The duty cycle of a linear actuator affects performance, lifespan, and reliability in real-world applications.
Duty cycle is the percentage of time a motor or actuator operates within a fixed time period without exceeding its thermal design limits, which primarily determine allowable run time. It is calculated as Duty Cycle (%) = (Run Time ÷ Total Time) × 100. For example, if an actuator runs for 30 seconds and rests for 90 seconds, the duty cycle is (30 ÷ 120) × 100 = 25%.
Duty cycle ratings are determined by how quickly heat builds up inside a motor during operation and how effectively it can dissipate during rest. Because load, voltage, speed, and ambient temperature all affect heat generation, the allowable duty cycle can vary significantly depending on the application.
Why is duty cycle important?
Ensuring that you run the device at or below the max recommended duty cycle ensures that you will get the longest life possible out of your actuator. When a manufacturer rates a product for a maximum duty cycle, it is typically based on lifespan testing. If you run an actuator or electric motor at a higher than rated duty cycle, you are likely to experience premature failure. There are a number of reasons that this can happen including but not limited to:
- Premature component failure due to heat
- Premature lubricant failure
- High levels of stress on mechanical components
- Motor will reach the natural end of its life sooner
As with most electronic devices, when linear actuators run, they produce heat. If the temperature of the unit is allowed to rise beyond a certain threshold, damage to the unit is likely. If the actuator has a maximum duty cycle of 20% and you are constantly running it at 25%, you will increase the likelihood of component failure. This could be the motor, circuitry or gearbox. Duty cycles are set low enough that the temperature will not rise to the point of causing damage.
Related article: Stepper Motors vs. Servo Motors - What's the Difference?
How is duty cycle calculated?
Calculating the duty cycle is straightforward, especially when your application requires the device to operate at a consistent pace. For example, if an actuator runs for 30 seconds and then rests for 30 seconds, its duty cycle is 50%, as it is running half the time. Essentially, the duty cycle represents the percentage of time the actuator is actively operating.
Common Duty Cycle Reference (10-Minute Window)
| Duty Cycle | Run Time | Rest Time |
|---|---|---|
| 10% | 1 minute | 9 minutes |
| 20% | 2 minutes | 8 minutes |
| 25% | 2.5 minutes | 7.5 minutes |
| 50% | 5 minutes | 5 minutes |
Applying Duty Cycle in Real Applications
In many applications, actuators do not operate on perfectly equal run and rest intervals. To determine the correct duty cycle, first measure the total time of one complete operating cycle, including both active movement and rest. Then divide the total run time by the full cycle time and multiply by 100.
For example, if an actuator extends for 20 seconds, pauses for 40 seconds, retracts for 20 seconds, and then rests for 80 seconds before repeating, the total cycle time is 160 seconds. The actuator is active for 40 seconds of that cycle, resulting in a 25% duty cycle.
We calculate duty cycles based on the peak efficiency of each product. However, as the load on the actuator increases or the speed rises, the duty cycle tends to decrease due to heat generation. On the other hand, operating at a lower load or slower speed than the peak efficiency point can lead to a higher duty cycle.
What factors can affect duty cycle?
Duty cycle ratings are determined at the product’s peak efficiency operating point, as specified in the data sheet. If the actuator is operated at or near that condition, the published duty cycle rating will apply. Deviations in load, voltage, or ambient temperature can increase heat generation and reduce allowable run time.
Some key factors that affect the duty cycle of an actuator include:
- Load: Higher mechanical load increases motor current, which increases internal heat generation and reduces the allowable duty cycle.
- Voltage: Higher voltage can increase speed and current draw under load, accelerating heat buildup and shortening allowable run time.
- Temperature: Higher ambient temperatures reduce the system’s ability to dissipate heat, lowering the safe duty cycle compared to operation in cooler environments.
Other operating conditions can also affect duty cycle. Humidity, restricted airflow, enclosure design, and side loading may influence heat dissipation and mechanical wear, which in turn affects internal temperature increases and long-term component wear. These factors must be accounted for during system design and actuator selection.
Duty Cycle in Micro Linear Actuators
Micro linear actuators typically have smaller motor windings and lower thermal mass compared to larger industrial actuators. As a result, they can reach their thermal limits more quickly under load. This makes adherence to the specified duty cycle particularly important in compact designs where airflow and heat dissipation may be limited.
In applications involving small actuators, even modest increases in load or ambient temperature can reduce allowable run time. Careful consideration of operating conditions is therefore essential when designing systems that rely on compact actuation.
What happens if a device is run past its duty cycle?
Operating an actuator beyond its rated duty cycle increases internal temperature and accelerates mechanical wear. Over time, this reduces performance and shortens overall service life.
- Motor overheating: Excess current generates heat that can degrade winding insulation and reduce motor lifespan.
- Lubricant breakdown: Elevated temperatures can reduce lubrication effectiveness, increasing internal friction.
- Gear and bearing wear: Continuous operation under load increases mechanical stress and fatigue.
- Performance degradation: Increased backlash, slower speeds, or reduced positioning accuracy may occur over time.
While occasional short-term overuse may not result in immediate failure, sustained operation above the rated duty cycle will increase the likelihood of premature component damage.
FAQ
What actuators can handle 100% duty cycle?
Actuators rated for 100% duty cycle are designed for continuous operation within their specified load and ambient temperature limits. These models are engineered to dissipate heat effectively during constant use. Always refer to the product data sheet to confirm whether a specific actuator is rated for continuous duty.
Can cooling increase duty cycle?
Improved cooling can reduce internal temperature rise in some applications, which may allow for longer operating periods. However, published duty cycle ratings are based on defined test conditions at peak efficiency and should be treated as the reliable operating limit unless validated through application-specific testing.
Does higher load reduce duty cycle?
Yes. Higher mechanical load increases motor current, which increases heat generation inside the actuator. Because duty cycle is primarily limited by thermal constraints, operating at higher loads typically reduces the allowable run time before rest is required.
How is duty cycle tested and rated?
Duty cycle ratings are established through controlled testing at the actuator’s specified peak efficiency operating point. During testing, the actuator is cycled under defined load and ambient temperature conditions while internal temperature rise is monitored. The maximum allowable run time is determined by the thermal limits of the motor and internal components, ensuring reliable operation within those conditions.
Duty Cycle Conclusion
Understanding duty cycle is essential when designing systems that rely on electric linear actuators. Because allowable run time is primarily limited by internal heat generation, operating conditions such as load, voltage, and ambient temperature must be considered during system design and validation.
By accurately calculating duty cycle and evaluating real-world operating conditions, engineers can reduce the risk of premature component wear, improve long-term reliability, and ensure consistent actuator performance over the life of the system.
If you need assistance selecting a product that meets your application requirements, please contact our sales team for assistance. Actuonix can create custom designs for all OEMs.
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