Why Do Motor Controllers Burn Out?

When the controller of a battery vehicle fails, the vehicle stops where it is, and the cost rarely ends with the board itself. The good news: most controller failures come from causes that can be spotted and prevented in advance.

The 7 Most Common Causes

• Insufficient current capacity: running constantly at the limit because of load, ramps or frequent starts wears out the power semiconductors.
• Overheating: mounting that does not sit flat on the cooling surface, an unventilated compartment or high ambient temperature.
• Water and moisture: washing, rain or condensation reaching the board causes short circuits and corrosion.
• Loose or oxidised power connections: poor contact on battery and motor cables heats up, arcs and creates voltage spikes.
• Reverse polarity and wrong wiring: a battery connected backwards, or mismatched motor phases and sensor cables.
• Disconnecting the battery while the motor is turning: braking energy has nowhere to go and the voltage rises.
• Short circuit on the motor or cable side: a motor with burnt windings or a crushed cable can take the controller with it.

Symptoms of a Failing Controller

• The vehicle does not move at all, or locks up with a fault code.
• Jerky starts and intermittent traction.
• Power drops after a while as over-temperature protection kicks in.
• Smell, discolouration or scorching around the controller.

Some of these symptoms can also come from a weak battery or a faulty motor. Before replacing the board, measure the battery voltage under load, tighten the power connections and check the motor windings to avoid unnecessary cost.

How to Protect the Controller

• Size the current class for peak current so the controller does not run at its limit.
• Mount it on a flat metal surface as the manufacturer recommends and keep airflow clear.
• Protect it from water and pressure washing; keep connectors closed.
• Check power cable tightness during periodic maintenance.
• Disconnect the battery with the vehicle stopped, and make sure any emergency disconnect is designed to work with the controller.

Repair or Replace?

A burnt power stage can be repaired, but if the root cause is not fixed the same failure returns. Rather than repairing a controller with no spare parts, no documentation or remote support, moving to a current model means less downtime in the long run. We describe replacing an imported controller with a locally made one in replacing an imported forklift controller.

Protection on NESDrive Drives

Multi-layer protection is standard on the NESDrive TULPAR and BAMSI series. See protection layers in a motor drive for how they work, and mounting and integrating a motor drive for installation tips.