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L298 Overheating issue


First, i'm not very good at electronics/hardware (i wish i were, but i'm more of a software guy)..so please bear that in mind in case i say something really stupid.

I'm hoping someone can advise me on how to debug a hardware issue i am having with a controller based on the L298 chip. The problem i'm having is one where the motor is overheating, to the point where at one time it started to smoke.  When i retried hours later, the controller still seemed to work, but it would only drive one motor forward.  

As a simple test, i unplugged everything and only connected a 9.6v nimh battery to the controller.  With just this, the chip on the controller got extremely hot.

Can anyone think of what may be causing this? Are there steps i can take to 'debug' this?

The controller is this: http://www.ghielectronics.com/catalog/product/315

And the motor specs are as follows:

Rated Input Voltage: 12 Volts
No Load Speed: 175rpm
Gear Reduction: 1:40
Stall Torque: 125 oz-in (9 kg-cm)
Weight: 4.7oz
Motor leads: 12" long 28AWG
Quadrature Encoder leads: 12" long 28AWG with 0.100 Header (Encoder Adpater board: +5V, Gnd, Channel A, Channel B)
Pulses: 480 Pulses per output shaft revolution
Drive Shaft Diameter: 6mm
No Load Current Draw: 130mA
Max Current Draw (Shaft Lockup): 1.5A
Wiring Specifications

Motor Power Supply Wire: Vcc Power In (0 - 12 volts)
Motor Power Supply Wire: Gnd Power In
Encoder Adapter Board Vcc: +5V to 12V
Encoder Adapter Board Gnd:
Encoder Adapter Board Channel A (0v-5v out)
Encoder Adapter Board Channel B (0v-5v out)

Thanks much for any advise

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Well, your motors are rated at 1.5A max, and the L298 can provide 2A per channel continuous current. So if everything was connected OK, you should not have had a problem.

Check for possible shorts (any electrical connection that wasn't intended). Check that the wires you used to connect the motors is sufficient to handle 2A of current. Disconnect each motor and test it by connecting it directly to your 9.6VNiMH battery, just to confirm the short is not in one of your motors.

If you had a short, you may have damaged your controller board. If this happened, you are probably looking at a new board, but don't give up until you have tested every other possibility.

Still, if the motor driver really gets hot with not motors connected to it, it sounds like a damaged board. If I understood you correctly and one of your motors started to smoke, you had a short or a bad motor, which may have tried to draw more current than your board could supply. Poof! Dead channel on your board. It may still be good for driving one motors, which is probably not what you need right now, but worth saving the board for a future project where you only need one motor, or you want to add a 3rd motor for some reason.

I think the controller is bad at this point as ignoble suggests given that its getting hot with just the battery connected. The wire I used come with the motor and are rather thick..so I think they can handle the current. Each motor runs fine when connected to battery alone. The controller is connected to a gadgeteer cerebuino board...that is the source of the 5v logic. Question...how would I check for a short on the controller? Do I connect the battery and then check for voltage or amps across the terminals on the board that the motors connect to? Also hw might this have happened in the first place if everything was connected fine? Could it have been because I ran it too long? Could the board driver have been pulsing too fast? Thanks much for the help.

Could you have the battery connected backwards?

I'm not trying to imply you are dumb, its just an easy mistake to make.

I did this with the PICAXE 28 project board I am embarrassed to say.  I added a 9-volt battery clip to my battery pack, not thinking that when I snapped the two 9-volt clips together, I would be crossing them.  I was doing the blinking LED test and of course it didn't blink.  Suspicious I ran ...one finger... over the motor driver chip on the board and guess what it was HOT!!!!!

While shaking my finger in the air, I popped the battery loose and got lucky.  Everything still worked after I fixed my wiring job.

Of course perhaps the board was bad out of the box.

Hi kingart3,

i was very careful to make sure that wasn't the case.  Also, the motors were running fine for a while..but later stared to behave irratically...for example one motor would run when moving forward, while both would work when moving backwards.

If both motors run fine when connected to batteries and don't get hot, they seem to be fine.

Do you have a multimeter? I'd first test to see if the motor outputs on the board appear to be shorted when powered off, then when powered on. Then, as you say, test that you get the expected output with a meter from the motor outputs. You can also test to see if the inputs are working OK coming in from your microcontroller.

I dont' think the problem occurred because you ran it too long. The specs for the motors you posted should work fine with that controller. Most likely you connected something wrong, or something got accidently shorted. There's a slim chance the motor driver chip was faulty to begin with, but I'd eliminate more obvious causes first.

As OddBot suggested, post some diagrams and help us help you.

Thanks ignoblenome, i will try your suggestions tonight.

one motor doesn't seem to run any longer...

i'm not very good at schematics.  it's a gadgeteer board and controller..they are difficult to connect wrong (for folks like me)

this is the main board: http://www.ghielectronics.com/catalog/product/351

and this is the motor controller: http://www.ghielectronics.com/catalog/product/315

You'll see 3 sockets on the right of the main controller..i connected it the socket from the motor controller to socket 1 of the board, both are type "P".

anyway will try your suggestions and post some of the readings...

Not connected to controller
-Motors work when connected to battery directly, one draws about .55amps and the other .48amps

When connected to the controller...
-When power is turned off there is no voltage  across any of the controller terminals

-Voltage: when power is turned off, the power connector show 10.45v. with no motors connected, the left motor connector on the board shows .69v and right motor shows .023v

-When power is on, and i run my app to move motors forward,  on motor runs and draws about 55amps, the other doesn't do anything

-Continuity: Now i'm not sure if i'm doing this right..i turned the power on and touched the black probe (from the dmm) to the + of the motor connector on the board and the red probe to the - of the motor connector.  One motor beeps but the other remains OL.

-resitance: testing by using the wires from the motors themselves... one motor is showing as 3.5 ohms, on the other as 2.6ohms.  why the difference?

So i guess it's safe to say the controller has one bad motor connector...

I agree. One channel of your motor controller is toasted. Save the controller and use it in the future as a one-motor controller board.

Buy a new controller.

An overheated motor will likely have shorted some of its windings together and allow it to pull more current. Attempting to drive that motor could damage your driver.