Braking Resistor Overheats After a Cycle-Time Improvement? Count the Energy
A braking resistor can tolerate an individual stop yet overheat when stops become frequent. After a cycle-time change, review repeated braking energy and cooling time. Peak power and average thermal duty are different requirements.
Energy example is simplified; it is not resistor-sizing advice.
What is happening?
Regenerative energy handled by a brake system becomes heat in the resistor when that architecture is used. Selection must satisfy resistance, peak energy, repeated duty, mounting, and protection requirements for the drive and chopper combination.
Check these five things
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Record the approved drive, chopper, resistor, and protection arrangement.
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Compare the old and new cycle frequency and load.
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Estimate braking energy using the validated application model.
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Inspect ventilation and installation conditions through approved procedures.
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Have the responsible engineer verify the complete repeated-duty rating.
Worked example
In a simplified thermal example, 2 kJ per stop every 10 seconds corresponds to 200 W average energy dissipation. The same stop every 2 seconds corresponds to 1000 W. Peak stopping behavior can be unchanged while average heating increases fivefold.
Quick diagnostic reference
| Quantity | Purpose |
|---|---|
| Resistance | Compatible electrical load |
| Energy per stop | Pulse capability |
| Stops per time | Repeated heating |
| Mounting | Heat dissipation |
The mistake to avoid
A larger wattage label alone does not prove compatibility. Never substitute an arbitrary resistance or bypass thermal protection to keep the machine cycling.
How to verify the fix
Verify the engineered combination under its approved repeated duty, including protection behavior and installation clearances. Record the new production cycle in the selection documentation.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
ABB: Drive manual, resistor braking and duty cycle. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.