Decreasing Laser Output

[Larry Preston]

I've had my 100W Red/Black only about a year now. If I had to guess I only have maybe 100 hours on the machine of actual run time. I have always run it conservatively at below 30% output as I mainly do wood engravings. The tube is cooled with a chiller unit that I basically leave running 24/7. I periodically check alignment and clean the lenses and mirrors once a month. They are seldom if ever dirty.

I had a need to cut 3mm birch plywood and therefore set my output upwards of 50%. I noticed on my milliampmeter, at the most, I get 8-10mA of current. I checked the tube color and can see that the tube is running slightly whiter than when it was new and therefore suspect the tube is ageing. But likely still okay.

Upon further investigation I have found others that experienced power supply failures where the output of the supply is low but still operating. It seems that the predominate failure mode of the supplies is a complete failure more often than not.

Due to the differences in costs I am leaning toward replacing the power supply first rather than purchasing a new tube. I would like to do a more definitive test and have found a few YouTube video where a load resistor is substituted for the tube and current reading taken while pulsing the laser supply.

-Does anyone know what size of resistor they are using? I assume it's on the order of 1 meg ohm, assuming 40kv/.04mA, as a rough estimate (they install a jumper to increase the output of the supply.)

-Have others experienced similar symptoms and what was the cause?

-I recently contacted Russ Sadler an anticipate purchasing a power comparator to gain a better understanding of how my machine is operating. How many others are aware and using his device?

- Finally, If and when I must replace the tube I am leaning toward the added expense of a 100W RECI tube. My current tube is a 100W EFR which came with the machine. What sources, or suggestions for a tube, have others used successfully?

Thank you,
Larry

[Dave Vigness]

Not sure what you mean by a power comparator, but if you are talking about his Dohicky, I love mine.

I would take three readings and start investigating from there. The DC voltage into the laser PSU from the controller, the actual wattage output via the Dohicky, and the mA reading.

Your 0 - 5V DC from the controller to the laser PSU can be capped in two different ways. A max power programmable in the controller, and a trim pot in the laser PSU. Most have a small unlabeled hole that has a trim pot inside.

[Larry Preston]

Thanks Dave for the response.

Russ in his YouTube video goes through the explanation of his DoHicky and calls it a comparator. I believe because there is no effort to trace it's performance back to a standard through calibration. I haven't yet put my DoHicky on order as Russ is in between batches. Once I receive it I'll definitely take a number of reading as you've suggested.

I just did a review of my Ruida controller settings.

As you stated:
"Your 0 - 5V DC from the controller to the laser PSU can be capped in two different ways. A max power programmable in the controller, and a trim pot in the laser PSU. Most have a small unlabeled hole that has a trim pot inside."

I just found that the maximum power setting had been changed in my Ruida controller. It was capped at 30% for laser no. 1. I can only surmise it has been that way for a long time. Since I never used the machine at the higher settings I never saw this issues. A rookie mistake for sure. I feel embarrassed to admit I overlooked the settings.

Thank you for the help.

[Dave Vigness]

Maybe a rookie mistake, but one you will remember. Better than the rookie that sets his at 100% and burns the tube out... says the guy that has his set at 100%. But I know I hit my 80W at roughly 60% and 23.5mA, via the Dohicky. Russ was kind enough to run a power curve after emailing him my test results. It showed me how bad my 'KH' tube really was.

It's an EFR F2 QC reject relabeled as a KH. The power curve looks more like a quarter circle, so low power engraving is near impossible. Going to take another shot at it not too far down the road having gone back and re-watched #115, but I'm not holding my breath for spectacular results.