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

[keithkyll]

The VFD has single phase input. It makes it's own 3 phase to run the 3 phase motor.
I checked VFD's to see if they make one for 1 phase in / 1 phase out. The only type I saw is for a DC brush motor. It has 4 wires. Two for the Field, and two for the Armature. We use 90 volt DC brush motors for 120 VAC, and 180 volt for 240 VAC.
These are common in low horsepower gearmotor applications, and somewhat expensive.
You are trying to do a class project of something typical in the industry. A 3 phase motor would be best.
You can get low horsepower 3 phase motors. Because you are only doing a demo and not driving anything, you can use a slightly bigger motor with a small controller. No more than a 1 horsepower.

 

[rsdoran]

The real problem here is not whether it is a student or on the job project, what is important is what you are trying to do.

What I suggest is start over, this time explain what the project needs to do, not what you have. In other words why do you need motor speed control? What will the motor be connected to that needs to have speed control?

 

[OZEE]

Good idea!

I've always found that the hardest - yet the single most important - part of any automation project is the definition phase. Once you have your project properly defined, the rest of it is just the mechanics of programming, design, whatever... If you can't adequately explain exactly what you need to do (flow charts, state logic maps, outline, whatever it takes to define it) you really shouldn't continue with the project. Without those definitions, you'll just end up wandering around in circles.

 

[Stationmaster]

I just read most of a thread from 2005 by a student with the handle "crying-baby". His professor wanted him to run an AC motor with the PWM output of a PLC.

Could this be the same professor?

http://www.plctalk.net/qanda/showthread.php?t=13451

Same lack of problem definition, similar language barrier, much effort applied trying to help......thread went 'round and 'round and eventually nowhere.

There are a lot of powerful, brilliant, minds on this forum heading down the exact same path.........

sogoatticus, be honest, have you even read the info at the link posted earlier by rsDoran regarding HOW TO ASK FOR HELP? Really? Honestly?

 

[sogoatticus]

ok..as the title of my project 'Speed contrl of single ph Ac Motor Using PLC'..there is no other description
except it tells the item required..single phase motor, Control pack, and PLC
this means that i cant use 3phase motor..my supervisor ask me to get the washing machine motor..

so i bought the motor like in the picture and get the circuit in the 1st post
from my fren for a clearer view of how its gonna work with the plc..

as i stated im planning to use a 4 switch relay for the plc to control the circuit and make the motor running like 2-3 different speed..
besides i planned to use different resistors for different speed..but u guys told me that cant use the resistors but instead to varies the frequency..
the idea using resistor i got it from here (cant find the link)

i wanted to make it simple as i can easy to understand and explain during presentation..
actually in the 1st post im only asking about the connection from the motor to PLC..(like what wire should i connect to the PLC,or i should use inverter,DC to AC converter)
but other precious info im very thankful which correct my mistakes and knowledge..

so now the problems,
1) what component should i use to make the motor running at 2 or 3 different speed?because im still confused whether the resistors can be used or not..

2) how am i going to connect the motor to PLC?where should i connect the hot,neutral,ground wire to the PLC?as i was told i cant connect the hot wire direct to the plc..but to connect it through relay..

honestly stationmaster, i havent read it all..i just read the earlier part.. i will read through all of it

p/s sorry for my bad english

 

[keithkyll]

Control Pack

Take a look at this. It's a Triac based controller with analog input. If your PLC doesn't have an analog or Pulse output, then use the 3 thermistor inputs. Put different size resistors in place of the thermistors, and switch with digital outputs.

 

[Steve Bailey]

You posted three methods for changing the speed of a single phase motor. Of these, there is only one that can be easily controlled by a PLC. Which do you think it is?

 

[keithkyll]

I just read most of a thread from 2005 by a student with the handle "crying-baby". His professor wanted him to run an AC motor with the PWM output of a PLC.

Could this be the same professor?

http://www.plctalk.net/qanda/showthread.php?t=13451

Same lack of problem definition, similar language barrier, much effort applied trying to help......thread went 'round and 'round and eventually nowhere...

The class was Electrical Engineering. The instructor didn't know much about PLC's, but included it in an assignment anyway. The student asked Engineering type questions on a PLC site. In that case, he needed a microprocessor in the middle. Here, we're trying to figure out what type of Control Module is needed. I think we can get him going, so it won't end up with everyone drinking beer on page 8 (like the other thread).

 

[rsdoran]

You posted three methods for changing the speed of a single phase motor. Of these, there is only one that can be easily controlled by a PLC. Which do you think it is?

Steve I think there are 2 that could be used with a plc, the variable ac transformer (variac) could use an analog controlled actuator to drive the dial.

The multispeed, as I have mentioned, could just use relays.

I have no idea where this will go but it has amazed me it has gone this far.

 

[Steve Bailey]

Ron,

I included the word "easily" for a reason. All three of the methods posted could be controlled by a PLC. The PLC control for one of the three will be significantly simpler than any control scheme for the other two.

 

[rsdoran]

Ron,

I included the word "easily" for a reason. All three of the methods posted could be controlled by a PLC. The PLC control for one of the three will be significantly simpler than any control scheme for the other two.

yep, totally agree.

 

[sogoatticus]

Take a look at this. It's a Triac based controller with analog input. If your PLC doesn't have an analog or Pulse output, then use the 3 thermistor inputs. Put different size resistors in place of the thermistors, and switch with digital outputs.

i will check whether the PLC have an analog or Pulse output

honestly im not sure which one is the easiest n can work using PLC..i guess the tapped winding is the easiest?change the line circuit using PLC?

 

[Stationmaster]

sogoatticus,

If you have (or can get) a tapped winding motor you don't need the Triac based controller, or analog or pulsed output.

Re-read post #14.

Stationmaster

 

[Steve Bailey]

sogoatticus,

The intent of my response was to try to make you think about your application instead of waiting for someone else to do the thinking for you. Look at the three methods for speed change you posted. Two of them involve physical movement of something. One of them involves simple electrical switching. Which sounds easier to accomplish?

Back to the three methods. You can not assume that every single-phase AC motor can have its speed controlled by all three methods. The motor's design will dictate which method can be used. Do not assume that simply controlling the voltage applied to an AC motor will give you control over the motor's speed.

 

[rsdoran]

I thought I mentioned that but just in case I did not.

NOT all single phase ac motors can offer any speed control.

Like I said, explain what needs to be done and the best help that can be obtained will be yours.