Unipolar/Bipolar Connections (2-Phase Motors)

Publish Time: 2018-01-11 Origin: Site

Unipolar / Bipolar Connections for 2‑Phase Stepper Motors

When working with 2‑phase stepper motors, you will inevitably encounter two fundamental wiring configurations: unipolar and bipolar. These terms describe how the stator windings are arranged and how current flows through the coils—directly affecting driver complexity, torque performance, speed characteristics, and application suitability.

What Are Unipolar and Bipolar Designs?

Unipolar (Center‑Tapped Windings)Each phase has a center tap, splitting the coil into two equal halves. Current flows in one direction only (from center tap to one end). Reversing polarity is done by switching between the two halves, not by reversing current. This allows simpler drive circuits (fewer transistors).
Bipolar (No Center Tap)Each phase uses a single continuous winding. To reverse magnetic polarity, the driver mustreverse current direction through the entire coil. This requires an H‑bridge driver but uses 100% of the winding at all times, typically delivering higher torque and better efficiency.

Lead Configurations & Connection Methods

2‑phase motors come in 4‑lead, 5‑lead, 6‑lead, or 8‑lead versions, each supporting different connection modes.

4‑Lead (Bipolar Only)

xed bipolar operation
Full winding in use
Best low‑speed torque
Requires H‑bridge driver

5‑Lead (Unipolar Only)

Common center tap for both phases
Simple ON/OFF control
Lower torque, suitable for basic applications

6‑Lead (Unipolar → Bipolar Convertible)

Default: unipolar (half‑coil)
Convert to bipolar (series): insulate center taps, use outer ends
Balanced performance and flexibility

8‑Lead (Fully Configurable)

Unipolar (half‑coil): use one coil per phase
Bipolar series: connect coils in series (high torque, lower speed)
Bipolar parallel: connect coils in parallel (higher speed, lower torque)

Connections	Resistance (Ohms)	Inductance (mH)	Current (A)	Voltage (V)	Holding Torque (oz-in)
Unipolar	Same as Catalog	Same as Catalog	Same as Catalog	Same as Catalog	Same as Catalog
Bipolar Series	Catalog X 2	Catalog X 4	Catalog X 0.707	Catalog X 1.414	Catalog X 1.414
Bipolar Half Coil	Same as Catalog	Same as Catalog	Same as Catalog	Same as Catalog	Same as Catalog
Bipolar Parallel	Catalog X 0.5	Same as Catalog	Catalog X 1.414	Catalog X 0.707	Catalog X 1.414
Customer'sDriver	Motor Choices	What to Do	How to Do It		End Result
Unipolar (6 Leads)	6 Lead Motor	Use as is (Unipolar)			6 Leads
Bipolar (4 Leads)	8 Lead Motor	Convert to Unipolar	Tie yellow and orange together and use AND Tie white and brown together and use		6 Leads
	6 Lead Motor	Convert to Series	Tape off yellow and white leads and don't use		4 Leads
	6 Lead Motor	Convert to Half Coil	Tape off black and red leads OR Tape off green and blue leads		4 Leads
	8 Lead Motor	Convert to Series	Connect yellow and orange and tape off AND Connect white and brown and tape off		4 Leads
		Convert to Parallel	Tie black and orange together AND Tie yellow and green together AND Tie red and brown together AND Tie white and blue together		4 Leads
		Convert to Half Coil	Tape off black, yellow, red, and white OR Tape off orange, green, brown, and blue		4 Leads

Performance Comparison

Torque

Bipolar: higher low‑speed torque (full winding)
Unipolar: lower torque (half‑coil operation)

Speed

Unipolar: lower inductance → better high‑speed performance
Bipolar: higher inductance → torque drops faster at high speed

Driver Complexity

Unipolar: simpler, lower cost
Bipolar: requires H‑bridge, more complex

How to Choose: Unipolar or Bipolar?

Choose Unipolar if: - You need high speed with moderate torque - Driver cost and simplicity are priorities - Basic positioning applications (e.g., printers, small conveyors)
Choose Bipolar if: - You need high torque at low speed- Efficiency and smoothness matter - Precision applications (e.g., CNC, robotics, automation)

Understanding unipolar and bipolar connections is critical for motor‑driver matching and application optimization. While bipolar designs dominate modern high‑performance systems due to superior torque and efficiency, unipolar remains a practical choice for cost‑sensitive, high‑speed scenarios. Clear wiring diagrams and technical guidance are essential to ensure your system is configured correctly for optimal performance.