For example, I have an air conditioner. How to know if such a device has a variable load or not ?

NOTE: Air conditioner is just an example. My question is in general how to know ?

  • \$\begingroup\$ is variable load or has variable resistor?? They are usually high surge then ON/OFF \$\endgroup\$ Commented Dec 13, 2019 at 23:52
  • \$\begingroup\$ @TonyStewartSunnyskyguyEE75 variable load \$\endgroup\$
    – Ali
    Commented Dec 13, 2019 at 23:58

2 Answers 2


How to know if the load is variable one?

Think about how the device works. Does it have a heating element? Does it have motors? Does it have controls that would change its operating setpoints?

Some examples:

  • Heaters (room heaters, hobs, ovens, etc.) are usually switched fully on or off by thermostat or timer control and rely on the thermal inertia of the heater and matter being heated to even out the surges of power. See Setting heat on electric stove for details. Is it variable? Yes. The average power consumed varies with the setting or the room temperature. On the other hand you could argue "No", the power consumed while on is always the same.
  • Your air conditioner will have a fan and a heat pump. The fan commonly has a three-speed control (so that's variable) but the heat pump may be fixed speed and just cuts in and out as required (so that's fixed power but intermittent).
  • Your food mixer has an adjustable speed control so that's obviously variable.
  • Any audio amplifier's power consumption will increase with volume.
  • Any motors' power consumption will increase with speed and with load.

One way to know if an appliance is a variable load on the electrical system is to monitor the current or power used or drawn from the source by the load. Another way is to observe the operation and see, hear or feel how it behaving.

Most loads vary by either turning on and off during use or through a manual or automatic change in motor speed or heat production during use.


Not the answer you're looking for? Browse other questions tagged or ask your own question.