24v power supply to cut or not to cut

Hi everyone i’m going to order the laserboard once back in stock, my question is, the board comes with it’s own power brick, so do you have to leave the 24v wire’s disconnected from the k40 psu, or do you just leave the wire’s on.

You can leave them connected, the Laserboard itself disconnects them at the board level.


And if you need 24vdc elsewhere in your system, you can steal it directly off the screw terminals on the C3D. I personally chose to remove this power from the C3D board and feed it into a terminal buss for my other needs

I plugged the power connector in the board 1 pin off and broke the optocoupler. I removed the 5 and 24 pins and wires to avoid doing it again.

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No, please do not recommend this.

The Cohesion3D Power Supply is 4 amps that has to be shared between 4 stepper drivers, the board logic, and the GLCD Screen. That leaves about 500mA for a peripheral that will control air assist. There is no room for anything else, the board is not designed to be able to feed a lot of current from the DC Jack to the screw terminal. This can damage the board and affect stability of operations.

A separate power supply for additional peripherals will always be the preferred way of doing things.

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To this same end, I removed the stock harness with 4-pin connector from my unit entirely and instead ran two new wires from L and GND to the appropriate screw terminals on the LaserBoard. Also note that my unit had an older Moshiboard with a different laser power connector, so I couldn’t have used it anyways …

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Thanks for all the advice now just to wait for stock to come in.

Yeah, I know the feeling… I’m just waiting for that next shipment update to happen…

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Ray, sorry I did not make myself clear. The 4 pin plug coming from the LPSU has 24vdc unused by the C3 D board. My understanding is that although it is connected to the C3D connector, there is no electrical connection to the board itself. Pulling 24vdc from the corresponding screw terminal on the C3D board would have no effect on the board itself

Please correct me if I have misspoken



No connection from the LPSU but there is a connection from the supplied power brick, so you would be risking overloading the power brick, it is rated to handle all the board functions, but not to run peripherals as well. Hope I am clear in my explanation. :slight_smile:

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Ok, sorry, I am a bit confused. The original question was

“ so do you have to leave the 24v wire’s disconnected from the k40 psu, or do you just leave the wire’s on.”

All I was suggesting is that since the 24 vdc from the LPSU is not used by the C3D board, you can use it for whatever you like providing you do not overload the LPSU. Nothing at all to do with the C3D board. Regardless of where you connect it, it is available.

Sorry for all the confusion

You can remove the that 24v connection and the 5v connection. I only have two wires in the power plug.

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David, to clarify:

The typical K40 LPSU does have a 24v rail but it is very underpowered. The whole reason that we ship a power brick is to take the load off of it. Yes, you could hook up some small 24v fan to it and everything would probably be fine. However, larger loads would be a problem. I have to consider the entire audience, including the infinite internet users that can read this, which is why I will never recommend hooking up anything to the LPSU. I have seen people blow up their LPSUs by overloading them and I don’t want to see it happen to anyone here.

An interview I did covers this:


The interview with me starts at 11:20. I recommend listening to the whole thing because it’s good.

“Use a separate power supply for everything you want to do” is in my mind right up there with “Never leave your laser unattended”, because I don’t want you to have a fire.

Wow Ray, that was very informative. I have been meaning to rewire my entire control system for some time now and this will definitely have an impact on my final design. Thanks for that.


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