View Full Version : trouble with batteries

07-17-2010, 01:00 PM
I have been using normal lead 9v battery for my line follower bot for quite some time but as see output across 2 output pins of l293d i get output as 8.78-9v (giving nearly 12 v at pin8 of l293d) and output current 12.3 mA . I m using 12 v 100 rpm motors which dont run when i apply the output.the question are:
1. when i connect a 9v battery directly across motor they run though slowly and output current is about 60 mA so why through l293d i m not able to run motors is current the factor??. what is the min current to run dc geared motors?? and as i m using batteries for some time may be they r drained out is this the factor??
2. previously i used to get 11 v output after ur help then made combined with comparator lm393 and got nearly 9v is reduced voltage due to changes i made or batteries the reason
3.should i buy li ion batteries or other type batteries from market as they are quite expensive are they useful for future uses and most impotantly not available in my local electronic store so i have to go to bigger market in Delhi a else shoild i get new 9v hw normal battery but will they give min output current and voltage through l293D

07-17-2010, 01:07 PM
Also pleazzzz tell how to increase speed of robot(motor) ,how these super fast line follower bots are made as i dont think my robot will be able to run so fast, which are the factors ,motors ,introducing resistors,or others

07-19-2010, 10:15 AM
L293D eats up some voltage. It is because there will be dorps across the H bridge in the chip. So, you will NOT get all the voltage you give at the PIN8.
The normal 9V PP3 battery cannot give you enough current, so it is NOT a good option for your robot, if you are to drive your motors with it, with load.
When you connect an H bridge, the output voltage drops, and in turn the battery will deliver less current.

If you are using 12V motors, your options are less in terms of battery. 12V motors DO work at lesser voltages, but wont, obviously give the same RPM and torque. The cheapest will be to buy 8 AA or AAA norma batteries, (put it in series )as it gives pretty good current. that will cost you about RS64. The downside being the size, and the weight. You can invest on rechargable Nicd, which is a very good option, in the long run.The chargers are cheap. You can get them from a supremarket, or from a studio. I dont know if they stock Nicd these days, now things have gone to Nimh.

Dont play with Li chemistry now. You need an expensive charger, and you need to be careful when you deal with high currents. I reccently burned an entire 8-wire relimate connector in less than 5 seconds, with a 6V nicd, just because of carelessness. A part of the table went in fire, so you can guess how dangerous it is to handle these things. Get a hang of things, then go to Li chemistry when you feel you can handle them.