Next in the list (now that the motors are here) will be the PSU. I think I understand what I'm doing but I wanted to ask if someone could stop me before I make any (or at least too many) terrible mistakes :) I know this is a rehash of threads to probably occur once a fortnight but its for a reason. I'm setting out the details because it's not just about buying the right thing - I want to make sure my understanding of what I'm buying and why is correct.

I have these 3.1Nm steppers and I plan to wire them as parallel: 4.2A, 3.2mH and 2.73V. Doing some magic calculations (based on magic spells found elsewhere on this forum) leads me to an operating voltage of 57.2V. The PSU would therefore need to provide [email protected]. But wait...

I plan to buy PM752s which can provide, inter alia, 4.09A or 4.64A. In fact they support up to 5.2A but the motor has a maximum of 4.2A. This would mean the appropriate setting would be 4.09A therefore the PSU would now only need to provide [email protected]. But wait, again...

Now as far as I understand it, I don't need to make the full 56.2V available, as nice as the idea might seem to me. There would be a performance drop but as the motors are probably outperforming the rest of the machine anyway, would this necessarily present a problem? Common figures seem to be 42V and 48V. Is dropping from 56V to 48V a travesty of epic proportions?

So what about the current? If needed, I could run two PSUs wired in parallel to provide more current (ie 2 x 42V@7A would effectively be able to provide 42V@14A). However, much as the full 56.2V may not be needed, so too the full 12.3A may not be needed. For an unregulated supply, the PM752 docs suggest the PSU might only need to supply 50%-70% of the motor rating. Picking an arbitrary 75%, the PSU would now only need to provide [email protected]. While 50%-70% would actually be 6.2A-8.7A, I assume (no! not assumptions! nooooo!) that more safety margin is always better than less.

Zapp's SPS407 - with 42V@7A(continuous) and 9A(peak) - would work on its own using the 50%-70% figures but would need to be doubled up to make my fairly arbitrary 75% minimum - though if doubled then for the same price I could consider the SPS705, two of which would provide 68V@10A. I gather this could be magically fettled to provide the ideal 56V-57V at the slightly-less-than-ideal 10A, but would move the cost bracket from £60-£70 to £120-£140.

CNC4You's 48V@12A, by contrast, would provide 97.5% and a few extra volts all on it's lonesome, but would still be under the ideal voltage.

I notice that Zapp also bundle their PS806 68V@6A with 3xPM752s and 3Nm motors, but that 6A falls below the 50% so I am presuming it would be too far a stretch in this very-similar-but-a-tiny-bit-different scenario.

Then we move onto sourcing the bits and building one but for some reason that makes me a little jittery compared to getting something made by someone who is competent to build something I plan to plug into the mains!

All of this leads to a point, eventually. If I choose "money" then it's 48V@12A@£57. If I choose "voltage" then it's 56V@10A@£138.

Am I on the right tracks and am I considering the right things to balance? I've picked up this idea that I can run on less volts, but am I being daft (well, the anwer to that is always yes) to think I should be considering anything less than 56V in this scenario?