WHAT IS A DYNAMOMETER?
Dynamometers, or “dyno’s,” are used for measuring motor torques and therefore power as a function of speed. More specifically, they may be employed for testing electric motors, internal combustion engines, hydraulic motors, pneumatic motors, etc. Dyno’s may also apply a known load to a motor for endurance testing while simulating real-world applications. There are several different types of dynamometers:
Power Absorption Dyno which converts kinetic energy into heat.
Inertial Dyno which measures the power required to accelerate a known mass.
Regenerative Dyno recycles the motor power.
Chassis Dyno tests motorized vehicles (i.e. truck or car).
Magnetic Brake Systems (MBS) manufactures power absorption dynamometers that incorporate MBS magnetic brakes.
The brakes for the dynamometers are sized based on power dissipation and required torque.
Performance curves for the brakes may be found in the magnetic brakes tab.
MBS DYNAMOMETER MODEL DB5-8.7T-FM
WHAT IS AN MBS DYNAMOMETER?
There are many ways to measure the input power and output power from a motor, but all too often there is not a good way to capture and translate all the data simultaneously. When building a system in-house, the development time, manufacturing costs and the lengthy process of documenting all the operations, make staying within budgets or deadlines extremely difficult. MBS provides reasonably priced systems that save companies time and money and allow them to focus on what is important - development and service of their products.
Each system comes as a complete unit which includes the Dynamometer Structure, Dynamometer Controller, Dynamometer Laptop Computer with proprietary MBS software, interconnecting cables, and a calibration weight. There are no software licenses required, no external calibrations or re-occurring charges. Both the controller and laptop computer need 120/240 VAC.
The majority of our dynamometers use natural convection air-cooled brakes; thus, there are no complicated cooling systems or highly costly compressed air. The MBS brakes, used in our dynamometers, can dissipate as much as eight times the power compared to other brake manufacturers (according to published specifications for the same size brakes and same cooling methods).
When purchasing a dynamometer, a customer may send MBS a motor which we will then mount and use for system verification. Upon uncrating, the customer receives a turn-key system.
HOW TO SELECT AN MBS DYNAMOMETER?
Minimum information required to select a dynamometer:
1. The type(s) of motor(s) to be tested
2. The power output of the motor
3. Know how the motor(s) mount to a structure
Face mount (i.e., NEMA 56C)
Base mount (i.e., 286T, 405T)
4. What information is required about the motor
Speed vs. torque curve
The time at which something fails
Having approximate speed and torque curves would help. Either provide the above information to MBS, who will help you select a system or follow the steps to select a system and provide the information from above and below to MBS when purchasing:
Step 1: Motor Power Output
Know the power dissipation. For most applications, the system/brake should be sized to dissipate the power output of the motor under test continuously. If only requiring speed vs. torque curves, the higher 30-second power dissipation curve may be used. Note that a cooling interval of 5 to 10 minutes is required prior to operating the brake at the 30-second power curve again. It is good practice to leave a little room for error which means do not select a system that will use the very limits of the brakes performance.
Step 2: Transmission
Know approximately how much torque the motor provides and at what speeds. Select a pulley ratio so that the brake provides more torque to the motor than the motor may provide. For example, if the motor may provide 1,000 in-oz. of torque, and the brake only provides 550 in-oz. of torque, using a 2:1 ratio (where the brake spins twice as fast as the motor) will convert 550 in-oz. of brake torque to 1,100 in-oz. to the motor. Verify that the maximum brake speed remains below the maximum speed of the motor multiplied by the pulley ratio.
If trying to obtain speed vs. torque curve, the stall torque of an MBS dynamometer must be greater than the stall torque of the motor.
Step 3: Load Cell and location
The size and location (i.e., measuring motor torque vs. measuring brake torque) of the load cell(s) may be determined after reading the specification/data sheets of the dynamometers.
Step 4: Transducers (voltage and current) - Optional
Know the type of power and range supplied to the motor under test.
* Speed limited by transmission
The primary function of MBS dynamometers is to measure the torque as a function of speed; it allows for the output power to be calculated. Our dynamometers have different set-ups and levels of complexity to test a variety of size and types of motors/systems. There are three types of motor mountings: Face, Base, and Carriage. The Face and Base mount styles have two standard frame sizes. There is the three (3) inch series for small motors and the five (5) inch series for larger ones. The frame size of the dynamometers is defined in Section 1 of How To Specify a Dynamometer.
Voltage and current transducers are optional items that are used to measure and record the input power to the motor under test. These are simple devices and are not meant for power analysis (i.e., noise, harmonics, power factor). Our dynamometers can measure and record three types of input power to the motors:
AC (single phase)
3-phase (3-ph) AC.
DC voltage and current transducers are required to test a DC motor. For a single phase AC motor, AC voltage and current transducers are required. To test a 3-phase AC motor, 3-phase voltage and current transducers are required.
There are two types of 3-phase voltage transducers:
3-wire, 3-phase (to measure line-to-line voltage: L1-L2, L2-L3, L3-L1)
4-wire, 3-phase (to measure line-to-neutral: L1-N, L2-N, L3-N).
For DC, AC and AC 3-phase motors holes for voltage and current transducers are pre-drilled. The transducers may be purchased with the system or at a later time. Other types of transducers (to measure pressure and flow rate) may be employed by the dynamometer when testing air or hydraulic motors.
The dynamometer structure, which the Unit Under Test (UUT) couples to, is equipped with a safety cover to prevent an operator from injuring his/her fingers with dynamometer's rotating parts. Another safety feature is a hard stop to prevent the load cell from exceeding load limits.
An optional item is the MBS-IR-1, a temperature sensor which monitors the instant temperature of the brake’s drag ring. It prevents the brake from overheating if used in the non-continuous torque region.
In our tandem dynamometers, we also offer thermocouple inputs to measure and record different sections of the UUT’s temperature. The measurements are graphed in the Test Output graph and are available in the Raw Data table.
The controller houses a data acquisition unit, a microprocessor(s) for the brake(s), power supplies and other system components. Controllers may come pre-wired for transducers and alternative inputs to be captured by the MBS software.
The footprint of the controller is approximately 17.25” wide x 17.0” deep and 7” tall. It weights around 28 lbs.
In the back of the dynamometer's controller are the input jacks to couple the signal cables from the dynamometer structure, a USB cable to couple to the computer and a DB9 style connector. One of the inputs in the DB9 is allocated for the “Ready Signal.” This signal allows the operator to start and stop a test remotely for time sensitive tests. The operator may configure and “arm” the dynamometer. When a signal ranging from 3.3 VDC to 10 VDC is sent to the controller, the system starts capturing data. When the test is done, or the signal falls below 3 volts, the test stops.
DYNAMOMETER LAPTOP COMPUTER
The MBS dynamometer comes with a laptop computer and preinstalled MBS software. Before initial use, some configurations may need to be completed (i.e. scale factors, display scale limits, units) but essentially the system is ready to run out of the crate.
The software does not have to be used exclusively with the attached laptop and may be installed on another computer. The laptop comes with the system for two main reasons. Firstly, this way the customer receives a complete working system. Secondly, the system has an allocated processor which is not being interrupted by other computing functions such as e-mail, the Internet, viruses, malware, etc.
The laptop's processor is powerful enough to run the dynamometer software; however, if using a different computer, the more powerful the processor, the better the system operates.
WHAT CALIBRATION IS REQUIRED?
The dynamometer comes with a calibration weight. It is used to calibrate the load cell that measures the torque of the unit under test. Calibration takes only a minute or less and may be performed as often as desired. For best results, calibrate both before and after a test to confirm that readings are still correct.
MBS DYNAMOMETER SOFTWARE
The measured information is captured and displayed by a laptop computer, using the proprietary MBS LabVIEW based software.
Graphs may be saved in bitmap format (.bmp) and the raw data as a text file (.txt). For custom analysis, the raw data, in tab-delimited format, may be exported into programs, such as Excel. The software is highly configurable. Users may select the display scale limits, operating units, file & graph titles, scale factors for transducer inputs, different types of voltage and current transducers.
Operators may apply the torque to the motor under test in different methods such as a step input, ramping (up or down) over a period of time or program a sequence of applied torques.
The sampling rate is adjustable giving the flexibility of good resolution for short term tests (10 – 15 seconds) to low resolution for longer tests (minutes, hours or days).
HOW ARE MOTORS MOUNTED?
The motors may be mounted in various ways: face mounted, base mounted, or carriage mounted. Typically, for electric motors, the fractional horsepower motors are face mounted, the 1 to 5 HP motors are base mounted and the 5 HP and up are carriage mounted.
SYSTEMS: INLINE vs. BELT COUPLED
The face and base mounted dynamometers may be either directly coupled or belt coupled to the motor under test. In-Line systems are the simplest and require the least maintenance. The belt coupled devices are very modular; changing the pulley ratios allows for a much larger range of speed and torque supplied to the motor under test.
LOAD CELL LOCATION
The MBS dynamometers use beam load cells to measure torque. Depending on the physical configuration for belt coupled systems, the load cell may either measure the torque of the motor or the torque of the brake. Location of the load cell needs to be determined based on the application of the dynamometer.
For the most precise torque measurements, the load cell measures the motor's torque by mounting it to a pivoting structure coupled to a load cell. Consequently, the range of the dynamometers' torque is limited by the load cell.
For the broadest range of torque (or to test a wider range of motors) the load cell measures the torque of the brake. Though measuring the torque of the brake increases the torque range of the dynamometer, it introduces more errors such as belt friction, pulley drag, bearing friction, etc. The accuracy of the load cell measuring the brake is better than 5%; the accuracy of the load cell measuring the motor is better than 1%.
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