MK1 Steel router build log 1500x800x200

[Neale]

Yes, you don't have to add together the peak demand to give a rating if you are using a linear PSU. For one thing, as you say, the chance that all four motors will be running at full power at the same time is tiny. The second is that the load via the drivers is more like a series of short pulses than a continuous current and the smoothing capacitors can provide this pulse load very easily, and the rest of the PSU components just see the average load. In practice, a rough rule of thumb is to calculate maximum load, and use a PSU rated at about 30% less. The final point is that because of the way the drivers work, you do not actually need a very smooth well-regulated power supply (within reason). My 68V PSU has a measured 10V or so ripple under load. This does not cause any problems at all.

These points are also why a cheap switch-mode PSU is less suitable. It does not cope with peak loads very well, so it has to be over-specified to cope with the maximum peak load, not an average load.

I use a 650 VA toroidal which replaced a 500VA transformer which failed. The bigger transformer was only a couple of pounds more, as I remember, but measuring the average power consumption of the machine, I could probably have used something smaller. That's driving 4x3Nm Nema 23 steppers, max current probably about 4A per motor.