Running 20kW Through a Hub Motor: What It Takes to Keep It Cool
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Yes, hub motors have been run at 20kW. HubSink prototypes were raced, and won, at the TT1500 at around 20kW, and riders report 18kW through a QS205 hub motor on a hill climb. It only works if heat is solved first, and the rest of the bike is built for the power. This guide explains why heat is the limit at 20kW, what cooling does, and what else has to keep up.
Why heat is the limit at 20kW
Current is power divided by voltage. At 84V, 20kW is about 238 amps. At 100V it is 200 amps. Heat in the copper windings rises with the square of the current, so doubling the amps makes roughly four times the heat. A direct drive hub motor also has its stator sealed in a shell with an air gap around it, so that heat has no easy way out. At 20kW the motor heats up in seconds, long before the magnets or copper are anywhere near their mechanical limits.
The rule of thumb among builders on Endless Sphere is to keep the hottest part of the motor under about 93C, with around 60C comfortable for continuous use. Past that, magnets can lose strength permanently. See why ebike hub motors overheat for the full explanation.
How cooling changes what a motor can take
Heat has to travel in two steps, from the windings to the shell and from the shell to the air.
- Statorade ferrofluid goes inside the motor and bridges the air gap. Grin Technologies measured heat conduction from windings to shell rising from 1.8 to 4.3 W/°C on one motor.
- HubSink fins go on the shell. In Grin wind tunnel testing on a Cromotor, HubSinks gave a 50 to 60% improvement in shell to air cooling and up to 20% more total heat flow on top of Statorade (Grin results).
Grin's lab figure is about 40% more sustained power from doubling heat dissipation at a steady load. Real riding is bursts, climbs and recovery, and there the benefit compounds. A cooler motor has lower winding resistance, so it makes less heat for the same power, and it recovers faster between efforts. That is why riders commonly run more than double the power and many report around five times.
What riders are running
- HubSink prototypes at the TT1500 race, around 20kW.
- 18kW through a QS205 hub motor on a hill climb with HubSink fitted.
- Quokka, with an Adaptto controller at 120 amps, HubSinks and ferrofluid, reported the motor running around 30C cooler on the same hills while going faster, over 80km of dirt and trail in mid 30s heat.
- Jesse Haubner, running an MXUS at 8kW, no longer had to stop to cool down on hills that used to thermal limit him.
- Hugh Pomeroy, on a 7500W fat bike, found the motor not warm at all after a full speed mountain climb.
Read the reports in the HubSink official thread on Endless Sphere.
What else has to keep up at 20kW
HubSink does not make power. Your controller and battery do. Before you go near 20kW, check:
- Battery discharge rating and voltage sag at the current you want
- Controller current rating, and phase wires and connectors sized for it
- Frame, dropouts, axle and torque arms, since hub motors put huge torque through the axle
- Brakes and tyres that can handle the speed
- A temperature sensor in the stator, read on your controller or Cycle Analyst
- Where you ride. This level of power is for off road and private use, so check your local laws.
Step up in stages
Fit Statorade and HubSink first, log your baseline temperatures, then raise power in steps while watching the motor temperature. The full method is in how to run more power through a hub motor without overheating.
Your guarantee: fitted with Statorade to a compatible motor, your motor will handle at least double the power from your controller without overheating, or stop overheating at your normal power, or you get a full refund within 30 days. Results like 20kW are what riders and testing show in practice, not a guaranteed figure.
Find your motor
Cooling guides by motor: QS205, MXUS, Leaf, 9C, Crystalyte, Cromotor and QS273. Compare Statorade, HubSink and vented covers.
20kW hub motor FAQ
Can a hub motor handle 20kW?
Riders have done it. HubSink prototypes were raced, and won, at the TT1500 at around 20kW, and customers report 18kW through a QS205 hub motor on a hill climb. It takes serious cooling, with Statorade inside and HubSink outside, and a controller, battery and wiring built for the current. It is not something every motor or build should attempt.
How many amps is 20kW?
Amps equal watts divided by volts. At 84V, 20kW is about 238A. At 100V it is 200A. That current is why the motor makes so much heat, since heat rises with the square of the current.
Does HubSink make my motor more powerful?
No. Your controller and battery supply the power. HubSink with Statorade lets the motor shed heat faster so it can handle more of that power without overheating.
What else do I need for 20kW?
A controller and battery rated for the current, phase wires and connectors that can carry it, a strong frame, dropouts and torque arms, brakes that can stop the speed, and a temperature sensor so you can see what the motor is doing.
Is it guaranteed?
The guarantee is for at least double the power from your controller without overheating, or no more overheating at your normal power, with a full refund within 30 days. Higher figures such as 20kW are what riders and testing show in practice, not a guaranteed result.