Laser tube arcing to machine

CO2 Laser Tube Problems – March Question & Answer session

Posted on

CO2 Laser tube arc to the machine body or stepper motor

I get sent a lot of questions from new and existing readers of my blog in regards to issues they have been having with their CO2 laser tubes. 90% of these questions are regarding certain common problems and can be answered with a simple copy and paste reply from previous emails.

I have decided to write this blog post as a place to send all new questions in regards to laser tubes. New questions and answers will be added as they come to me.

Firstly let me refer you to a previous post I wrote about the construction of different types of laser tube, it is very basic and written with new users in mind. different types of co2 laser

Ok onto the questions and answers.

I will start with the most common question

Q. When I press fire or start the machine why does the tube arc/spark from the High voltage connection (red cable) to the machine body or stepper motor?

A. Firstly let me start with an analogy comparing electricity to water. Water will always take the path off least resistance, imagine you have a bucket of water with a hole in the bottom, you fill the bucket at a constant rate. This rate ensures the bucket is brimmed with water but does not overflow. Now you reduce the size of the hole in the bottom of the bucket, what happens?
The bucket will overflow.

This analogy has very little in common with this issue, but it helps to paint a mental image in your head of how resistance paths affect the flow of electricity. 

The CO2 laser tube is filled with a gas from the factory, this gas mixture and the percentage of its elements is crucial in order to create an environment in which a 1000mm electrical arc can be maintained. When this gas or mixture percentage escapes or is depleted the high voltage arc will not be able to occur inside the tube and will find a path of less resistance. In our case, this is usually the closest conductor that is connected to ground (earth). This is usually the machine body or the stepper motor. 

Now let's talk about why this problem is much more serious than just a broken CO2 tube.

That electrical arc you see is between 22,000-34,000v and up to 40ma of current, now if you were to become the path of least resistance or you happened to touch the machine whilst this arc occurred say ie with your left hand. The path of least resistance would follow your arteries and through your heart, stopping your heart resulting in death.

Safety aside lets's talk about the damaged to other components this can cause. When this arc hits your stepper motor it will induce a huge voltage up to 1000x  higher than the machines maximum 24v dc required to drive the stepper motors. This can travel from the drivers to the control board and the power supplies. I have seen machines in the past that were complete write-offs due to owners continuing to run with a damaged tube.

But my replacement co2 laser tube has the same problem.

It makes me angry to say it but this is also a common problem. Most china tubes are dead on arrival. This is usually due to how they are shipped or the quality of the adhesive they used to attach the mirrors and lenses.

Other issues that can cause occasional arcs

The temperature of cooling water, not only does it cool the optics but it also travels the length of the arc to cool the gas mixture and help the mix recombine and regenerate the co2.

Connection and condition of HV cable to tube.

Connection and condition of LV (Blue cable)

Current (ma) meter failed

 

I hope this answer sufficiently answers your question. If you have any further queries please feel free to contact us.

 

Laser tube arcing to machine

Laser tube arcing to machine

 

 

 

 

Leave a Reply

Your email address will not be published. Required fields are marked *