ONYX Motor Magnet Temperature Limits and Demagnetization

How hot can your ONYX motor get, and when should your controller begin reducing power?

The QS205, Sotion H02, Sotion H16, QS260 MAG V4, QS273 MAG V4, and 150mm QS260 V4 spoked motor all use N35SH neodymium magnets rated for approximately 150°C.

Stock 72V and 80V ONYX controllers already have motor-temperature protection configured. This guide is especially useful for owners adjusting aftermarket FarDriver, Kelly, or Moxin controllers.

Here’s what ONYX owners should know:

• 145°C: A practical motor-temperature thermal-throttling reference for everyday riding with aftermarket controllers.
• 150°C: The commonly specified maximum operating temperature for N35SH magnets.
• 180°C: Above the N35SH rating and a serious demagnetization risk, particularly during sustained exposure.
• Controller temperature readings usually come from the stator, not the magnets.
• Cooling modifications can improve sustained performance without changing magnet temperature ratings.

Understanding Motor Magnet Grades and Temperature Ratings

The QS205, Sotion H02, Sotion H16, QS260 MAG V4, QS273 MAG V4, and 150mm QS260 V4 spoked motor use N35SH (35SH) neodymium magnets, commonly rated for approximately 150°C.

Neodymium magnets, also called NdFeB magnets, come in different grades describing their magnetic strength and resistance to high temperatures.

Neodymium Magnet Temperature Reference

All grades listed below refer to sintered NdFeB neodymium magnets.

These are approximate magnet-grade ratings, not maximum operating temperatures for an entire motor.

What Does N35SH Mean?

• N: Neodymium (NdFeB).
• 35: Approximately 35 MGOe maximum energy-product class.
• SH: Super High temperature/coercivity classification, commonly associated with a maximum operating temperature of approximately 150°C.

Coercivity describes how strongly a magnet resists losing its magnetization.

N52 vs. N35SH: Which Is Better?

N52 magnets have a higher maximum energy product than N35SH magnets, but standard N52 magnets are typically rated for approximately 80°C.

N35SH magnets have a lower maximum energy product but are commonly rated for approximately 150°C.

For high-performance hub motors, that additional temperature resistance is particularly valuable during sustained high-power operation.

Stronger magnets aren’t automatically better for motors that operate at higher temperatures.

What Does a 150°C Magnet Rating Actually Mean?

N35SH magnets are commonly rated for a maximum operating temperature of 150°C. This doesn’t mean they immediately suffer permanent damage when they reach that temperature.

For ONYX owners, three temperatures are worth understanding:

• 145°C: A practical motor-temperature thermal-throttling reference for everyday ONYX riding with aftermarket controllers. This is typically a stator temperature reading, not a magnet temperature.
• 150°C: The commonly specified maximum operating temperature for N35SH magnets.
• 180°C: Above the N35SH operating rating and a serious demagnetization risk, particularly during sustained exposure.

The 180°C reference exceeds the N35SH rating by 30°C. It is also the approximate maximum operating temperature associated with N35UH magnets, a higher-temperature grade. It is not an established failure temperature for N35SH.

What Actually Causes Permanent Demagnetization?

As magnet temperature rises, its intrinsic coercivity decreases. Intrinsic coercivity describes how strongly a magnet resists being permanently demagnetized by an opposing magnetic field.

During high-current motor operation, opposing magnetic fields can become strong enough to cause irreversible magnetic weakening, particularly when the magnets are already hot.

This explains why permanent demagnetization can occur below 180°C. The exact temperature depends on the magnet’s coercivity, the magnetic fields inside the motor, and its operating conditions.

Magnets also temporarily lose some strength as they heat up. That reversible loss normally disappears when they cool. Permanent demagnetization is different because cooling won’t restore the lost magnetization.

How Long Can a Motor Operate at Higher Temperatures?

A brief temperature spike isn’t the same as maintaining that temperature throughout a long ride.

For N35SH magnets, these temperature ranges provide useful guidance:

• Below 150°C: Within the commonly specified magnet temperature rating, although other motor components may have lower limits.
• At 150°C: At the magnet’s rated maximum operating temperature. This isn’t automatically a recommended continuous operating target for the complete motor.
• Above 150°C: Outside the commonly specified N35SH operating range, with increasing risk of permanent magnetic weakening.
• Around 180°C: A serious demagnetization risk, particularly during sustained exposure and high magnetic loading.

These temperatures refer to the magnets themselves, not the stator temperature displayed by the controller.

There is no universal exposure time at which permanent damage begins. Five minutes at a particular temperature cannot be considered safe or damaging without knowing the motor’s magnetic operating conditions.

Winding insulation, magnet adhesives, and other internal components also have their own thermal limits.

The complete motor design determines how much heat it can tolerate and for how long.

How Thermal Throttling Protects Your ONYX Motor

Thermal limiting, also called thermal throttling, allows a properly configured controller to reduce motor current as temperatures rise.

For everyday ONYX riding, 145°C is a useful motor-temperature thermal-throttling reference on many FarDriver, Kelly, and Moxin controller setups.

The exact settings and behavior vary between controllers. A 145°C thermal-throttling reference isn’t necessarily the temperature where current reduction first begins, and it isn’t a universal factory setting.

Drag racing setups may use different limits because short, high-power runs have different thermal demands than everyday riding.

What Happens When Thermal Throttling Starts?

Imagine climbing a long hill while your motor temperature continues rising.

As the motor reaches its configured thermal-limiting range, the controller reduces available current. You may notice weaker acceleration or reduced power.

That’s thermal protection working as intended, not necessarily a sign of motor damage.

As the motor cools, available power can gradually return according to the controller’s settings.

Temperature may continue rising briefly after reducing power because heat stored in hotter motor components takes time to reach the sensor. This is called thermal lag.

Thermal protection depends on using the correct temperature sensor configuration and appropriate controller settings.

What Temperature Is Your Motor Sensor Actually Measuring?

The motor temperature displayed by your controller usually comes from a sensor located in or near the stator.

The stator contains the windings, while the permanent magnets are attached to the rotating assembly.

These components don’t necessarily operate at the same temperature.

• The stator can become hotter than the magnets during high-current operation.
• The magnets may heat up and cool down at different rates.
• Cooling modifications can change the temperature difference between components.

For example, a displayed stator temperature of 145°C doesn’t automatically mean the magnets have reached 145°C.

The temperature shown by a FarDriver, Kelly, or Moxin controller depends on the motor’s sensor location and configuration.

This is also why temperature readings from different motor models shouldn’t be compared without considering their construction, cooling, and sensor placement.

What Makes an ONYX Motor Generate Heat?

Motor heating increases during repeated hard acceleration, sustained hill climbing, heavy loads, and extended high-power riding.

High phase current is particularly important because electrical resistance in the motor windings generates heat.

Winding heating increases approximately with the square of current.

Doubling winding current can produce approximately four times the resistive heating, assuming winding resistance remains constant.

Phase Current vs. Battery Current

Phase current is the current flowing through the motor windings, while battery current is the current supplied by the battery to the controller.

At low motor speeds, phase current can be substantially higher than battery current.

This means a motor can generate considerable heat during hard acceleration or steep hill climbing even when battery current appears relatively modest.

Increasing controller phase-current limits can therefore substantially increase motor heating, particularly during high-torque, low-speed riding.

Statorade, Hubsinks, and Water Cooling

Cooling systems improve a motor’s ability to transfer heat away from its internal components.

Under the same workload, effective cooling can lower operating temperatures, slow temperature buildup, delay thermal throttling, and increase sustainable power.

Statorade

Statorade is a magnetic cooling fluid that improves heat transfer from the stator toward the motor shell in compatible hub motors.

This helps heat escape through the shell into the surrounding air.

Correct fluid quantity and motor compatibility are important.

Hubsinks

Hubsinks are external cooling fins that increase the motor shell’s surface area, helping release heat into the surrounding air.

They can complement internal heat-transfer methods such as Statorade.

Water-Cooled Motors

Water-cooled hub motors use circulating coolant to carry heat away from the motor and release it through a radiator or another heat exchanger.

This can improve sustained high-power performance when the cooling system is properly designed.

However, coolant temperature, stator temperature, winding temperature, and magnet temperature aren’t interchangeable.

For example, coolant may remain relatively cool while the windings are considerably hotter.

Cooling effectiveness depends on motor design, coolant flow, radiator capacity, and operating conditions.

Comparing cooling systems requires looking at temperature behavior under the same workload, including how quickly temperatures rise and when thermal limiting begins.

Statorade, Hubsinks, and water cooling don’t change a magnet’s temperature rating. They help the motor remove heat and sustain power longer before reaching its thermal limits.

Practical Motor Temperature Advice for ONYX Owners

1. Know your motor: Identify its specifications and operating limits.
2. Check your temperature sensor: Make sure your controller uses the correct sensor configuration.
3. Configure thermal protection: For many everyday ONYX setups, 145°C is a useful thermal-throttling reference.
4. Watch temperature trends: Pay attention to how quickly temperatures rise during demanding rides.
5. Reduce power when necessary: Easing off the throttle reduces heat generation.
6. Understand your cooling system: Statorade, Hubsinks, and water cooling affect how heat moves through the motor.
7. Avoid confusing ratings: Magnet temperature ratings, controller temperature readings, and thermal protection settings are different things.

Final Advice

N35SH magnets are commonly rated for 150°C, while temperatures around 180°C exceed that rating and present a serious demagnetization risk. Your controller usually measures stator temperature rather than magnet temperature, and thermal limiting helps manage motor heat during demanding riding.

Understanding these differences makes it easier to interpret temperature readings and manage sustained motor performance.