Power Outage: How to Set Up Auto-Start for the Frequency Converter and Avoid Downtime?

Power Outage: How to Set Up Auto-Start for the Frequency Converter and Avoid Downtime

Short-term power outages or voltage "sags" are common causes of pumps, fans, and conveyor stops. After power is restored, the frequency converter (FC) blocks the output due to an "Undervoltage" (UV) error, requiring manual operator intervention. As a result, production lines experience downtime, causing losses for the enterprise. In this article, we will explore how the Auto-restart function works, how to set it up, and in which cases it is safe and where it is strictly prohibited.

Why Doesn’t the FC Start Automatically? It’s Not a Bug, It’s a Feature!

Most frequency converters come factory-set to block operation under low voltage conditions. This is done for two main reasons:

Operator safety. A voltage spike can cause sudden starting of machines, saws, mixers, or other equipment when personnel are nearby.

Equipment protection. If the motor is still spinning by inertia, an uncontrolled "start from zero" can cause inrush current, overload the gearbox, or trigger the FC protection.

Solution: The "Auto-Restart" Function

What is it?

Auto-restart is a software option in the FC that automatically clears the "Undervoltage" error and performs a recovery start after power returns, without operator involvement.

How does it work? Two key mechanisms

Simple auto-restart: after a set delay (e.g., 5 seconds), the FC performs a smooth restart "from zero." This option is suitable for systems where the motor is guaranteed to be stopped.

Flying Start: if the shaft is still spinning by inertia, the FC measures the frequency, "captures" the current speed, and synchronously accelerates to the set point. This prevents shock loads and inrush currents.

Why is Flying Start needed? Starting "from zero" while the motor is still spinning may cause a current peak and mechanical shock to the gearbox. The "capture" function eliminates these risks.

Where it is Allowed, and Where It Is NOT Allowed to Use Auto-Restart

Recommended for

Ventilation and smoke extraction systems where continuous operation is critical for safety and microclimate.

Pumping stations (water supply, sewage) where constant pressure increase is necessary.

Conveyors, provided there is no manual loading in the work zone.

Compressors and chillers with automatic control.

Strictly prohibited for

Metal and woodworking machines (lathes, milling machines, saws) due to high injury risk.

Presses, guillotines, and other cutting equipment.

Mixers with manual loading.

Lifting equipment (cranes, winches) where sudden start threatens life.

Below are the main Auto-restart parameters for popular frequency converter manufacturers:

Enable auto-restart in the parameter menu.

Set the delay time (Restart Delay Time) considering network stabilization and cascade startup.

Set the number of attempts to avoid endless reboot cycles.

Activate Flying Start for fans and pumps where a rotating shaft is possible.

The Auto-Restart function is an effective tool for minimizing downtime and automating production processes. However, before activating it, be sure to assess the risks to personnel and equipment. Safety remains the highest priority.

Not sure about the proper settings? Contact our technical department for consultation. We will help select optimal parameters, conduct testing, and ensure safe and reliable auto-start of your equipment.