What Is a Dynamometer?

The Basics

A dynamometer is an apparatus that measures mechanical force, speed, or power. In a typical engine/dynamometer test cell, the end of the engine crank shaft is coupled to the dynamometer via couplings and a drive shaft. When the engine is running, the dynamometer can exert a braking force on the engine.

Sensors on the dynamometer measure engine 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.

FeaturesWater BrakeEddy CurrentDCAC
Motoring AbilityNoNoYesYes
InertiaLowVariesHighLow
Control StabilityLowGoodVery GoodExcellent
Speed CapabilityHighHighModerateHigh
Power Line RegenerationNoNoYesYes
Control ResponseSlowModerateFastFastest
Cooling RequirementsHighHighLowLow
Electrical RequirementsNoneLowHighHigh
TechnologyOldOldOldNew
Power RangeHighHighModerateModerate

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.

AdvantagesDisadvantages
  • 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.

AdvantagesDisadvantages
  • Precise Control
  • Low Maintenance
  • Widely accepted in the automotive industry
  • High Inertia
  • Moderate Cost
Back to Chart

DC Dynamometers

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

AdvantagesDisadvantages
  • 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

AC Dynamometers

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

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

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.