A Better Way to Wire Your DC Power Supply?

The Problem

The basic enclosed power supply is the workhorse of the DIY CNC world. It is used in most small scale 3D printers and CNC routers. Unfortunately they are not the easiest items to wire cleanly. They are also difficult to add a power switch to. It gets even uglier when you add things like power controls for DC Spindles.

But I think we might have a solution...

A Simple Solution

un plus assembled.jpg

For a little side project, I had a few of these PCBs made. This is a simple little PCB that screws right onto the terminal block of the power supply. It cleanly adds a universal AC input socket with a switch. This assembly can be easily mounted to the wall of an enclosure.

The DC power is brought out to a large terminal block. The DC output has two sets of terminals on a pluggable terminal block. The right set of two terminals are powered whenever the switch is in the on position. The left two are controlled by a 5V signal (and the switch). This can be used as an on/off control or a replacement for your speed controller using a PWM signal. GRBL and TinyG both have PWM options for speed control.

How would it be used?


Mount the PCB assembly to the power supply terminal block. Connect your device to either the always on terminals or the logic controlled terminals. You can use both sets if you have two devices and you want one to always be on and one to be controlled via a logic signal. Connect your logic signal to the smaller terminal block. You could also wire a simple switch that connects +5V to the logic input for low-voltage manual control.

Here it is being controlled via a signal generator with a 0-5V square wave.


Not all power supplies are alike. You need one with the correct orientation and the AC connections on the right side. Inventables power supplies are like this. The PWM-responsive circuit is designed for a maximum of 48VDC and about 8.5Amps before active cooling will be required. 

Note: This does not have a knob for speed control- It needs to be done via your controller.


This is design for people comfortable with AC line voltages.  There are several places with live exposed voltages. The end user should ensure the application is safe. Make sure to select the appropriate power supply (48VDC max) for your application. Do not exceed the maximum current of 8.5A. With this said, the scattered wire alternative is probably less safe.

Carry it or bury it?

We are in the process of determining if there is enough demand for this product. If you think we should sell it, sign up on the product page to be notified when it is available. If the signup count hits about 40 in a reasonable time, we will stock it. Also feel free to comment on this post too.

The sell price is probably going to be in the $20-$30 range, which is cheaper than the existing speed controller. It will be sold as a kit that requires very basic solder skills. We will include detailed instructions for usage.

If it proves to be a popular product we might make version for other power supply types.


Kevin O. said...

Is the PWM input 3.3V safe? I believe the TinyG pwm outputs are 3.3v only

Photographe de l'Ouest said...

This design is not good for enclosure box because the green connector is not feet to power connector..

jimustanguitar said...

I like it! I'd want to use it for more projects than just the ShapeOko though, and they wouldn't all have the same terminal block on the power supply... Would a board with the switch and phoenix connectors be more hackable if it terminated to a "whip" that you could wire to your power supply however you needed to?

Bart Dring said...

I am not understanding the comments complete, but the tinyG works fine with this. There will be a little time for a few tweaks before production so keep the suggestions coming.

Hugh said...

I like the idea.
What about making the kit so the connectors and the switch can be mounted on either side so as to be used with the L N G on either the left or right side. Also I would like to have a 6 position connector

Kevin Brady said...

I like the idea generally. I'm not totally convinced unreinforced frp has the mechanical strength for reliability in this application. A thicker pcb can help somein this regard. More information on the copper weight and trace width would be handy.

Bart Dring said...

@hugh - That is an interesting idea. The MOSFET would probably need to to be spun around. I'll investigate that.

@Kevin Brady - The board is very stiff because it is so short. The stiffness can lead to stresses put on the power supply terminal block. This should be used with a panel or enclosure for safety and support.

The design will be open source. You can use the gerber files to determine the copper cross section.

hotho said...

Carry it! I'll snap one up once available.