Replacing a Cheap Chinese CO2 Laser Tube

New Laser Tube on the Bench

I never run the laser cutter unattended. The machine stopped working while cutting a 4 mm plywood sheet. I saw it cut fine, and in the middle of the job, the beam did not cut anymore with the head still moving. While I was wondering about this for a few seconds (Problem with the job? Wrong settings? Did I reduce the laser power to much at this sequence?), the machine started to produce a strange screeching noise. I immediately hit the emergency stop button to shut down the machine. Actually, it was the first time I had to use that button.

It was hard to locate the source of that screeching sound. It happened when I fired the laser, so I concluded it must be either the laser power supply or the CO2 tube itself.

A reader of this blog had mentioned to me that in his laser machine (from the same vendor) the power supply stopped working after a few months. So, I thought that could be my problem, too.

Here are pictures from the 50W Laser power supply I have:

Laser Cutter 50W Power Supply

Laser Cutter Power Supply

External and internal visual inspection of the power supply did not show any obvious failure point. I ordered a new power supply: maybe it is good to have a second one at hand, right?

Over the course of the following days, while the power supply was on its way to me, I researched possible failure points and tests. A simple arcing test (be careful!) showed that the power supply seems to operate as it should. But that arcing sound was exactly what I was hearing from the machine.

I verified all the cables and connectors. Closer investigation revealed that the arcing came from the Anode connection of the laser tube.

Laser Tube Anode

Laser Tube Anode Connection

There was no obvious sign what could be wrong with the connection on the outside. I decided to inspect the connection and remove the cable and isolation material.

Laser Tube Anode Cable Removed

I expected that the high voltage wire would be soldered to the anode, as shown in the video below:

But it turned out that the wires were just wrapped around the anode. The anode is a kind of graphite (?) material, so, in general, it is really hard to solder it in a way that the cable would be really connected, or I might destroy the tube with to much heat. So maybe, there was a connection problem and the arcing is inside the connection?

I decided to clean the anode and soldered a thin wire to it (actually, the solder connects with the wires but not to the graphite itself).

Thin Wire Soldered

Heat Shrink Tube

The thin red wire gets soldered to the high voltage cable. Multiple layers of heat shrink tubing and electrical isolation tape, including an outside silicon tube used to properly isolate it with a test run. I fired the laser and still had the same problem.

So what could be the problem be? I noticed an orange film (biofilm?) inside the tube. I’m changing the de-ionized water (with a bit anti-algea in it) every 2-3 months, maybe this was not frequent enough? Changing the cooling water did not help, and I was not able to observe any arcing in this area.

A closer inspection of the anode connection inside the tube to the anode ring in the tube showed that the solder joint might be the problem and not making contact anymore.

Anode connection

Anyway, I reached the point of ordering a replacement tube.

Within three days (wow, that was FAST from China), the new tube arrived from Cloudray. It was well-packaged and unbroken (that was my biggest fear). The picture below just shows the tube inside a package, which was inside a larger box.

New Laser Tube

But how to make the connections? The new tube had this graphite style connection point:

New Tube Anode

I was worried about breaking the tube with too much heat. The solution (thanks to a hint from Christoph Z.) was to use a special precision connector socket (Mouser part number 571-1-5050871-9), exactly what I needed:

AMP Connector (Source: https://www.mouser.ch/datasheet/2/418/NG_CD_5050871_A2-1251367.pdf)

The connector perfectly fits the anode and cathode connection points of the new tube:

Connector

That way, I have a good contact and still can remove the cables if needed.

Soldering thin wires to the outside of the connectors:

Thin Wires connected to Connectors

The first layer of shrink tubing added and connected to the high voltage wire:

Connection to High Voltage Wire

Below, we look at how it plugs to the tube, with more layers of tubing to be added:

New Tube Anode Connection

Here is the final connection with more shrink tubing and an extra silicon isolation tube:

Tubing around high voltage anode

Laser Cathode connection:

New Tube Cathode Connection

The good news: the new tube works like a charm. I had to spend another 30 minutes to re-calibrate the mirrors, and then, the laser cutter was working again.

Conclusion

• I have used the laser cutter probably around 600 hours. I kind of expected a lifespan of around 1000 hours, but without a datasheet, this is a hard to verify.
• I do not run the tube at 100 percent power and have limited it to 80 percent, so I don’t believe I have overpowered it, which usually degrades it faster.
• I’m using an industrial chiller (see 50W Laser Cutter Upgrades), so over-temperature should not have been a problem.
• The tube immediately stopped working. I did not see any degradation over time. That coating inside the tube around the anode side is worrying me. Maybe I should exchange the cooling water more often?
• Having a spare/replacement tube at hand would be a good thing. And maybe a spare power supply!
• I know now how to replace a CO2 laser cutter tube.

Happy Replacing!

For additional information, check out the following links:

• Getting Control over a 50 Watt CO2 Laser Cutter from China
• 50W Laser Cutter Upgrades
• Upgrading a Laser Cutter with Cohesion3D Mini and LCD
• TE Connectivity / AMP Connector: https://www.mouser.ch/datasheet/2/418/NG_CD_5050871_A2-1251367.pdf