Electric scooter motor ventilation: Cooling a motor-wheel, benefits and precautions

Ventilating an electric scooter motor involves drilling holes in its casing and adding fins to allow air to circulate through the motor. The purpose is to dissipate heat from the windings more quickly, so that the motor maintains its torque for longer and does not trigger its thermal protection. The benefits are significant with intensive use and on the track. However, there is a corresponding drawback: a ventilated motor is no longer waterproof. Here's how it works, how it's installed, and in what situations it's a good idea.

Why does a wheel motor get so hot?

In a hub motor, heat is primarily generated in the copper windings located at the center of the motor. To escape, it must first pass through the air trapped within the motor housing, then reach the housing and the rim, and finally, the outside air. Some of the heat also travels through the axle to the arms. This path is lengthy. Consequently, during a long uphill climb, repeated accelerations, or a track session, the temperature rises faster than it can dissipate.

Alternatively, a hot motor loses torque, and beyond a certain threshold, it risks damaging the insulation of its wires or its magnets. The details of these mechanisms are explained in our guide explaining why an electric motor overheats.

What a ventilation system does

The principle is simple: holes are drilled in the motor casing, and a fan blade assembly is attached to them. When the wheel rotates, the fan blades stir the air and force it through the motor. The cool air then comes into contact with the motor windings, carrying the heat away directly, rather than having to pass through the entire motor housing.

The effect depends on the riding speed: the faster the wheel spins, the more air circulates. Therefore, the ventilation system is most effective on tracks and during sustained use. When stationary, it provides almost no benefit; this is also the time when the motor no longer generates heat.

We don't provide a specific numerical increase in degrees; it depends on the motor, the controller, the settings, the rider, the ambient temperature, and the course. What we can say is that, on our motors, the ventilation significantly improves cooling during intensive use or in competition. That's why we recommend it for track machines.

Our motor cooling system

Our motor cooling fan is a PETG-printed part with six blades. It is compatible with all of our motors in the MHS, MHT, XHS, and XHT series. Here's what its product description says:

• It is mounted on the motor casing, on the side with the cables
• The casing is perforated with holes that are 10 mm in diameter to allow for air passage
• It is attached using M4 screws, for which holes need to be drilled and tapped in the flange
• The base model is designed for a rear motor with the cooling fan on the right side. For the opposite configuration (front motor, or cooling fan on the left), please specify this when placing your order.

The direction matters because the wheel always rotates in the same direction when moving forward: therefore, the part is manufactured for a specific position on the machine.

Assembly precautions:

Drilling without damaging the motor

The drilling is performed with the motor casing disassembled, away from the open motor. Aluminum or steel shavings are the number one enemy: a shaving attracted by the magnets can become lodged in the air gap, scratch the magnets, or damage the varnish on the windings. Each hole is deburred, the casing is carefully cleaned, and the inside of the motor is inspected before reassembling.

Respect the cables and the sensor

The casing on the cable side also houses the motor phases, Hall sensors, and often the temperature sensor. It's important to identify the paths of these components before drilling, and to check after reassembly that no wires are pinched.

If you don't want to do it yourself,

We offer drilling and assembly services in our workshop upon request, with charges based on the time spent, using our labor services.

Water and dust: the true cost

Once the motor casing is breached, it allows whatever the air carries to enter: water, mud, sand, dust. Water can reach the Hall sensors and the windings, causing corrosion, jerks, or sensor failures. Sand and dust accumulate, and metal particles stick to the magnets.

Therefore, our guideline for this article is: a motor with a fan should only be used in dry conditions and on tracks, or it should be protected by a grill. For a scooter that is used daily in the city, in all weather conditions, this is not the right solution. It is better to opt for a wider motor, which generates less heat under the same load, or a more conservative controller setting. See our guide on motor sizes.

Ventilation, ferrofluid, larger motor: which one to choose?

Other methods exist for cooling a motor. Ferrofluid, a magnetic liquid placed in the air gap, improves heat transfer without exposing the motor to the air; we discuss this in our guide on ferrofluid for motor cooling. A wider motor produces the same torque with less current. And adjusting the current limits of the controller remains the simplest solution. On a circuit machine, ventilation is often the most direct solution.