Problems with motor using a L293D motor driver

Other Hardware Motors, Mechanics, Power and CNC
1

Hello.
I have some problems with my motor setup. I've got a motor connected to a L293D motor drive rwith an arduino board. The program works as it should, but the motor is going too slow. I tried to mesure the voltage, which said the motor supply was 3,2 volts. I have connected +5 volts to both pin 8 and 16 on the motor controller. I was hoping that my motor would get 5 volts, but apperently it doesn't.
Here is a link for the L293D and setup: http://luckylarry.co.uk/arduino-projects/control-a-dc-motor-with-arduino-and-l293d-chip/

I hope someone can help me, thank you :wink:

Ecologically

2

I tried to mesure the voltage, which said the motor supply was 3,2 volts

I assume you measured that at 100% PWM.

I was hoping that my motor would get 5 volts, but apperently it doesn't.

You've got two transistors' worth of voltage drops because of the H-bridge.
Just jack-up the supply voltage for the motors.

3

The L293 uses Darlington output stages, so it will drop about 2V internally. For a low voltage supply it's a poor design because high loses are unavoidable. MOSFET H-bridge chips will do much better.

4

Thanks for the respons.

So, if I increase the power supply for the motor or the chip, it should work correctly. orr.....?

Ecologically

5

I've now tried to boost up the supply for the motors to 6,2 volt, but the voltage for the motors is still the same (3,2 V). Should I buy another H-bridge, or is it anything I can do?

6

Did you measure the voltage at 100% duty cycle PWM?

7

I measured the voltage between the two pins from the L239D, which are going to the motor.

8

That isn't what I asked.

9

well, then i'm not sure what you asked for meant.

10

Did you do an "analogWrite (motorPin, 255);" ? (aka 100% PWM)

11

no, i didnt do anything like that. I just used the code from the exemple.

12

The example doesn't use PWM, just switching direction. It ought to be getting more voltage to the motor if there's more voltage at the supply.

If the power supply isn't up to the task though the motor may be overloading it - have you measured the supply voltage when the motor is running?

Also I note that the example circuit has poor decoupling - the 220nF ceramic capacitor they describe as "optional" is required for reliable operation as with any logic circuitry. The electrolytic decoupling of 10uF is rather small, I would prefer 1000uF or similar

13

Yes, i tried to measure the voltage when the motor was running, but no good luck. Do you think i need to buy another kind of H-bridge, or should it work proporly with the one I got?

I use a 10uF and two 0,1 uF for the motor

14

but no good luck.

What is that supposed to mean?
Did you measure the supply voltage with and without the motor running?

15

Well it seems like when I measure the voltage with the motor connected, i only get 3,2 volts, but if I remove them i get 4,5 volt( which is the voltage from the battery).

16

Could it be that the H-bridge doesn't work at that low voltage?

17

What is the battery voltage with and without the motor running?

18

I measure the voltage from the battery without the motor attached:
Then I get 4,3 volts from a 4,5 volt battery, which is okey. And I get 4,4 volts from the pins from the l293d which is supposed to go to the motors.

Then i measured the voltage with the motor:
Then I also got 4,3 volt from the battery, but only 2,5 volts from the motor pins on the l293d.

I got no clue what the problem could be...

19

The motor i'm using is just a basic motor which was cheap, but its working proporly when I attach it directly to the battery.

20

Earlier you said:

I've now tried to boost up the supply for the motors to 6,2 volt, but the voltage for the motors is still the same (3,2 V). Should I buy another H-bridge, or is it anything I can do?

I'm simply trying to figure out why that is happening - the loss of 2 volts is a given with Darlington outputs, I was trying to figure out why this had increased to 3V loss - though this could simply be more resistive losses with higher current.

The L293 is never going to be efficient at low voltages with Darlington outputs. Its still going to be no better that 80% or so at 12V which is rather lame.