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Topic: L293D slows DC motor down (Read 934 times) previous topic - next topic

LPDE

First time using an L293D to control the direction of a DC motor.

I noticed previously when I connected the motor directly to the 5V pin, or to a digital pin with the blink example uploaded, the motor would spin fast. However when I connected it through the L293D, following adafruits example as I want to control the direction:

https://learn.adafruit.com/adafruit-arduino-lesson-15-dc-motor-reversing/an-experiment

it rotates slower. Is there a reason for this?

terryking228

Hi,
The reason is that the L293D is a bipolar transistor technology and has a voltage from of as much as 1.5 volts.

Measure the voltage on the motor..
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

LPDE

#2
Mar 02, 2017, 05:43 pm Last Edit: Mar 02, 2017, 05:54 pm by LPDE
Thanks for the reply, I get 1.8V from the motor. What would be the next steps if I want to get the speed up as if it was directly plugged into a digital output on HIGH or 5V?

Here is a link to the motor I'm using:

https://www.amazon.co.uk/gp/product/B010SP427I/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

terryking228

#3
Mar 02, 2017, 05:59 pm Last Edit: Mar 02, 2017, 05:59 pm by terryking228
Hi,
Either use higher voltage supply (I often use 6 AA for 7 to 8 volts) or find a different motor driver with FET technology that has small voltage drop.
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

LPDE

Thanks for the reply, what driver would you recommend that has the smallest voltage drop?

being small in size would also help!

MarkT

And never power a motor from the 5V logic rail, logic chips don't fare well with inductive spikes and
voltage drop-outs happening on their supplies.  Separate power for motors and servos is strongly advised.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

LPDE

#6
Mar 03, 2017, 12:04 pm Last Edit: Mar 03, 2017, 05:42 pm by LPDE
Quote
And never power a motor from the 5V logic rail, logic chips don't fare well with inductive spikes and
voltage drop-outs happening on their supplies.  Separate power for motors and servos is strongly advised.
So if I must power a motor from the Arduino, only use a digital pin unless I power it external with batteries or a regulated power supply?

MarkT

So if I must power a motor from the Arduino, only use a digital pin unless I power it external with batteries or a regulated power supply?
What?

Power the motor from a separate supply to the Arduino 5V logic supply to protect the 5V supply from
spikes and drop-outs.

Arduino pins cannot power a motor at all and will likely be destroyed/damaged by back EMF.

Arduino pins are for signals.  At most they can power a low power LED, they cannot handle inductive
loads.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

LPDE

Apologies, I misunderstood. I now know not to use the I/O pins!

Appreciate the help!

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