# Need help determining power supply for 6 stepper motors

Hey there, I am going to run 6 stepper motors (17HS10-0704S to be specific) from 6 TMC2209 stepper drivers (running at 24V). They will be connected in parallel.

I was hoping to be able to power these 6 motors along with a Raspberry Pi Zero W (at 5V so 24v-5v step down converter) from a LRS-100-24 Meanwell power supply (108W, 24V, 4.5A).

From my calculations, the 6 motors will draw about 60W (2.9V x (0.7A x 2) = 4.06W + some headroom for inefficiency = 10W) which is 2.5A drawn from the power supply. On top of that, the Raspberry Pi foundation recommends 1.2A to power the pi zero w although I doubt it will run at that current continuously (see this). Along with that, I will be running a few neopixels so maybe another +0.3A. Finally, I will be running a small Noctua fan for cooling (+0.05A). This all adds up to about 4A. That being said I am not planning on running the motors at max current, maybe only about half (so 0.35A/phase) so this calculation is only for the worst-case scenario.

My problem is I don't have enough space in my enclosure to use a bigger power supply so I am stuck with the form factor of these Meanwell supplies or smaller. Would the power supply mentioned above be sufficient for this?

Thanks.

I would go fore a 10 Amp power supply. 6 motors * 0.7 Amp = 4.2 Amp. Adding current for the processor might cause that power supply to shut down.
Don't bother soo much about Watt. Current is the important factor.

Wouldn't that calculation be 6 * (0.7 x 2) = 8.4A as the 0.7 is only per phase?

What if I'm running the motors at half their rated current? I don't need to max torque for my application.

You've got a point.
Reducing the current to that level will cripple the steppers a lot, reducing the torque they can provide.
Make a test running one motor, setting different currents and see what happens! Choose the most heavily loaded stepper!

No, that is wrong. The wattage is the important factor. The current driver ( TMC2209 ) works similar to a buck converter. Therefore, the current drawn from the supply is less than the motor current. However, a sufficiently large bulk capacitor near the TMC2209 is very important. The full motor current flows between the bulk capacitor and the motor (in both directions!).

So I tried out one motor, and I am able to get it to work for my application very well at around 0.3A (current measured from my bench power supply). With this, I guess the calculation then would be: 6*0.3A = 1.8A, correct?

Go on as long as things work....

Those motors are about 2W stationary, lets say upto 4W dynamic. six lots is thus 24W.

Allow for driver inefficiency, 2A at 24V is plenty I think. [ seems to agree with measurements! ]

You calculation is incorrect, a 0.7A 4.2 ohm motor takes I-squared-R, not twice that, since the coils are driven in quadrature. When one coil has 0.7A the other has 0A.

If you use a buck converter to power the Pi Zero, it won't be pulling anything like 1A from 24V.

Depends how the driver is configured. The motor is designed for 0.7A current on both coils simultaneously ( see datasheet of the motor ).

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