Troubleshooting Guide for Overheating and Burn-out of Braking Resistors

Troubleshooting Guide for Overheating and Burn-out of Braking Resistors

It is normal for braking resistors to generate heat during operation; their function is to convert the regenerative energy produced during braking into thermal energy and dissipate it. However, when the temperature rise exceeds the normal range, or faults such as burnout or an open circuit occur, this usually indicates a problem with the selection or usage of the resistor. Most on-site faults are not due to defects in the resistor itself, but rather result from issues with parameter matching, heat dissipation conditions or changes in operating conditions. The following five-step troubleshooting process can help to quickly identify the root cause of the problem.

1. Check whether the power configuration matches the duty cycle

This is the most common cause of failure. Many selection processes are based solely on the resistor’s rated power, whilst neglecting the actual braking duty cycle (ED%). Resistors with the same rated power can handle significantly different levels of continuous power under operating conditions of ED=10% and ED=50%. In applications involving frequent starting and stopping, such as cranes, lifts and servo systems, the braking duty cycle is typically high. If selection is based on the power standards for general industrial applications, the resistor will operate in an overloaded state for prolonged periods, leading to excessive temperature rise, reduced service life and even burnout.

Resistors with different structural designs are suitable for applications with varying duty cycles. Aluminium-cased resistors are encased in an aluminium alloy housing; they feature a large heat dissipation area and a compact design, making them suitable for centralised installation within cabinets. Ceramic-tube resistors utilise a mullite ceramic core, with the resistive wire available in iron-chromium-aluminium, nickel-chromium or constantan alloys. They offer stable temperature resistance and strong resistance to short-term overloads, making them suitable for high-energy, high-duty-cycle braking conditions.

II. Checking whether the resistance settings are appropriate

If the resistance value is too low, the braking current will exceed the permissible rating of the braking unit, which may result in damage to both the resistor and the braking unit; if the resistance value is too high, the braking torque will be insufficient, and the regenerative energy generated during motor deceleration cannot be effectively absorbed, causing the DC bus voltage to remain persistently high and resulting in repeated overvoltage alarms from the inverter. The correct approach is to calculate the minimum permissible resistance value based on the maximum permissible braking current of the braking unit; once determined, the resistance value should not be increased arbitrarily.

3. Verify that the heat dissipation conditions meet the requirements

If a resistor is installed inside an enclosed cabinet, in close proximity to other heating elements, or if its air inlets and outlets are blocked by dust, this will prevent heat from being dissipated effectively, causing the operating temperature to rise significantly. You should check whether there is sufficient ventilation space around the installation site, whether the heat-dissipating surfaces are obstructed, and whether dust on the resistor’s surface needs to be cleaned. Such issues do not usually require the component to be replaced, but if left unaddressed for a prolonged period, they will accelerate the ageing of the resistor.

IV. Derating due to ambient temperature

The rated power of resistors is typically specified based on an ambient temperature of 40 °C. When resistors are installed in high-temperature enclosures, in areas exposed to direct sunlight outdoors, or in close proximity to other high-temperature equipment, the actual permissible power rating must be derated in accordance with the ambient temperature. The higher the ambient temperature, the greater the power margin that must be allowed for during selection. Many overheating faults that frequently occur in summer are caused by a failure to take power derating in high-temperature environments into account.

V. Comparison of Actual Operating Conditions and Selection Parameters

Has the load increased following the equipment retrofit? Has the frequency of start-stop cycles increased? Has a new function for lowering potential energy loads been added? Following changes in operating conditions, the original resistor configuration may no longer be suitable. The actual braking frequency and energy per braking cycle at the site should be compared with the initial selection parameters to determine whether there are any deviations from the operating conditions.

VI. Quality Inspection of the Resistor Body

Having ruled out the above five factors, one should then consider issues relating to the quality of the resistor itself: insufficient temperature rating of the material, loose winding structure, or ageing insulation or moisture ingress. Such faults typically manifest as localised overheating, resistance drift or a deterioration in insulation performance.

Methods for rapid on-site assessment

After switching off the power, touch the surface of the resistor: if it is uniformly warm across the entire surface, this usually indicates a problem with the power configuration or heat dissipation; if a localised area is abnormally hot, or has even discoloured or turned black, this is most often due to a fault in the winding or a poor connection; if there is a burnt smell or smoke near the resistor, shut down the machine immediately for inspection; under no circumstances should you continue to operate it whilst the power is on.

About Jianhong Jitai Braking Resistors

Shenzhen Jianhong Jitai Technology Co., Ltd., established in 2013, is a National High-Tech Enterprise specialising in the research, development and manufacture of high-power resistors and load test equipment.

The company specialises in ceramic tube resistors (power range: 10W–10kW), aluminium-cased resistors (power range: 80W–12kW), resistor boxes and load cabinets; standard products are dispatched within 72 hours.

The product features a mullite ceramic core, with the heating element available in iron-chromium-aluminium, nickel-chromium or constantan alloys. The aluminium alloy casing and corrugated winding structure enhance heat dissipation. Resistance values, power ratings, installation dimensions and protection ratings can be customised to suit the customer’s specific operating conditions. It is widely used in variable-frequency drives, servo systems, lifting equipment, new energy, rail transport and industrial automation.

If you require assistance with selecting and calculating the appropriate braking resistor for your specific application, please do not hesitate to contact us for technical support.