Have you ever encountered these issues: difficulty in climbing hills by your electric bike, sudden vibrations during riding with unusual noises from the rear wheel, or reduced range that persists even after battery replacement?

In the event of encountering any of these problems, there is a high probability of demagnetization of the motor of your electric bike. The discovery upon disassembling the motor will be rust covering it, as shown in the image below.

So, what causes motor demagnetisation? And is there any way to prevent it?

The presence of issues such as lack of power when climbing hills, riding vibrations, unusual noises from the rear wheel, or reduced range while using your electric bike — and these problems persist even after replacement of the battery — is an indication that your electric bike motor has demagnetized. Once you disassemble the motor, you will see rust inside. So, what is the exact cause of motor demagnetization? And how can we prevent it?

Demagnetisation phenomenon and causes

The occurrence of motor demagnetization is not uncommon during electric bike operation. The presence of issues such as weak hill climbing, riding vibrations, rear wheel noises, or reduced range, along with the persistence of these problems after battery replacement, often serves as an indication of motor demagnetization. Take a look at the motor, though, and you'll see that it's covered in rust. The manifestation of motor demagnetization is poor performance during operation, such as uphill struggles or riding vibrations. The cause of this phenomenon is often high temperatures and continuous vibrations within the motor.

The Effects of Heat and Vibration

So, what exactly causes this problem? And what measures can we take to prevent it? What is the underlying cause of motor demagnetisation? As it happens, elevated temperatures and vibrations are the two main catalysts. Consider a magnet in your hand: after exposure to flame, its magnetic properties vanish completely. Basically, even a tiny bit of force, like a small hammer blow, can slowly weaken its magnetism until it basically disappears. It's like, when you've got an electric motor that's been running for a long time in really high temperatures or it's been vibrating non-stop, its magnetic properties slowly go down over time, and that's what causes demagnetization.

For example, when riding an electrically-powered bicycle, a punctured tyre without proximate repair options makes pushing the bike really hard. If you carry on, you might have to put more weight on the bike, which will increase the power used and the heat produced. This will make the motor get hotter and hotter. This heightened temperature disrupts the motor's thermal balance – the dissipation of heat cannot keep up with the production of heat, leading to an accumulation of thermal energy within the motor. At the same time, vibrations from the flat tyre rolling on the road surface go straight to the motor without anything in between. These two bad things together make it much more likely that the electric bike's motor will stop working.

Improper Matching and Mechanical Failures

Well, there's also the chance that the electric vehicle controller and motor just aren't a good fit for each other. So, for example, you might have a controller that's too big paired with a motor that's too small. The occurrence of this mismatch can also result in an increase in motor temperature, thereby increasing the risk of demagnetization. Additionally, the acceleration of motor demagnetization over time can be caused by mechanical component failures, including non-resetting brake systems, damaged bearings and differential issues, if not promptly repaired. The importance of note: improper controller-motor pairing or failure to promptly repair mechanical components like the braking system or bearings. The result: an increase in the risk of motor demagnetization. The presence of a no-load speed that exceeds 20% of the rated speed can be an indication of motor demagnetization. Therefore, when selecting an electric vehicle, the principle of slightly over-specifying the motor power should be followed to reduce the likelihood of demagnetization occurring.

Avoid High Current Surges

Over time, there may be varying degrees of demagnetization of electric vehicle motors, particularly noticeable in vehicles with extended usage. The minimisation of this risk is possible through the avoidance of high current surges and frequent starts and stops during daily use. This is to prevent motor overheating that could cause demagnetization. For instance, the prevention of excessive current overheating the motor is possible by avoiding continuing to ride with a flat tyre.

Preventing Other Damage

To prevent demagnetization of electric vehicle motors, another crucial point is to avoid prolonged operation in waterlogged environments. While most electric vehicles on the market boast excellent waterproofing, products from smaller manufacturers may have defects. If water enters the motor's interior, the magnets and magnetic cylinders may rust. Over time, rusted magnets will experience increasingly severe demagnetization. Therefore, during daily riding, avoid prolonged exposure to water to prevent internal rust and demagnetization, and protect the motor by paying attention to riding details. After the temporary license plate transition period ends, this area will no longer prohibit road access—truly good news!