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Wednesday, May 17, 2017

K40 Coolant Flow and Termperature Sensing


The K40 laser needs coolant that is maintained at the correct temperature to prevent damage to the tube. It is not uncommon to forget to turn on a coolant pump or to have a pump or water system failure while running the K40. 
Sensors are easy to install in a converted K40 and the protection of the laser tuber certainly warrants the installation annoyance and cost of a flow sensor.

It is also desirable to know the temperature of the water and the tube. This post also outlines the installation of an inexpensive water temp sensor and control.


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Your donations help fund additional research, tools and parts that I will return to the community as information.
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Flow Sensor


The loss of cooling water will certainly cause damage to the laser and the laser power system. Every system should have a flow sensor plumbed in series with the pump and the lasers cooling jacket.
The sensor that I use is:

This sensor needs to be installed on the output side of the laser. I made a hanger to hold it upright on the side of a 5 gal bucket. This way it insures that water is flowing out of the laser and it can detect any leaks from the pumps output to the sensors input.

Electrical connections;

The flow sensor is connected in series with the interlock circuit and in effect stops the laser from firing if there is no flow. 
See Build Schematics  for full machine details

If you for some reason do not want to add a sensor at least insure that the pump comes on with the machine. You can simply plug the pump and machine into the same power strip and turn them both on at the same time.

The End of My Tube Fell Off!

If you did not install a water sensor then at some point the pump will not be on, due to failure or  simply forgetting to turn it on, and the tube will overheat.

If the tube overheats the water jacket on the end of the tube can de-laminate and fall off.

Apparently if you are careful to keep it off the optical output area of the jacket you can use EPOXY it back on. I would surmise that high temp epoxy would be best.


Temperature Monitoring

The laser must stay within its coolant operating range if it is to operate consistently and reliably. The cooler the laser is kept the more power it will be capable of. The power capacity of the laser will change with temperature therefore it is important to monitor the water temperature and prevent the laser from operating is the temp gets to high.
Install temperature monitoring electronics such as:

This device's relay contacts (NC) is also wired in series with the interlock circuit and will disable the laser from firing if the temperature is to high or low. The probe is put into the bucket near the output or the flow sensor.
See Build Schematics  for details.

This controller can be set up to produce an audible alarm outside of its set-points. (See the manual). I mounted it on thr front of the machine but plans are to move it up to the control panel later. The unit requires 12VDC so an additional supply is needed. Before I installed the 12V supply in my conversion I used a 12V brick plugged into a power strip. 

Enjoy and comment
Maker Don

K40 Coolant Pumps


Information about common water pumps and coolant flow specifications


Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Water Pumps

From +Scott Marshall :"When all is well, the stock system should fill a 1 gallon jug about 1/2 full in 60 seconds. About 1/2 gpm or 2 Lpm. .................. the Little Giant PE-1 is a good quality replacement pump which is just right for the k40 and available worldwide."

Enjoy and comment
Maker Don

K40 Lens Specifcations, Orientation & Cleaning


Some links that pertain to K40 lenses


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Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Lens focus, orientation & cleaning:


Lens Application Vs Focal Length:

From Epilog
From Trotec
From Engravers Network
1.5-inch lens

  • Optional lens for high resolution engraving.
  • Recommended for raster engraving above 600 DPI resolutions.
  • Recommended for small font or fine detail engraving.
  • Produces spot size of 0.003 to 0.0065 inches in diameter.
  • Good cutting lens for thin (less than 1/16 inch) material.
2-inch lens
  • Standard lens on most laser systems.
  • Multipurpose for both engraving and cutting applications.
  • Recommended for raster engraving from 300 DPI to 600 DPI resolutions.
  • Produces spot size of 0.004 to 0.007 inches in diameter.
4-inch lens
  • Produces focused beam over longer vertical distance
  • Specialty lens typically used for engraving within recessed area (bowl or plate).
  • Used for cutting thick materials.

Enjoy and comment
Maker Don

K40 Laser Tube Specifications, Maintenance, Failure & Replacement


A collection of information about laser tubes and their care.

Warning: run your laser with properly treated distilled water as a coolant.


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Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Laser tube operating conditions (Reci Laser):

  • Water cooling: using purified water; 2 to 5 liter/minute, (31GPH-80GPH)
  • Water temperature: 10-40℃, (50F - 104F)
  • The operating environment: temperature 2-40℃,(35.6F - 104F; humidity 10-60%.
  • The working current: test current is 29mA. Maximum working current is 29mA. The running current must be kept below 27mA. The life span can reach 8,000 hours if the current is kept below 25mA.
  • The ammeter must be connected to the negative electrode of laser tube.When it is working under over high current for long term, the negative pole will appear light yellow and the life span will be shortened rapidly.
  • To protect dust from going into the insulation sheath, please wrap it with plastic film.

Laser Cooling and Condensation

Laser Tube Replacement

Tube Installation depends on the tube and there are multiple ways to connect to the pins on the tube. Pick your poison.

Basic Anode Connection Termination Methods

Unplug your laser from the mains power and let it sit for 1 hr.

Observe how the anode wire is connected to the tube including the wire routing and restraints.
Install the new anode wire in exactly the same way.

At the Anode end of the laser tube
  • Remove the silicon sheath from the anode connection. Minimize forces on the anode pin. It should pull off but if not you may have to cut it off.
  • Your anode wire may be twisted, screwed or soldered on the anode pin.
  • Remove or reterminaate the old anode wire. 
  • Replace the anode wire in the same way it was connected, twist, solder or screw.
    • If soldering use minimal heat. Some recommend using Teflon tape to hold wires that are twisted see video below.
  • Route and restrain the wire in the same way. Usually tie wraps around the tube moving away from the anode end toward the cathode end.
  • Flow silicon around the anode wire connection (use the white tube that came with your K40) 
  • Push the silicon tube over the wet silicon filling the tube. If you had to cut off the tube you will need to replace it with a peice of silicon tubing.
  • Add more silicon to the top of the silicon tube if needed
  • Let dry for 24hrs before using the machine
Alternate silicon: Permatex Blue RTV Gasket Maker. Available in auto and big box hardware stores.
703 adhesive silicone rubber insulation/potting/electronic waterproof sealant (the stuff that comes with the machine)

Other Methods

The videos below for removing a laser show connection and disconnection of the tube form its supply and can be used as reference example:
  • Videos
  • Replacement Tidbits from the web:
    • "Disconnect power from unit!!
      Gently pull the existing silicone tube off the terminal post by gently twisting and pulling it along the wire itself.

      Use a soldering gun to heat the existing terminal post to gently release the existing wire connections. Then cut and clean up those wires. Also clean out the silicone tube of the old residue. Of course you need to remove the water connections and drain the tube. When installing the new tube keep the same orientation as the old tube and reconnect the water lines. Before attaching the power leads, screw down the retaining brackets and make sure the grounding wire is secured properly.

      Since you are replacing a tube, you already have a tube and terminal posts to practice on first. Make sure the wire leads are stripped at least 1/2" long, enough to be hand wrapped tightly around the protruding terminal post. The advantage of Rosin Core Solder is that it contains a built in FLUX which helps to clean and bond.

      Before the wire strand is wrapped, make sure the silicone tube covering the wires is cleaned and placed back onto the wire. Once the wire strand is wrapped around the post, quickly heat and add some solder. Let it sit for a few seconds to cool and bond. The connection will be very secure. Just push the silicone tube back over the entire connection, completely fill the tube and connection with quick drying silicone and in about 3 hours once the silicone drys, you are back in business."

Arching [needs content]

Reattaching the Water Jacket

Under shipping pressure or in the event the tube overheats the water jacket can become detached. 
Seems as if you can epoxy it back on! Check out this post.

Cleaning the laser tube water jacket

Replace all the water in reservoir with a couple of liters of vinegar and tap water... let it run for 12-24 hours replace all water with tap water only let it run for a bit... place outlet tube into a waste pan and flush adding a bit more tap water as your reservoir drains. Purge all water and replace with distilled water and some algaecide drops for aquariums. 

Laser Tube Specifications

Parallax: Laser Failure Modes and Warranty Info 

Enjoy and comment
Maker Don

Tuesday, May 9, 2017

K40 High Voltage Transformer Tests

High Voltage Transformers are Dangerous



I do not recommend opening the LPS and trying to perform a repair. A typical LPS can cost only $70 -80 and a High Voltage Transformer (HVT) is $20-30 the difference it not usually worth exposing yourself to these voltages and identifying a dead HVT is at best uncertain.


Other related posts are:


Please consider donating (button to the right of this post).
Your donations help fund additional research, tools and parts that I will return to the community as information.
For other information on the K40-S build use the  K40-S BUILD INDEX with schematics

Testing a K40 Laser Power Supply High Voltage Transformer

A common failure item in a K40 is the HVT in the LPS. This transformer is what converts line voltage to up to 20,000 VDC and when applied to the laser creates ionization. This HVT has a primary, and secondary. Although not yet verified we believe it has a HV diode and ballast resistor on the secondary. These transformers are potted so the internals are not exposed.
You cannot test the secondary circuit of these transformers without a tester. This test attempts to simulate the switching circuit on the primary as a meas of detecting an open secondary.

I am also working on a more definitive DIY HVT tester but this test can be done with household items so I thought I would throw it out there.

Donate your dead LPS and HVT to a cause

I am using dead power supplies to test ways to diagnose and identify what is causing these supplies to fail. Please donate your dead LPS or HVT to this cause and help the community get to a more reliable system.

If you want to donate leave a comment.... or get to me at +Don Kleinschnitz 

Testing Procedure

Note these instructions are for the HVT that has a 3 pin connector. I will update this post later for other types. The theory of the test is the same for them all.

HVT's are difficult to test because the HV diode in the secondary has a high forward voltage. What this means is that to find out if the secondary is shorted a large voltage is needed. An ohm meter is of no use and will read an open. The primary can be tested with a DVM.

Step 1: Unplug the machine and wait 1/2 hr. 
Then with an insulated wire ground the anode of the laser tube. To ground the anode tape one end of a wooden dowel to a wire whose end it bare and connect the other end solidly to earth ground. Grip the insulating dowel with one hand and put the other behind your back gripping nothing. Touch the bare-wire end of the wire to the anode, an arc may occur. 

Step 2: Remove the LPS from the machine. 
This means that you will have to remove the large HV wire from the anode of the Laser. With all wires disconnected from the supply remove the cover of the LPS. If your HVT has a plug connecting it to the PCB, unplug it. You can leave the HVT mounted or dismount it to test it depending on the type of HVT. There are two general types of HVT one with a connector and one mounted directly to the PCB. The second type will require removal of the HVT from the PCB.
This post outlines HVTtypes: LPS Repair & Test

Step 3; Test The Primary
With an DVM set on a low ohms scale read the resistance across the black and yellow wires in the 3 pin connector. It should be nearly 0 ohms. If not ... donate it to me :)! its dead.

Step 4: Create a Spark Gap
Connect a wire to the red wire in the 3 pin connector. Tape the red HV lead to this wire. Do not electrically connect these wires together. Rather, create as small a gap as possible between these wires. This is our spark gap and will indicate if we can develop HV in the secondary.

Step 5: Wire up the primary
Connect one side of a 9V battery to the black wire in the 3 pin connector. Connect one end of a wire to the yellow pin on the 3 pin connector leave this end free.

Step 6: Test the HVT
Rapidly touch the wire that is connected to the yellow pin on the 3 pin connector to the other terminal of the 9V battery. An arc should occur across the gap you created in step 4. If it does not ... donate it to me :)! its dead. If it does arc your HVT MAY or may not be good.

About the HVT Test

The validity of this test has not been completely verified. Although this test should show if the secondary is inoperable it does not determine if the secondary can output the correct levels or quality of voltage. It also may not detect a shorted HV diode. If this test fails it is highly likely that the HVT is dead. If it does not fail it may mean that the HVT MAY be bad and MAY not :(.
To this point I do not have a bad HVT to verify this test with. If it works for you please leave a comment.

Enjoy and comment
Maker Don