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# Reversing a 3 phase asynchronous motor using limit switches

#1
03-17-13, 08:45 AM
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Reversing a 3 phase asynchronous motor using limit switches

Does anyone know how to reverse direction of rotation of 3 phase asynchronous motor using limit switches

#2
03-17-13, 08:52 AM
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With three phase motors, you only need to reverse two legs of the three phase to change direction of the motor. Hope this helps.

#3
03-17-13, 09:15 AM
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In your diagram, the left hand illustration shows a motor reversing method using two contactors.

The right hand drawing (can't see detail) may be a way to activate the contactors but it looks like you can activate both contactors at once which would be a major problem.

Normally limit switches are interlocked.
Not all motors can be instantly reversed by a limit or end switch.

What is this going to be used for ?

#4
03-20-13, 10:35 AM
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So can someone explain to me how this works??

#5
03-20-13, 10:41 AM
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With three phase motors, you only need to reverse two legs of the three phase to change direction of the motor
Tolyn posted that in a previous post.

That's how to reverse a three phase motor.

Now..... is that what you were asking or are you referring to your diagram ? That diagram is very hard to read. I can't expand it. Do you have a link to it somewhere ?

That circuit is pretty basic....... what does it control ?

#6
03-20-13, 11:06 AM
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Maybe this is better.So i don't understand when is limit switch s4 in use and when s6 and what is with s1 s2 and s3 - what they do.Any kind of help is welcome

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#7
03-20-13, 11:22 AM
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Yes.....that is better. The reason for so many switches is that are control switches mounted to the contactors. One switch latches the contactor on so you don't have to hold the button. Another switch locks out the opposite contactor so that you can't push both switches at once.

I'll explain better when I return later.

#8
03-20-13, 11:32 AM
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Thanks for fast answering.I found this in my book but I don't have any scheme for this but maybe you could help me.It can be simple.I would be very grateful:

You need some device that remembers which switch was hit last. This
could be something as simple as a relay with extra sets of contacts.
If you want the motor to cycle continuously, you need at least a 3
pole double throw relay. Two of the contact sets connect the motor to
the power source so that the motor runs one way with the relay
energized, and the other way with the relay de-energized. Connect
supply + to the normally open contact on one set, and the normally
closed on the second. Connect supply - to the reverse normally on and
normally closed contacts of those two sets. Connect the motor between
those two commons.

Now, you need one limit switch to turn the relay on and one to turn it
off, and the relay using one of its contacts to remember which was
last.

The limit switch that turns the relay on must be normally open and
supply power to the coil. A third normally open contact parallels
this so the relay can keep itself energized after a pulse from this
switch.

The other switch has to be normally closed and is in series with the
above circuit. When it is bumped, it de-energized the coil, which
opens the contact that had been remembering that the relay was on.
Remembering to stay off takes no contacts.

#9
03-20-13, 11:58 AM
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So that I can think more about this and come back with an appropriate answer...... is this a classroom project..... an idea that needs to be illustrated
OR
Is this for an actual real life application ?

A real life application for the circuit you have posted could be a motorized video projector screen or a motorized door.... like in a garage.

#10
03-20-13, 12:34 PM
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I don't know how to say this in english but I can say this can be motor for garage door and ill I need is schema for previous post

#11
03-21-13, 12:35 AM
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The modified illustration shows everything labeled.
I'll post the actual instructional text later today.

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