Powering many external devices via circuit board (safely)

Hi all,

I'm attempting to power around 40 stepper motors via daisy-chained shift registers as per the schematic below. My understanding is that each of the 28byj-48 motors (and ULN2003 driver) can draw up to 200 mA and 40 of them connected at once may require up to 40*0.2A = 8 Amps. The power supply I was looking to use is a cheap "switching mode" one off amazon that you can get for around $20. It is indexed to supply 5v and up to 10 Amps. Can you please evaluate the circuit and tell me if it is safe, or let me know of alternative means of powering such a large amount of steppers and shift registers. Similarly, let me know if other components would be required to make the circuit safer or function properly.

Additionally I was wondering what thickness of wire would be needed to connect the power supply terminals to a PCB, and whether a cheap universal PCB would be capable of carrying 10 Amps.

Thanks for helping me stay safe!

There is a bit of a mismatch don't you think ?

I don't understand. The power supply has a current rating that specifies the maximum current it can output, if only 100 mA were required it would be fine as current is "pulled" not "pushed " into the components. Unless I'm misunderstanding

This is likely a language problem. In most cases, you can change the word "power" to the word "control" and make more sense of your posting. Power is what makes the servos move. Control is what tells them to move.
The size of wire needed is pretty much dependent on the LENGTH of wire. The internet has sites that will tell you the diameter of wire necessary to carry the current you require.

Add a 0.1uF cap to the VCC pin and Gnd of each shift register for reliable operations.

1 Like


Sorry, my misunderstanding from reading your post too quickly

You connected your arduino 5v out pin to the breadboard. If power adapter you are buying fails you probably will burn your board. I think you meant to connect it to Vin but not sure

1 Like

yeah don't push 8A through the breadboard..

Good spot. I may have made that error when soldering. thank you!!