.

I doubt that it’s the tube, as cooling the supply doesn’t affect the tube.

Although it sounds callous, sometimes the cheapest and fastest way to debug a problem is to throw hardware at it and replacing the supply is way cheaper and easier than a new tube.

If the new power supply doesn’t solve the problem, you will have:

  • Eliminated the most likely cause
  • Put a known-good spare on the shelf against future need

Out of curiosity, how old is the laser and how much usage has it had?

Definitely let us know how it works out, because somebody else will definitely benefit from your experience!