I have a question about tuning the PSU to the tube power ratings. So I have received my new 90W CO2 Laser and I am just getting ready to start running test cards. I decided to go ahead and check the power output (mA) at different power settings on the Ruida controller. According to RECI “The Model T series tubes max operating current must be controlled at 28mA or less. And working life can reach 8,000 hours if the current is 24 mA or less.”.
Here are my results:
25% power = 6mA
50% power = 18mA
65% power = 24mA (Max recommended by RECI for continuous power)
75% power = 27mA
80% power = 30mA
85% power = 31mA
90% power = 31mA
95% power = 31mA
100% power = 31mA
It is my understanding that many people adjust their PSU so that when it is set to 100% max power it is at the tubes recommended power level. My question is, what are the advantages of doing this other than making the scale make sense and I guess protecting the tube just in case somehow the settings got changed to 100%.
I like the idea of being able to use the entire 0-100% scale on the Ruida controller, especially since I do all my power settings in LB which helps me understand what 60% power setting in LB equates to. If I had my laser set to 65% and my power setting in LB set to 60%, then it hurts my head a little. LOL.
I guess I would like to know if there are any other logical or necessary reasons I should adjust this? Or should I just set it to 65% and move on?
As your table shows, there’s not much advantage to increasing the current over the “continuous power” level, so capping the current at that point won’t cost much cutting ability. The tube’s optical output power also decreases as the current increases, so the “continuous power” is reasonably close to the actual maximum.
The tube’s output power will decline as it ages, so you could, in principle, crank up the maximum current to compensate. This would be the start of a death spiral, but would maintain the same cutting results at the same PWM power settings while you order a new tube.
The three power supplies I’ve had (one having died) all have maximum currents somewhat above the tube’s rating, but I haven’t bothered fiddling with their settings. Basically, I just run test cuts, pick a reasonable power level based on the results, and reserve the ability to (briefly) put the screws to the tube on those rare occasions when it’s necessary.
I was actually convinced to do this but a buddy of mine made me question my decision. So I thought I would see if there is other reasons that I am not seeing.
Your reply made me remember a post I read about the PSU output power. So if I recall the conversation correctly, the way my PSU is set currently, it is outputting 31ma at all times. And the Ruida controller is capping the power coming in. Is this correct?
If so, then lowering the output of the PSU to around 24mA would essentially extend the life of the PSU on some level, correct?
I found this list of advantages from another post that I thought I would share for those that may be searching for this info as well.
There are a number of benefits to going through this calibration:
• You preserve your tube from accidental overdriving - it makes it hard to make a costly mistake.
• You get to use all of the 1024 PWM (Pulse-width modulation) steps available - where, by managing it in software, you lose all of the steps above your soft limit.
• You can be confident that what you set on the job is what you are getting, without having to calculate - 90% gets you 90% of what you have available.
• It reduces wear and tear on both the PSU and the tube.
The DC output current from the power supply varies directly with the PWM percentage from the controller. The minimum value may be below the level required to reliably fire the tube (or below the controller’s minimum limit) and the maximum value may be well above the tube’s rating, but neither will bother the power supply in the least.
@jkwilborn has the right idea: adjust the power supply to deliver half the tube’s rated current at 50% PWM. That will get it close enough to the right setting without overstressing things on the high end. You can then run your PWM vs current test again to verify 99% produces just about the rated current, and maybe tweak it just slightly if you’re fussy.
Not enough to notice, given all the other ways the power supply circuitry has of suddenly going toes-up.
@ednisley is correct, do adjust your lps for the maximum value you desire.
There are two trains of thought here…
I prefer to adjust for maximum current, as I think of it in mA…
If you don’t know, like the rest of us do, the maximum current probably doesn’t directly relate to maximum watts out.
If you wish to base your percentages on power, you have to find where the output is the greatest and use that mA value as a maximum…
If you go through the percentages with a wattmeter or use a piece of acrylic, you can see the power curve, close to a line, which isn’t too bad of a linear shape.
My whole time with co2, I’ve used percentage of current, not watts out. I think the watts out will be better and that’s how my current machine is setup. This usually occurs below the rated current, so it also helps with limiting current to the tube.
Maybe @ednisley has one of pieces of acrylic or a graph he did.
The Ruida has a field for setting the pwm lower/upper limits. It’s in the last field of the vendor settings.
I read this as a working currrent of 24mA and a maximum of 28mA…?
I tried to adjust the pot on my PS but the pot would only turn just over a half a turn total. I did not feel comfortable trying to force it at either end. Are they normally hard to turn?
Also it made not difference in mA from one end to the other. Not sure what is going on or what to do next.
I saw this setting. I was not sure how that correlated with the Min/Max settings on the machine. So if I set the Max Power in the Vender settings to say 65% (24mA), does this make 100% max power equal 24mA in the Ruida interface? Just trying to understand how all these Min/Max settings work.
I read that they are 20 turn pots. That is why I was surprised that I could not turn it more than a half turn. And mine is also hard to get the screwdriver on. It is a white plastic philips screw. Does that sound correct?
This is the lv supply… not the laser power supply…
Find the one connected to the lasers anode.
You are adjusting current limits, not voltage.
Yes, but it’s a pain… take simple numbers… if your maximum comes about at 50%, then to get a real 50% you need to take the ratio of them. In this case it’s easy 25% to get 50%… and a single digit skip is actually two…
I only do this with the laser off and after sitting for at least 10 mins. Also I can see the screw if I shine a light in the cooling grid on the side just next to the screw. But I have to be very gentle to get it on the screw.
And yes I need to order some of those screwdrivers.
I’ve been operating on the assumption you were talking about adjusting the high voltage supply of a CO₂ laser. The picture shows the low-voltage supply for the steppers / controller / LEDs / whatever.
If you twiddled that pot, use a voltmeter to reset the output voltage to whatever it’s supposed to be, probably 24 V, which you can find on the label stuck on the case. Reset the voltage
before doing anything else.
Well that makes sense. LOL. The good thing is that it was all the way counterclockwise when I tried to adjust it so it should be right back where it was.
I am not sure where the correct pot is then. There are no more access holes on this PS. I do see a couple other small PS’s but I am guessing they are not for the laser.
