Wiring up board (had digital display)


Machine: k40W
Firmware: Smoothie
Question: Hey I finally got around to installing the Laserboard and gCLD controller on my K40, took literally 10 mins, awesome! I’ve only added air assist and a bed before this so i’m a little hesitant tinkering with the wiring…

Everything works great, Thanks so much! just a couple of questions moving forwards:

Firstly I hadn’t got around to adding a lid switch before, I ordered one from you with my board although it came with two pin connector so was wondering if there is an interlock feature (and where do i connect) or should I be cutting the end off and wiring it into pins 5 & 6 or something on the PSU?

Secondly, I got a little excited and made the face plate adding the power switch before I had read the install instructions,and seeing the 24v out is now not used, doh! is there anyway I can turn off the Laserboard with the switch instead of at the plug? and also this switch seems to disconnect the 5v (pin 13), Everything still seems to work without it, should it stay connected or can it be left out?

Lastly (bonus question), I originally had the digital display control, based on what i understand of the PSU pin out, it was receiving pin 7 (laser test fire), 8 (Gnd), 9 & 10 Pot) yet it had the ability to turn the laser on and off. just wondering how this works because it seems happy whether these are connected or not.

(Brian Bell) #2
  1. On the LPSU pinout you have numbered you will notice the black jumper between 5 & 6… that where you connect the waterflow sensors, interlocks, etc… 2. Typically the main power switch is a DPDT rocker that interrupts the hot and negative AC line in so it kills everything. My solution would be to wire the AC input of the c3d laserboard to the AC already present in the machine (i cut out the crappy outlets in the back and used the hot and neutral from them to run my additional power supplies). 3. With the stock digital power control board disconnected i think the laser will continue to function but i think it is at 100% possible power which is likely WAY too much power. I strongly suggest adding a 20mA DC milliammeter so you can accurately monitor the actual current draw of the tube and not exceed 15ma. You also need to add a pot (or reconnect the digital panel and leave it inside the electronics bay) because you still need a way to define a hard current limit. More on that here: Cohesion3D PWM Control and Potentiometer vs 'Digital Panel'


Ah awesome, thanks for your help Brian. didn’t see that FAQ before, super helpful! Yeah I’ve already left a hole in the face plate for the mA meter, just waiting for it to arrive, didn’t realize I still needed the pot tho, I guess I’ll order an analogue so i can get rid of that digi display.
Took me a second to get what you meant with the AC, didn’t think of piggy backing the brick AC off the main switch. looks like i’m gonna have to re-cut that face plate after all haha

Thanks again, much appreciated!


I would definitely not recommend modifying the wiring of the C3D power brick.

The wiring inside the K40 and a number of other, even more expensive Chinese lasers is complete shit and the C3D needs a good, clean power source. If anyone asks about disconnects or other board freezing issues the first thing I tell them is to plug the C3D power brick into a different outlet or if that doesn’t do it then a different circuit in the house entirely.

(Clif Jones) #5

It is not recommended and probably voids the warranty but I did what Brian said. I directly wired in the C3D 24VDC supply into the main power. That being said, I have a background in electronics and I know the risks so I’ll share what else I did.

  1. Use a ground fault circuit interrupter (GFCI) outlet, always. During the early part of my modifications, current was leaking to ground (probably from that cheap laser power supply). The GFCI can save you and is useful in finding out if you have properly grounded the unit.
  2. The K40 is not grounded and that binding post on the back is insulated from the case. Ground everything to the frame and then to the ground on your 3-prong cord. Ground the lid too, since you have that current meter with high voltage, power switch, etc. and just a hinge connecting it to the rest of the case.
  3. There is no fuse or breaker on the K40. I didn’t feel comfortable with the 15/20A breaker protecting me as those small power wires would be in flames long before the breaker kicked. Look at your smallest wire carrying power and at least fuse it to protect the smallest AC power wire.

I actually replaced the auxiliary outlets on my K40 with 3-prong outlets and had 1 outlet switched off of the C3D mini board to control my air-assist compressor. Here are some pictures. I have since thrown away the blue laser power supply and put a better one in.

This is the power harness assembly for my new auxiliary outlets and the hard-wired C3D 24V power supply.

Here it is installed. You can see the C3D 24V supply in the bottom left corner of the picture. I just attached it to the case with good double-sided tape.

I cut the hot power feed line to the main power switch and installed an inline fuse.


ah nice, thanks for sharing your pictures as well. Yeah that was one concern of mine by the fact the K40 had no fuse coming into the box. I was lucky enough to have grounded outlets already on my k40 and so only cleaned up the grounding bolt on the case to make sure i had good grounding.

Hadn’t realized the lid wasn’t grounded tho so will chuck a lead on that for sure and probably put an inline fuse to the main switch wire and GFCI (once I understand it a little better) as you have, even if i don’t wire in the power brick.

Really appreciate both of your help and recommendations on this!

(Dave) #7

Using 12V fuses in a 120V line is very dangerous. Low voltage fuses may arc and actually ignite once the fuse blows. Have a google for “Fuseology” article by Buss.

(Clif Jones) #8

Actually, you are right. I probably shouldn’t have posted that picture since it was a temporary fix to have something fused in that horrible ungrounded LASER cutter so I could have it make some of its own replacement parts. :slight_smile:

I had to buy some new fuse holders in addition to some other things. Here is my final setup with the exception of an etched PCB for the low-voltage interconnects.

The glass fuse is in the black assembly on the red wire.
The yellow wire on the left grounds the lid and connects to the common ground, tied in at the now new power supply. Yeah, the cheap original power supply blew out pretty quick. :frowning:

I’m almost done modifying this machine. It was a fun project.

closed #9