3-Phase motor control using a PLC

[Tom Jenkins]

LMAO, Alaric.

I've used a lot of PLCs to run motors, but I never thought of using a motor for running a PLC!

 

[taz3m]

Alaric this os too good a motor with its shaft directly connected to the PLC.. is it to the input or proving a source to the power supply...???
hahaha

Too good man...

 

[wildswing]

Alaric...question about your ingenious design...what happens when the PLC's wiring harness runs out of slack ????

 

[khalil]

Exactly like that. The only thing you'd have to be cautious of is welding and wearing the relay contacts out themselves. PLC relay outputs were never designed to handle inrush or stall currents and aren't build with the safety factors contactors/DOLs are.

unless you use Solid State Relays. !! but I generally use VFDs to control a motor from PLC.

 

[Paulus]

Alaric...question about your ingenious design...what happens when the PLC's wiring harness runs out of slack ????

Reverse the motor???

 

[Jeev]

unless you use Solid State Relays. !! but I generally use VFDs to control a motor from PLC.

I use VFDs in open or closed loop or DOLs where I can get away with it.

 

[Peter Nachtwey]

I wouldn't attempt this with a PLC

http://eu.renesas.com/fmwk.jsp?cnt=...algorithms/&title=AC Motor Control Algorithms

This is just the basics or AC motor control 101. Most people here are not up to the math that is required to implement this. Nor are the PLCs unless you buy a card designed to rotate the phases. Sure you may understand these equations but like I said this is just the simple stuff.

Renesas is a chip manufacturer. Chip manufacturers have excellent application notes. They want people do use their chips in your designs.

TI and Freescale have good application notes too.

 

[Brian123]

This is just the basics or AC motor control 101. Most people here are not up to the math that is required to implement this. Nor are the PLCs unless you buy a card designed to rotate the phases. Sure you may understand these equations but like I said this is just the simple stuff.

I think what Peter is saying is to use one of his controllers. They are much better at motion control than a PLC. Maybe he could even provide a wiring diagram. Peter?

Brian

 

[leitmotif]

Reverse the motor???

Use sliprings to let the PLC spin in place.
OR you can do it at one of the poles of the earth provided PLC turns at same rotational speed (RPM) as earth. Check for proper rotation direction in toilet bowl (hmm does the water spin in the same direction as earth rotation?)) This may however be in utter defiance of Einsteins Theory of Relativity. Some study may be required.

So much for humor. Now pragmatic. Could you run a motor directly off a PLC -- YES
IF the PLC contacts have correct ampacity and dieelectric strength.
Motors (small) can be turned off and on with a simple switch. Larger ones require heavier contacts in olden days ie live front switchboard this was done with knife switches now we use a relay. You would do same with PLC for the same reasons.

Dan Bentler

 

[MASEngr]

I've got a PLC connected to and controlling a 3-phase motor.

PLC -> MODBUS -> VFD -> 3-phase motor

You'd be damned crazy to connect a PLC directly to a 3-phase motor.

 

[MASEngr]

OR you can do it at one of the poles of the earth provided PLC turns at same rotational speed (RPM) as earth. Check for proper rotation direction in toilet bowl (hmm does the water spin in the same direction as earth rotation?)) T

Actually, that's a common misconception. The Coriolis effect doesn't change the direction of water flow. It's really just hydrodynamics.

http://www.badastronomy.com/mad/1996/coriolis.html

 

[Peter Nachtwey]

I think what Peter is saying is to use one of his controllers.

Not yet. Nothing was mentioned about performance requirements. In this case I am assuming the application is simple.

They are much better at motion control than a PLC.

I think it is clear that controlling an AC motor directly is not possible. Our controller can't control an AC motor directly either. A drive is required. Yes, a motion controller is much better than a PLC for motion control but there are simple solutions for simple problems. The key here is that a drive is required.

For simple problems, the best solution would be to directly connect to a drive using Ethernet or device net or some other network.

Our controller gets the call when axes must be synchronized, execute complex motion profiles, or the PLC scan is too slow or not deterministic so our user programs are needed instead. There was no mention of needing anything to demanding.

 

[kbpatton]

I'm at the end of my shift and this pic gave me a good chuckle.

 

[bkottaras]

I'm at the end of my shift and this pic gave me a good chuckle.

This is some awesome stuff.
Question for Alaric though!
If we go with a Control Logix instead of the Compact Logix do we need a bigger motor????

 

[Dua Anjing]

no just a suitable gearbox