Cuts better at 50% power than at 100%, what is the problem?

[Linda Smith Alabama]

Chinese 60w laser cuts better at 50% power than at 100%. It barely fires at 100% power so we use it at 50%, and seems like it's getting worse. What do you think the problem is... laser tube, power supply, or optics?

[Harper Abbot]

sure doesn't sound like optics.

Does the power degrade over the course of the cut - does it drop power as the cut continues? It could be an overheat issue - like a component loses power as it is heating up. Not driving it so hard would keep it cooler, thus not overheating, and retaining power.

Since it's a chinese machine maybe you should just buy both components? Spares are good.

[Linda Smith Alabama]

It doesn't degrade over the length of the cut, it simply cuts better with a power setting of 50% than it does at 100%. Around 50% seems to be the peak, with the power getting lower as it increases or decreases from there.

[Dan Hintz]

Assuming this is one of those systems that uses a potentiometer to set the tube current... check the resistance over the pot's entire range of travel to make sur eit is increasing/decreasing appropriately.

[Linda Smith Alabama]

No.. this doesn't use a potentiometer. The power, I assume, is controlled by the computer and software. I wish there were a way to check the output power of the power supply to determine if the output was bad or if the tube can't convert the voltage to light. I just need a better way to determine if a new power supply of a new tube is whats needed.

[Viktor Voroncov]

Do you have possibility set power from laser panel? Or only from software?

[Linda Smith Alabama]

Only from the software; won't do anything without the software running. It uses a Leetro MPC03 PCI controller card and Lasercut software.

[Viktor Voroncov]

Sorry, in this case my possible advice will not work :(

[Kim Vellore]

I am guessing it would be the power supply. At 50% it is able to supply the current to keep it running and at 100% the power supply is not able to keep up and the laser is not firing properly. If the laser power is ok from low to some point higher then it starts failing I would start with checking the Power supply. Not sure how these are made if it has a DC power supply or a HV supply for the tube...
Kim

[Linda Smith Alabama]

Well, it looks like it is putting out the power, but whether it's getting to the tube or not I don't know. I hooked up a simple electricity meter to see if there is more power at higher power settings. Here are the results:

2.2 amps doing nothing (this includes the water pump & fans)
3.0 amps cutting at 5% power
3.4 amps cutting at 10% power
3.7 amps cutting at 20% power
3.8 amps cutting at 30% power
4.1 amps cutting at 40% power (best cut)
4.2 amps cutting at 50% power
4.3 amps cutting at 60% power
4.5 amps cutting at 70% power
4.6 amps cutting at 80% power
4.7 amps cutting at 90% power
4.8 amps cutting at 100% power (barely any output)

The power increases consistently but I don't know if that means anything. The best cut was at 40%, as power increased output decreased. Any ideas?

[Norberto Coutinho]

If yes, try with a new set. After with a new lens if you have a spare too. Or first with the lens and after with mirros.

[Dan Hintz]

I'm not sure I like that power curve very much... it tends to taper off in the wrong direction...

[John Frazee]

When I first had my chinese laser set up, the tech was doing something and switched some things around that made mine do similar. When I set it to engrave at 10% it powered up at 90%. When I set it at 90%, it barely fired. Everything was flipflopped. He corrected it.

[Chuck Stone]

.. on the bright side, consider the savings on your electric bill..

It sounds like something in the software isn't kosher, but I don't know.
It seems like if it were a tube problem it might not be so consistent.. but
I'd still check the connections, look for dry caps.. things like that.
(I have no idea about the machine)

[Linda Smith Alabama]

I got some advice on how to check input voltage from the computer at the power supply and that checks out OK. Try this on for size... visibly looking at the laser tube with power at 10% the purple light is barely visible and will not burn thru a tissue at the end of the tube. At 30% the light is brighter and will burn a hole through a tissue at the end of the tube. At 90% the purple light is VERY bright but will not burn a hole through a tissue at the end of the tube (my silly husband put his FINGER at the end of it and didn't feel any heat!)

I'm at a total loss!!! How can the light be so bright with almost no output?

[Larry Bratton]

It's a Chinese secret.:)

[Chuck Stone]

I'm at a total loss!!! How can the light be so bright with almost no output?

Unless I'm not understanding the question, if the light is bright, you ARE
getting output. But if it isn't focused, it won't burn. (or not much)

[Dan Hintz]

It's very possible one of the internal mirrors has lost alignment...

[Linda Smith Alabama]

Ok Guys... Let me Clarify... When I said:

"At 30% the light is bright and will burn a hole through a tissue at the end of the laser tube. At 90% the purple light is VERY bright but will not burn a hole through a tissue at the end of the tube (my silly husband put his FINGER at the end of it and didn't feel any heat!)"

That means the area I'm putting the Tissue is at the end of the LASER TUBE... Before the first mirror. My silly husband put his FINGER at the end of THE TUBE ITSELF and didn't feel any heat at 90%

Just FYI: At 10% the Tube Lights up slightly and get brighter as the power percentage is upped to 20%, 30%, ect.

[Norberto Coutinho]

Try to do a test with your room in the dark. Watch carefull for leakage inside the tube or in the HV cables conections. Are you using distilled water? Are you working in the correct water temperature ( up to 20 Celsius Degree ? )... more power, more the water will be hot.

[Chuck Stone]

That means the area I'm putting the Tissue is at the end of the LASER TUBE... Before the first mirror. My silly husband put his FINGER at the end of THE TUBE ITSELF and didn't feel any heat at 90%.

but is that before the laser beam is collimated and/or focused?

[Linda Smith Alabama]

but is that before the laser beam is collimated and/or focused?

Yes, it is. But the laser should be putting out around 60 Watts of power. At 30-40% the output is enough to burn a hole in paper in a second. The higher the percentage of the power, the more the laser Glows but the lower the output.

[Dan Hintz]

It's sounding more and more like an internal mirror is out of alignment...

[Linda Smith Alabama]

It's sounding more and more like an internal mirror is out of alignment...

Hey! When you are you saying that the "internal mirrors" may be out of alignment, are you actually saying that there are MIRRORS in the LASER TUBE ITSELF? If so then you may be right. Being the newbie I am, I didn't know there were actual mirrors in the LASER TUBE itself. This may explain our problem. Even at 30% power, the laser diameter is less than .125" at the end of the tube. Looking at pictures posted last night, I saw laser diameters up to .375" (***OUT OF THE TUBE, BEFORE THE FIRST MIRROR)

But, if the "internal mirrors" your referring to are the three reflecting mirrors, then we're on a different page. This whole discussion is about whats coming out of the laser tube.

[Dan Hintz]

There are two mirrors within the tube itself... one with 100% reflectance, and the other with <100% reflectance (this is the end the beam comes out of). If one of those mirrors becomes dislodged, the beam is not sent through the partially reflective end and no beam... this problem can increase as power increases.

[Linda Smith Alabama]

OK... We may be on to something! I'm learning everyday! Lets say that is the problem.. is there any way it can be fixed?

[Dan Hintz]

On a glass tube, no.. at least not a way that's financially wise. When glass tubes cost $3-400, you'll spend that much getting a glassworker to fix the mirror alignment, not counting refilling the tube.

I'm not saying this is the problem, but it sure sounds like a good bet at this point.

[Linda Smith Alabama]

Looks like we'll be buying a new tube, and debating a new power supply too (what do you all think?)

Here's a video taken tonight of the tube in the dark. This is showing the output end of the tube, changing power from 15%, 30%, 60% and 90%. http://www.youtube.com/watch?v=56AjnV5AxjY

Remember, at 30% it will cut; at 90% it won't.

[Chris Terrell]

How much use has the laser tube had? If it's had a lot of use, I'm wondering if this might be a symptom of an ageing or faulty tube. Sorry I can't offer more than a question, I'm new to laser cutters myself (use one at work at school) and am still at the base of the learning curve... reading these posts is helping. Best wishes solving the problem.

[Ernie Balch]

Sounds like the tube is overheating and the internal mirrors are going out of alignment. Does the pink plasma in the tube get brighter with increased power? If it does but the laser power does not increase then something must be causing the internal mirrors to detune the laser. Think of temperature or tube mounting stress.

[Ron Chapellaz]

Hey guys, this thread is a year and 5 months old. I'm pretty sure she likely has solved the problem by now...