Joe90's BIG RAT Build.

[Neale]

It's easy to get too wound up about these things. Whether you should use 60%, 70%, or 80% really doesn't make a bit of difference - if you are using a linear (i.e. toroidal transformer, etc) anyway, in practice, the average load will be way lower. Doesn't matter to the transformer - as long as it's rated for the average load with a bit left over, its thermal mass is so great that a few seconds a bit over rated current won't worry it. The rectifier is coping with short high-current pulses anyway as it charges the capacitors towards the peaks of the cycle. And capacitors aren't that critical as regards value as this is a CNC machine, not an audio amplifier. Ripple is not an issue. My drivers, for example, are rated for something like 20-80V input. A few volts more or less ripple ain't going to bother them any. I use a 650VA transformer that gives me around 67V and it doesn't even get warm.

Different case if you are using a switched-mode, stabilised, power supply. They are much less tolerant of peak loads and you might be safer over-specifying if you use one of those. Which is why linear PSUs are generally recommended!