One of the most important tools every electric RC hobbyist should own is an infrared temperature meter, often called a temp gun. It is inexpensive, easy to use and can help prevent costly damage to motors, electronic speed controllers and batteries.
It does not matter whether you build your own RC models or operate ready-to-run vehicles. Heat is one of the biggest enemies of an electric power system. Monitoring the temperature of the components helps identify excessive load, poor cooling or a developing mechanical problem before a component fails.
There are many infrared temperature meters available. I have used the Duratrax Flashpoint infrared temperature gun for many years. It is simple to operate and provides a quick way to monitor an RC power system.
Keep in mind that infrared meters measure surface temperature. Readings can vary depending on the surface material, colour, reflectivity, distance and measurement angle. For the best comparison, measure the same locations each time.
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How to Use a Temp Gun Effectively
Temperature checks should become a regular part of operating an electric RC vehicle. During normal use, periodically check the brushless motor, electronic speed controller and battery. When testing a new setup or after changing the propeller, gearing, battery voltage or vehicle load, check the temperatures much more frequently.
Take the measurements as soon as practical after the vehicle stops, preferably within approximately 30 to 60 seconds. Waiting too long allows airflow, heat sinks and the surrounding structure to remove heat, which can make the reading appear lower than the temperature reached during operation.
Follow the instructions supplied with your temperature meter. Take readings from several locations because the hottest point may not always be where you expect it.
- Check the motor case near the windings.
- Check both ends of the motor.
- Check the ESC heat sink and case.
- Check the battery in several locations.
- Record the highest stable reading.
Be careful when measuring shiny metal surfaces because their reflectivity can produce inaccurate infrared readings. Measuring a consistent painted, anodized or non-reflective location will normally provide a better comparison between runs.
As LiPo batteries begin to age, check their temperature more frequently. An aging pack may develop higher internal resistance, causing it to produce more heat while delivering current.
Factors That Influence Temperature Readings
Several operating conditions can change the temperature of an RC power system. The most important thing is to recognize a temperature that is unusually high compared with previous runs under similar conditions.
- Higher outdoor or ambient temperature
- Aggressive throttle use
- Increased vehicle weight or motor load
- A larger propeller or more aggressive gearing
- Binding bearings, gears or driveline components
- Restricted airflow or blocked cooling passages
- An aging or damaged LiPo battery
- Longer run time
- Higher battery voltage
Record the ambient temperature along with the component temperatures when comparing different runs. A motor operating at 55°C on a cool day is not experiencing the same temperature rise as a motor reaching 55°C on a very hot day.
Using a Temp Gun for the First Run of a New Setup
When operating a new setup for the first time, begin with conservative gearing, propeller size and run time. Do not immediately complete a full-length run and assume the components will remain within a safe temperature range.
For an RC airplane, a short ground test may help identify an obviously overloaded system. However, a long full-throttle ground run may provide less cooling than the motor and ESC receive during flight. A wattmeter should also be used to check current and power before flying.
For an RC car or boat, begin with a short run of approximately 30 to 45 seconds. Bring the vehicle back and immediately measure the motor, ESC and battery.
If the temperatures remain comfortably below the limits specified by the manufacturers, operate the vehicle for another short period and check again. Increase the run time gradually until you reach the intended operating time.
A temperature of 60°C or 140°F can be used as a conservative warning point during early testing, but it should not be treated as a universal limit for every component. Motors, ESCs and batteries can have different allowable temperatures. Always follow the lowest applicable limit provided by the component manufacturer.
If the temperature rises rapidly or exceeds the recommended limit, stop testing and allow the system to cool. Reduce the motor load, improve cooling or shorten the run time before testing again.
What to Change When the System Runs Too Hot
- Install a smaller or lower-pitch propeller.
- Use less aggressive gearing.
- Improve airflow around the motor and ESC.
- Check the drivetrain for binding.
- Reduce vehicle weight where practical.
- Reduce the battery voltage if the setup is overloaded.
- Use a larger motor or ESC when the application requires more continuous power.
- Reduce the maximum run time.
Only change one variable at a time when possible. This makes it easier to determine which adjustment corrected the temperature problem.
Determining Maximum Run Time
Temperature is only one factor that determines maximum run time. LiPo capacity also needs to be considered. A common starting guideline is to use no more than approximately 80% of the battery’s labelled capacity during a run.
After completing a measured run, recharge the battery and record how many milliamp-hours are returned to the pack. Compare this value with the battery’s labelled capacity.
For example, suppose a 5,000mAh battery is operated for 4 minutes and 15 seconds. If the charger returns approximately 4,000mAh to the battery, the run used about 80% of the labelled capacity:
4,000mAh ÷ 5,000mAh = 0.80, or 80%
That run time can be treated as an approximate maximum for those operating conditions. Do not assume the same run time will always be safe. More aggressive throttle use, higher temperature, additional vehicle load or an aging battery can change both capacity consumption and component temperature.
The RCexplained General Calculator includes a run-time tool that estimates total run time using the elapsed test time, battery capacity and the amount of capacity returned during charging.
Open the RCexplained General Calculator
Temperature Checks Can Save Your RC Electronics
A temperature meter cannot replace proper current measurement, correct component selection or manufacturer specifications. However, it provides a quick warning when an RC power system is operating under more load than expected.
Use a wattmeter or ESC data logger to measure current, and use the temperature meter to confirm how the system handles that load over time. Together, these tools can help prevent damaged motors, overheated ESCs and stressed LiPo batteries.
A few seconds spent checking temperatures after a run can save a considerable amount of money and help keep your RC setup operating reliably.