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I'm trying to pick a power supply and need a little more guidance before I'm comfortable spending money on one.

This site explains how to calculate your figures for power supplies but isn't too descriptive. https://learn.watterott.com/silentstepstick/faq/

Their example:

What power supply do I need?
A power supply (Psup) with a few times higher voltage than the motor phase
voltage and a current of roughly the power of the motor (Pmot) plus the
mechanical output power (Pout) is at least needed.

For example 3 stepper motors with 2 coils/phases and every phase has 
3.3 Ohm with a 1.2A current rating and a voltage of 4V.

Pmot = 2 coils * 4V * 1.2A = 9.6W (standstill power without load)
Pout = 0.20Nm * (2pi * 1000rpm / 60) = 20.9W (mechanical power)
Psup = 3 * (Pmot + Pout) = 91.5W (electrical input power)

At 24V this is a current of 3.8A (I=91.5W/24V).

I'm using a single 3.2V stepper motor with 2.0A/phase

Here's my calculations using their formulas:

Pmot = 2 coils * 3.2V * 2A = 12.8W
Pout = 1.2Nm * (2pi * 1000rpm/60) = 125.7W
Psup = 12.8W + 125.7W = 138.5W
Vsup = 24V
Isup = 5.77A

I just kinda assumed I should use a 24V supply and got the current from that and the power. I have seen other people use a 12V, but wasn't sure what would be best. At 12V I would need a supply that's 11.5A!! Right?

So assuming I go with a 24V supply, would I try to find one that's 24V and as close to 5.77A without going over? Or is it ok if I use one that's 6A. I couldn't find anything in the TMC2130 datasheet about max input current limits.

Any advice is greatly appreciated.

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The important thing to look at here is the first wattage calculation you did. The 12.8W that the motor will consume is the max wattage you will ever want to drive the motor (regardless of power supply voltage).

Think about it like this. If you where to connect that 24V power supply directly to the motor it would probably be a very smokey experience. But that doesn't mean we cant use a 24V power supply. We now just need to limit the current by some proportion to make sure that the motor doesn't get more than 12.8W.

To do this the TMC2130 has an AIN pin that allows you to reduce the current going to the motor. I believe this device also allows you to do this digitally as well.

So to answer your question you can use either a 12V or 24V supply. You will just need to set the AIN so that you are using about 10% (@24V) of the current the motor would typically draw at that voltage.

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  • \$\begingroup\$ Thanks for the info! I believe the TMC2130 uses the tiny potentiometer and a digital option depending on which operating mode you're using. I'll be using StealthChop. But I'll have to look at the datasheet again to remember which current setting method to use. One other question: Will I experience any type of difference in motor performance as far as audible noise or torque capabilities whether I use a 12V or 24V supply? \$\endgroup\$ – conn250 Sep 25 '18 at 17:54
  • \$\begingroup\$ It will make some difference but It is generally because of the performance of the motor driver at different voltages. Without going into to much detail a power supply closer to your stepper motors specified voltage is better because it allows for use of the motor drivers full range. So in this case I would use a 12V supply. \$\endgroup\$ – Meozaa Sep 26 '18 at 22:39

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