Confirming PSU spec for steppers.

[Jonathan]

A small problem with wiring the secondary in parallel is that if the amount of turns on them is not exactly the same the transformer is not as efficient.
I got around this by rectifying the two windings separately then combining them at the DC side.
Just a thought. ..Clive

If they're mismatched that configuration will still draw less current from the winding with a lower emf.

The following quick simulations I just did demonstrates this:





The first graph shows the current drawn from each winding for the aforementioned mismatched transformer with a light load and the second graph shows the same supply with a greater load. This shows that the effect if greatest when the load current is low, so although the currents are mismatched they will both be within the rating for a light load. Similarly, the mismatch is smaller when the load is greater, so if the rating of one winding is exceeded it is unlikely to be by enough to cause a problem. Also, there are a lot of other factors besides load current involved here, so the above simulation is by no means comprehensive.

In short it's extremely unlikely for the windings to be mismatched enough for either method to cause problems, so although I'd advise buying a transformer rated for half the voltage so you can put the secondarys in series, if you find one for the right price which has to be wired in parallel I wouldn't worry.