Why this happens
Motors, controllers and batteries all lose some energy as heat, and more so on climbs, with heavy loads, in hot weather and with hard acceleration. Controllers and battery management systems protect themselves by limiting power when they get too hot. Comparing temperatures against your own baseline reveals problems such as dragging brakes, a failing bearing or a blocked heatsink before they cause damage.
What you need
Tools
- Infrared (non-contact) thermometer
- Smartphone for notes and photos
Materials
- Notebook or spreadsheet for a temperature log
- Small piece of matt masking tape (for shiny surfaces)
Before you start
- Do not touch motor housings, brake discs or controller cases straight after riding; they can be hot enough to burn.
- Infrared thermometers often have a laser pointer; never point it at anyone's eyes.
- Do not pour water on hot components to cool them.
Step by step
- 1
Learn your thermometer's limits
Infrared thermometers read surface temperature, and shiny metal reflects heat, giving falsely low readings. Stick a small piece of matt masking tape on the motor cover, controller case and battery case once; measuring on the tape gives more consistent results. Hold the thermometer at the distance its manual suggests so the spot stays on the part you want.
- 2
Take a cold baseline
Before a ride, with the vehicle parked in the shade, measure the motor, controller, battery case and ambient air or a nearby wall. These cold readings tell you how close the parts are to ambient and help you spot sensor errors. Write them down with the date and time.
- 3
Measure straight after a normal ride
After your usual commute, stop safely, switch off and measure the same spots within a minute or two, because parts cool quickly. Record the readings with the distance, load, weather and whether you climbed hills. Repeat this over several rides to see what is normal for your vehicle in your conditions.
- 4
Compare after a hard ride
After a demanding ride, such as a long climb, a pillion or a hot afternoon, take the same readings. Expect the motor and controller to be warmer than your normal baseline. The question is whether the increase is reasonable for the extra load and whether the parts cool back down at a normal rate.
- 5
Look for one part that is out of line
If one part is much hotter than usual on an ordinary ride, investigate. A hot wheel hub with a hot brake disc suggests brake drag. A hot hub with a cool disc on a normal ride may mean a bearing or motor issue. A hot controller may have a blocked or covered heatsink. A noticeably warm battery case after a gentle ride is worth reporting.
- 6
Check connectors and cables too
Point the thermometer at visible connectors and cables near the motor and controller. A connector noticeably warmer than the cable either side of it has high resistance from looseness or corrosion. Note it, then with the battery disconnected and the vehicle cool, inspect and clean it as described in the connector guides.
- 7
Adjust habits and keep the log
If temperatures climb on certain routes, try gentler acceleration, a lower power mode on long climbs and stopping to cool in the shade. Keep logging monthly. A gradual upward trend in motor or controller temperature on the same route is an early warning worth showing your service centre.
How to tell it worked
You have a log showing normal cold and after-ride temperatures for each part, so an abnormal reading stands out, and any hot spot has a likely cause you can check or report.
Stop and call a technician if
- The battery case is hot, swollen, smoking or smells unusual.
- A connector or cable is hot enough to discolour or soften its insulation.
- The vehicle repeatedly cuts power for over-temperature on ordinary rides.
Questions
What temperature is too hot for a hub motor?
Limits depend on the motor's design and insulation class, so check your manual. In practice, compare with your own baseline: a sudden rise on an ordinary ride is the warning sign.
Why does my scooter slow down on long climbs?
Many controllers reduce power when the motor or controller gets hot, to protect them. Gentler riding, a lower mode or a short cool-down break usually helps.