Power Derating Calculator
Every resistor datasheet publishes a derating curve — 100 % rated power up to some reference temperature, then a linear ramp down to zero at the maximum element temperature. This calculator applies that curve to your real ambient, then adds an extra 20 % safety margin for end-of-life drift, mounting variance and worst-case airflow.
Inputs
Calculated values
- Derating factor
- 87.5 %
- Effective deliverable power
- 87.5 W
- Recommended max load (with 20 % safety margin)
- 70.0 W
- k(T) = (T_max − T) / (T_max − T_ref) for T_ref < T < T_max
- P_actual = P_nameplate × k(T)
- P_recommended = P_actual × 0.80
Aluminum-housed power resistors (5 W – 1500 W) with documented derating curves
View aluminum-housed rangeThis calculator provides preliminary sizing only. Always validate with the drive manufacturer's worksheet and prototype testing.
How to use this calculator
- Enter the resistor's nameplate power in watts.
- Set the reference temperature from the datasheet — 25 °C is common for metal-film, 70 °C for aluminum-housed power resistors.
- Enter the actual ambient temperature inside the enclosure (not room ambient).
- Set the element's maximum operating temperature — datasheet value, typically 275 °C for cement and 350 °C for wirewound.
- Read the effective deliverable power and compare against your circuit's worst-case dissipation.
- If the worst-case dissipation exceeds the recommended-with-margin value, upsize the resistor or improve cooling.
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Wirewound Resistors
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Cement Resistors
Cost-effective power-sampling and current-limiting resistors with vertical / horizontal mounting
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Standard samples are provided free of charge in reasonable quantities (shipped within 2–3 business days). Custom samples are delivered within 2–4 weeks. Please use the form on the right to tell us:
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- Target part number or key specs (power / resistance / package)
- Application scenario and estimated annual volume
- Shipping address and expected delivery date