Dc motor controller(forward reverse)

**ppcandieq** · 11th November 2009 03:10 AM

Hi all..

need some advice..now,i'm doing a project using PLC..i've to control 4 power window motor using PLC as a controller..I have problem with how to make a forward reverse circuit using relay 24V without a switch coz output from PLC act as a switch..need some advice how to design the controller circuit coz relay is 24v(output from PLC) but power window motor only 12V..i just need forward reverse controller n relay contact wiring(12v) to power window motor..

Plz help me..
Next monday is my presentation..

Thanks...

**Boncuk** · 11th November 2009 03:34 AM

Hi ppcandieq,

use an L298 (ST-semiconductor dual full bridge). It works up to 46V with an output of 4A.

You must have three output signals from the PLC, two for direction and one to enable/disable the outputs for braking.

Here is the functional table.

Boncuk

**tcmtech** · 11th November 2009 03:47 AM

You could just use two outputs per motor to drive two SPDT relays so that when both are off the motor is off and when each is activated they either tell it to go forward or reverse.

**ppcandieq** · 11th November 2009 05:46 AM

Hi Boncuk,

I dun understand bout ur suggestion..can u help me give the detail information???

tcmtech,

can u explain me the detail of your suggestion??

**Boncuk** · 11th November 2009 06:29 AM

Hi ppcandieq,

I also don't understand how a PLC can output 24V. PLC are logic devices operating at 5 respectively 3.3V.

To control a motor the supply voltage of the PLC has no effect on the motor drive circuit which must accept logic level control though.

You can either use relays via transistors to be connected to the I/O pins of the PLC or use a full H-bridge.

Relays get annoying when used frequently because of their clicking noise. An H-bridge does the switching (silently) using internal power MosFet transistors.

Using relays or an H-bridge you must take care that both outputs have the same level to stop the motor and reverse direction after it has come to a full stop.

Otherwise you might burn up the relays and/or the motor.

Boncuk

**ppcandieq** · 12th November 2009 03:41 AM

hi boncuk..

from the output of PLC,it use to ON the relay..
n as i know,power window motor is 12V right?
So,i use the 12V power supply to the contacter of the relay..
But,i forgot the circuit controller already..
thats why i need a forward reverse controller circuit..

**tcmtech** · 12th November 2009 04:46 AM

To do the two relay method you connect the motor leads one to each common of each relay. Then connect the normally open contacts of each relay to positive and the normally closed contact to the negative.

When one relay is activated it takes that motor lead from negative to positive. When the other is activated it takes the other lead from negative to positive thusly reversing the motor in reference to the other relay.

Most commercial PLC system I have ever been around used either 24 VDC or 120 VAC for the outputs. Or just a basic isolated relay unless it was an application specific output device. But yes there are probably many other styles as well.

**ppcandieq** · 12th November 2009 05:49 AM

tcmtech..

thanks 4 ur advise..can you give me the wiring circuit???

**Boncuk** · 13th November 2009 03:34 AM

Hi ppcandieq,

here are a circuit diagram and a PCB layout.

Function table is printed in the schematic.

The PCB design is single sided and measures 2.4875X1.65inches. Relays are capable of 8A. Relay brand is "FINDER".

Boncuk

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