If you’ve ever worked with brushless DC (BLDC) flat gear motors—whether as an engineer designing industrial automation, a HVAC technician calibrating damper controls, or a robotics builder troubleshooting joint actuation—you’ve probably asked this question: Why does the motor get warm when it’s running, and how much warmth is normal? As a supplier focused exclusively on BLDC flat gear motors, I field this question at least three times a week, and the answer isn’t as simple as a one-size-fits-all number. Let’s break down the science, the variables, and what “normal temperature rise” actually means for your application, straight from the people who design, test, and ship these motors every day. BLDC Flat Gear Motor
First, let’s clarify what temperature rise even means, because it’s a critical distinction from just “how hot the motor feels.” When we talk about temperature rise in motors, we’re referring to the difference between the motor’s operating temperature and the ambient temperature around it. So if your shop is a constant 25°C (77°F) and your motor’s surface runs at 45°C (113°F), that’s a 20°C (36°F) rise. If the same motor ran in a 35°C (95°F) environment and hit 55°C (131°F), that’s still a 20°C rise—same heat output, just a hotter baseline. That’s not a trivial detail; if you misinterpret absolute temperature as rise, you could either oversize your cooling system unnecessarily or miss a hidden performance issue.
The core of why BLDC flat gear motors run warm (and why their temperature rise matters) comes down to how they convert electricity to motion, with two key sources of loss that create heat: copper losses and iron losses. Copper losses are the big one for most of our flat gear motors, especially when they’re under load. The armature windings in the motor draw current, and as that current flows through the copper wire’s resistance, it dissipates energy as heat—this is Joule’s first law, plain and simple, and it scales with the square of the current draw. So if a motor runs at 1 amp, that’s a certain copper loss; run it at 2 amps, and the heat from copper losses quadruples. For flat gear motors, which are compact by design, those windings are packed tightly into a small space, so that heat doesn’t have a lot of room to escape on its own.
Iron losses, on the other hand, come from the motor’s stator and rotor cores, which are made of thin steel laminations to reduce waste. When the magnetic field from the windings flips to turn the rotor, it creates tiny, shifting currents in those steel cores (called eddy currents) and magnetic hysteresis (the energy lost as the magnetic field realigns each cycle). These losses are much smaller than copper losses for most operating loads, but they get worse at higher speeds or when the motor is running on a variable frequency drive (VFD), which is common for BLDC motors. It’s a secondary source, but it adds up, especially in applications where the motor is running at 100% speed all day.
Then there are the gear-specific losses, which are unique to gear motors and a huge part of why flat gear motors behave differently than regular BLDC motors without gears. Flat gear motors use a compact, parallel-shaft gear train (often with planetary gears or spur gears, depending on the torque requirement) to reduce speed and increase torque. Every time a gear tooth meshes, there’s friction between the metal surfaces, and the lubrication (grease or oil) used to reduce that friction generates additional heat. Unlike inline gear motors, which have more space around their gears for heat to dissipate, flat gear motors are designed to be low-profile, so their gear train is nested right next to the motor’s windings and cores. That means heat from the gears mixes with heat from the motor, and it can be hard to tell which is contributing how much to the total temperature rise. A common mistake customers make is blaming the motor for overheating when it’s actually the gear train running hot from too little lubrication or overloading the gear beyond its torque rating.
Now, let’s talk about the actual numbers. In our years of testing BLDC flat gear motors, we’ve found that under standard continuous operating conditions (where the motor is at its rated torque and speed, in a well-ventilated environment at 25°C ambient), the normal temperature rise is between 30°C and 55°C (54°F to 99°F). That translates to an absolute surface temperature of 55°C to 80°C (131°F to 176°F), which is warm to the touch—you can hold it for a few seconds, but it’s hot enough that you wouldn’t rest your hand on it for a minute. But there are caveats, because not all motors are built the same, and not all applications are the same.
For example, a small flat gear motor rated for 1Nm of torque for use in a small lab automation door actuator will have a much lower temperature rise than a large industrial flat gear motor rated for 50Nm of torque for use in a conveyor system. The smaller motor has thinner windings, less current draw, and a smaller gear train, so its rise might be as low as 20°C (36°F) at continuous rated load. The larger, higher-torque motor might hit 50°C (90°F) at full load, which is still well within acceptable limits.
Then there’s the difference between continuous operation and intermittent duty cycles. A lot of our customers use BLDC flat gear motors in applications where they only run for 5 or 10 minutes at a time, then shut off for an hour to cool down. In those cases, the temperature rise will be way lower—often 10°C to 20°C (18°F to 36°F)—because the motor never has time to build up sustained heat. The problem only comes when you push a motor past its rated duty cycle: if a motor is rated for 20% duty cycle (meaning it runs 2 minutes, rests 8 minutes) and you run it 8 hours straight without stopping, the temperature rise will spike, sometimes into the 70°C (126°F) range, which is too hot and can damage the insulation on the windings over time.
Another variable that surprises a lot of first-time users is ventilation and ambient conditions. If your motor is installed in a sealed control panel with no airflow, or in an environment where the ambient temperature is 40°C (104°F) instead of 25°C, the temperature rise will be higher. Heat dissipates from the motor’s surface based on the temperature difference between the motor and the air around it; if the air is already hot, there’s less gradient to pull heat away, so the motor runs hotter for the same load. We recently had a customer who complained about their motor running at 70°C, which they thought was a failure—turns out their entire factory floor was a steady 38°C, so even though the motor’s rise was only 32°C, the absolute temperature was higher than what they were used to seeing in their old cooler test lab.
So what counts as too much temperature rise, and when should you worry? The short answer is: when the rise exceeds 55°C (99°F) for continuous rated load in a 25°C ambient, or when the absolute temperature (the actual surface or internal temperature) gets above 85°C (185°F). That threshold comes from the insulation class we use for most of our BLDC flat gear motors—Class F insulation, which can handle up to 155°C (311°F) without failing, but we build in a safety margin so the insulation never gets close to that. A rise over 55°C means you’re either overloading the motor, running it beyond its rated duty cycle, or it’s not getting enough ventilation. We’ve seen motors run at a 65°C rise for a few hours at a time and keep working, but over months, that extra heat will degrade the lubrication in the gears, break down the winding insulation, and shorten the motor’s lifespan by years.
There are also steps you can take to keep temperature rise in a healthy range, and as a supplier, we work with every customer to optimize this for their application. First, match the motor’s rated torque to your actual load—don’t overspeed the motor or run it beyond its continuous rating. A common mistake is thinking a motor with a higher peak torque is better for continuous use; peak torque is only for short bursts, not all-day operation. Second, make sure the motor is installed with proper airflow around it—don’t bolt it to a metal surface that traps heat, or seal it in a tight housing without vents. Third, choose the right gear ratio for your application: a gear ratio that’s too low will make the motor run faster than it’s designed for, increasing iron losses and heat, while a ratio that’s too high will make the motor work harder to move the load, increasing copper losses.
We also do internal testing on every motor we ship, because we know that temperature rise is a key performance indicator. Our in-house test lab runs each motor under its full rated load for 8 hours straight, measuring temperature at the windings, the motor surface, and the gear housing, using thermocouples placed in exact locations to capture the hottest spots. We publish that test data for every motor model we sell, so customers don’t have to guess what performance to expect. Last year, a customer designing outdoor smart gates came to us because another supplier’s motor kept overheating in the summer heat—we looked at their load requirements, adjusted the gear ratio slightly, and added a 10% safety margin on the motor’s continuous torque, which brought their temperature rise down from 62°C to 41°C, even in 35°C ambient.
Another thing to note: BLDC flat gear motors are more efficient than brushed DC or AC gear motors, so they run cooler overall, which is one of their biggest benefits. Brushed motors have losses from the brushes arcing and friction, adding 10-15% extra heat that BLDC motors don’t have. That efficiency translates directly to lower temperature rise, longer lifespan, and less energy use—something that’s become increasingly important for customers looking to reduce their operating costs. We recently tracked a customer who switched from brushed gear motors to our BLDC flat gear motors in their bakery conveyor system: their motor temperature dropped by 28°C, their energy use went down by 18%, and they haven’t had to replace a motor in 18 months, compared to replacing two a year with their old setup.
At the end of the day, temperature rise isn’t a flaw in a BLDC flat gear motor—it’s a byproduct of converting electricity to motion, and a healthy motor will run warm. The key is understanding what’s normal for your specific motor and application, and what steps to take if it gets too hot. If you’re in the market for a BLDC flat gear motor for industrial automation, HVAC, robotics, or any other application, and you want to know exactly what temperature rise to expect, or you’re troubleshooting a motor that’s running too hot, our team is here to help. We don’t just ship motors—we work with you to match the right motor to your load, duty cycle, and environment, so you get reliable performance for years to come.
If you have questions about temperature rise for your specific application, need a custom motor recommendation, or want to discuss your project requirements, don’t hesitate to reach out to our team. We’re here to help you find the right solution for your needs.
Helical Gear Motor References
- Bolt, G. “Electric Motor Losses and Efficiency.” Industrial Motor Systems, U.S. Department of Energy, 2021.
- Kerr, S. “Gear Motor Heat Generation and Thermal Management.” Gear Technology Magazine, vol. 34, no. 2, 2019, pp. 45-52.
- National Electrical Manufacturers Association (NEMA). Standard MG1-2023: Motors and Generators, NEMA, 2023.
- Zhang, L. “Thermal Analysis of BLDC Motors with Integrated Gear Trains.” IEEE Transactions on Industrial Electronics, vol. 67, no. 8, 2020, pp. 6512-6521.
Hangzhou ANG Drive Co., Ltd.
We’re well-known as one of the leading bldc flat gear motor manufacturers and suppliers in China, also support custom service. Please feel free to wholesale high quality bldc flat gear motor made in China here from our factory. Contact us for more details.
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