How do I connect wires when I replace my laser tube?

Hi all, first post here and super new to CO2 lasers!

I bought a used K40 machine (had my pants pulled down but we live and learn) turns out the laser was knackered. I have a new one coming today which has the cables pre-soldered onto the laser so I just need to attach them to the existing wires on my machine.

My question is, what is the safest way to do this? IE insulation? Will heat shrink be ok or do I need something more substantial?

I was thinking heat shrink then a piece of water hose filled with silicone?

Welcome to the forum!

Two things!

The “K40 Intro” in the top navigation should be very helpful to you. It’s a summary of a lot of hard-won experience with K40-class lasers. Note that it has valuable information on how to keep your brand-new tube from also becoming knackered!

Heat shrink definitely won’t be enough. There’s around 20,000 volts going to the laser. The dielectric strength of heat shrink is in the hundreds of volts, not the tens of thousands of volts; it’s two orders of magnitude too weak. If by “water hose” you mean silicone hose of the type used for water in the laser, that’s OK, and you don’t need to fill it with more silicone. You can use heat shrink around the joint, but then encase it with silicone hose for 5cm or more on both sides of the joint. You can hold the silicone hose to the wire with zip ties. Make sure it can’t slip, and err on the side of more hose around it. Be generous!

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Thank you for the reply! Can I use a crimp connector instead of solder?

Okay great so: connect the cables together with (hopefully a crimp?) something, cover the joint with 10cm+ of silicone hose, heatshrink the whole thing and everything is ok?

Should I heat shrink a couple times before the silicone hose? As obviously the hose has a greater diameter than the cable.

All you need to do it wrap the wire around the post. This is extremely high voltage and a gas-tight connection is not needed.
It’s not necessary but you can use a connector of some sort that slides over the post but crimp it on the wire first.

Do not solder!

Forces on the post in the tube can crack it.

Slide a piece of silicone tubing over the joint and then fill it with silicone and let it set up for 24hrs.

More here:

The tube I have already has the wires connected at each end, I need to attach those cables to the existing cables.

So you are trying to splice two HV wires together?

You can use these connectors:

Or you can just splice this way:

Slide a peice of silicon tubing 2+ inches long on one end of the wire. The tubing needs to be larger than the wire so you can get silicon inside. The bigger the better.

Solder the two wires together. When you solder do not leave points in the joint. You want a smooth ball joint.

Slide the tubing over the joint and then fill it with silicon.
This stuff works
If you can’t get that stuff choose an RTV with a high dielectric strength.


I don’t think my soldering skills are good enough to do a ‘ball solder’ !

is this any good?

Give it a try! No downside… :slight_smile: It’s just the same as creating an ugly joint with to much solder.

  • Twist the wires together…
  • Works best if you put the wires into something that holds both ends so that the joint is steady and horizontal or have another person hold it.
  • Heat the wires with the iron (under the wire bundle) until the wires are hot enough to melt the solder
  • Quickly apply lots of solder to the top of the wire …
  • Pull back gently while applying solder at the same time …

It does not have to be perfect.

If the joint has points in it try it again with more solder and plenty of heat.

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ok thanks for the advice I’ll give it a go. Does the above silicone look like it will do the job?

I can’t find the specs but I think it will be fine. In this case more silicon is better. Use the largest diameter tube in the order of 1/2" you can and insure that it extends at least 1" from the joint (2’ would be better) on each side of the joint.

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Ill let you know how I get on

thanks for the help guys

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Also, does the negative cable also need this level of protection?

Nope, the cathode return wire has < 30ma.

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Okay so I can just heat shrink the negative cable and all will be well? I noticed it is significantly smaller in diameter

Yup solder and heat shrink… or you can use a single pin connector, I would do the first :slight_smile: