Magnetic motor contractor with motor overload - help

backendcode said:

Hello Guys,

I am working on my first real world project to control the conveyor system. The control panel has PLC, terminal block for the proximity sensor and motor contactor with motor overload and of course other components of control panel such as power supply, transformer etc and I don't think as a PLC programmer I need to care more about those components. It's nice to think that those "other components" don't matter to you as a programmer, but you will learn that they are indeed very important to you.

Question: As a PLC programmer, What factors I need to consider about contractors and motor overload
It is really as simple as how and when to pull the starter in, and how and when to release it.

Here is info about my contractors:-

MOTOR CONTACTOR 10AMPS 24VDC LOW CONSUMPTION COIL 1NO AUXILIARY CONTACT

Here is the info about my motor overload

OVERLOAD RELAY 0.8-1.2A 1NO AND 1NC AUXILIARY CONTACT

The control panel drawing also shows there is feedback going to PLC input card for each motor run and motor overload. Am I going to use the status of those input addresses to find the fault in motor and motor overload and turn on the fault indicator light and stop the light until someone will reset the fault I guess?
I would guess so too, but that is really up to the customer as to what sort of feedback and status signals they require.

What is the purpose of this feedback going to PLC input card and what is the purpose of contractors auxiliary contact (Which is normally open) and auxiliary contact of motor overload(1 NO, 1NC)
The purpose of the aux contact on the starter would be so the end user would, through your code, know if the motor is running without having to actually go look at the motor. This same input could be used for the purpose of giving an alarm if the motor is supposed to be running, but isn't.
The contacts on the overloads would serve the same purpose as those on the starter, but give information only about the status of the overloads.

Please help me to understand the purpose of this information provided?
The information was likely provided to give you an idea of what the customer would like in terms of feedback from the starter and the overloads when the project is finished.
I know you want to concentrate on the program, but you might want to get a better handle on the overall scope of the project before writing too much code.

Thank you!

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BobB said:

I have always had an issue with wizz bang programmers that have been to school and have no idea of how a process works to be honest.
I also see designers of critical systems who do not even monitor and alarm critical circuit breakers for example.
24VDC circuit breaker turned off or tripped in a generator system that supplies the trip coils? Ain't gonna work!
Never mind - GOB? (Grumpy old *******).
Most are not taught properly these days and it is better to try and turn hindsight into foresight wherever possible.

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BobB said:

PLC programmers should know and understand the operations of all components in the system as they ALL can have an effect on the program. I am a controls sparkie first and foremost - I built switch boards, commissioned them, designed old fashioned control circuits when there was no such thing as a PLC, tested, commissioned, lots of service work - broken down machine and no drawing.
Got into PLCs when I had to sell them!
I would suggest you show us what you have done and then you may get back some comments.
No one is going to do your work for you without getting paid lots of $$$$$.

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ThatGuy17 said:

Knowing what you are controlling in the field is critical. It will help with understanding what signals you need to send and are receiving, especially when fault finding an installation.

I am relatively new to PLC programming but have been an industrial electrician in manufacturing plants and chemical storage facilities. knowing what to expect from devices at each point of the process has been a huge help to me.

My advice would be to sit down in front of a cabinet with some drawings and figure out what you are looking at and how it works electrically.

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keithkyll said:

It's a contactor, not contractor.
On the overload, the NC is wired in series with coil. It prevents operation of the contactor when tripped.

You have two choices for status signals to the PLC. You can use either or both.
The NO contact on the overload can be used to signal the PLC that the overload is tripped.
The NO aux contact is used to indicate status of the contactor. When you energize it, you look for feedback from the aux contact to tell you it really did energize.

Wiring:
PLC output to overload NC contact. Other side to coil +.
24DC to contactor aux. Other side to PLC input. Signal is "Motor is Running".
24DC to Overload NO contact. Other end to PLC input. Signal is "Motor Overload is Tripped". You don't necessarily need this. When you turn on the PLC output to the coil, if it doesn't pull in then you can assume that the overload is tripped.

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willxfmr said:

Bubba.

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backendcode said:

willxfm,

Thank you for pointing out my each question and It was clear and helpfull!

please look at my PLC code I posted in this thread!

Thank you again

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