Why cant the current from the socket turn on the air conditioner but the current in capacitor to turn it on ?
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The power to start a motor turning is dramatically more than the power to keep it turning. The capacitor stores power allowing that initial surge to be satisfied without overloading the circuit.
The breaker on your AC would trip each time the compressor starts without it.
The power to start a motor turning is dramatically more than the power to keep it turning. The capacitor stores power allowing that initial surge to be satisfied without overloading the circuit.
The breaker on your AC would trip each time the compressor starts without it.
Ever tried pushing something really heavy and needed some help to get it moving, but once it’s moving you can.manage yourself?
It takes more force to start motion than to keep something in motion, because friction is lower once it’s moving. Starting up a motor or an AC unit is the same. You need an extra kick to get the motor going. It’s also the reason that vacuum cleaners need a higher rated fuse. When they’re running, it doesn’t need to be that big. But when you switch them on, there’s a surge. So, AC units use a capacitor to store up an extra bit of charge so you can get that initial kick.
The reason for the difference in friction is going to need a bit of imagination. Friction happens because when you zoom in enough, surfaces are rough. Imagine it as being like a landscape of tiny pointed mountains. When two things are sitting on top of each other, the mountains on one find a way to lock together with the valleys of the other. To get the surfaces sliding past each other, you need to separate the mountains and valleys. But when the surfaces are already moving, it’s like the peaks slide past each other. Stop, and they can lock together again.
Electric motors are interesting in that they draw more current the slower they are turning. A motor that draws 5 amps at top speed might draw 30 amps when it is not spinning. Contrary to some other responses, it it not due to static friction, but to an effect called back emf.
Electric motors spin by putting electric current through loops of wire creating electromagnets. Through clever wiring connections, the poles of those magnets shift as the motor spins allowing for continuous rotating forces. But it turns out that the universe fights changes in magnetic fields, and the faster the motor spins the more quickly the magnetic field changes. The way that the universe fights the changing magnetic field is by producing electric voltage (this is how generators work) in the opposite direction of the applied voltage. This reversed voltage is called back electromotive force or back emf. A motor’s top speed is set by when the back emf counteracts the applied voltage. Back emf acts like a resistor, limiting the amount of current in a circuit. If the current is low, then thin wires can safely be used without overheating.
When a motor first starts up, as the motor isn’t spinning yet, there isn’t any back emf yet, therefore the effective resistance in the motor is very small, and a huge current flows through the motor. This surge only lasts until the motor is up to speed, but can be enough to blow a standard household circuit breaker. A capacitor will store energy and then give it to the motor during startup to avoid pulling excessive current from the household circuit. Once the motor is spinning, the household circuit can safely handle the load.
The current isn’t there to support a slug of current like DC capacitors are, it’s there for a phase shift
Your air conditioner is fed by AC power which wiggles up and down. If you put a capacitor in series in AC power it shifts the timing of the wiggles so the output of the cap is some amount of the wiggle width off from the source
AC motors have windings/coils that we feed this wiggly power into. Really big 3-phase motors take 3 slightly offset wiggles which let them generate lots of torque from the start.
You only have a single wiggle phase in your home so we use the starting capacitor to generate a second phase and feed a second winding to give the motor an extra kick to help it get up to speed where the single phase can easily support ot
Unlike DC motor that uses a + and – pole an AC motor doesn’t have that so the capacitor is there so for a small second it reflects the voltage to go backwards in order to spin the motor (this is a starting capacitor) without it your appliance wouldn’t turn ON.
But once ON you would no longer need the capacitor. If a fan has been ON for a long period of time and you turn it OFF and then tried turning it ON again (after a while) and it doesn’t work. The capacitor is your faulty part.
They use induction motors, and require either 1 or 3 phase power. The phases generate a magnetic field that makes the rotor spin.
With 3 phase there’s a spinning magnetic field generated that can start from a standstill (even though it’s still hard)
With 1 phase you instead have a pulsing magnetic field, and is not rotating. The motor needs 2 phases to start itself (otheewise it could start both ways). It uses a capacitor to “cheat” a second phase into existance that can start itself (still not easy)
More precise reason from here:
The pulsing magnetic field from one phase can thought of as 2 spinning fields, a clockwise spinning one, and a counterclockwise one. The effect of the pulsing field is the same as the combined effect of the 2 spinning ones.
If the armature is spinning “with” a magnetic field it’s torque increases (to a point), so if you have a clockwise spinning rotor, then the clockwise “imaginary” field has a stronger effect than the counterclockwise, and it keep spinning that way.
With a standstill motor, both fields’ effects are the same strength, so they can’t overpower eachother. You need something to get it to spin (even you bumping it works)
The start capacitor does exactly that. It creates a second weaker phase that makes one of the directions stronger, and it starts spinning. Once it started, there’s no more need for it
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