Stepper Motor Pinout Diagram

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Identify stepper motor wiring — unipolar vs bipolar, coil pairs, and centre-tap leads — using resistance measurements to map any unmarked connector correctly.

A stepper motor converts digital pulse sequences into precise mechanical rotation by energising electromagnetic coils in a defined order. Before connecting any stepper motor to a driver, you must correctly identify its winding configuration from the connector pinout.

The two most common configurations are bipolar and unipolar. A bipolar motor has two independent coils, each with two leads, giving a total of four wires. The driver reverses current direction through each coil to step in either direction. Because current flows through the full coil winding in both directions, bipolar motors produce more torque per unit volume than equivalent unipolar types.

A unipolar motor has two coils each with a centre-tap wire, producing five or six wires total. The five-wire version joins both centre-taps internally to one common lead. With a unipolar driver, only half the coil winding is active at any step — the driver switches current from the centre-tap out through one end lead, then out through the other, always in the same direction per half-winding. Six-wire motors expose both centre-taps separately, allowing the motor to be used in bipolar mode by leaving the centre-tap wires unconnected.

Identifying coil pairs by resistance is reliable and works on any motor regardless of wire colour coding. Set a multimeter to resistance mode and probe every combination of wire pairs. Leads belonging to the same coil will show measurable resistance (commonly 1 Ω to 50 Ω depending on motor size). Leads from different coils show open circuit (infinite resistance). On a six-wire motor, the end-to-end resistance of a full coil will be exactly twice the resistance from one end to the centre-tap — this identifies the centre-tap.

Once coil pairs are mapped, assign them to the driver's A+/A− and B+/B− terminals respectively. Phase order determines rotation direction — swapping the A+ and A− leads reverses direction without altering any other wiring.

How to wire stepper motor pinout

Count the motor's wires A four-wire motor is bipolar. A five-wire motor is unipolar with a shared common centre-tap. A six-wire motor is unipolar with separate centre-taps, usable as bipolar by leaving the centre-taps floating. Eight-wire motors have dual coils per phase and can be wired in series or parallel for different torque/speed characteristics.
Map coil pairs using resistance measurement With the motor unpowered and disconnected, set a multimeter to resistance mode. Systematically probe every wire combination and record readings. Build a table: list wire numbers 1–4 (or 1–6) and record resistance between each pair. Pairs with finite resistance belong to the same coil; all other combinations should read open circuit.
Identify centre-taps on five- or six-wire motors On a coil where you have identified three wires with mutual resistance readings, the centre-tap is the wire that reads approximately half the full end-to-end resistance when probed against either end wire. For example, if end-to-end reads 8 Ω, the centre-tap reads approximately 4 Ω to each end.
Assign coil pairs to driver terminals Label the two coil pairs as Coil A and Coil B. Connect Coil A wires to the driver's A+ and A− output terminals, and Coil B wires to B+ and B−. The initial polarity assignment determines rotation direction, which can be reversed in software (by reversing step sequence) or by swapping one coil's leads at the driver.
Set driver current to motor rated value Locate the motor's rated coil current from its datasheet or nameplate. Set the driver's current limit (usually a potentiometer or DIP switch on the driver board) to match. Excessive current causes overheating; insufficient current causes missed steps and reduced torque. Many drivers have a current reduction mode for when the motor is idle.
Test rotation direction and step count Send a known number of steps (e.g. 200 steps for a standard 1.8 °/step motor, which should equal one full revolution). Observe rotation direction. If direction is opposite to requirement, swap the A+ and A− leads or reverse the step direction in firmware. Do not swap B leads at the same time — change only one coil at a time to avoid confusion.

Specifications

Standard step angle (most common)	1.8 ° per step (200 steps per revolution)
Alternative step angle	0.9 ° per step (400 steps per revolution) for finer resolution
Typical coil resistance range	1 Ω to 50 Ω depending on motor size and rated voltage
Centre-tap resistance (unipolar, relative to end-to-end)	Approximately 50 % of end-to-end coil resistance
Common NEMA frame sizes	NEMA 11, 14, 17, 23, 34 (frame size in tenths of an inch across face)
Microstepping resolution (driver-dependent)	Full, half, quarter, eighth, sixteenth step — up to 1/256 step on advanced drivers
Holding torque	Specified at rated coil current; drops proportionally with reduced current

Safety warnings

Never disconnect a stepper motor from its driver while the driver is energised. Removing the motor leads causes inductive voltage spikes that can destroy the driver output stage. Always power down before changing connections.
Do not exceed the motor's rated coil current. Stepper motors can draw rated current continuously even when stationary (holding position). Inadequate heat dissipation causes winding insulation breakdown and permanent motor damage.
Stepper motor drivers can produce dangerous voltage spikes on the output terminals under certain fault conditions. Do not touch driver output wires while power is applied.
When using a stepper motor in a mains-powered system, all high-voltage wiring must comply with the relevant electrical installation standard for your region (NEC/NFPA 70, BS 7671, AS/NZS 3000, or IEC 60364). Low-voltage stepper wiring must be physically separated from mains wiring.

Tools needed

Digital multimeter with resistance (Ω) mode
Bench power supply with current limiting (for initial testing)
Wire stripper and crimping tool
Small flathead screwdriver (for driver current trim potentiometer)
Oscilloscope (for verifying step pulse timing, optional but recommended)

Common mistakes

Connecting both wires of the same coil to A+ and B+ on a bipolar driver: this shorts the driver output and will not produce rotation. Always ensure each driver output pair receives one wire from a single coil.
Setting driver current too low to avoid heat: the motor will run but miss steps under any load. Heat is normal and expected — the driver and motor must be sized and cooled appropriately, not current-starved.
Confusing a five-wire unipolar motor for a four-wire bipolar motor: a five-wire motor on a bipolar driver will produce erratic or no motion and risks driver damage. Always count wires and measure resistance before connecting.
Using too long or too thin motor wiring: inductive reactance in long leads combined with chopper drivers causes unwanted EMI and can interfere with step pulse signals. Keep motor wiring as short as practical and routed away from signal wiring.
Reversing direction by swapping both coil pairs simultaneously: this does not reverse direction but can produce the same mechanical output while creating confusion in the wiring documentation. Change only one coil's polarity at a time.

Troubleshooting

Motor hums and vibrates but does not rotate: Cause: Both driver outputs are connected to wires from the same coil, or step pulses are not reaching the driver Fix: Disconnect power. Re-verify coil pairs with multimeter resistance test. Ensure A output wires come from one coil and B output wires from the other. Also verify step pulse signal is present at driver input using an oscilloscope or LED indicator.
Motor rotates but skips steps or stalls under load: Cause: Driver current limit set below motor rated current, or supply voltage too low for operating speed Fix: Increase driver current limit to match motor rated coil current. Ensure supply voltage is adequate — many drivers perform better with supply voltage significantly above motor rated voltage when using current chopping mode. Verify power supply can deliver peak current without voltage sag.
Motor and driver overheat rapidly: Cause: Driver current set above motor rated current, or motor is held energised at full current when idle Fix: Reduce driver current to motor rated value. Enable the driver's automatic current reduction (idle current reduction) feature if available — this reduces hold current by 50 % when no steps have occurred for a defined period, substantially reducing heat generation.

Frequently asked questions

How do I identify a stepper motor's coil pairs using a multimeter?

Set the multimeter to resistance (Ω) mode. Probe every possible pair of wires. Wires belonging to the same coil will show a finite resistance reading (typically 1 Ω to 50 Ω). Wires from different coils show infinite resistance (open circuit). Group the low-resistance pairs — each group is one coil. On a six-wire unipolar motor, the centre-tap wire will read half the coil's end-to-end resistance.

What is the difference between a bipolar and a unipolar stepper motor wiring scheme?

A bipolar motor has four wires (two per coil) and requires the driver to reverse current direction through each coil. A unipolar motor has five or six wires including a centre-tap per coil; the driver switches current through only half the winding at a time, always in one direction. Bipolar wiring delivers more torque; unipolar drivers are simpler in construction.

Can I run a six-wire unipolar motor as a bipolar motor?

Yes. Leave the two centre-tap wires unconnected (insulate them to prevent shorts) and connect the remaining four wires to a bipolar driver — two wires per coil to the A and B outputs. The motor then operates in bipolar mode, using the full winding and producing more holding torque than in unipolar mode.

Why does my stepper motor vibrate but not rotate?

The most common cause is a miswired coil — the motor is receiving the correct step pulses but the coil pair assigned to B is actually both halves of coil A, or vice versa. Re-verify coil pairs with a multimeter. Also check that enable input is active and driver current is set appropriately for the motor's rated current.

What does 'holding torque' mean for a stepper motor?

Holding torque is the maximum torque the motor can resist while energised and stationary without slipping to the next pole position. It is specified at the motor's rated coil current. Operating a stepper at reduced current (to reduce heat) proportionally reduces holding torque. Always match the driver current limit to the motor's rated coil current for full holding torque.

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