Brake Dynamometer: Everything You Need To Understand

A brake dynamometer measures a machine’s torque and brake power. The term dynamometer itself applies to various parts of a machine, so it is essential to specially consider it in the context of brakes.

Brake Dynamometer Device

Everything you need to know about brake dynamos and their many varieties is covered in this article.

What Is the Brake Dynamometer Device?

The brake dynamometer device measures the braking and engine power of any vehicle. It does this by estimating the force or power transmitted in the vehicle. As brake dynamometers can measure the force engines generate, they are known as motor testers.

Also called brake dynos or dynamos, brake dynamometers are essential in the testing stages of any vehicle. This is because it informs manufacturers of the braking abilities of the vehicle. From the data obtained after testing with a brake dynamometer, manufacturers can detect problems that exist with the vehicle before releasing them to the consumer.

Considering the importance of brake dynamometers, it may be tempting to run a test stand or test cell on your vehicle’s brake and engine capabilities to understand its limits. However, a brake dynamometer is very expensive, costing around a million dollars and virtually ensuring that all testing can only be done by manufacturers.

How Does a Brake Dynamometer Operate?

A brake dynamometer works by applying a brake to a motor and subsequently assessing how much force is required to stop the motor. The brake applied serves as an opposing force to the motor, making it easy to measure and estimate the amount of force needed to stop the motor.

Use of Brake Dynamometer

The measurement obtained is actually the primary aim of using a dynamometer, as different mathematical expressions can be derived. Consequently, the engine force and brake power of the machine can be calculated.

The origin of the brake dynamometer can be traced to the early 1820s when Gaspard de Prony developed a mechanical friction material brake. While different brake dynamometers are available today, they all operate on the same basic principle.

What Is the Difference Between Power Absorption and Transmission Dynamometers?

The difference between absorption and transmission dynamometers is that absorption dynos absorb the power output of the motor to which they are coupled, while transmission dynos do not. Both of these are the two broad types of brake dynamometers under which the different subtypes fall.

Transmission Dynamometers Brake

Absorption brake dynamometers measure and absorb the power of the engine being tested by continuous restraint through a fluid. The absorbed energy escapes in the form of heat. This is the most common type of brake dynamometer.

On the other hand, transmission brake dynamometers do not absorb the power output of the machine being tested. Instead, the power output in transmission dynamometers is transmitted directly to a load connected to the engine and strain gauges are used to estimate the strain on the load. This type is much simpler than absorption dynamometers, and examples include belt transmission dynamometers and torsion dynamometers.

What Are the Different Types of Brake Dynamometers?

The different types of brake dynamometers fall under two broad categories – absorption and transmission. They include eddy current, prony brake, rope brake, hydraulic brake, and high speed dynamometer, compound brake, electric dynamometer. Although these different types have different applications, they operate under the same basic principle of brake dynamometers.

Eddy Current Dynamometer

An early type of dynamometer used to gauge engine performance was the eddy-current dynamometer. This dynamometer operates using an engine connected to a revolving disc, which a magnetic field propels. It is possible to control the field’s strength by varying the current through the coils.

Eddy Current Dynamometer

The rotating disc generates eddy currents in the stator (housing electromagnets and a rotor disc connected to the engine’s output shaft), which heats up due to resistance. The induction of eddy currents in the stator rather than the disc is essential in controlling the generated heat. Newer eddy current brake dynamometers use cast iron discs, resembling vehicle brake pad rotors.

The use of eddy current dynamometers is widespread because they have no inherent size limit and are useful for several purposes. Also, these brake dynamometers have high brake power per unit weight, smooth torque development, and a simple design.

Prony Brake

The prony brake dynamometer is the most simple design of a power absorption dynamometer. This brake dynamometer is composed of a wooden block, frame, brake shoes, rope, and flywheel. A prony brake dynamometer’s operation depends on the transformation of power into heat. For this, dry friction is used.

The working principle of this drake dyno is using a brake attached to the flywheel to stop the engine and measuring the weight that an arm connected to the brake bears while opposing the rotation of the flywheel. To enhance friction in this setup, spring-cushioned bolts are adjusted to draw the wooden blocks together.

As all of the power output the prony brake absorbs is converted into heat, it usually requires appropriate cooling techniques. Although this dynamo principle is similar to a spring balance, it delivers force measurements in a more technical way. Therefore, its use in modern technology is common and justified.

Rope Brake

This power absorption dynamometer employs multiple turns of rope wound around a rotating drum connected to the output shaft. One end of the rope is coupled to a spring balance, while the other links to a loading device.

Rope Brake in Vehicle

Due to its low cost and quick construction, this dyno is becoming more and more well-liked among smaller production firms. Unfortunately, its use is curtailed by the relatively lower accuracy of obtained measurements because of temperature fluctuations.

The accuracy of the results is hampered by these fluctuations since they alter friction coefficients. Therefore, rope brake dynamos are unsuitable for operations that require intensive and meticulous dynamometer testing.

Hydraulic Brake

Also known as a water brake dynamometer, a hydraulic dynamometer operates on the principle of dissipating power in fluid instead of dry friction. The construction of a hydraulic dynamometer follows a similar principle to that of a fluid flywheel, as it comprises an impeller or an inner rotating element connected to the engine’s output shaft. The impeller rotates within a fluid-filled casing.


Hydraulic Brake in Car

The rotation of the impeller consequently causes the outer casing to rotate as well due to the generation of centrifugal force. However, there is resistance to this rotation by the torque arm, which bears a weight.

The frictional forces generated are measured by the spring balance connected to the casing. A constant supply of water controls any heat produced during the operations of the dyno, although some hydraulic dynamometers use other fluids. While the method of computing results is different from other brake dynos, the results of hydraulic dynos are still very precise.


A compound brake dynamometer combines two different dynamometers rather than using them individually. The rationale behind this is that, in some circumstances, there are more benefits to using two distinct dyno setups as opposed to one. In compound dynos, the constituent dynamometers work simultaneously.

While there are benefits to using a compound dyno, many companies avoid using it because obtaining results is more complex. Also, if the individual dynamometers generate a lot of heat, the total heat output of the compound dynamometer can be enormous.

The higher the heat produced, the more advanced cooling techniques will be. Likewise, more advanced cooling techniques require a stronger power supply. Therefore, companies may actually end up greatly increasing their operating costs when using compound dynos.

What Are the Pros of a Brake Dynamometer?

The pros of a brake dynamometer include more significant testing and engine efficiency. Also, cost-effectiveness and improved knowledge of the engine and braking capabilities are benefits of the device. While there are several kinds, one thing they all have in common is that they make cars safer.

Specifically, a brake dynamometer makes it possible to understand an engine’s and brake’s working. Makers can gain more insight into the limits of the brake and the engine. Also, if there are any issues or concerns, the right changes can be implemented.

Brake dynamometers also increase engine efficiency since they allow for improved fuel management and consumption. Since less fuel is consumed by the consumer and also considering the shorter testing time in manufacturing companies, brake dynos make vehicles more cost-effective.


With a brake dynamometer, it is possible to measure the strength of the brake and engine.

Here are some important details about brake dynamometers:

  • A Brake dynamometer works by applying resistance to a motor and measuring the force needed to stop it.
  • Brake dynamometers include absorption (eddy current, prony, rope, hydraulic, compound) and transmission types.
  • Brake dynamometers inform manufacturers of the limits of the brake and engine of their vehicles.
  • These devices can improve the efficiency of fuel usage in vehicles.

All things considered, a brake dynamometer makes a car safer and more affordable for you and the maker.

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