Power Supply Build for Router CNC

[Jonathan]

Does the output voltage change linearly with the input voltage?

For the purposes of this discussion, yes near enough.

I'm thinking 235V into the 25+25 transformer would produce about 51V out (wired in series). Wish I'd put together a spreadsheet for the calculations now! Considering there's a 2.2V drop in the rectifier I think the 24+24 is probably the best choice in that case - I suppose I've just got to go away and crunch the numbers again.

If the transformer is wound for 230V to 25+25, then putting 235V in will indeed get 235/230*50=51V, however the tolerance is +10%, so 50*1.1=55V will be the limit. The rectifier drop is 1.1V, not 2.2V. The reason is (for the purposes of this discussion!) you only ever have 2 diodes conducting at a time and the forward voltage drop of two diodes will be about 1.1V. That means with 55VAC in to the rectifier, you can expect 55*sqrt(2)-1.1= 76.7V peak.