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Hello.
I'm using some steppers.
I'd like to extend the length of their wire but I wondered what was the maximum length for extentions cord without geting the motor erratic?
thanks a lot
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Your main concern is going to be power loss. Depending on the length and diameter of your wire, you could lose a "significant" amount of power in the wires at high currents. The motors would become "erratic" if they don't have enough power left over for the torque they need to generate.

As an example, using 20AWG wire (about 1 ohm per 100 feet), 6 ohm stepper, and a 12V driver, what if the cables are 10 feet? Total resistance is 6 ohms + 0.1 ohms + 0.1 ohms = 6.2 ohms. Current will be 12V / 6.2 ohms = 1.94A. The stepper will dissipate 1.94^2 * 6 = 22.5W and the wires will dissipate 0.75W, so you will lose about 3% of the total power in the wiring.

If the voltage stays the same and your wires get longer and longer, you deliver less and less power to your motors. If you have a "smart" motor driver that can increase its voltage to keep the current constant, then you can preserve motor power even as the wires get longer.

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