Message from Russ on our Bodor problem

[Mike Henry]

It is pretty easy to find high voltage wire. For example 20 kV wire is available from McMaster-Carr here:

https://www.mcmaster.com/standard-electrical-wire

and they have wire capable of higher voltages as well. Digikey, Mouser, Allied Electronics also supply high voltage wire, I think. It's several $/foot but you won't need much.

[Tim Mellor]

Rather than get a 20kV wire for a supply operating in that region good practice would be to head to one rated for about twice that for a safety factor. This is maybe where the original thread stemmed from if the Chinese skimped on the spec. Also note there is different ratings for AC and DC voltages which is fairly common for a lot of electrical items. 40kV is about where to aim for these smaller Lasers.

[Evan Winn]

How can I check the rating on my existing wire?

[Tim Mellor]

How can I check the rating on my existing wire?

Unless it is written on the side of it (and the rating is to be trusted ) you need some specialized electrical testing equipment.

Generally most wire is built for mains style applications so dielectric testing gear that I own such as my Victor VC60E http://www.victor-multimeter.com/produc ... r-720.html tests at 2.5 or 5kV which is actually higher than most testers go (I also own a 1kV PAT tester). To 'test' 20 or 40kV wire you would need to be able to generate 4-10 times the rated voltage which for most is not practical.

In the case of the Lasers wire best is to look for tracking or carbon marks under where the wire sits and if in doubt spend the few $ and swap it out. If it however is working however leave it alone

[Tim Mellor]

Below is part of a reply I gave to a PM regarding the possibility of sleeving cable that might be useful to others. It contains some gross simplifications and some assumptions and the best solution is still replace the cable.

The conductor is unimportant for size electrically mainly an issue if you go to light for mechanical strength. If you sleeve an already suspect or failed wire then you are relying fairly much just on the dielectric strength of that sleeve.

As a rule of thumb 1kV of electricity will jump a gap of 1mm (depends on environment and more) so assuming your current wire has a failed insulator 2mm in wall thickness (without considering any carbon tracking which would make it a conductor) it will only take 2kV of your potential voltage to pass to the sleeve so the sleeve will need to cope with the rest to ground assuming also there is little or no air gap between them. This is where standoffs can help but they are not a solution for insulation failure.

So for example if you found a bad section of wire and added a sleeve of normal heatshrink it would still likely fail as the breakdown of heatshrink is likely to be well under 10kV which is less than a typical Laser Voltage.

Personally I wouldn't sleeve it with an electrically unknown tube.

For interest this is me playing with about 12kV to give you an idea of what sort of airgaps can be jumped https://youtu.be/Qx7eH9snu3U Cable in use BTW is the stuff I linked to in the thread.

[Gene Uselman]

For context, this is the same Bodor BCL-0506 MU desktop that I have struggled with since 2016. It is now working most every day in a Trophy shop and the owner loves it... but now it is arcing to the frame, which has always been a problem- at first feeding into the control circuits. The whole sordid tale is in a couple threads above. I am getting some high quality HV cabling from Ron at Rabbit Laser and running it in silicone tubing for insurance and will carefully route it to avoid the many obsticales that originate in the Bodor modification of a 60W machine to take a 100W Reci tube and power supply. I strongly suspect that they used the lower grade HV cable from the 60W machine, and then routed it poorly. Thanks to Ron and Tim for their technical help . Gene

For general info- once a cable arcs thru the insulation it will be compromised at that point, which I knew 50 years ago when I went to school for electronics [such as it was back then- we worked on tube computers] but Tim kindly reminded me of.