60-70v unregulated power supply recommendations

[Neale]

One reason I went with 2x45V in parallel rather than 2x24V or 2x25V in series is that it gives a few volts headroom. As has been said already, these transformers are specifically wound in a way that allows parallel connection safely but you shouldn't parallel-connect arbitrary transformer windings. Phasing is important; get it wrong with series-connection and you get zero output but get it wrong with parallel-connection and you are going to have a very hot transformer very quickly (before the fuse blows...) I'm using 625VA, but from some power measurements I have done on my machine, I reckon that 500VA is plenty. However, the bigger transformer was only a few quid more and it fitted the space available, so I went with the over-specced option. If I were building these things commercially, I would go 500VA or maybe a touch less and still be confident that I was going to run within ratings. I have a habit of over-building my own kit...

This link gives some results I measured on my own power supply. Yes, there is still a lot of mains frequency ripple on the DC side but the stepper drivers are very voltage-variation-tolerant. After all, they are typically specced to run between 24-80V absolute max, something like 28-70V in practice. While it is true that there will be some back EMF when the motor is decelerating, I didn't see any obvious evidence of large spikes on the oscilloscope amongst the general high-frequency switching noise (although I accept that this kind of thing will be difficult to see) but you have to remember that there are the smoothing capacitors that are going to take the sting out of these voltage spikes.

Overall, and even though I'm not the kind of guy who generally accepts blind "do this and you'll be OK" kind of advice without a bit more analysis, the answer is that everyone who has used 2x24 or2x45 transformers with 3x4700uF or 2x6800uF capacitors with the AM882/EM806 class drivers has been very happy with the results and you are unlikely to do better than this.