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Constant Power vs. PWM Control

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So, in my other articles we covered the difference between Analog and Digital Control Panels (and why you need to add a current meter to a digital panel) as well as the difference between Analog and Digital DC Ammeters. If you have not read them yet please check them out before moving on to this article. It will provide helpful info that is expanded on here.


On a stock K40 with an M2 Nano board there is only one power setting per job. You set the power on the control panel and run the job at that specific power. It doesn’t change. This limits the ability to do true 3D engraving and being able to bring out those subtle differences in photos or complex rasters.

Many choose to upgrade their stock controller with one that offers Pulse Width Modulated (PWM) laser power control. This basically means the controller can continuously vary the laser power while the job is in process. With PWM controllers you can do true 3D engraving and the detail on photos and complex scans are much more refined.

From here on out we will assume that we are talking about a K40 upgraded with a Cohesion3D Mini controller. The C3D Mini is a drop in replacement for the M2 Nano and can be installed in about 15 minutes with, in most cases, no modifications to the machine and no special tools. We will also assume the design and control software is LightBurn.

Once you install a PWM controller the factory power controls becomes a way to set a hard power limit and does not have to be changed anymore. The idea is to set the K40’s max power output to 15mA with by firing the laser and adjusting the power from the panel. Once you set it to 15mA you can leave it alone after that because the controller and software take it from there.

With the C3D, as shipped, there is a soft power limit that is set in config file. the max laser power is set to 80%. The main reason for this is that people with digital control panels and no milliammeter have overdriven their tubes and power supplies because they do not know how much current they are outputting to the tube. This 80% soft power limit is in place to help lessen the chance of someone damaging their machine.

For instance, if you have a digital meter and set your power level to 100% and the cut or scan power setting in LightBurn is set to 100% you will still only get 80% of the possible output of the power supply. If you have an analog panel and set the hard limit to 15mA, then set your LightBurn settings to 100% you are getting only 80% of the hard power limit of 15mA.

So, without all that reading (and assuming you have a digital control panel and a Cohesion3D mini), the percentage on the digital panel is a calculation of the maximum power output of which the laser PSU is capable. This can vary from machine to machine and, without a milliammeter, it is nearly impossible to tell. additionally the C3D has a soft power limit set at 80% to prevent overdriving the tube. So, if you set your panel to 50% and lightburn power is 90% then you are getting 90% of the 80% of the 50%.

Once you have a firm grasp on how these power limits and power values work, and you can accurately set your hard limit on your control panel, then you can modify the configuration of the C3D so it will output 100%. This means that 50% in LightBurn will now actually be 50% of the hard power limit you set on the K40.





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