start-up power consumption ?

[donkey41]

air conditioner power consumption start up

hello there,

i've heard that if i need to run an Air Conditioner (general purpose room AC) from a generator, i should buy one which can withstand as much as twice the power consumed by the AC .. because when AC starts, it takes about double the power it consumes normally.
for example, if my AC consumes 1.8 kW for normal operation, it would take about 3.4 kW when it just starts-up so therefore i should consider at least 3.5 kVA generator.

is it true ? if yes then why ?

regards.

 

[Kral]

The starting current of an induction motor varies from model to model, but it will be at least 2X the running current. Under normal operating conditions, the motor develops a back emf which opposes the mains voltage. The back emf is due to the motion of the rotor winding through the magnetic field. When the motor starts up, there is no back emf because the rotor is not moving. Under startup conditions, the current is dependent on the winding resistance only.
Regards,
Kral

 

[sunderwood]

If you use a variable speed drive for your air conditionner you can start up slower and avoid the large initial current.
Like Kral said, you get a large starting current because you apply full voltage to an R-L circuit (with low impedance) and no back emf.
If you start by applying a lower voltage then ramp it up, you'll be fine with a smaller generator.

 

[layoutmaster]

but watch out... with the cost of a variable speed drive + small generator probably you can get the bigger generator and, in additon to drive the inicial larger AC current, you'll able to use it for other devices...