Inrush Current Time of Squirral Cage Motor

The inertia of the load affects inrush time.

• If the motor had no load, then it would come up to speed quickly, and the inrush current would start to fall off after only a few cycles.
• If the motor were driving a shaft with a dirty-great-flywheel on it, then the fall-off point could be many tens of cycles away from the energise time.

So, without knowing what the motor is coupled to, it is impossible to say.

ok.. suppose it is connected with load. so tell me how many cycle will it lasts?

Please refer to the final sentence in #1.

Light load. 2 seconds. About a 100 - 120 cycles.

Heavy load. 5 seconds. About 150 - 300 cycles.

What do you mean by: "how many cycle"? Do you mean 50/60 Hz "cycle", or revolutions of the motor shaft "cycle"?

cycles of 50Hz supply...

This isn't going to be easy.

Bye bye.

What, you could not manage to google the answer - yeah I guess that must constitute something not easy.

Bye bye

This is a typical torque-speed curve.

The equation is J*dω/dt= M-Mresistant where ω is the rotational speed, M is the motor torque and M resistant is the resistance the motor has from the load.

As you see the value of M is function of ω and the resistant torque is also function of speed (ω or even ω² as in fans or pumps) and/or angle. This makes an answer quite difficult if no information about the load is available.

In the case of loadless start the whole torque (less internal frictions, very small in modern motors) is used only for acceleration so that the functional zone at the right end of the graph is very soon reached.

As the fellows said before: it takes as long as it takes. You can measure it in your setup.

In the meantime: goodbye.

If the load and motor are not chosen the right way then you can also measure a burned coil! It is better when you can estimate the time before assembly and measurements. But one has to know how to do it and unfortunately not many master it.

why are you concerned with inrush on a motor, I am currently trying to figure the thyristor value on a samsung projection tv, the inrush limiter has a strange number on it, samsuck wants me to by a primary board from them, mouser elect had the bracket value thyristors for .90c a piece so I bought four of different values since the tv is 43 miles away, now I will see if I can measure resistance value of the one that blew the solder from circuit and replace, the tv is friends or I would not be trying to fix, anyhoo the unrush circuit for it is for a reason to bring the cold side up without shock trauma, a squr cage motor does not have this sensativity, I would like to hear from others why this circuit yoyr trying is needed,

Sinc
Mitch ret peugeot mech

1. Post #6 is correct. Like any inductor switched onto an AC supply, a motor stator winding draws a current which depends on the point in the voltage wave at which it is connected.
2. Worst point is zero volts. The fundamental law, back-emf voltage = N x rate of change of flux (N= no. of turns, flux = that coupled with the winding) governs. Back emf = supply voltage less any resistance drops.
3. Doubling of the normal on-load peak flux occurs at 2. - this causes saturation and currents which can be very high because only leakage inductance and resistance limit current. N.B. Leakage inductance is inductance of winding without iron core.
   
4. When there is a remanent magnetization of the core, flux can be more than doubled, because core is even closer to saturation when energized.
5. On a 3 ph motor, there is always one phase which hits a bad point on wave when switched on!
6. Locked rotor and starting currents are a different issue. The starting current duration and shape depends on the load inertia and drive torque at below rated speed.
   

Please look at posts #6 & #14. The factors that affect the time that the magnetising current takes to die down to normal steady state are the damping from resistance and the magnetic core losses. In transformers the transient can be 10s of seconds. Motors are not so bad, because the designed flux densities overall are not so high. The magnetic core losses depend on the hysteresis loop of flux through which the core passes on each cycle. With saturation this is not a fixed value, so it is very difficult to calculate the decay curve and not productive anyhow - since it is different every time the motor is started!