What’s an eddy current dyno?

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An eddy current dynamometer (EC dynamometer) is the most popular type of dynamometer used in chassis dynamometer construction. Typically air-cooled, there are water-cooled versions of the dyno that are used primarily for very high horsepower or high torque applications. An eddy current dynamometer uses an electrical core that is moved through a magnetic field to produce the necessary resistance needed to test the power of a motor. Iron cores are the most common, however aluminum, copper, and other conductive materials are also used in dynamometer manufacture. Most EC dynos use a series of large cast iron discs, similar to disc brakes used on a vehicle, to place the required resistance against an engine or chassis when performing a power test.

While some types of dynamometer use water to generate resistance against rotational power and torque, an eddy current dynamometer uses an electromagnetic charge to resist the rotational power of an engine through a chassis dynamometer. The chassis dynamometer measures the actual amount of horsepower and torque an engine produces as measured at the transmission tires. This type of power measurement and monitoring is important because it measures the actual power of an engine. Components like the transmission, drive gears, and engine accessories are power thieves in the form of parasitic loss. The eddy current dynamometer measures the power output of the engine at the wheels after all of these components have drained power from the engine, providing an actual or true power figure.

Prior to the use of an eddy current dynamometer and a chassis dynamometer, the power levels of any given engine were calculated using a water brake dynamometer. This gave an accurate power figure for the engine taken at the flywheel. It was later understood that parasitic loss claimed a lot of horsepower from an engine and subsequent power figures were taken on the tire for a more accurate description of how much horsepower a vehicle produced. This type of dynamometer uses a computer to adjust the amount of electromagnetic braking force required to measure a vehicle’s power on the chassis dyno.

Braking the dyno against a high-powered engine creates heat. The most common style of eddy current dynamometer is air cooled. On some of the larger designs, a water-cooled version of the dynamometer is used to better control the heat generated from trying to stop the crankshaft from spinning in a high-powered engine. Maintenance determines when cast iron brake discs need to be replaced to maintain proper power measurements.

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