How to calculate potentiometer needs

Written by jonah quant
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How to calculate potentiometer needs
You can calculate the power rating required for a potentiometer in a circuit. (Jupiterimages/ Images)

A potentiometer is a voltage divider with variable resistance depending on the physical position of a moving contact over a bar of resistive material. Potentiometers are manufactured in both rotational and linear variants. A common use of potentiometers is as knobs controlling analogue circuits, such as volume controls in audio systems. Manufacturers rate potentiometers with the maximum resistance in the voltage divider and the maximum electrical current that can flow through them. You can calculate the minimum power a potentiometer must be able to handle to work in a particular circuit.

Skill level:

Things you need

  • Diagram of the circuit where the potentiometer will be used

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  1. 1

    Calculate V_end_to_end (the maximum voltage that your circuit applies to the non-moving ends of the potentiometer) and V_moving_contact (the maximum voltage in your circuit at the moving contact.) The precise way of performing these calculations depends on the circuit in question.

  2. 2

    Calculate I_end_to_end, the maximum current that flows between the non-moving ends of the potentiometer, by evaluating the following formula:

    I_end_to_end = V_end_to_end / R

    Replace R with the resistance of the potentiometer.

  3. 3

    Calculate W_end_to_end, the maximum end-to-end power the potentiometer will dissipate (measured in Watts), by evaluating the following formula:

    W_end_to_end = I_end_to_end x V_end_to_end

  4. 4

    Calculate W_moving_contact, the maximum power the potentiometer will dissipate at the moving contact (measured in Watts), by evaluating the following formula:

    W_moving_contact = V_max_moving_contact x I_end_to_end / 1.5

    The correction factor of 150% accounts for the fact that heat dissipation is more efficient at the current location of the moving element because, on the average, heat is conducted on two directions away from the moving element and along the bar of resistive material.

  5. 5

    The minimum power rating required for the potentiometer in that particular circuit is

    W_potentiometer = max{W_end_to_end, W_moving_contact}

    That is, you must use a potentiometer with a manufacturer rating of at least W_potentiometer Watts and R Ohms.

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