AC Dynamometer / AC Dyno Test Bench — Four-Quadrant Motor Testing System

Four-quadrant AC dynamometer test benches covering 5–2,000 Nm, 8,000–18,000 RPM, 0.75–250 kW, ±0.2% accuracy.

What Is an AC Dynamometer?

An AC dynamometer (also called an AC dyno or AC dynometer test bench) is a four-quadrant precision testing device used to measure and control torque, speed, and power in electric motors, engines, and powertrain systems. Unlike absorption-only dynamometers (eddy current or magnetic powder), an AC dynamometer operates in all four quadrants — it can act as both a load (braking/absorbing) and a drive (motoring), and in both forward and reverse rotation.

The system consists of an AC motor (asynchronous induction or permanent magnet synchronous) paired with a four-quadrant variable frequency converter. This enables precise control of load conditions across the full operating envelope of the unit under test (UUT), from zero RPM through maximum rated speed.

EconoTest AC dynamometer models (EC5A to EC2000A) cover torque from 5 Nm to 2,000 Nm, speeds from 8,000 to 18,000 RPM, power from 0.75 kW to 250 kW, and achieve torque and speed measurement accuracy of ±0.20% full scale.

How Does an AC Dynamometer Work?

An AC dynamometer works through the bidirectional energy control capability of a four-quadrant frequency converter:

1. Loading mode (generator mode): The AC dynamometer absorbs mechanical energy from the unit under test by acting as a generator. The absorbed energy is converted to electrical power and fed back to the grid (regenerative) rather than dissipated as heat, significantly reducing energy costs during endurance testing.
2. Motoring mode (drive mode): The AC dynamometer drives the unit under test — for example, spinning up a transmission input shaft or providing motoring torque to an electric motor under test. This enables efficiency mapping, back-driving tests, and hybrid powertrain simulation.
3. Four-quadrant operation: By combining loading and motoring in both clockwise and counterclockwise rotation, the AC dynamometer can simulate all real-world operating conditions a motor or powertrain experiences during its service life.
4. Torque control: A high-precision torque transducer and speed encoder continuously monitor output. The frequency converter adjusts current in real-time to maintain the commanded torque or speed setpoint with ±0.20% accuracy.
5. Energy regeneration: Unlike eddy current or hysteresis dynos that dissipate absorbed energy as heat, the AC dynamometer recovers braking energy and returns it to the facility power supply, substantially reducing net energy consumption during braking and endurance tests.

Key Advantages of AC Dynamometers

AC Dynamometer vs. Eddy Current Dynamometer

Parameter	AC Dynamometer	Eddy Current Dynamometer
Operating quadrants	4 (motoring + loading, both directions)	1 (loading/absorption only)
Zero-speed torque	Available (motoring mode only; loading torque requires motion)	Not available
Energy recovery	Yes — regenerative, feeds power back to grid	No — all energy dissipated as heat
Speed range	8,000–18,000 RPM	Up to 50,000 RPM
Best for	EV motor efficiency mapping, powertrain, hybrid testing	High-speed motor and engine endurance testing
Cooling requirement	Air-cooled (converter cabinet)	Water-cooled (all models)
Capital cost	Higher	Lower
Operating cost	Lower (energy recovery)	Higher (all energy as heat)

AC Dynamometer vs. Magnetic Powder Dynamometer

Parameter	AC Dynamometer	Magnetic Powder Dynamometer
Operating quadrants	4	1 (absorption only)
Zero-speed loading torque	Available at low speed (near zero)	Full rated torque at zero RPM
Speed range	8,000–18,000 RPM	2,000–5,000 RPM
Power range	Up to 250 kW	Up to 15 kW (ECF2000 continuous)
Best for	EV powertrain, high-power motor testing	Production line testing, servo/geared motors
Consumables	None	Periodic magnetic powder replacement

When to choose an AC dynamometer: Your application requires efficiency mapping across all operating quadrants, four-quadrant testing (both motoring and loading), speed above 5,000 RPM, or energy cost reduction on long-duration tests.

Technical Specifications

All EconoTest AC dynamometer parameters are confirmed from our official product specifications. All parameters can be customized upon customer request.

Parameter	Range (EC5A – EC2000A series)
Rated torque	5 – 2,000 Nm
Max speed	8,000 – 18,000 RPM
Rated power	0.75 – 250 kW
Torque & speed accuracy	±0.20% full scale

Detailed model-by-model specifications (torque, speed and power for each model in the EC5A–EC2000A series) are provided with your quotation based on your application requirements.

Note: For applications requiring speeds above 18,000 RPM or power above 250 kW, see our High-Speed Motor Test Bench (up to 25,000 RPM, up to 800 kW) or contact our engineers for a custom configuration.

System Components:

• AC dynamometer motor (PMSM or induction, customer choice)
• Four-quadrant frequency converter cabinet (regenerative, back-to-grid)
• High-precision torque transducer (±0.20% FS)
• Non-contact speed encoder
• Industrial PC with real-time motor performance analyzer
• Motor testing software (automated test sequences, data acquisition, report generation)
• Coupling, coupling guard, base frame, and safety interlock system
• Optional: environmental chamber (−45°C to +150°C), battery simulator, cooling system controller

Applications by Industry

Automotive — EV Motor and Powertrain Testing

AC dynamometers are the primary tool for automotive EV motor validation. Test items include efficiency mapping (MAP), peak torque, peak speed, T-N curve, NVH, EMC/EMI, thermal management, and durability. The four-quadrant capability is essential for hybrid powertrain testing where the electric machine alternates between motoring (driving the vehicle) and generating (regenerative braking) modes.

Typical automotive applications:

• PMSM / ASM / EESM traction motor validation
• E-axle (integrated inverter + motor + transmission) performance and durability
• Hybrid drivetrain calibration
• Starter-generator characterization

Aerospace — Ground Support Equipment and Propulsion

Aircraft ground support equipment, electric actuators, and MEA (More Electric Aircraft) propulsion components require four-quadrant testing to validate both power generation and motor mode performance. AC dynamometers at power levels up to 250 kW cover the range for aircraft accessory drive testing.

Marine — Ship Propulsion and Generator Testing

Marine electric propulsion systems and shaft generators require high-torque, medium-speed testing. Higher-torque models in the EC5A–EC2000A range (up to 2,000 Nm) are appropriate for these applications. Four-quadrant capability enables simulation of both propulsion and regeneration conditions.

Industrial — Motor Manufacturing Quality Control

For industrial motor manufacturers, AC dynamometers provide comprehensive end-of-line performance verification covering efficiency, power factor, torque ripple, and speed regulation. Automated test sequences reduce cycle time compared to manual test bench operation.

AC vs. Eddy Current Dynamometer: Which to Choose?

Choose an AC Dynamometer if:

• You need efficiency mapping across all four quadrants (motoring and loading)
• Your motor application involves bidirectional operation or regenerative braking
• You need to reduce energy costs on long endurance tests (regenerative energy recovery)
• Testing involves hybrid powertrains or e-axle systems
• You need automated efficiency map generation per standard drive cycles

Choose an Eddy Current Dynamometer if:

• You only need absorption (loading) mode — no motoring required
• Speed requirements exceed 18,000 RPM (ECW series reaches 50,000 RPM)
• Budget is a primary constraint and energy recovery is not required
• Your application is combustion engine testing or single-direction motor validation
• Your application is small, high-speed motor testing

AC vs. Magnetic Powder Dynamometer: Which to Choose?

Choose an AC Dynamometer if:

• Speed exceeds 5,000 RPM
• Power exceeds 15 kW
• You need four-quadrant (motoring + loading) capability
• You want no consumable powder replacement over the system lifetime

Choose a Magnetic Powder Dynamometer if:

• You need full rated torque at exactly zero RPM (static load holding)
• Speed range is below 5,000 RPM
• Your application is production line batch testing (servo, geared motors, wiper motors)
• Torque range is up to 2,000 Nm at low speed

AC Dynamometer Selection Guide

Follow this 4-step process to identify the correct AC dynamometer model:

Step 1 — Define motor rated torque and peak torque
The dynamometer rated torque must be equal to or greater than the motor’s peak torque (not just continuous rated torque). Select the next model up if your peak torque falls between two models.

Step 2 — Define maximum test speed
The dynamometer maximum speed must exceed your motor’s maximum test speed with adequate margin. EconoTest engineers will recommend the appropriate margin for your application.

Step 3 — Verify continuous power
Confirm the dynamometer’s rated power covers your continuous test cycle. For short-duration peak power tests, a slightly lower-rated model may suffice — consult EconoTest engineers.

Step 4 — Determine test mode requirement
If you only need loading (absorption) mode, an eddy current or magnetic powder dynamometer may offer better value. If motoring, efficiency mapping, or energy recovery is needed, an AC dynamometer is required.

Quick selection reference:

• The EC5A–EC2000A series covers 5–2,000 Nm, 8,000–18,000 RPM and 0.75–250 kW — EconoTest engineers will match the exact model to your torque, speed and power requirements
• Beyond 2,000 Nm or 250 kW: contact EconoTest for custom configuration

Test Items Performed on an AC Dynamometer Test Bench

The EconoTest AC dynamometer test bench covers the following standard test items. Custom test sequences can be added per customer specification:

Performance Tests:

• No-load test (speed, current, voltage, power)
• Rated load test (output power, torque, efficiency)
• Peak torque measurement
• Peak speed measurement
• T-N (Torque-Speed) characteristic curve
• Efficiency map (MAP) generation across speed/torque grid
• Back EMF test
• Torque fluctuation and speed fluctuation measurement
• d-q axis inductance measurement
• Electromechanical time constant
• Electrical time constant

Dynamic Tests:

• Motor start-up test
• Frequency response bandwidth measurement
• Torque control response time
• Speed control response time
• Dynamic position tracking error
• Inertia simulation
• Forward/reverse speed difference rate

Durability and Thermal Tests:

• Durability test (continuous operation at rated conditions)
• Temperature rise test
• Overspeed test
• Thermal resistance measurement
• Braking torque test

Driver/Inverter Tests:

• Driver performance test
• Locked rotor test
• Speed regulation rate measurement

Frequently Asked Questions

Get Specifications or Request a Quote

EconoTest engineers respond to all RFQ inquiries within 24 hours.

To receive a technical proposal, please provide:

• Motor type (PMSM / ASM / EESM / other)
• Rated torque (Nm) and peak torque (Nm)
• Rated speed (RPM) and maximum speed (RPM)
• Rated power (kW)
• Required test items (efficiency map, NVH, EMC, durability, etc.)
• Environmental requirements (temperature range, humidity)

Contact EconoTest:

• Email: [email protected]
• Phone / WhatsApp: +86 156 1877 0706
• Address: 3F, Building 2, No. 511 Xiaowan Road, Fengxian District, Shanghai, China

Request a Quote Now →

All specifications confirmed from EconoTest official product documentation. Parameters are customizable upon request. EconoTest (Shanghai EconoTechnology Co., Ltd.) — National High-Tech Enterprise.