PSU : prices and differences

[Jonathan]

Gytis,

If your unsure then has a guide just check the voltage coming into building, if it's on the high side then go for the lower transformer to be on safe side.

Measuring it at a random time is pretty meaningless - at any one point on the grid the mains voltage can and does vary by several volts over time. I'd advise getting a transformer based on the standard mains voltage tolerance (i.e. 230+10%=253V in the UK), otherwise the power supply can't be described as stable and safe for the drivers.

So with a 230V to 33V transformer, using the 10% tolerance and 1.1V drop for rectifier, you can expect up to 33*1.1*1.414-1.1=50.2V. Granted that's not likely to occur at all often, but it is over the rated voltage of the drivers so using the 30V transformer is would be less of a risk. If using a 35V transformer (i.e. the spare one I had) then I'd add in some extra diodes or a linear regulator circuit to keep the voltage within the specification.