zc-smart-blind thermal duty cycle

Overview

The zc-smart-blind includes a built-in motor thermal duty-cycle limit. This reduces the risk of tubular blind and curtain motors overheating during extended or repeated operation.

When the limit is reached, the blind will temporarily move in short bursts separated by pauses. This stop-start movement is expected thermal-protection behaviour.

When does thermal protection begin?

For a unit that has remained powered and idle for four minutes or more, the motor can operate continuously for four minutes before duty-cycle limiting begins.

The controller tracks accumulated motor run time:

• Each second the motor runs adds one second.
• Each second the motor remains off while the controller is powered removes one second.
• The thermal duty-cycle limit is activated when the accumulated run time reaches four minutes.

Several movements in quick succession can therefore reach the limit, even if no individual movement lasts four minutes.

What happens when the limit is reached?

If movement is still requested when the accumulated run time reaches four minutes:

1. The motor enters a 30-second protection period.
2. During this period, the motor is switched on for 1 second and off for 4 seconds.
3. This five-second cycle is repeated six times.
4. By this time the run timer will have counted down enough for another 18 seconds of continuous operation.
5. If movement is still requested, the 30-second protection period and 18-second continuous period repeat.

During sustained movement, this provides an average motor duty cycle of approximately 50%. 
Note: this is only likely to occur due to misconfiguration and a motor without limits set correctly.

Example: movement requested over 20 minutes

Movement Request and Motor output

Accumulated motor run time

Behaviour during duty cycle limit.

In this example, the unit has been powered and idle for at least four minutes before movement is requested:

• Minutes 0–4: The motor operates continuously.
• Minutes 4–10: The motor alternates between the 30-second protection period and 18 seconds of continuous operation.
• Minutes 10–15: No movement is requested. The accumulated run time reduces to zero at approximately 13 minutes 46 seconds.
• Minutes 15–17: Movement is requested again. The motor operates continuously for the full two minutes.
• Minutes 17–20: No movement is requested. The accumulated run time returns to zero at minute 19.

How long does recovery take?

The accumulated run time reduces by one second for every second the motor remains off while the controller is powered.

After four minutes of powered idle time, a fully accumulated run-time counter will have returned to zero, allowing another four minutes of continuous motor operation.

Switching off the controller does not necessarily reset the accumulated run time. Recovery should be allowed while the controller remains powered.

Is this a fault?

Stop-start movement after several minutes of repeated operation is the expected thermal duty-cycle limit protecting the motor.

Contact zencontrol Support if:

• Stop-start movement begins before four minutes of motor operation following at least four minutes of powered idle time.
• The motor does not return to continuous operation after the protection period.
• The blind behaves unexpectedly during a normal single movement.