Choosing Power Wire Wound Resistors and determine Resistor Power :

1. resistor power is calculated by Power W=I²R

2. W = Resistor Power

3. I = maximum loading current

4. R = rated resistance value or maximum resistance of adjustable resistor

5. Do not over load Resistor. Never over loading the resistor beyond the specify voltage, rated power and loading current.

6. For Resistor need to be worked continuously 100% duty cycle, choose Resistor with rated power at least 1.2 to 4 times higher than the actual loaded power. This can extend resistor service life and lower resistor surface temperature. We don't suggest loading resistor more than 80% of the rated power for continuous and long loading time application. Our power resistor can be worked at full load continuously. However resistor surface temperature can be very hot.

7. For maximum / surge power larger than the rated resistor power, please tell the actual working condition like peak / surge voltage, resistance value, duty cycle, loading time and repetition rate.

8. For Surge Voltage application, if loading Voltage larger than the rated Voltage according to resistor rated Power and Resistance value, please tell us the Peak to Peak Voltage range, Duty Cycle, Repetition Rate per unit time or Frequency and loading time.

9. For short period of time overload, resistor can withstand 5~10 times of the Rated Power in 5 seconds, depends on the current pulse width, resistor series and cooling system.

10. For very low ohmic Power Resistor, it is better to tell the working Voltage, Loading Time and Duty Cycle of your application. As different Voltage can induce different resistor current. In turn different raw materials and production process is needed to withstand the generated high current and temperature.

11. Maximum working voltage for a Resistor is limited by Ohm's Law, rated resistance and power, resistor dielectric and insulation.

12. In case of high frequency application, had better choose Low-Inductive Resistor.

13. We can customize Power Resistors according to customer's application need like Resistance, Rated Power, Resistor Size, Mounting Fixture and Inductive / Low Inductive, Pulse Voltage condition etc...

Adjustable Power Wire Wound Resistors DSR-F, Rheostats FVR / Rheostat Boxes FVRB application note :

1. The maximum current to be determined is the current of the existing application before the Adjustable Power Resistor or Rheostat is inserted. This consideration is for Circuit Electrical Current adjustment.

2. When the resistance value is adjusted to the maximum resistance, maximum Resistor Power is occurred.

3. For a normal / uniform Adjustable Wire Wound Resistor and Rheostat, Power is designed by the square of maximum Loading Current times the rated maximum  Resistance value. Power=I²R.

4. The loading current is limited by the resistance wire's current carrying capacity. Loading Current beyond this can damage the adjustable resistor.

5. For Rheostat and Adjustable Power Resistor, when the resistance value is decreased, the workable Rheostat power is also decreased. The workable power at the adjusted resistance value is the ratio of adjusted resistance value to the rated maximum value of the rheostat or adjustable power resistor.

6. The main role of Adjustable Power Wire Wound Resistor DSR-F and Rheostat FVR / Rheostat Box FVRB is to decrease the electrical current in the circuit.

7. Maximum Loading Current capacity for a Rheostat / Adjustable Wire Wound Resistor can be calculated : rated Power = I² x rated Resistance.

8. The above is for continuous adjustable load current or resistance application.

9. For other adjustable load current application, please refer to our Load Bank page.

other Application note :

1. When resistor at full loading, resistor surface temperature can be up to 200C to 500C. This depends on which resistor series. If resistor surface temperature can be kept lower than 150C to 200C, resistor service life can be extended.

2. external force cooling fans or cooling system can lower resistor surface temperature.

3. Keeping all other components apart from Resistor, especially  temperature sensitive component.

4. Do not touch the Resistor surface when it is connected to a power source due to high resistor surface temperature.

5. Below is one of the Derating Curves for Power Resistors, for individual resistor's derating curve, please contact us.

       

6. Clean Resistor Tab Terminals before use. Cannot clean Resistor surface with organic solvents.

7. Do not scratch surface of Resistor with any hard or pointed object.

8. UL 94V-0 class coating, provided Resistors should work within specification and should not be worked near any flammable material.

9. For Silicon Coated Resistors, smoke might be emitted during initial power loading. This is normal and the resistor is safe. It is a normal phenomenon for Silicon Coated Resistor. Assuming the initial loading is 100% for 1-3 hours, afterward there will not have any smoke emission.