INSTRUCTIONS:

To find K40 conversion information use the "INDEX", "SEARCH" or "LABELS" sections in the sidebar.

Tuesday, January 12, 2021

Connecting and splicing the HV connection

Installing a new tube

If you own a laser machine, sooner or later you will have to install a new tube. There are various methods for doing this and various opinions on what is the right way. There is always more than one right way but the methods outlined here I feel are the simplest verified methods I know of.

DANGER WILL ROBINSON!

This is 20,000 volts. Unless you are experienced with High Voltage (HV) power, you may not realize this does not act like any other electric circuit you have ever been exposed to. Its behavior is unpredictable and it can KILL YOU!

The red wire used to provide power to the anode is a special HV wire that is capable of insulating this high of voltage. NO other common wire is capable of insulating this high of voltage. This high voltage has no problem penetrating electrical tape as well as many other common insulating materials.

If you do not use HV connection and fabrication techniques and materials your machine may be unsafe and also may prematurely damage your LPS.

Installation Overview

Tubes usually come with bare pins or pigtails installed. In rare cases, it may have a High Voltage connector. A method from below can be chosen that best suits your needs, skills, and part availability. 

The Cathode Connection

For the negative, you can use any type of splice you get from the home store. I would solder or crimp on the splice and finish with heat shrink. This wire must stay away from the HV (red) lead. It should be routed directly back to the LPS pin -L, usually the leftmost pin and connection on the LPS.

CAUTION: do not connect the cathode connection to L which is on the rightmost LPS pin and connector.

The Anode Connection

Before we talk about the anode connection it’s important to realize that 20,000-volt connections do not act like the kinds of connections we normally use. What we normally know as “insulating materials” do not adequately insulate at this voltage. Other fabrication and environmental conditions, such as moisture, dirt, dust, and sharp points in the assembly, can cause HV leak problems 

  • HV easily arcs through conventional connection and insulation methods
  • 20,000 volts can easily arc 2" to a grounded surface
  • 20,000 volts creates corona and corona tracks from sharp points
  • 20,000 can create conductive tracks in dirty, dusty materials, etc when not properly insulated
  • 20,000 volts at 30ma is capable of killing you and or damaging most any electrical/electronic circuit …

For connecting the anode wire your options are:

  • Add a HV connector ***** inline with the existing HV cable and the new tube's pigtail. This makes it easy to change the tube in the future. HV connector must be installed correctly. I seal the ends with high dielectric constant silicon RTV **.
  • Solder the HV pigtail end directly into the LPS (like is it currently connected) which requires you to get access to the inside of the LPS and unsolder the wire and solder in the new pigtail. This only works if the pigtail is long enough to reach your LPS. This connection is the best as there are no discontinuities in the HV wiring. However, it is the most involved method and it requires access to the HVPS internals.
  • Make your own splice using plastic/silicon tubing and HV resistant silicon.
    • Slide tube over the open end of the pigtail. The bigger the diameter tube the better. Silicon tubing generally can have a smaller diameter than PVC plastic tubing.*** The key is to get enough thickness of silicon to adequately insulate the HV from its surrounding. The tube should be sized such that it will extend at least 1" from either side of the joint's edge of insulation.
    • Join the pigtail to the existing LPS HV lead by twisting them like this:
    • You can leave the joint like this but I like to solder it. If you solder it, use bulb soldering****. Soldering or not, ensure there are no sharp points of wire sticking up.
    • Apply a liberal amount of the RTV over and around the joint.
    • Slide the tube over the joint and RTV. You want the RTV to fill the tubing with no air pockets.
    • If the tubing is not full of RTV add more into each end of the tubing until you get an adequate squeeze-out. Pretty is not important here, filling the tube with silicon is!
    • Let the splice cure for 24 hrs before applying power

Stuff to make your own splice:

** Blue RTV. You may be able to get this at auto supply stores, Walmart or https://amzn.to/3qc9xob

*** You can find silicon tubing on Amazon I recommend 1/2 or larger. I have also used larger diameter 1/2-3/4 PVC tubing as an alternate material. It's the total thickness of silicon that does the insulation work.

****Ball Soldering: https://www.spellmanhv.com/en/Technical-Resources/FAQs/Technology-Terminology/What-is-Ball-Soldering

***** HV Connector: https://amzn.to/2K8rVPn


Enjoy and please comment,

Don