Why this happens
Heat is the earliest visible sign of many faults: a loose or corroded connector has extra resistance and warms up, a dragging brake heats its disc, and an overloaded component runs hot. An infrared thermometer reads surface temperature from a distance, but shiny surfaces and wrong distance give false readings, so technique matters.
What you need
Tools
- Infrared thermometer with a laser pointer and adjustable emissivity if possible
- Notebook or phone for readings
Materials
- Matt black electrical tape (a small piece for shiny surfaces)
- Masking tape and a marker for labelling measurement points
Before you start
- Never point the laser at eyes, people or animals.
- Do not touch parts to confirm heat; motors, brakes and charger bricks can cause burns.
- Do not open battery, motor or controller covers to measure inside them; scan only what is visible from outside.
- An infrared thermometer reads surfaces only; it cannot tell you the internal temperature of a battery.
Step by step
- 1
Understand the spot size
Check your thermometer's distance-to-spot ratio, often printed near the screen. At a ratio of 12:1, the measured circle is about 1 cm wide at 12 cm away. If you stand too far back, the reading averages the part with its cooler surroundings. Get close enough that the spot is smaller than the part you want to measure, without touching it.
- 2
Deal with shiny surfaces
Polished metal, chrome and bare aluminium reflect infrared and read far too low. For repeatable checks, stick a small piece of matt black electrical tape on shiny points you measure often, such as a brake caliper or motor casing, and aim at the tape. If your thermometer has adjustable emissivity, leave it at the default for tape and painted surfaces.
- 3
Take a cold baseline
Before a ride, with the vehicle at room temperature, measure your points: charge port, visible connectors, motor casing, controller casing if it is exposed, both brake discs or drums, both tyres and the charger brick. They should all read close to the air temperature. This baseline tells you the thermometer and your technique are working.
- 4
Measure straight after a normal ride
Ride your usual route, park safely, switch off and measure the same points within a few minutes. Expect the motor, brakes and controller casing to be warmer. Note each reading. What matters most is not the absolute number but whether matching parts differ: two brake discs, two tyres, or the two pins of a connector should be similar.
Tip: Measure in the same order every time so the time since stopping is consistent.
- 5
Check the charging chain
During charging, measure the charger brick, the plug at the wall end, the plug at the vehicle end and the charge port, without unplugging anything. The charger brick is normally warm. A plug or charge port that is clearly hotter than the cable on either side suggests a poor contact. Stop charging and unplug at the wall if anything is too hot to rest a hand near.
- 6
Compare left with right
Look for asymmetry. A front brake disc much hotter than the rear on a gentle ride can mean a dragging caliper. One tyre hotter than the other may be under-inflated. One terminal of a connector hotter than its neighbour points to a loose or corroded contact. Mark any suspect point with masking tape so you can recheck it.
- 7
Log and trend
Write each reading with the date, air temperature, route and charge level. Recheck monthly and after any repair. A point that slowly warms over several weeks is a developing fault even if it has not yet caused a problem. Take trends and suspect points to a service centre with your notes, which makes their diagnosis faster.
How to tell it worked
You have a baseline of normal temperatures for your vehicle, and you can quickly spot a component that runs hotter than its pair or hotter than it did last month.
Stop and call a technician if
- Any battery casing, charge port or plug is noticeably hot, discoloured or smells of burning.
- A connector keeps heating up after you have cleaned and reseated an accessory plug.
- The battery is swelling, hissing or giving off smoke: move away and call 112.
Questions
Why does my brake disc read cooler than I expected?
Shiny metal reflects infrared and reads low. Stick a small piece of matt black tape on it and measure the tape instead.
Can I measure battery temperature with it?
Only the outside of the casing. The cells inside can be hotter; if the casing itself is hot, stop using the battery and get it checked.