LaserBoard LPSU Connection Guide

LPSU Connection Guide

The Cohesion3D LaserBoard has multiple laser control mechanisms and can drive a variety of CO2 Lasers, Diode Lasers, and even CNC Spindles. In this article, we will explore the various ways to connect to a CO2 Laser Power Supply Unit (LPSU).

Your power supply may look like one of these, or it may look different. The important part is determining the connections you will need to get your LaserBoard talking to the LPSU to control your laser. You’ll notice all of these power supplies are blue, and roughly the same size. These are all made to work in a 40 watt laser cutter, like the K40.

K40 Style LSPU

Here’s a typical LPSU found in a K40 laser cutter.

In the image above, the connector header on the right has four terminals. From left to right, the connections are: 24V, G, 5V, L. Connect G (Ground) to Laser Gnd and L to the Laser Fire on the LaserBoard.

Note: The 5V and 24V are not used and should not be connected to the LaserBoard. The LaserBoard has its own dedicated 24V power supply.

The image above shows another K40 power supply. Some of the terminals are labeled differently, but what we care about is on the right connector block. From left to right, the connections are: 24V, G, 5V, L.

Note: The connections in that specific order are common, but you should always check for labels or documentation for your specific power supply. As with the previous power supply, connect G (Ground) to Laser Gnd and L to the Laser Fire on the LaserBoard.

In the image above, the connector block on the right has six terminals. The printed text to the right of the connector block shows the following connections from left to right: H, L, P, G, IN, and 5V. Connect G (Ground) to Laser Gnd and L to the Laser Fire on the LaserBoard.

Note: The 5V is not used and should not be connected to the LaserBoard.

Higher Power LPSU

If you’ve got a larger laser than a typical K40, you will probably have a larger power supply. It may be black instead of blue and it may have more connections. We simply call the power supplies below a “higher power LPSU”. lpsu-01

As shown above, the connector block on the right has six terminals. The printed text above the connector block shows the connections from left to right: H, L, P, G, IN, and 5V. Connect G (Ground) to Laser Gnd and L to the Laser Fire on the LaserBoard.

In the image above, the connector block on the left has six terminals. The printed text above the connector block shows the connections from left to right: TH, TL, WP, G, IN, and 5V. Connect G (Ground) to Laser Gnd and TL to the Laser Fire on the LaserBoard.

Note: Your connector may look different, and may be labeled differently. If it has H or TH this is Trigger High and should match up to H. If it has L or TL this is Trigger Low and should match up to L. If you have both, use TL for the connection. If you don’t have TL you can use TH. Choose one, do not connect both of them. Ground may be labeled as GND or just G.

Power Adjustment Potentiometer

We also suggest you wire a potentiometer to G IN 5V to set the relative max power the laser will use when firing. In the image above, the wiper (IN) is on pin 2, which is the bottom pin. This is the type we offer.

Some potentiometers will have the wiper in the center, so check the specifications on the one you have to determine which is the wiper pin. If turning the knob clockwise lowers instead of raises the current, you’ll need to switch the wires on pins 5V (pin 1) and G (pin 3). When connected properly, the potentiometer will control the maximum laser power.

You can simply set it to a safe value like 80% of the tube’s maximum power. This could be 15-17mA for a 40w machine, but you must absolutely do your own testing to determine what the maximum power of your laser, tube, and power supply combo is, and then set a safe maximum value from there.

If you find that engraving is still too powerful when setting the power in software, you can use the potentiometer to lower the laser power for finer detail.

More detail about the potentiometer and power control is here: PWM Control

Setting Maximum Laser Power

Setting the maximum power of your laser so that you can leave the control up to LightBurn will depend on how your machine is configured.

If you’ve got an analog ammeter, potentiometer, and a test fire button:

With the lid closed and all safety interlocks engaged, press test fire button, dial the potentiometer up or down until your ammeter shows 15-17mA. You can now leave the potentiometer set in this position and in LightBurn 100% power should equal 15-17 milliamps. This should ensure you do not overpower your tube.

Note: While you can leave the potentiometer set as-is, there are times you may want to dial it down even further. See the article on PWM Control for more info.

If you’ve got an analog ammeter and potentiometer, but no test fire button:

With the lid closed and all safety interlocks engaged, home your laser and then place a piece of scrap material under the laser head. We will be firing the laser at 100% power at the material (a thick piece of scrap wood can be used). Open the console in LightBurn and send the following command: G1 X50 S1.0 F400

This command will fire the laser at 100% power while moving the head to the right. While this is happening, dial the potentiometer up or down until your ammeter shows 15-17mA.

If you need to do this more than once, be sure to home the laser after each time you send the command. You can now leave the potentiometer set in this position and in LightBurn 100% power should equal 15-17 milliamps. This should ensure you do not overpower your tube.

Note: While you can leave the potentiometer set as-is, there are times you may want to dial it down even further. See the article on PWM Control for more info.

If you’ve got a digital panel and ammeter, but no potentiometer:

The digital panel does allow you to change the power of the laser and you can use the ammeter to see the actual output of the laser. The digital panel will allow you to set a percentage for the laser power (between 0% and 100%) but that alone does not tell us the true power output of the laser. This is where the ammeter comes in.

While test firing the laser, you can see the value on the ammeter and then adjust the percentage on the digital panel until you get the desired output, typically between 15-17 milliamps. As with the potentiometer method above, once you know the setting (in this case using the percentage shown on the digital panel) you can safely set the upper limit for maximum power output.