View Full Version : motors problem

06-21-2010, 01:56 PM
i m supplying 9v to 8 pin in l293d but it is just giving 7v output not sufficient to run motor but i have a bot in which they used only 9v and motor worked perfectly well and should i go for 12v battery or look for changes in connections

06-21-2010, 08:09 PM
i have a bot in which they used only 9v
"they used" ?????

Anyway, what power supply are you using to power your motors(batteries, eliminator, etc)?
If you are using a 9V battery, like I am guessing, then it is usual for you to get 7V while driving the motors.

Also, make sure you the enable pin is given a clean logic high input.

06-22-2010, 01:29 PM
why ?? why?

They dont teach people punctuations these days in school?? I remember some guy not using punctuations - and even after I asked him to use a full stop, he didnt get the point !!
dear prashu, if you are not the same guy I am talking about, please use at least a full stop when you post again.

As for your question ::

--> L293D will eat up some voltage.
--> Never use the normal 9v pp3 batteries to drive a motor with load. They dont have enough current in it, unless you are using a very small motor.


What is the voltage rating of your motor?
What batteries are YOU using/plan to use. (The type - if it is NiCd, NiMh, li-ion, normal AA, alkaline,lead acid)
What battries did THEY use
Are you using the same motors as THEY used?
On which pins did you measure the '7V' (Where did you keep the negative of your meter, and which pin did you connect the positive of the meter)
What voltage did you give to pin 16?

--> post a schematic. This will help the community to help you better.

06-24-2010, 12:52 AM
It could mean its a Ready Kit- most of the kits use the 9v battery since it is cheaper than any other cell.
The wholesale price of the blue Hi-watt 9v battery is Rs.5-00.

06-25-2010, 11:06 AM
i was using 9v at vcc to drive motors ,and was getting 7 v as output . thanks for ur suggestions. i tried with 12 v supply as input at vcc .now i am able to get 10.5 v as output sufficient to drive motor

06-25-2010, 11:25 AM
first reply to your questions
i m using 12v 100rpm motor .
i m using 2 9v batteries separately one to convert to 5v using lm7805 and other combined with 3v (9+3=12v) to give voltage at vcc
yes i m using the same motors they used.
i measure 10.5 v at output pins now
i gave 5v at pins 1,9,16.
then they used 9v to drive same motor at vcc i m using 12 v why i have to add 3v batteries extra

06-25-2010, 12:57 PM

They do not have enough current. change to lith-ion if possible with high current capacity and voltage.

06-25-2010, 05:52 PM
Directly connect your motors to the power source and measure the voltage across the motors. If there is a substantial voltage drop then you will have to change your batteries. Go for Li-ion batteries as vikas suggested or for NiMh batteries.

06-25-2010, 07:23 PM
Your 9V battery will drain out pretty soon mate.

06-26-2010, 02:52 AM
I Connected 2x 100RPM motors with wheels driven by a L293D. Pin 16=5v via 78L05, Pin 8=9v Hi-Watt blue.
The total weight is about 500gms. the lightest I could make in half an hour using available material.

The motors were wired for a 'spin' and I left it running on the table.

The 9v battery drained to 7.4v in 40mins and the vehicle stopped due to low voltage. The total current draw was around 280ma with a new battery.
The battery was still good enough to run my 6v motors @ 200ma for another 10 mins. till the battery went down to 3.8v.

....good enough for 4 bucks !!!