Laser tube arcing

[Dtcrafts]

Hi Guys

So today just after starting the laser decided not to fire, at first we thought the PSU had gone but on closer inspection we found the High voltage (red) lead going to the tube has a soldered joint just before the tube it is covered with tape and in turn is covered by a piece of silocon tube and ten taped at both ends
It had arced right through the tape and tube, once re taped and put back into the rubber tube the laser fires again the question is what would cause this to happen in the first place
any suggestion on this
thanks
Dave

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[RayNikkel]

If the connection from the lead wire to the tube is secured and properly covered and still arcing your tube is dead.

[Dtcrafts]

no
the tube is fine as said after retaping and covering everything works fine
the question is what would cause this to happen in the first place, jus trying to find the answer so maybe we can prevent it from happening again
Dave

[wmgeorge]

It had arced right through the tape and tube, once re taped and put back into the rubber tube the laser fires again the question is what would cause this to happen in the first place
any suggestion on this
thanks
Dave

Your working with 20,000 volts plus or minus a few thousand here and common electrical tape is not going to do it. Surrounding the splice with RTV silicone will help and keeping the splice out in the open away from metal and water will help. So it still works, you could have fried the power supply long term.

They do make a high voltage splice kit and I have used on HV power feeds, but just not having a splice... as replacing the wire with one long enough is cheaper.

[RayNikkel]

Only three things cause that arc, one is bad tube and other is poor connection and in your case looks like number three, the connection was not covered well enough. Most new tubes now come with a thick plastic cap that fits over the end of the tube and connection to prevent that. Just make sure it is well covered and you should be fine

[RayNikkel]

Here is a picture of the acrylic cap I'm talking about, it works much better then tape. http://www.diytrade.com/china/pd/571...aser_Tube.html

[wmgeorge]

Here is a picture of the acrylic cap I'm talking about, it works much better then tape. 130 Watt Co2 Glass Laser Tube - MT-04130 - Mactron (Hong Kong Manufacturer) - Engraving & Etching Machine - Machinery Products - DIYTrade

Ray, I believe he said the Wire was spliced not the connection to the tube. High voltage (red) lead going to the tube has a soldered joint just before the tube ...

[RayNikkel]

Ray, I believe he said the Wire was spliced not the connection to the tube. High voltage (red) lead going to the tube has a soldered joint just before the tube ...

Oh ok. I guess I missed that. It would be best not to have a splice in that very high voltage line. I would replace the entire line to a single strand.
I'm very OCD when it comes to my machine.
I have seen many posts on the topic of tube arcing so I just assumed. Thanks for the clarification. My first post on this forum and I already messed up lol.

[Dtcrafts]

Ray, I believe he said the Wire was spliced not the connection to the tube. High voltage (red) lead going to the tube has a soldered joint just before the tube ...

hi
yes thats right the splice is about 10 inches from the tube, why its there we dont know
And now knowing that just taping was the cause i cannot believe they would do this at the factory, anyways I have got some RTV silicone and will put joint in some sort of split plastic bottle and encapsulate the whole thing in the silicone until my electrical friend is around to replace the whole cable

[wmgeorge]

Actually can you get a un-split tube over the wire? Then slide it down over the wire, but first fill it up with the RTV silicone, and let set until its firm. Keep it away from metal and moisture, use plastic wire ties as needed and it might be fine? Usually the connection at the tube is an issue because of the condensed moisture. Same thing. dry it off and use the RTV.

[RayNikkel]

Actually can you get a un-split tube over the wire? Then slide it down over the wire, but first fill it up with the RTV silicone, and let set until its firm. Keep it away from metal and moisture, use plastic wire ties as needed and it might be fine? Usually the connection at the tube is an issue because of the condensed moisture. Same thing. dry it off and use the RTV.

Well it's sure a lot better then the old days when we had to solder the connection at the tube. I destroyed a few tubes doing that.
I personally would not play around with trying to cover that spliced line, it's fairly simple to just replace it.

[wmgeorge]

My new machine has a splice also in the HV line and its done just as I suggested.

You can not successfully solder to the tube connection its titanium or something like. You can gob a ball of solder on but why, its not a good connection. Just use a mechanical connection like a split bolt connector or similar, or even a wire nut and carefully tighten with the copper wire under.

[KH0UJ]

A shrinkable tube is just fine, 26000 volts will jump up to three inches if the insulator is burnt or had high carbon deposit due to the HV, RTV silicone has an acetic acid in it, acid = resistance, not really good for insulating continuous high voltage on my opinion.

[Dtcrafts]

hi
well i took a small PET bottle split it down one side and drilled a hole in the bottom put the cable in it and filled with RTVI am a bit reluctant to have it hanging outside the cabinet though , the rear lid is quite heavy and I dont want it to nip the cable, so I think I might just make a little wooden cradle for it to sit inside
Dave

[wmgeorge]

I blocked my splice up on a piece of clear acrylic. Clear silicone is the only thing I have seen used on these HV connections. Once cured it has a high resistance to voltage.

[cinematic2]

If the connection from the lead wire to the tube is secured and properly covered and still arcing your tube is dead.

Anybody said it is still arcing?

[cinematic2]

You can not successfully solder to the tube connection its titanium or something like. You can gob a ball of solder on but why, its not a good connection.

Soldering is the best way to connect HV and the rod but not for loosers.
It needs high soldering skill not to destroy laser. I saw how it goes long ago in Beijing but now nobody makes it any longer.
Old specialists are gone.

[Zootalaws]

A shrinkable tube is just fine, 26000 volts will jump up to three inches if the insulator is burnt or had high carbon deposit due to the HV, RTV silicone has an acetic acid in it, acid = resistance, not really good for insulating continuous high voltage on my opinion.

Some RTV silicone releases acetic acid while it cures, but not after it is cured. That can be enough to attack solder joints, however. You can choose 'neutral cure' RTV silicone which releases alcohol or some other inert substance while curing.

We make sea-water-rated controllers for marine use and use neutral cure for that exact reason. Our PCBs are completely enclosed in silicone.

For the OP, neutral cure silicone is easily obtained in the UK.