Issue with laser starting at full power


When using the included ac-dc power brick that comes with the laser, it automatically starts in full power cutting mode and not lower power “target” mode. This is obviously very dangerous.

should i use the D9, 12v pin to power the laser instead of the power brick?

Thanks for any assistance.

In past forum topics that have had a similar problem, the issue turned out to be that the pin was floating and need a pull-down resistor added to the pin, but it is hard to say if that is what happening here without more information.

  • What pin are you currently for your PWM input to your laser?
  • Does it come on briefly or stay on?
  • Are you using Marlin’s laser support to drive the laser or do you plan to use fan commands?
  • Is the laser modulated when you drive it using g-code?

should i use the D9, 12v pin to power the laser instead of the power brick?

You would need a 10A to 12A power supply to power both the MPCNC and your laser. You could probably solve/hide your problem by using a board pin to power your laser, but you should be able to figure out a solution using your current setup.

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Hello Jogger,
Robert is correct. Most people solve this problem by putting a pull down resistor on the TTL control pin. That is the safest and easiest solution.

However, I thought I would answer the question you asked because you may damage something if you attempt to proceed anyway do this wrong. Can you power a laser through the Control board? It is SOMETIMES possible. I have done this with one of my lasers. But you need all the correct hardware/firmware.

The laser needs to pull AMPs. Not just any 12V DC connection will work. So you will need to use one of the Heater connections. One that is intended for Extruder or Heat bed. Those can usually provide a couple AMPs at 12 -24 volts. There are some articles written up on how to do this all over the web. I don’t know what Pin D9 is on your board. If it isn’t one of your heaters then no DO NOT USE IT.

Make sure your control board and its power supply can provide enough AMPs to cover the entire machine and the laser. Most of these CNC machines use less than 3 amps just to move around. Ryan’s power supplies used to be 3 amps max and they worked fine for MPCNC and Lowrider. But then you need to check what your laser uses. Look on its power brick to get a rough idea. If they gave you a power brick that provides 3 amps at 12 v then you can guess that your laser will use less than that. And that you will need a power supply that can provide between 5-6 amps to power both the machine and the laser. I am guessing here.

On your control board specs it should say the max current it can take. I know several 3D printers can max out some 12-20 amp power supplies so you are probably ok there but you should still check.

Then you need to figure out if your laser can actually function with its power being signaled like that. If your laser has any kind of documentation then check it. Because you may end up breaking it by turning its power on and off like that. The laser I am using like this has documentation saying I can either use TTL or connect the power through the control board like this. aka it was designed with this in mind. It won’t destroy the laser driver.

The last part of making this work is the firmware. Marlin firmware has several safety features intended to prevent fires. If you turn a heater circuit on and it doesn’t detect changes on a temp sensor then it will shut down your heater pin. Meaning your laser will power off. So you have to get into your firmware and disable these thermal protection runaway features. Again there are articles out there show how to do this.

So to recap. It may be possible for you but it is not without risk. It will probably be easier to add a pull down resistor to your Control pin. Its just a resistor that connects your control pin + to the -. Simple.

Hope that helps.

thanks, ive been going back and looking at your and dkj4linux on the laser going back a few years. Seems like you guys have had an adventure figuring out how things work! Its been very educational.

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