saving motor
controllers from over voltage
Our client had the issue that the motor controllers in his maschine would fail randomly. He couldn’t reproduce the issue with his test setup. We located the problem, created an additional PCB and fitted it into the client’s machine in a minimally invasive approach.

At a Glance

Client Information
Special Elevators, CH

The client offers a unique lift system for safe, efficient and comfortable access to hard to reach locations up high and down low. The lift is the world's first mobile service lift and is attachable to rails.

Random failures

Unfortunately, in the latest batch of lifts some motor controllers would randomly fail. This caused down time for our clients customers and additional support and warranty costs. As the client was unable to reproduce any failure, first troubleshooting was required prior to creating a quick and minimally invasive solution.


Together with our engineers the client interviewed the operators of the lifts to get more information. We narrowed down the problem to the descending phase of operation. In parallel we analyzed the defective motor controllers.

With the information from the operators and the analysis of the motor drives, we were able to create a theory of a potential root cause. The lift was equipped with various measurement devices to further troubleshoot the system and to provide before and after data validation for the client.

Root cause

Whenever the machine would rapidly break the DC current of the intermediate circuit would spike. The sudden raise in current would overwhelm the BMS and cause ist to shut down. The energy from using the motors as generators while moving down could not go anywhere and the voltage would spike. This spike then damaged the motor controller’s electronics.

The fun fact was that it only occurred when using the emergency decent which was faster than the normal decent. So apparently some operators misused the lift in order to save time.


Aiming for a quick and minimally invasive solution, we adapted a braking chopper from our portfolio to the customers needs. The final product was composed of a small PCB to control the intermediate circuit voltage, and a power resistor to safely transfer excessive energy to the environment as heat. The solution could be retrofitted in the field using standard tools. Only 4 screws and two wires had to be connected.

reference Use Cases

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