AAB 333 series general purpose motor brake

AAB 333 Series: IEC Frame Armature Actuated Brakes with Torque Adjust

Features & Benefits

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Series 333 features torque and wear adjustment capabilities and is a direct interchange with European brake manufacturers.

  • Ideal for high cycle applications
  • Coil Insulation: Class 180(H)
  • Optional manual release
  • Few moving parts 
  • Comes standard with carrier friction disc

hero detail
Metric Frame Size 72 - 278
Torque (lb-ft) 3 - 300
Torque (Nm) 4 - 400
Enclosure Open
Additional Options Available IP Rating: 54

Questions about Modifications? Contact Customer Support

Phone: 414-272-1100
Email: [email protected]

AC Rectifiers, In-Line

Brake Size: size 72-90 115 Vac size 72-112 230 Vac

AC Rectifiers, Separate

Brake Size: All

Band Seal (Boot)

Brake Size: All

Conduit Box

Brake Size: All

Electronic Brake Release Indicator Switch

Brake Size: All

Electronic Wear Indicator Switch

Brake Size: All

End Cap Plug

Brake Size: All

Maintained Manual Release

Brake Size: All

Non-Maintained Manual Release

Brake Size: All

Space Heater

Brake Size: All

Tach Machining

Machining on brake housing. Brake Size: All


Through-shaft seal in magnet body. Brake Size: All

Frequently Asked Questions

How can I identify a brake for repair or replacement when the identifying nameplate is removed or unreadable?

There is some basic information that can help us to identify the brake.

Gather the basic Information:

  • If the brake is to be replaced and the brake part number is not available, note the hp, rpm, frame size, shaft size, voltage, orientation (horizontal, vertical above or below) and any environmental or ambient considerations and treat as a new application. The mount bolt circle and mount register (pilot) are critical. There are many pre NEMA brakes still in operation today that do not conform to NEMA C-face standards.

Two examples of gathering unknown brake information:

Example One:
Description: The brake is about 9 inches in diameter. The spring is located at the center, the coil has an identifying sticker, the support plate isn’t flat, pressure plate has four tabs and the lever arm extends through the housing. The brake has brass parts. The friction disc is 7 ¼ inch in diameter and has a square hub. By description and picture, this brake is obsolete. The coil and disc continue to be available; other parts are not.

Action: The disc & coil are available, parts are not. Replace the brake. Focus on the mounting bolt circle and the brass disc pack option.

Example Two:
Description: The brake is about 9 inches in diameter. The spring is at 6 o’clock, the solenoid and coil at five o’clock. There are a series of capacitors on the right side and the voltage is DC with a black mechanical switch attached to the solenoid. By description, picture, HP & RPM information, the brake was identified for part replacement and repair.

Action: The brake is an early revision of a current brake. The part sheet was identified for repair part selection.

Stearns coils are marked with a part number. If the marking is destroyed, coils can be identified by measuring the outside and inside dimensions. Coils range from the size 4 family to size K9. The size 4 family of coils ( 4, 4+, K4, K4+, L4, M4, M4+ and P4+ ) and the size 9 ( 9 & K9) are similar in size within their groups. Identify the specific size 4 or size 9 coil by measurement, the brake torque as identified by HP & RPM and counting the number of friction discs.

Friction Discs:
Stearns formulates & manufactures friction discs to meet the performance specifications, and dimensional requirements, of the brake. Stearns supports and guarantees the performance of genuine Stearns parts. Discs and hubs can be identified by length, outside diameter, inside shape and the number of teeth on a gear profile hub.

To identify discs: measure, count the teeth or tabs, location of gear cutting as inside or outside diameter and number of discs.

Parts, Castings and Stampings:
Measurements, combined with digital pictures or sketches, are the quickest way to identify the correct brake and repair parts list. If parts are no longer available, move to identifying the mounting dimensions for a replacement brake as described in the “gather basic information” section. The replacement release rod and housing release mechanisms were identified by a sketch or picture. The lever arm was identified as obsolete by picture and dimensions. The casting number, along with basic sizing information, was used to select a replacement.

Kit brakes:
Shaft extenders and fan covers are proprietary to motor manufacturers. If the full brake number can be identified, the shaft extender hub may be available as a repair part. Other repair parts are available through Stearns distributors. Otherwise, kit brake replacement occurs through the motor manufacturer.

How do I install a brake so that it is compatible with a VFD (Variable Frequency Drive)?

When a VFD is used, the brake must have an independent power supply as the brake will only release with a specific voltage and frequency. For reference, if the application is holding only, most likely you are using a VFD motor controller. These controllers can provide dynamic stopping electrically.

Does Stearns have replacement parts available nationwide? If so, what information is required to specify the part?

Stearns parts are available throughout North America, through local Power Transmission distributors – including all of the major national chains. Stearns model number & revision and/or serial number (located on brake nameplate) is all that is required to identify the brake, and a description of the part you need will be all that is necessary to order.

How is a brake wired to a motor?

Stearns Brake coils are single phase coils and can be wired directly to single-phase voltage inside the motor junction box. For more information, please contact the motor manufacturer.

Do you have replacement parts available and, if so, what information is required to specify a part?

Stearns parts are available throughout North America through distribution. Stearns model number, revision and/or serial number (located on brake nameplate) is required to identify the brake. Please include a description of the part you are replacing.

Are Stearns brake coils 3-phase or single-phase? How do I wire for each?

All Stearns coils are single phase. See reference document for wiring instructions. Solenoid coils can have two, three or four leads. A two lead coil is a single voltage and frequency coil. A three lead coil is a single voltage coil with a dual frequency option and a four lead is dual voltage & single frequency. Each has a specific wiring requirement which is detailed in the coil kit or the brake installation sheet.

The coil label information should be compared to the power supply as well as the wiring diagram. A general wiring sheet can be found here.

Solenoid coils have a brief inrush or pull in amperage requirement that is much higher than the amperage necessary to keep the brake released. The inrush time is measured in milliseconds yet still needs to be considered in the power supply especially in smaller single phase motors. Stearns AC coils are single phase. DC Solenoid coils have a polarity requirment. The solenoid coils do require a fixed frequency and a voltage within plus or minus 10% of the rated voltage.

Stearns solenoid coils must be wired separately from any Variable Frequency Drive (VFD) output as the coil pull force is designed with a fixed frequency.

When the brake is wired across the motor, there can be a delay between removing power to the brake-motor and the brake spring setting action. The amperage necessary to keep the brake power released is very low. The brake will continue to be power released until the motor is no longer generating at or above the holding amperage.

Wire brakes separate from the motor for a rapid stop and generally in gravity affected loads such as hoists and lifts.

Direct acting brakes with a small air gap do not have the inrush amperage requirement. Direct acting brakes have a DC coil. An AC to DC rectifier is selected based on the DC amperage, available AC power supply and performance specifications such as rapid set, rapid release, filtered full wave or half wave power supply. The AC rectifier input voltage is matched to the required output DC voltage. The rectifier should be selected at the same time as the brake specifications are set. Rectifiers can be installed in the electrical panel or closer to the brake. Armature actuated brakes should be wired separately from a Variable Frequency Drive output.

Solenoid coils can be changed at site depending on available voltage. Direct acting brake coils are part of the magnet body assembly and are changed out as sub-assembly. A separately wired brake voltage may be different than the motor and drive voltage.

Voltage and amperage should be checked as close to the brake as possible. Line power drop and wire gage size should be considered due to cable run length and other electrical equipment sharing the same power lines. Coils are wound with voltage spike resistant wire.

Use a fuse chart for correct fuse selection, considering the inrush and holding amperage requirements as listed on the coil and in the catalog. Reaction times for solenoid & AAB style brakes are listed in the catalog. Solenoid style brakes generally react under 40 ms for brakes less than 20 lb-ft, and 60-80ms for larger brakes. Direct acting brake reaction time is affected by the rectifier choice.

The common coil failures are: incorrect wiring, incorrect power, high or low power, and finally an incorrect air gap on solenoid product.

Installation sheets are shipped with brakes, housed on our website's resource library and can be requested directly from Stearns.

What is the acceptable ambient temperature range for Stearns brakes

Acceptable ambient temperature range is between 20°F to 104°F (-7°C to 40°C). Brakes can be modified for warmer or colder environments.  

What size circuit breaker should I use for my brake?

Stearns provides coil inrush and holding values for end users and OEMs to be able to appropriately size breakers and circuits for their applications.  Due to variables outside of Stearns' control, we are unable to advise what size breaker to use.  For example, wire runs over a distance, other items in the circuit, etc. 

Can you adjust your brakes for wear?

Yes, our brakes can be easily adjusted for wear. In addition, our larger Solenoid Actuated Brakes (SAB), 87 series and above, have automatic wear adjustment.

We are the only manufacturer that offers self- adjusting brakes. This major feature greatly reduces brake maintenance, by eliminating the time required to periodically adjust the brakes for wear. Especially if the brake is mounted on a hoist on the ceiling of a plant, or in another hard-to-reach area.

To adjust brakes for wear, please consult the Installation and Service Instructions provided with the brake, or consult our resource library for the appropriate documentation. For any questions, please contact Stearns for application assistance.

Is the “duty cycle”, or number of stops over a given time period, important to know in choosing a brake?

Yes. Knowing the duty cycle is essential to choosing a brake. If the duty cycle includes dynamic stopping, not just holding duty, heat is generated within the brake. In this case, the thermal capacity of the brake must be considered when selecting the brake.

How many cycles can I get from my brake?

The life of our brakes is very much dependent on cycle rate, energy the brake sees, ambient temperature, among other values.

For longest life, for holding only applications, our Armature Actuated Brake (AAB) products generally provide for the longest life between servicing.

For applications which require dynamic stopping, our Solenoid Actuated Brake (SAB) products are best in class due to the self-adjusting feature, requiring less maintenance which provides a greater uptime on a torque to torque basis.

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