What is the power consumption of a brake?

Topic:

• What is the current draw of a brake?
• What is the power consumption of a brake?

Solution:

maxon's catalog specifies the supply voltage and winding resistance of any brake (e.g. AB20: 24V, 227 Ohm).

• The current draw can be simply calculated based on Ohm’s law based on the brake’s applied voltage and winding resistance:
  I = U / R
  e.g. AB20: 24V / 227 Ohm = 0.105 A
  
  
• The power consumption of the brake is:
  P = U x I = U² / R
  e.g. AB20: 2.5 W

Additional notes:

• Most brakes require the specified supply voltage only for opening (i.e. unlocking and releasing the motor shaft). Once this has been done (-> "Opening time"), it is possible for many brakes to reduce the supply voltage to a lower level (typ. approx. 50% of the specified supply voltage) in order to reduce the brake's power consumption in "Open" state. However, this possibility must be clarified for the concrete brake in use and also requires that the motor or brake controller supports such a reduction of the brake's supply voltage. With most standard motor controllers (as well as the EPOS4 and ESCON), only a fixed DC voltage for the brake can be switched via a digital output.
• If the brake is closed (i.e. not voltage applied and the motor shaft is "locked" due to this), there is  no current draw present. 

Cross reference:

• What is the power consumption of a controller?