What’s an elec. motor dyno?

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An electric motor dynamometer measures power, torque, and rotational speed of a main motor, using adjustable speed drives. It can replace the load side during testing on the prime mover, and torque is a key concept in its measurement. RPM and torque are measured in newton-meters.

An electric motor dynamometer is a specialized dynamometer that can measure the power, torque, and rotational speed of a main motor, such as a motor or other electric motor. It can also drive a load and not just absorb energy under measurement. The electric motor dynamometer can make use of adjustable speed drives. The power can be direct current (DC) or alternating current (AC). Electric motor dynamometer can be load or prime mover to measure rotation power and load torque.

Revolution per minute (RPM) is a measure of rotational speed. For example, a spindle spinning at 3,600 RPM makes 60 revolutions per second. When an engine is loaded by friction or other loads, the RPM typically drops from the “no-load” RPM to the “load” RPM. Simple handheld equipment, such as a tachometer, can measure RPM.

Mechanical load is measured as torque, usually in newton-meters (Nm). In mathematics, torque is the product of force and distance from the axis. 1 newton is the force exerted to lift a weight of 2.2 lb (1 kg). If a person were to support a 1 kg load at the end of a pole 39.3 inches (1 m) long, the torque to keep everything stable is 1 Nm.

Rotational torque load is also measured in newton-meters. If a rotating shaft is driven at 1 Nm to maintain a constant flow of water at 2 gallons (7.6 L) per minute, then there is a suggested relationship between torque and power for the described system. A simple dynamometer is capable of creating specific torque and could replace the water pump on this system. Dynamometer torque only needs to be set to 1Nm, and tests can be performed on the main engine in any configuration.

An electric motor dynamometer can replace the “load side” during testing on the prime mover. The prime mover can be any power source, such as an electric motor or a turbine driven by wind, water, or steam. This type of dynamometer is relatively simple test equipment that can provide a variety of torque values.

Measurable torque is a key concept in an electric motor dynamometer. A person wearing protective gloves can introduce a load torque to a driven shaft, but there is no torque reading in that arrangement. A spring scale attached to a leather strap and partially wrapped halfway up the driven shaft and creating friction on one shaft can be a basic setup for torque measurement. As the drive shaft rotates, the force of friction is measured as read on the spring scale and multiplied by the radius of the shaft. From this, the load torque can be derived.

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