What Is a Dynamometer?

The Basics

A dynamometer is an apparatus that measures mechanical force, speed, or power. In a typical dynamometer test cell testing an engine, motor or transmission is coupled to the dynamometer via couplings and a drive shaft. When the device under test is running, the dynamometer can exert a braking force on it.

Sensors on the dynamometer measure engine (or other device) speed and torque. Knowing these values, the dynamometer can be used to calculate engine-power output. Dynamometers allow us to reproduce a desired speed or torque for a test under controlled conditions.

There are Several Types of Dynamometers

Dynamometers use different methods to induce a braking force on the device under test. What exactly are the benefits of different types of dynamometers? The following dynamometer comparison chart lists the characteristics of Water Brakes, Eddy Current, DC, and AC dynamometers, and the headings link to descriptions.

Features	Water Brake	Eddy Current	DC	AC
Motoring Ability	No	No	Yes	Yes
Inertia	Low	Varies	High	Low
Control Stability	Low	Good	Very Good	Excellent
Speed Capability	High	High	Moderate	High
Power Line Regeneration	No	No	Yes	Yes
Control Response	Slow	Moderate	Fast	Fastest
Cooling Requirements	High	High	Low	Low
Electrical Requirements	None	Low	High	High
Technology	Old	Old	Old	New
Power Range	High	High	Moderate	Moderate

Water Brake Dynamometer

A water brake is a bladed rotor that churns water inside the dynamometer housing. The more water inside, the greater the braking force exerted on the device under test.

Advantages	Disadvantages
Low Cost Low Inertia	Difficult to Control High Maintenance

Eddy Current Dynamometer

An Eddy Current absorption dynamometer produces braking torque using the principle of eddy currents induced in a rotating metallic disk, immersed in a magnetic field. It is basically an eddy current brake mounted in trunnion bearings. Its advantages are maintenance, control, simple construction and desirable speed-torque characteristics. The speed-torque characteristics make the eddy current dynamometer ideal for engine testing, and its versatility also allows effective use in testing transmissions, turbines, electric motors, gears, pumps and many other machines.

Advantages	Disadvantages
Precise Control Low Maintenance Widely accepted in the automotive industry	High Inertia Moderate Cost

Go to Eddy Current Dynamometers page.

Back to Chart

DC Dynamometers

A DC dynamometer is a DC motor that has been trunnion mounted.

Advantages	Disadvantages
Motors and Absorbs Fast Response Air Cooled (No water required) Line Regenerative	High Cost (Dynamometer and Power Amplifier) High Inertia Requires high amperage electrical service

Go to DC Dynamometers page.

AC Dynamometers

An AC dynamometer is similar to a DC dynamometer except it uses an AC motor and is powered by alternating current.

Advantages	Disadvantages
Motors and Absorbs Very Low Inertia Very Fast Response Line Regenerative	High Cost Requires high amperage electrical service

Go to AC Dynamometers page.

Talk to the Experts

If you are in the market for a dynamometer, dyno control, test automation, or data acquisition system, please contact our Regional Sales Managers for further assistance.