Pacific Scientific POWERMAX II stepper motor

Pacific Scientific POWERMAX II Stepper Motor: Performance Benchmark and Flexible Customization for NEMA 23 Framework

Product Overview and Industry Status

In the field of industrial automation, stepper motors, as the core executing components of open-loop positioning systems, directly affect the production efficiency and operating costs of equipment in terms of torque density, dynamic response, and long-term reliability. The POWERMAX II series hybrid stepper motors launched by Pacific Scientific (now a brand under Danaher Motion) have become a global performance benchmark in the NEMA 23 (2.3-inch base) size class due to their excellent torque output, innovative magnetic circuit design, and highly flexible customization capabilities. The maximum holding torque of this series of motors can reach 253 oz in (approximately 1.79 Nm), ranking among the top in the same size class. At the same time, the unity of economy and high performance is achieved through design for manufacturability (DFM). POWERMAX II not only offers standard models, but also supports various customization options such as low inertia rotors, integrated screws, special windings, etc. It is widely used in fields such as electronic assembly, medical equipment, packaging machinery, laboratory automation, and CNC machine tools.

Core Technology: Sigmax ®  Patent magnetic circuit

The core technological advantage of the POWERMAX II series lies in its patented Sigmax ®  Magnetic circuit design (US Patent No. 4712028, 4713470, 4763034, 4827164). During excitation of traditional hybrid stepper motors, some magnetic flux leaks from between the stator teeth and does not participate in torque generation, resulting in a decrease in efficiency. Sigmax technology embeds samarium cobalt (SmCo) rare earth permanent magnets in the stator teeth to focus the magnetic flux on the most effective working air gap position between the rotor and stator, thereby significantly suppressing magnetic leakage and increasing the torque generated per ampere of current. Compared with traditional hybrid design, Sigmax technology enables the motor to output larger holding torque and dynamic torque at the same current, while achieving higher current utilization and lower heat generation.

According to the different magnetic circuit structures, POWERMAX II is divided into two sub series:

P series (standard hybrid): adopts traditional hybrid rotor and stator structure, without rare earth magnet insertion. Provide cost-effective solutions suitable for most general positioning applications. Its step angle accuracy is ± 3% (non cumulative) of each step when there is no load, maintaining a torque range of 42-253 oz in.

M series (enhanced hybrid): Adopting Sigmax technology, samarium cobalt magnets are embedded in the stator teeth. Compared to the P series of the same size, the M series can provide higher torque output and better current utilization. Its step angle accuracy has been improved to ± 1.5% per step, making it suitable for situations with higher requirements for dynamic performance and positioning accuracy.

Rotor structure and inertia options

POWERMAX II offers two rotor structure options to accommodate different motion profile requirements:

L-type rotor (standard laminated rotor): using traditional silicon steel sheet laminated structure, with moderate rotational inertia. Suitable for most general motion controls, providing smooth operating characteristics.

J-shaped rotor (low inertia rotor): By optimizing the rotor geometry and material, the rotational inertia is reduced. A low inertia rotor can generate higher angular acceleration under the same electromagnetic torque, thereby achieving faster start stop and shorter positioning time. Especially suitable for applications that require frequent acceleration, deceleration, and fast positioning, such as surface mount machines, picking and placing mechanisms, etc.

Taking a double stack motor as an example, the standard rotor inertia is 3.57 × 10 ⁻³ oz in · s ² (0.022 × 10 ⁻³ kg · m ²), while the low inertia rotor is 2.59 × 10 ⁻³ oz in · s ² (0.016 × 10 ⁻³ kg · m ²), a decrease of about 27%. Theoretical normalized acceleration comparison shows that P22 series motors with low inertia rotors can increase acceleration by 30%, while M22 series motors can increase acceleration by 63%. It should be noted that the half stack model does not offer a low inertia rotor option.

Model Code and Selection Guide

The complete model code of POWERMAX II includes multiple information bits such as motor type, size, stack length, rotor type, winding, shaft options, connectors, etc. Taking the example model P21NRXS-LNN-NS-00 as an example for analysis (please refer to the original factory selection guide for the actual model code format, and here we will explain the general rules in conjunction with the document content):

The first character (series): P=POWERMAX II

Second character (stack length/machine base): 2=NEMA 23 frame; The following numbers indicate the stack length (1=half stack, 2=single stack, 3=double stack? P2H (half stack), P21, P22, etc. appear in the document, need to be compared).

Subsequent characters (rotor type, winding, etc.): N=standard rotor (L-type), R=specific winding code, X=option to be defined, S=shaft type, etc.

Conclusion: LNN-NS-00 may indicate standard lead, no encoder, standard shaft, etc.

The document lists various winding options, represented by letters A to G for different rated current and resistance combinations. For the P2H half stack series, the following typical windings are provided:

5.2 A/0.22 Ω → Maintain torque at 59 oz in

2.6 A/0.90 Ω → Maintain torque at 59 oz in

3.68 A/0.44 Ω → Maintain torque 42 oz in

2.6 A/0.76 Ω → Maintain torque at 59 oz in

1.3 A/3.04 Ω → Maintain torque at 59 oz in

1.84 A/1.52 Ω → Maintain torque 42 oz in

2.5 A/0.84 Ω → Maintain torque 61 oz in

1.25 A/3.36 Ω → Maintain torque 61 oz in

1.77 A/1.68 Ω → Maintain torque of 43 oz in

1.61 A/1.92 Ω → Maintain torque of 60 oz in

0.80 A/7.68 Ω → Maintain torque of 60 oz in

1.10 A/3.84 Ω → Maintain torque 42 oz in

Users can choose the appropriate winding based on the output current capability and required torque speed characteristics of the driver. All rated parameters were measured at 25 ° C.

Detailed technical specifications

5.1 Basic Electrical and Mechanical Parameters

Number of phases: 2 phases

Step angle: 1.8 ° (full step), 200 full steps per revolution

Step accuracy:

M series (including M-J low inertia): ± 1.5% per step (no load, non cumulative)

P series (including P-J low inertia): ± 3% per step (no load, non cumulative)

Insulation Class: NEMA Class B (130 ° C)

Insulation resistance: 100 M Ω @ 500 Vdc, 25 ° C

Working environment temperature: -20 ° C to 40 ° C

Storage temperature: not specified, but usually within the same working range.

5.2 Axle Load Capacity

Maximum radial load: 20 lb (approximately 89 N), acting on the midpoint of the standard shaft extension.

Maximum axial load: 13 lb (approximately 58 N), oriented towards the motor (push in).

Bearing lifespan: POWERMAX II uses oversized 30mm bearings (ordinary NEMA 23 motors typically use 22mm or smaller bearings). The fatigue life of bearings (L ₁₀) exceeds 10000 hours under the conditions of meeting radial and axial load limits and a speed not exceeding 10000 full steps per second. Compared to similar motors using 22mm bearings, the lifespan is approximately four times longer.

5.3 Thermal performance

Thermal resistance: measured when there is no heat sink installed in still air. The specific values vary depending on the model (not directly provided in the document table, but mentioned as' Thermal resistance measured with motor hanging in still air ').

Temperature rise: At rated current, the winding temperature can reach 130 ° C (B-level insulation limit). When the ambient temperature is 40 ° C, the surface temperature of the motor may be high, and good ventilation should be ensured during application.

5.4 Inductance and Resistance

The phase inductance is given in the form of a small signal inductance and measured using an impedance bridge at 1 kHz and 1 A. The typical range of inductance values for different windings is from approximately 0.45 mH to 20.4 mH. Low inductance windings are suitable for applications that require high-speed response, but require drivers to provide a higher current rise rate; High inductance windings provide smoother torque at low speeds, but require higher driving voltage.

Size and Installation

The installation flange of POWERMAX II NEMA 23 motor complies with NEMA standards, with a positioning stop diameter of 2.3 inches (58.4 mm) and a bolt hole center to center distance of 1.856 inches (47.14 mm) (typically 2.625 inches spacing). The length of the motor varies depending on the stack length and rotor type:

Half stack model (P2H): approximately 1.60 inches (40.6 mm) in length

Single stack model (P21/M21): Approximately 2.06 inches (52.3 mm) in length

Double stack model (P22/M22): Approximately 2.4 inches (61.0 mm) or 3.10 inches (78.8 mm) in length (depending on rotor type).

The standard diameter of the motor output shaft is 0.250 inches (6.35 mm) with a flat surface. We can customize shaft extension length, dual axis extension, screw integrated shaft, etc. as needed.

Wiring and connector options

POWERMAX II motors offer multiple lead out methods:

Flying Leads: Standard configuration includes 8 or 4 26 AWG PTFE insulated wires, with color coding in accordance with industry conventions (phase A: black/orange; B phase: red/yellow; Center tap: white/red, white/yellow, etc. Users can choose between bipolar series, bipolar parallel, or unipolar connections based on the type of driver.

Optional connector kit: Pacific Scientific offers cable assemblies with pre installed connectors for the GW series, such as GW0000F (8-wire) and GW0000H/L (4-wire). These connectors are easy to plug and unplug quickly, reducing wiring errors. The correspondence between connector pin definitions and wire colors is detailed in the document.

Phase sequence: Observing from the motor installation end (i.e. flange end), the motor shaft can rotate clockwise or counterclockwise according to a specific power sequence (e.g. A+, B+, A -, B -). The specific phase sequence diagram can be found on pages 9-10 of the document.

Performance curve and acceleration comparison

POWERMAX II provides a complete torque speed curve (the curve is not directly printed in the document, but it is mentioned that it can be obtained through optimizer 3.0 software). Generally speaking, double stack motors have higher holding torque and low-speed torque than single stack motors, but due to increased inductance, the torque decay at high speeds is faster. Low inertia rotors perform better at high speeds because their lower rotational inertia allows for faster acceleration.

The document provides a comparison of theoretical normalized acceleration (based on no-load, 90 ° C temperature rise, bipolar drive):

Motor model, rotor type, inertia (oz-in-s ² × 10 ³), normalized acceleration

P21NRXX standard L 1.68 1.00

P21NRXX low inertia J 1.30 1.27

M21NRXX standard L 1.68 1.23

M21NRXX low inertia J 1.30 1.59

P22NRXX standard L 3.57 1.00

P22NRXX low inertia J 2.59 1.30

M22NRXX standard L 3.57 1.18

M22NRXX low inertia J 2.59 1.63

It can be seen that when the M series using Sigmax technology is combined with a low inertia rotor, the acceleration can be increased by 59-63%, significantly improving the dynamic response of the system.

Customization capability and accessories

The "Design for Manufacturability" (DFM) concept of POWERMAX II enables it to achieve high customization at a lower cost:

Axis modification: flat, keyway, threaded hole, extended shaft, dual axis extension.

Integrated lead screw: It can be directly processed, rolled or ground on the motor rotor, eliminating the need for couplings and saving space.

Encoder installation: Incremental encoders (optical or magneto resistive) can be installed to achieve closed-loop control or position verification. Encoder options can be found on page 53 of the document.

Reducer: Can be equipped with a high-performance gearbox to increase output torque or change output speed.

Special winding: In addition to standard A-G windings, specific current/inductance combinations can be designed according to customer requirements.

Application scenarios and selection suggestions

Typical Applications

Electronic assembly equipment: SMT machines, dispensing machines, and flying needle testing machines require high acceleration and precise positioning.

Medical equipment: infusion pump, sample processing system, scanning table, requiring low noise and low vibration.

Packaging machinery: label machines, sealing and cutting machines, material conveying, require reliable open-loop control.

Laboratory automation: liquid processing workstation, microplate conveying, requiring compact size and long lifespan.

CNC machine tools: small carving machines, 3D printers, winding machines.

Selection steps

Determine torque demand: Calculate the required holding torque and dynamic torque based on load torque, acceleration torque, and friction torque.

Choose stack length: Single stack is suitable for medium torque requirements; Double stack provides higher torque but also greater inertia.

Choose series: If higher acceleration and efficiency are required, prioritize the M series (Sigmax); If cost is sensitive, the P series is sufficient.

Select rotor type: For applications with frequent start stop, choose low inertia (J) rotors; Select standard (L) rotors for smooth operation or high inertia loads.

Choose winding: Based on the output current and supply voltage of the driver, select the winding that can provide the required torque speed characteristics. Usually, low inductance windings are advantageous for high-speed operation.

Confirm mechanical interfaces: shaft diameter, shaft length, flat or keyway, installation hole position.

Consider accessories: do you need encoders, reducers, connectors, and cables.

Quality Assurance and Environmental Compliance

The POWERMAX II motor comes with a two-year warranty, demonstrating Pacific Scientific's confidence in product reliability. The motor adopts a new polymer encapsulated stator and a polymer end cap with threaded inserts, which improves heat dissipation performance and facilitates the installation of encoders or brakes. The exposed laminated structure helps to dissipate heat directly from the winding into the surrounding air. The motor meets the NEMA Class B insulation requirements and has passed the corresponding vibration and impact tests (specific standards need to refer to the complete manual).