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.