L293D motor control problem

Other Hardware Motors, Mechanics, Power and CNC
1

Hi!

I have a DC motor that I would like to control with an L293D H-bridge IC. When I apply 9V directly from the batteries to the motor, it works fine, however when I apply it through the L293D IC with full speed (enable is connected to 5V here) it barely starts! You can feel and hear the difference that it's weaker. I suppose it should have no noticable difference.

Have someone encountered this problem before? Am I doing something wrong? Any explanation?

It's a 12V DC motor (0.32A), but works just fine with 9V (6xAA). It's wired up like this on a breadboard (see pic), I have common grounds everywhere (Arduino, 9V battery, L293D all common grounds). And the simple code I'm using for this:

int lmp = 10;
int lmg = 11;

void setup() {
pinMode(lmp,OUTPUT);
pinMode(lmg,OUTPUT);
}

void loop() {
digitalWrite(lmp,HIGH);
digitalWrite(lmg,LOW);

delay(2000);

digitalWrite(lmp,LOW);
digitalWrite(lmg,HIGH);

delay(2000);
}

Thanks!
David

l293d.jpg
l293d.jpg775×470 46.3 KB

2

Is that 0.32A the stall current? (It draws stall current at start up.)

The L293 drops about 2V (iirc) btw, so you won't get the full 9V, closer to 7V.

3

Hi,
Do you have a DMM?

Measure the voltage at your motor terminals.

You do have gnd of the 293 connected to the Arduino gnd and the motor battery gnd.

Tom... :slight_smile:

4

The L293D is old technology. It "looses" about 2.5volt in bridge mode at that motor current.
Not a big problem if you compensate for that.
e.g. a 15volt supply for a 12volt motor.

If you don't want that, then get a modern mosfet-based motor driver board.
Leo..

5

Have someone encountered this problem before? Am I doing something wrong? Any explanation?

Basically you are trying to use an inadequate power supply for a motor - small 9V batteries cannot source
much current, they struggle above 100mA or so.

You need a supply capable of powering a motor, a 0.32A motor (rated current) probably has a stall
current of 1 to 2A, so your supply should handle 0.5A without cutting out or dropping in voltage much.
A 12V SLA would work. The voltage drop in the L293 is still going to affect the top speed though.