How to Prevent Your Linear Actuator from Retracting Underload

Back Driving Underload

When a linear actuator underload and no longer being powered, you may find that the linear actuator may retract by itself (i.e. back drive). This is particularly the case for actuators using motors that are side mounted (perpendicular) to the shaft. 

What Causes Back Driving?

While the actuator is under a large amount of weight, the internal DC motor can act as a generator producing a small amount of voltage. When this happens, the actuator can begin to retract. To limit this back driven voltage from occurring, continue reading to learn how to minimize this from happening.

CEMF Brake Using a SPDT Relay

The easiest, non-evasive and cheapest way to prevent back driving from happening is to use a Single Pole Double Throw Relay (SPDT) with a wiring harness.

Why use a relay? To prevent the motor from retracting, the relay is used to short the terminals in the motor and create a closed loop inside of the DC motors magnetic wire coils. When this happens, the counter-electromotive force (CEMF/Back EMF) in the closed loop of acts as a torque brake and keeps the actuator from moving when under large loads.