# How to determine stepper motor voltage / drive current?

I have an STP-42D132-01 stepper motor which I want to use with an A4988 / TMC2208.

So far the motor is rotating but only very very weak. There is almost no torque.

At the moment my PSU shows that the motor only takes ~300mA when driving without any load.

I was not able to find any datasheet or specs for the motor.

The only information I got is from the label:

1.8Deg/Step 12Ω

No. 20901 *

Shinano Kenshi co ltd japan

The motor is very small (3x4x4 cm) - If I assume it is a 12V motor what is a realistic drive current per phase?

Would this make any sense?

$${12\text{V}\over12\text{Ω}} = 1\text{A}$$

• "There is almost no torque" - how much torque is that, and how much do you need? What voltage are you running the TMC2208 on, and how is it set up (microsteps, hold current etc.)? Commented May 28, 2022 at 2:39
• Similar motor but with lower resistance - jameco.com/z/… Commented May 28, 2022 at 2:48
• Try running it at 1A and see how warm it gets (it will take a few minutes to warm up). If it feels too warm reduce current. If cool, increase the current. Motors of that size are usually good for 1-2A.
– Drew
Commented May 28, 2022 at 5:59