Assistance with L298

[mohbet]

Hello, I am very new to this stuff, so any help is greatly appreciated: I am trying to drive a 9V DC motor with using an L298n and a pic. I’ve installed the sensors and pic and the program and tested them, all seems to fine on that area; however, my problem lies with the L298: I've build the circuit shown on the data-sheet to control a motor using one of the build-in H bridges with 4 diodes. I’ve tested if the L298 is working as it should by checking the voltages it applies, all that seems to be working as well. But whenever I connect the motor in between the output terminals the voltage drops drastically, and the motor does not turn at all, although the current sensor shows an increase in current drawn. I am using a small motor and within the built-system whenever I connect a 9volt dc battery directly, it draws only around 150ma, so I presume L298 should be capable of supporting that current? Any ideas on what I am doing wrong? Thanks for the help.

 

[bloody-orc]

Show us your schematic please.

are your batteries/voltage supply capable of giving you enough power to run your motors. Is anything similar happening, when you don't have the pic connected to the H-bridge?

 

[audioguru]

A brand new 9V alkaline battery can supply 150mA for a few minutes then its internal resistance increases and its loaded voltage drops. It is below 7V in less than 1 hour.

A "150mA" motor might draw 1.5A when it starts or when it is stalled. 1.5A will kill a 9V battery very quickly.

 

[Hank Fletcher]

I'd do as bloody-orc suggests, and start troubleshooting by getting the h-bridge and motor working without the pic, so you'll know if your pic program is at fault. That said, what's the input requirement for an L298? If the voltage requirement is greater than what the pic can provide (I'm presuming 5V? Sorry, I still don't know a lot about pics), then that could be the problem. The input voltage requirement for most h-bridges is usually scaled to their (motor) supply voltage, so check the L298 datasheet (I'd look for you, but I'm lazy today!).

A "150mA" motor might draw 1.5A when it starts or when it is stalled. 1.5A will kill a 9V battery very quickly.

Maybe he should try working things out with a 9V wall wart?

 

[audioguru]

The inputs to an L298 are TTL logic voltages at a very low current. If the PIC has a 5V supply then it can drive them fine. The logic supply on an L298 is 5V.

I have a huge 1A wall-wart but I have never seen a bigger 1.5A one.

 

[mohbet]

Hmm... As a voltage source I was using a 300watt computer power supply I've ripped apart ,it should be able to supply up to 12amps or something from the 5volt output(I am using a Zener-diode to drop the 12 volt output to 9volt (according the its spec-sheet the diode should be able to supply up to 2amps)).I tried separating the PIC to isolate the problem as you suggested, it seemed to work fine without the L298, so I built myself my own H-bridge and it worked just fine. So I guess my l298 was busted. Thanks for the help and the suggestions!

 

[jontromanab]

l298 problem

hiii guys..........

i am a new member...
i am trying to create a mobile robot project.for controlling the dc motors i am using the l298.it will driven from the parallel port of my pc.
this are the corresponding voltages that are going into the l298 pins:---

1. 2.8mv
2.
3.
4. 12.58v
5. -0.7v
6. 5.13v
7. 2.4v
8. 3.1mv
9. 5.13v
10. -0.7v
11. 5.13v
12. 2.5v
13.
14.
15. 3.0v

as the 2,3,13,14 pins are the output pins.......i should be getting 12v as corresponding output for driving the motor.............IS IT OKK??? ......................................but i am getting nothing.

(as the 5,7,10,12 are the input pins i have given an instruction 80 where 2.4 v is the high & -0.7 is the low)

please someone help me getting the outputs as 12v for driving the motor................its really urgent