Help About Magnetic Contactor For Thesis

1. how to determine the value of a current to drive the coil of an ac magnetic contactor.

Once the size of the contactor is decided, the value of the current is already generally known. If you have studied the web, you will know that all manufacturers give pick-up VA and sealed VA values. The former being of the order of 10 times the latter for AC coils.

2. when the switch is triggered (cuz of the coil) is there a current flow in the switch side of the contactor? if so, then what is the value?

Of course, this is the raison-de-etre of the contactor for God's sake ! The main current depends on what the load is. Which is usually a motor. Which is usually started DOL. Therefore the main current is 6-8 times the rated FLA of the motor.

3. from my other research, why theres a need to connect a relay driver before the magnetic controller? whats the use of that relay driver? (the diagram is MCU--->relay driver--->magnetic contactor---> circuit (output)

Large contactors have high inrush (pickup) VA. If you try to switch a large contactor by a pushbutton, it will probably weld and get detroyed. So you use an interposing relay, usually called a "Slave relay"

For lots of good stuff, download and study this paper from Eaton :

http://www1.eatonelectrical.com/101s/Module19/shell.htm

and whats with the huhu ? Crying ?

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1. how to determine the value of a current to drive the coil of an ac magnetic contactor.

Once the size of the contactor is decided, the value of the current is already generally known. If you have studied the web, you will know that all manufacturers give pick-up VA and sealed VA values. The former being of the order of 10 times the latter for AC coils."

Perhaps I can shed a little more light on this part. The contactor current carrying capacity determines the size of the contacts, which then also determines the weight and mass of the armature components that make up the electromagnet. The electromagnet coil must provide the necessary force to move the armature, plus it must provide sufficient holding force for the contacts. This is because, once the current starts to flow through the main contacts, magnetic fields around the current carrying components (the stationary and movable contacts) oppose each other and attempt to force the contacts open again.* So the electromagnetic force must be able to hold the contacts closed under that force. The more current flowing through the contactor, the more force the coil must exert. The more force you want from the coil, the more current it will need to draw.

*Some contactor designs rely only on springs to force the contacts open, but without the aid of the electromagnetic field force, the springs must be stronger so the next effect is virtually the same as to the amount of force the magnet must exert to overcome it and hold the contacts closed.

Oh yeah, and DO YOUR OWN HOMEWORK!

I only added to the answer because I thought it might be useful for others who maybe did not fully know the whys and hows of contactor design.

3. from my other research, why theres a need to connect a relay driver before the magnetic controller? whats the use of that relay driver?

its because of the microcontroller MCU's output is a DC voltage approx 0-5V..

can you explain sir why they use the relay diver connected to the contactors..or wats the use of the relay-driver really..

tnx sir..

One can design a coil of 5V for example, for some small power contactor. Current will be proportionately high... VA ÷ 5. Sometimes not practicable at all.

The power consumption (VA) is the main reason. The output contacts of a PLC, for example, cannot handle the power of a contactor coil .... except for small contactors. So the necessity of the interposing relay.

Are you the OP (original poster)?