Hi Ed, first, the two phases will not be drawing 2 amps simultaneously as the phase currents are in quadrature phase. So probably the peak current to a single motor would be 2.8 amps. Second, I believe that if you are using modern chopper drives, though the motor current may be 2amps, the supply current, from a higher voltage, will be significantly less as in effect they give a transformer action. (They act as switch mode power supplies in a buck converter mode.) IIRC the eBay PSU I bought for my little mill is rated at 6 amps, as you say has 2 sets of output terminals but they are paralleled up inside, so just giving more contact are for the current. I certainly have no issues running 3 motors, one of which is a size 34, off this supply. I've never measured the total current, it will be a week or so before I can but happy to do so if you can wait?

John.

FWIW Some "posh" power supplies have a pair of tags for the actual current output with adjacent tags for voltage sensing. These should be connected at the load end of the wiring to the two "power" leads. The idea is that the power supply winds the voltage up to make sure that the voltage at the load end of the wiring is correct. The voltage sensing wires can be as thin as you like, the power wiring must be adequate for the current being drawn.

Example a 5V PSU delivering 10A over a pair of 1.5mm cables. The actual voltage at the PSU terminals might be 5.4V, giving 5V at the far end of the cables.

Without the remote sensing, setting the PSU voltage to 5.4V on a 10A load would give you your 5V, but if the load current reduced, the voltage would rise up to the maximum of 5.4 V which could upset the circuit.

Frank

Steppers driven using multi-stepping use a maximum of 1.4 times the rated current per phase, if set up properly.

Steppers driven in normal modes use twice the rated current per phase.

Whatever you choose, get something that has some headroom (1.5 to 2 times your expected current) to allow for transient high currents, plus an over-rated supply will run cooler and last longer.

Neil

I am far from an expert in this, but I wonder if the NEMA 17 motors are strong enough. My first attempt was with NEMA 17 and found they didn't have the grunt.

I'm now on NEMA 23 motors (6Nm) and I'm still not happy that they're powerful enough.

The CNC conversions sets offered by the site you're buying from start from 3Nm NEMA 23 with I think end up as 0.59 Nm.

I expect this is fine for a 3D printer which has light moving parts, but If you are milling then you are moving a lot of mass against resistance and pushing the material onto the cutter as well.

I tried a single motor on one axis fist and then reviewed.

I echo the comments earlier that it would be marvelous if the low cost stepper motor people published a torque curve so that it was more than trial and error.

Iain