I’m running a chinese CO2 laser, new 100W tube, psu is rated to 180W and is about 18 months old with very light use.
I was doing some work in Lightburn (moving objects around) and it crashed on me. I rebooted the pc and restarted LB. I opened up a saved file that I have used many times and set up my next run, it was a simple etch that I have done thousands of times before from this file. Instead of a smooth etch, the power of the etch varies during the run. I can see the power varying on the external digital power meter readout I have (peaks at around 4amps) and on the built in amp meter on the machine. I then restarted everything, created a sample file in Corel Draw, exported it to LB and started the etch, same result. I then opened a LB file that I have used for the last 2 years and deleted all but one word and ran it, same result. The laser power during the etch is fluctuation. It’s not a random fluctuation, it’s entire lines of the whatever I’m etching.
I’m at a loss, I don’t understand why the etches are now failing. Cutting is still fine, admittedly I haven’t tried a dot mode etch yet.
Attached is a pic of the etch, the red circles show where the power has increased during the etch, and it’s along the whole word, not just where the circle is. Also attached is the LB file of the word. Other than reinstalling LB, does anyone have any other ideas as to why this is happening?
Update on this (and for anyone else that may have something similar). Problem is the newish psu, it now won’t drive the tube correctly at low power. Any power setting over 20% is ok, any power setting under 20% and the power to the tube jumps all over the place. Which is why a cut works fine but a slow, low power etch doesn’t.
If anyone has a recommendation for somewhere to fix a psu, I’d appreciate it (although it may not be worth it given the price of a new one).
The maximum output voltage of the HV power supply must match the breakdown voltage of the laser tube. Because the firing voltage of a CO₂ laser tube depends on its overall length, which varies based on the rated power output, using a power supply intended for a larger tube will tend to mis-fire a smaller tube.
Also, the higher-power power supply will deliver a maximum current higher than the smaller tube should operate at, so it will tend to abuse the tube.
Since you’re in the market for a new HV supply anyway, get a “100 W” supply matched to the tube and see if that improves the situation.
It’s an etch / fill. I do use the min max power settings for all etches, typically the setting that worked best with the material I am using (to get a shallow etch with dark colour) was 250 speed, 12.5 max, 12.5 min power.
All CO2 tube psu’s I have seen or come across have adjustable trim POTs on them to limit the max current. Tube manufacturers have nominal current ratings, for example my new YongLi 100W tube rating is 25mA, So a higher rated psu should never overdrive the tube if the POT is used to set the max current output?
But, as I have now found out and subsequently had confirmed overnight, if the psu is too big it can run into problems driving the tube at very low currents for fine etching, specifically the poorer designed psu’s or those built with inferior components. The previous tube I had in the machine was a 150W Recci but I changed it out as I now need a smaller dot size and left the 180W psu in with the POT limiting the current. After a few weeks of good etching I ran into this etch problem so something has failed in the psu. Swapping out the psu with a 100W psu I had on the shelf has solved the etch problem.
Just for interest, I’m going to get a dohicky and plot the power curves that the 2 psu’s give thru the 100W tube.
That may be correct on average, but the voltage applied to the tube will be far higher than it should be, which will cause problems with the current limiting whe the tube first fires. I think the problems you’ve been seeing come from that mismatch.
Hmm, interesting, this is all at odds to what I have previously been told (earlier generations of tubes did have issues with voltage but they are now supposedly fixed). I have a contact at Yongli, they say the tube I have - AS2 (W4) - can be used with a larger psu (eg 180W with current limiting) BUT there may be times when the power control is not accurate, especially at low power. The puzzle I have is how it all worked fine for the last 6 weeks and has now gone pear shaped.
Regardless, thank you for your help, the simple answer is “match your psu to your tube”.
