Application Assistance: Electromagnetic Brakes
When selecting a Motor Technology, Inc. brake for your application, there are several key factors to keep in mind.Please browse through the following list of questions that generally need to be answered when choosing a brake.
1) Are you going to use the brake as a stopping brake or a holding brake? i.e. Does the brake need to stop the motor from rotating or does the brake simply need to keep a stationary load from moving?
· If you plan to use the brake as a stopping brake:
1a) Is a brake really necessary? Rotating motors can often be brought to a fairly quick stop using dynamic braking. Dynamic braking entails shorting the motor leads together right after power is removed from the motor. Although this won’t stop the motor as quickly as a brake could, it is still much faster than simply allowing the motor to coast to a stop. Note: While Motor Technology does not provide the necessary controls/circuits for dynamic braking, the basic effects of dynamic braking can usually be achieved with an inexpensive, manual switch. Please feel free to contact our application engineers for assistance with any dynamic braking questions.
1b) What is the inertia of the load that the motor is moving?
1c) At what speed will the motor be operating at when the brake is engaged?
Important: The larger the inertia, and the faster the motor speed, the longer it will take to bring the motor to rest and the shorter the brake life will be due to the wear of the brake’s friction pad material.· If you plan to use the brake as a holding brake:
1d) Is a brake really necessary? All permanent magnet motors have an inherent cogging/detent torque that exists due to the attraction between the magnets and the steel of the armature.In many applications, this torque is enough to prevent an external load from rotating the motor shaft when the motor is off. Note: Motor Technology gearboxes actually "step up" the potential holding torque due to motor cogging. The holding torque out at the gearbox shaft will be equal to the cogging torque at the motor shaft multiplied by the gearbox speed reduction and divided by the gearbox efficiency. Please feel free to contact our application engineers if you have any questions related to the concept of motor cogging torque.
1e) What is the required holding torque of the brake?
2) Are you going to use the brake on a gearmotor? If so, the gearbox will act to "amplify" the brake torque acting on the motor. The brake torque out at the gearbox shaft will be equal to the brake torque at the motor shaft multiplied by the gearbox speed reduction and divided by the gearbox efficiency.
3) Would you like to use a parallel brake or a series brake on your motor? The major advantages and disadvantages of each type are listed on the "General Specifications" page.
· If you would like to use a parallel brake per Configuration #1 as shown on the "Wiring Schematics" page:
3a) Are you aware that two power sources are needed? (One for the motor and one for the brake).
· If you would like to use a parallel brake per Configuration #2 as shown on the "Wiring Schematics" page:
3b) Are you aware that there might be a slight delay (of several hundred milliseconds) between the time that power is removed from the motor and the time that the brake engages? This potential delay is caused by motor back EMF generating a current through the brake coil.
3c) Are you planning to use this configuration on a system that has an aiding load condition? (i.e.: Lowering a heavy door, or any other gravity assisted application). In this case, the aiding load could continue driving the motor after power is removed from the motor. This could cause the motor to generate a current that could keep the brake coil active and prevent the brake from engaging. The best option for this type scenario is a parallel brake per Configuration #1 as shown on the "Wiring Schematics" page.
· If you would like to use a series brake as shown on the "Wiring Schematics" page:
3d) Do you plan to operate the motor at conditions of little or no load? If so, a series brake may not stay disengaged properly during motor operation. Since a series brake coil "sees" the same current as the motor, a low load current can mean that the brake coil does not have enough power to keep the brake disengaged. The best option for this type scenario is a parallel brake.
If you have any questions, concerns, or ideas concerning your brake application, please don’t hesitate to contact our Application Department. We’re ready to listen and willing to help !!
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