4' x 4' x 8" Router Build

**Neale** · 08-10-2023

The main reason for using one of the cheap Chinese switch-mode power supplies is that they are cheap, small, light, and cheap. And did I say cheap? However, as has been mentioned in this thread and also alluded to in the Gecko document, they do not suffer overload gracefully. That is, they will trip out if they detect any combination of overload, overvoltage, or whatever (and assuming that the protection circuitry is up to it) and the stepper drivers do not like this - any loss of power is going to mean at best restarting the job and at worst a ruined job as the software has now lost control of machine position. That is why a SMPS needs to be over-rated for the load for those rare just-in-case situations when all the drivers are hitting peak load together. The "linear" power supply - transformer, rectifier, capacitor - will, within reason, accept peak overloads without flinching and just carry on, as long as the average load is within its capabilities. This is why they seem to typically be under-specified as the stepper motors only demand peak current in relatively short bursts and seldom all together.

As m_c says, it used to be the case that stepper drivers would only accept DC and you therefore needed some kind of power supply for them. These days, there seem to be more and more drivers around that will accept an AC input of the appropriate voltage directly and contain all the circuitry needed to generate DC internally. Then you just need the corresponding transformer and it's all a lot easier.

I have a CNC router and CNC mill in my workshop that use the classic transformer/rectifier/capacitor combination, and a CNC lathe that I am currently updating which uses newer drives which accept AC. All of these work just fine. I do use the cheap Chinese SMPS boxes, but for some combination of 5V/12V/24V for the control electronics depending on the machine. The SMPS boxes are fine for that application.

**JonnyFive** · 09-10-2023

Originally Posted by Neale

The main reason for using one of the cheap Chinese switch-mode power supplies is that they are cheap, small, light, and cheap. And did I say cheap? However, as has been mentioned in this thread and also alluded to in the Gecko document, they do not suffer overload gracefully. That is, they will trip out if they detect any combination of overload, overvoltage, or whatever (and assuming that the protection circuitry is up to it) and the stepper drivers do not like this - any loss of power is going to mean at best restarting the job and at worst a ruined job as the software has now lost control of machine position. That is why a SMPS needs to be over-rated for the load for those rare just-in-case situations when all the drivers are hitting peak load together. The "linear" power supply - transformer, rectifier, capacitor - will, within reason, accept peak overloads without flinching and just carry on, as long as the average load is within its capabilities. This is why they seem to typically be under-specified as the stepper motors only demand peak current in relatively short bursts and seldom all together.

As m_c says, it used to be the case that stepper drivers would only accept DC and you therefore needed some kind of power supply for them. These days, there seem to be more and more drivers around that will accept an AC input of the appropriate voltage directly and contain all the circuitry needed to generate DC internally. Then you just need the corresponding transformer and it's all a lot easier.

I have a CNC router and CNC mill in my workshop that use the classic transformer/rectifier/capacitor combination, and a CNC lathe that I am currently updating which uses newer drives which accept AC. All of these work just fine. I do use the cheap Chinese SMPS boxes, but for some combination of 5V/12V/24V for the control electronics depending on the machine. The SMPS boxes are fine for that application.

Thanks Neale, really appreciate you taking the time for such a detailed response.

These are the drivers I have:

JazzCNC suggested running them at 55VAC and just using a transformer which is what I have in my control schematic.

I’m not looking to build this on the cheap, I want it to be right and I want it to be reliable. Although I can move my gantry easily turning the ballscrews by hand the gantry will be heavy when it’s finished, I’m guessing 50kg, so there will be momentum creating voltage spikes and the system needs to tolerate them.