Brake Resistor Calculator

Instructions for use

Enter the Minimum Brake Resistor Ohms required by the Inverter. Leave the Watts entry blank (or enter a value if you prefer to reduce the options). The calculator will list the best combinations of resistors and connection arrangements. Select a "Watts Continuous Rating" and "Connection Option" that suits your application. For higher resistance combinations and overload details see "Selecting the Correct Dynamic Brake Resistor" below.

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Selecting the Correct Dynamic Brake Resistor

Satisfy only two criteria to size Dynamic Brake resistors:-

1) Match the resistors to the drive by entering the Minimum External Resistance in our calculator to suit the drive. This is shown in the drive details on this site. The Inverter Manufacturer lists the Minimum resistance or resistance range in the product manuals.

2) Total Resistor Power; is decided by the energy to be returned from the load and the motor size. Rule of thumb is - a typical horizontal conveyer or similar load required to stop occasionally and can stop in less than 2.5 seconds at full braking, will need a resistor continuous power just less than 10% of motor power. Just less, means a small allowance for the mechanical losses that help brake the load.

High braking loads and/or frequent stops will need to be calculated or estimated to suit the energy returning and the resistor power selected. Contact us if you need help with this.

Prices and connection options of the most effective combinations are worked out for you in our Resistor Calculator above. 

Notes:

To size the kW rating of the resistors - follow these three simple rules.

The small aluminium resistors

1) For Brake times of 25 seconds and over, continuously rate the resistors at the power returning from the load - see note (a).
2) For braking times below 25 seconds, take the average power to be dissipated in the busiest 25 seconds.
3) Do not exceed 10 x the resistor continuous kW rating during any overload period, however short.

The larger caged resistors

1) For Brake times of 120 seconds and over, continuously rate the resistors at the power returning from the load - see note (b).
2) For braking times below 120 seconds, take the average power to be dissipated in the busiest 120 seconds.
3) Do not exceed 10 x the resistor continuous kW rating during any overload period, however short.

Temperature:

(a) The small Aluminium clad resistors take 25 secs to reach normal maximum working temperature when absorbing rated power continuously.
(b) The larger Caged resistors take 120 secs to reach normal maximum working temperature when absorbing rated power continuously.

WARNING!

1. A lower resistance than recommended will pass excessive current and will damage the Inverter.
2. The Minimum Resistance can be exceeded, but if the resistor value is excessively high, reduced braking will result.
3. Insufficient total resistor Watts will result in high resistor temperatures.