Need help with the circuit of an AC motor and the PLC

[milldrone]

OZEE,

I'm just notifying you that you made it into my collection of PLC programmer quotes. You will recieve full credit for your contribution

 

[Lancie1]

Cohorts and friends,

Let us start over and address the actual problem. I think this is the best description given so far:

3rd- ok2..i admit..i have only a little basic in circuit design and PLC..this is a project i need to do..'Control the single phase A/C motor using PLC'.....as the PLC use DC input...the PLC is in the univ lab..im not sure what brand..but i remembered it uses the syswin software..

My interpretation of this is that only ON/OFf Forward/Reverse CONTROL of a single phase AC motor is needed. Speed control was NOT specified in the above quote, although apparently Sogoatticus thought at first that it was. The Speed Control (or not) question needs answering before any progress can be made.

[NOTE TO OTHER BEGINNER STUDENTS: Please state your homework problem exactly as given by your instructor. Your interpretation of what he "meant" may be exactly wrong! Why try to disquise your homework questions? Honesty is the best policy. If you are not honest as a student, then I don't want you graduating and joining the workforce. I see enough dishonest workers already.]

Sogoatticus also stated that he is using a 240 volt "washing machine motor". It has been my experience that most washing machine motors in the US are single speed, 120 volts, with Forward and Reverse terminals, but I suppose in Malaysia they are 240 volts and could also be multi-speed.

The problem as defined now:

1. Control a single phase AC motor using a PLC. We can assume that it is an Omron PLC with 24 VDC Inputs and Outputs. The Omron SYSWIN software is available in the school lab.

2. Use an existing 240 volt Forward/Reverse single phase washing machine motor as the motor to be controlled (assume 1/3 Horsepower, he read off the voltage but forgot the more important Kilowatt and Full Load Amp ratings).

3. Keith has the best advice so far: "Do not connect hot directly to the PLC. Connect a 24DC supply to the PLC to run the relay. Connect the hot to the relay."

Questions based on the problem definition:
A. What is the sensor in your drawing? Are you still using the sensor? Is it a RPM sensor? Is the sensor ouptut an analog signal? Does your PLC have the necessary input to accept the sensor signal? (With your description so far, you can only start, stop, and reverse the motor, not control its speed.) To control speed, you need some type of analog or PWM output.

 

[leitmotif]

1st of all thanks for all the information..
2nd-to Stationmaster i cant see the twin tower from my window..i need to get outside of my house to get the view.

3rd- ok2..i admit..i have only a little basic in circuit design and PLC..this is a project i need to do..'Control the single phas A/C motor using PLC'..the circuit i uploaded is my frens circuit for conveyer belt..its not for speed control but direction control..
i roughly design a circuit but the circuit is kinda for Dc circuit like in the picture..as i stated im also using relay..
im not sure which wire (hot,neutral,ground) to connect to the plc..
for the motor im using 240vac(stated on the motor) which is a washing machine motor..
the PLC is in the univ lab..im not sure what brand..but i remembered it uses the syswin software..

maybe im asking too much here..but please dont scold me bcoz im a noob..i can back off from the forum and close this topic if neccessary..

As a student who received lots of good knowledge here let me tell you how to get them to help you.
1. IDEALLY take a photo of the motor and another of the name plate and post here. If you cannot do that then tell us ALL of the names and numbers on the motor.
2. Do the same as in #1 for the PLC.
3. Tell us what the motor is going to do. What do you want to make work by driving it with a motor (air compressor, washing machine, etc etc) Even if it is just go around or start stop reverse run etc etc in class that is fine.

That will get you started.
Now if you have the PLC -- READ THE MANUAL.
Come back here and state on page so and so I read thus n such and I do not understand.

These guys will not do the work for you (I will -- send $100.00 to get my interest). If they see you making an attempt they will help.

Dan Bentler

 

[rsdoran]

His flag is Malaysia and their power is 240vac http://www.kropla.com/electric2.htm

Seriously take a look at this: http://catb.org/~esr/faqs/smart-questions.html

As mentioned there are differences with washing machine motors so may need to offer details on EXACTLY what you need to do or as I said before, state all the details as concisely and precisely as you can.

STOP, take a deep breath, and do not get to excited about any responses. Take your time and use Word or something to write out the project in detail, this way it will not get lost, then copy/paste it as a reply.

Once we know the specific details then a simple answer may be offered. In the meantime there is information that may help http://www.patchn.com just look around. More can and will be provided when enough information has been provided.

 

[Stationmaster]

OZEE,

I hope the "fire extinquisher" comes with better instructions than we've been given by the op re this "project".
(good one)

Stationmaster

 

[sogoatticus]

Cohorts and friends,

Let us start over and address the actual problem. I think this is the best description given so far:My interpretation of this is that only ON/OFf Forward/Reverse CONTROL of a single phase AC motor is needed. Speed control was NOT specified in the above quote, although apparently Sogoatticus thought at first that it was. The Speed Control (or not) question needs answering before any progress can be made.

im sorry but there is a minor correction bout the topic..i mistype the topic..the actual is Control Speed of a single phase AC Motor using PLC..im trying to do it on my own for the speed control..planning to use several resistors for variable current..but my main problem is to connect the AC motor circuit to the PLC..i tried google but found many complex circuit which i hardly understand..

the sensor in the pic can be ignored as i will use the tachometer for the rpm detection..the pic is for conveyer belt which is frens project.thats y there is a sensor..my mistake making the pic as a distraction..
i will upload the motor details and the PLC by tomorrow (monday)..
the main thing that i need to do is to control the motor speed,start/stop using the PLC n not manually..the direction is only the additional features..my supervisor didnt want to help me at all as i need to find the info by myself..

 

[keithkyll]

You can not control the speed of an AC motor with resistors. To change the speed, you need to change the frequency.
I will say it again! You need a Variable Frequency Drive. VFD. That is how it is done in industry. Everyone uses VFD's.
The PLC controls the VFD. The VFD controls the motor.
Study (Google) VFD's first, then you will understand everything else.

 

[Stationmaster]

You cannot "CONTROL" the speed of an a/c motor with resistors. You cannot connect your motor directly to a PLC. You must have "many complex circuit which (you) hardly understand."

The best that you could hope for is to "SELECT" a speed of an A/C motor. Is that what you are trying to say?

Try modelling your plan after a "ceiling fan" speed select circuit. The motor can be made to run at different speeds for a demonstration but it will not run a conveyor belt in an industrial application.

You still cannot connect your motor directly to the PLC.

Try connecting L1 and L2 directly to your "supervisor". The problem will go away.

 

[rsdoran]

I have never seen a single phase AC motor using a VFD in an industrial plant myself. I know there was a thread once on using one but for an industrial environment it would make more sense just to obtain a 3ph motor.

I have no idea what he means about using resistors for speed control, never seen that either but a variac or triac could be used in some cases and it not be that complicated.

I would wait and see if he provides the motor information, including wiring to see if it is a multspeed motor, then it could be as simple as using a few relays.

Current does not control speed of an AC motor, it will control/limit the work (torque) it is capable of doing.

There are variable speed gearboxes but it would probably be cheaper to obtain a 3ph motor and use a VFD.

sogoatticus, if you are not familiar with VFD's then read this:
http://www.patchn.com/mtrwhtpaper.htm

http://www.patchn.com/what_is_a_drive.html

 

[sogoatticus]

so now i will get the VFD for controlling the motor..i guess my supervisor didnot know that AC motor speed cant
be controll using resistors bcoz i showed him my draft circuit and he said it was ok..maybe that time he thought
im using a Dc motor..may i know how much does VFD cost in the market?

The best that you could hope for is to "SELECT" a speed of an A/C motor. Is that what you are trying to say?

sori i dont understand this part

at the motor stated
240V 50Hz
wires = blue(neutral), white(hot), green(ground)
the other 2 (yellow,blue) is also hot wire which connect to the capacitor(black box) if im not mistaken
it will change the speed if i change these wires. inside the switch box i saw a small circuit..i think
its a rheostat for speed adjust as well

PLC in the lab is Omron Sysmac CQM1-CPU21 Programmable Logic Controller

 

[rsdoran]

If that box has a potentiometer on it then it probably has a triac ckt involved: http://www.geocities.com/budb3/arts/eltron/motcntrl.html

Trying to do something like this in conjunction with a plc could get complicated if not knowledgeable of working with electronics.

You could probably get a .25HP and single phase in 3 phase out drive for about $3-400 US, maybe less, just depends. This would be the easiest way to use an AC motor with and control speed.

Or you could change the motor to a DC unit and control the speed using resistors etc.

 

[Stationmaster]

You could use a small dc motor controlled by a corrected version of your (friends) original "reversable" shematic to mechanically turn the knob on the speed control box in the photo. If turning the knob by hand will "control" the motor speed then turning the knob with a dc motor should have the same result.

 

[sogoatticus]

If that box has a potentiometer on it then it probably has a triac ckt involved: http://www.geocities.com/budb3/arts/eltron/motcntrl.html

Trying to do something like this in conjunction with a plc could get complicated if not knowledgeable of working with electronics.

You could probably get a .25HP and single phase in 3 phase out drive for about $3-400 US, maybe less, just depends. This would be the easiest way to use an AC motor with and control speed.

Or you could change the motor to a DC unit and control the speed using resistors etc.

i wont need the switch box as i will cut it off later and take the motor and wires only..the shop sell to me 1 set with the plug and switch..i will only take the motor for the project

 

[keithkyll]

I was wrong, Ron (rsdoran) is correct. The motor must be 3 phase for a VFD. That one won't work. You can get a VFD for $99.00. This one will work for 230 volt, 50 Hertz. There are many brands available - check your local area.
With this controller, you need an analog output on your PLC.
Take that motor back to the surplus dealer, and tell him you need a 3 phase with a VFD.
Anyone: Does his PLC have an analog output or option?

 

[sogoatticus]

I was wrong, Ron (rsdoran) is correct. The motor must be 3 phase for a VFD. That one won't work. You can get a VFD for $99.00. This one will work for 230 volt, 50 Hertz. There are many brands available - check your local area.
With this controller, you need an analog output on your PLC.
Take that motor back to the surplus dealer, and tell him you need a 3 phase with a VFD.
Anyone: Does his PLC have an analog output or option?

my project is using a single phase..cant use 3 phase ..if i cant use VFD for single phase..does that means i need to use other methods?i dont think i can use DC motor to manually control the knob as i will not achieve the main purpose of the project