What is intermittent duty?
Intermittent duty is when a motor or gear motor has a duty cycle that isn’t running continuously without any time of break. This could be 10 seconds on and 50 seconds off, 10 seconds on and 5 minutes off, or any other on-off combination.
Why is it important?
It is important to understand your application and duty cycle requirements because applications running intermittently can fit into smaller motor packages than those running continuously at the same speed, torque and power. Choosing the best motor to match your duty cycle can save space and money. (Visit our blog for help calculating energy efficient motor operation costs.) This is because a motor running intermittently generates less heat, so a smaller, lighter motor can do the job.
For example, let’s say you need a DC gear motor for a harsh environment. The motor needs to run at approximately 200 rpm and use 18 in-lbs of torque. Each motor is paired with a Parallel Shaft 1900 gearbox. The best gearmotor fit for this application would change depending on its intermittent duty cycle:
Continuous: PM8014 (small)
- Housing diameter: 80mm, housing length: 14cm
- Output speed: 201.2 rpm
- Output torque: 18.6 in-lb
- Output power: 0.0594 hp
- Current: 1.04 amps
- Efficiency: 52.3%
10 seconds on and 50 seconds off: PM6015 (smaller)
- Housing diameter: 60mm, housing length: 15cm
- Output speed: 201.0 rpm
- Output torque: 19.1 in-lb
- Output power: 0.0610 hp
- Current: 1.45 amps
- Efficiency: 36.6%
10 seconds on and 5 minutes off: PM6013 (smallest)
- Housing diameter: 60mm, housing length: 13cm
- Output speed: 188.8 rpm
- Output torque: 17.4 in-lb
- Output power: 0.0520 hp
- Current: 1.33 amps
- Efficiency: 32.7%
Each of these gearmotor options has similar speed, torque and power specifications, but the size of the motor gets progressively smaller as the time between cycles lengthens. The current draw for the gear motors tends to increase as the motor size decreases, meaning smaller motors will have to work harder. If the motors were to run continuously this could shorten their life, but because they have time to cool down between cycles, the issue is eliminated for intermittent duty applications. The efficiency of the motor also decreases for the same reason, but this becomes less significant as the resting time between cycles increases.
The motor performance specs are a little low for the 10 seconds on, 5 minutes off application, but by knowing the precise duty cycle the motor will run at, we can determine if these shortages will impact the performance or life. If the exact duty cycle isn’t known, we use a “worst-case” duty cycle. This will ensure that your motor can run safely without overheating if something happens to cause the duty cycle to shift from its expected running time. You can also upload your specs and work with our team to make slight modifications to the gearmotor to increase performance or efficiency while still maintaining the smaller package size.
What makes Groschopp excel with intermittent duty applications?
Our proprietary MOTORTEC software uses advanced algorithms to quickly search hundreds of thousands of speed, torque, power and duty cycle combinations to find the most desirable motor or gear motor type for any application. To our knowledge, we are the only manufacturers in the fractional horsepower motor industry with these capabilities. We have also done extensive testing on many of the gearmotor combinations which allows us to further understand how different products perform under varying duty cycles.
