July 2, 2026 · root

Overheating of the motor and controller: causes and engineering solutions

Introduction Overheating of the motor and controller; a frequent cause of failures in electric vehicles and industrial equipment. This text describes the system approach: diagno...

Introduction

Overheating of the motor and controller; a frequent cause of failures in electric vehicles and industrial equipment. This text describes the system approach: diagnostics, root causes, engineering measures for cooling and algorithmic solutions at the firmware level and control settings. Practical for engineers, service technicians and experienced enthusiasts.

Diagnostics: How to distinguish motor problem from controller

1. Symptoms of motor overheating:

drop in power and torque during warming up;
smell of heated insulation or smoke;
a sharp increase in current on the load;
Abnormal vibrations and noise (bearings, backlashes).

2. Symptoms of controller overheating:

emergency errors in voltage or current;
the controller goes into LIMP-mode or turns off when the temperature rises;
heating of the radiator, melting of thermal shrinks on power wires;
CAN/UART communication errors at high load.

3. Diagnostic tools:

current mites, oscilloscope (peak currents, noise);
thermal imager or contact thermometer for tracing hot zones;
Logging of controller telemetry (CAN/UART) and BMS;
Check phase resistance and motor isolation.

Root causes of overheating

Incorrect selection of the engine under load (congestion zone, low efficiency). Compare the working point of the engine with the requirements: see the selection recommendations in the material about QS Motor.
Insufficient cooling: Passive radiator is insufficient during prolonged overload.
Control errors (FOC/vector switching): incorrect PID settings, current limiters, integral errors.
Incorrect position sensors (displacement of the Hall / encoder) -> incorrect phase synchronization -> unnecessary current peaks.
Power problems: battery drawdowns, poor contacts, faulty BMS, high ESR capacitors -> pulsation and inverter overload.
Electromagnetic interference and resonances in cables, poor wiring of the power unit.

Engineering solutions: hardware measures

Refrigeration and heat management

Calculate thermal balance: P loss = I rms^2 * R phase + switching losses in MOSFET/IGBT. Determine the required heat flow.
Apply active cooling: directed flow fans, liquid cooling based on a heat exchanger for high power.
Increase the radiator area and improve contact through heatpaste/thermal pads.
Optimize wiring: minimize the length of power lines, use multi-core tires and reliable connectors.

Components and protection of the power unit

Use MOSFET/IGBT with low Rds(on) and high switching frequency, but taking into account switching losses.
Install deglitering and snubber circuits to reduce overvoltage.
Quality filters at the input/output of the controller, additional capacitors with low ESR near the power board.
Reliable current protection (fast fuse, soft-start) and temperature protection by sensors on the radiator and motor body.

Engineering solutions: algorithmic and controller settings

Fine tuning of FOC and limitations

Configure the PID for current and moment circuits: reduce the integral component at the risk of saturation.
Restricting RMS current, not just peak current: the controller must rely on I rms or the thermal budget model.
Use a dynamic temperature limit: Reduce the current/moment curve when a threshold is reached.
Turn on recovery mode and load management to reduce long-term load – see examples of setting up Votol (current, recovery, temperature protection).

Work with position sensors

Check and calibrate Hall sensors and encoders: bias or jitter leads to improper switching and current surges. Details about the selection and configuration of sensors - in the guide to Halls and encoders.
When using high-resolution encoders, include filtering and noise compensation.

Firmware and telemetry

Logistic of the temperature of the motor and controller, RMS current, battery voltage. Built-in algorithms for thermal buffer prediction (thermal modeling).
Implement emergency scenarios: power reduction, phasing out consumers, safe parking.
Work with firmware that supports FOC with adaptive settings: examples of implementation of algorithms are in the materials on FOC management.

Practical procedure for eliminating overheating (steps)

1. Remove telemetry at normal load: current, voltage, temperature, errors.

2. Perform control measurements: R phase, inductance, condition of windings and bearings.

3. Check position sensors and their cables; if suspected, temporarily switch to synchronous strategy with the encoder.

4. Evaluate the thermal balance and, if the RMS coefficient is higher than acceptable, reduce current limits or add cooling.

5. If the reason is in the controller (peak switching losses) is to optimize the snubber, the choice of transistors and switching frequency.

6. Introduce temporary default restrictions in the firmware (thermal derating) until the hardware cause is eliminated.

Monitoring and testing after corrections

Start a cycle of stress testing: long driving at a fixed load and monitoring the temperature curve.
Check recovery from heat shock (heating/cooling): no degradation of efficiency or increased current.
Test in real field conditions: acceleration, braking, recovery, reload cycles.

Examples of Common Mistakes and How to Avoid Them

Problem: Proper operation in short cycles, overheating in a long cycle. Solution: Replace passive cooling with active + RMS current restriction.
Problem: Current surges due to incorrect Halls. Solution: check phase synchronization, if possible switch to encoder.
Problem: The controller shuts down during recovery. Solution: configure the recovery profile and battery voltage boundaries, synchronize with BMS.

References to profile materials

Configuring current parameters, recovery and temperature protection in Votol controllers: https://deller.pro/2026/01/nastroyka-votol-toki-rekuperaciya-start-zashchita-temperatury/
FOC and Adaptive Strategies: https://deller.pro/2026/01/foc-upravlenie-edet-myagche/
Motor selection and evaluation (QS Motor): https://deller.pro/2026/01/podbor-elektromotora-qs-motor/

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