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detect zero current of motor ac in order to switch the output of microcotroller pic16

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maryem

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I am doing a project controlling an asynchronous motor 230V / 6Amax with triac which is controlled by a microtrolleur, now I want to add to the circuit a part to detect the zero-current in motor side caused by the presence of Limit switch and inject the result to the microcontroller, can I use the gold shunt resistors or it is mandatory to use a hall effect sensor witch i find them more expensive . i don' have much idea in this type of circuit can someone help please thanks
 

MaxHeadRoom78

Well-Known Member
You can use a slot opto with a 2/rev slotted disc which is essentially zero rpm = zero current.
An alternative is a D.P. L.S. and use the other contact to detect the L.S. tripped, which is the easiest.
Max.
 

dr pepper

Well-Known Member
Most Helpful Member
Ok if I got this right.
The micro fires a triac and drives a motor, the limit switch is inline with the motor windings nothing else, you want to know if the supply to the motor is interrupted by the switch.
If the switch has a spare contact, or you can fit one in place of it that does just use it to feedback to the micro, if you cant arrange this then use a relay with the same coil voltage as the motor and use one of its contacts to feed back to the micro, if a relay isnt fancy enough then you could use an opto isolator.
 

MaxHeadRoom78

Well-Known Member
An alternative is a D.P. L.S. and use the other contact to detect the L.S. tripped, which is the easiest.
Max.
Also if a simple S.P. Micro switch, a duplicate can be added on the same mounting and use the same striker to activate.
Max.
 
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maryem

Member
i need just to switch the output of microcontroller when the motor reach the limit switch when the windws is closed
 

MaxHeadRoom78

Well-Known Member
Double Pole Limit Switch, they are a bit rarer than single pole so two can be mated up to use the same striker..
Max.
 

Tony Stewart

Well-Known Member
Most Helpful Member
We have no idea about your electro-mechanical requirements.
except there is a uC , 230V 6A motor, a window and a limit switch.

Normally when someone has no idea, we try to get them list all the requirements relevant to the problem.
Inputs, Ouputs, process, resources, protection

There are current transformers used for AC detection and protection , Hall sensors and active current sensors used in cars.

But we have no idea on start surge current = "locked rotor current" and this will be the same for an abrupt start or stop except the duration, which depends on mass for starting and stop for trip period etc.
 

Les Jones

Well-Known Member
Most Helpful Member
Yet another possible solution would be to use a very small mains transformer with the primary connected in parallel with the motor. Although this is sensing the voltage across the motor (Rather than the current trough it as you initially asked.) it would achieve the same result without the concern over the value of the starting current. The low voltage from the transformer would be rectified, smoothed and limited with a zener diode before connecting to the microproccesor. You can find suitable transformers in old clock radios etc. This is just a variation on the methods of using a relay or optical coupler suggested by "dr pepper". Why don't you just connect the microcontroller to the micro switch and program the microcontroller to remove the drive to the triac when the limit is reached ?

Les.
 
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