Why does one motor run hotter?

So I'm using the Duet Wifi. I had leveled all my motors at 1000ma when I set it up, which worked ok. Having just printed an enclosure and added a cooling fan for the drivers, I decided to try upping the voltage to match what the motor ratings say. My Exruder is rated for 1.68, and my X Y and Z motors are rated for 2.5 amps if I'm reading the datasheet correctly. So I upped the XYZ motors to 2000ma just to try it.

So the curious thing to me is the Y motor gets noticeably hotter than the other two. Just comparing to the heatbed, It feels like about 45 degrees where the other two feel like maybe 30 if that.

First of all, you shouldn't run the motors at a muh higher current as needed.
The first step would be to measure the temperature as feeling is very inaccurate. You don't tell what kind of printer you use, but I simply would guess that the y-axis is moving not as smooth as the x-axis and therefore more force is needed to move it.

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

As a general rule, setting the current to 80% of the motor rating is best practice. If one motor is hotter than another, it's probably doing more work. If the geometry of your machine means that the X axis only has to move the hot end, but the Y axis has to move the X axis carriage as well, then I'd expect this to be normal behaviour. In any case, 45 deg C should not be an issue. Check the data sheet for your stepper motors but most are rated at 80 deg C. HTH

I always thought, steppers would get hot, no matter if they move or stand still ( holding )?

Maybe you've allowed the colder stepper to switch in idle mode or with a lower holding current?

2000ma is the max of the duet wifi drivers to my knowledge, and still not quite 85% of the rated current of the motors which is 2.5 amps.

It's a kossel, it doesn't appear that the Y tower is doing anything more than any other, particularly when printing simple objects. but it's consistently warmer than the other motors even at a lower rating of 1200Ma. I don't think it's a problem temperature since it's not too hot to touch or anything. It just seemed curious to me.

You could measure the phase resistances of all 3 motors with a multimeter, to check that they really are the same, in case one of the motors is incorrectly marked.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].