12v 7AH lead acid+arduino+motor driver =smoke WHAT HAPPENED?

Hey guys, i have a problem. Im building a robot and can not understand the basic motor driver voltages that are used for the device. Im trying to hook up my arduino uno r3 to a dual hbridge motor driver as shown.

http://dx.com/p/l298n-stepper-motor-driver-controller-board-for-arduino-120542

Everything worked when i was using a 9.6v 800mh battery connected to the board. Then i decided to upgrade motors to these
http://www.princessauto.com/pal/en/Dc-Motors/12V-DC-Gear-Motor-with-Drive-Wheel/8291700.p

and connected my rechargable lead acid battery to the motor driver and smoke came out :astonished:

So m question is, how do i find a motor driver that connects to arduino that can run off the battery i have. Is it the current or the voltage or a combination of both that is causing this. Whats the easiest motor driver to interface with the arduino that can use lead acid batteries to run it.?

appreciate the help :grin:

You have to start with the motor.
The motor is 12V, and your battery is 12V, that is good.
What is the stall current ?
Could connect the motor to the battery and block its rotation and measure the stall current ?
Once you know that, you can look for a driver board.

That lead acid battery could have a shortcut current of hundred (or more ?) amperes. You should use a fuse. During testing you could also use a light bulb in series with the fuse as extra protection.

from your motordriver specs

Driven part of the peak current Io: 2A per bridge

There are no specs with your motor. So you’ll have to do like Erdin asks. I guess your motor will use more than 2 Amps.

As to other motor drivers:
http://pololu.com/ has several
I’m using Robot Power Products - MegaMoto Motor Control Shield for Arduino. I’m really pleased with it’s working but there was/is no library.

Best regards
Jantje

You should always use a fuse with lead-acid or LiPo batteries, otherwise the wiring can catch fire during
a short circuit. These batteries can put out kilowatts of power.

But back to the problem: what smoked? How quickly? The L298 (it doesn't handle much current before
getting really hot (heatsink/fan are mandatory to take it to its theoretical 2A limit per motor - about 7W are
dissipated in the L298 driving a 2A load, even 1A load could dissipate 2.5W). Looks like the heatsink on
that board would be good for about 2W without a fan.

MarkT:
Looks like the heatsink on that board would be good for about 2W without a fan.

Yeah - they always put dinky heat-sinks on those things, don't they (crazy thing is, I've never been able to find those heat-sinks sold separately, nor an aluminium extrusion profile that would work, either)?

The L298 can also be configured in a bridged mode to give you 4A of current output into a single motor (you're gunna need a bigger boat - I mean heatsink).

That said - without knowing the stall current rating of the motor - all this speculation is moot point.

I have some of those motors, but I don't recall what I measured the current as.

Best thing for the OP to do is to carefully remove the motor from the gearbox (IIRC, this can be done with a little work), then measure the resistance of the windings via the motor terminals; rotating the motor a bit (take multiple readings, then average them). Then use Ohm's law @ 12 VDC which will give you a close value to the stall current of the motor.

I used to recommend the "clamp the shaft, apply voltage and measure current" method, but after learning (and reading more) on the above method (valid only for DC motors, btw) - it is much safer (especially for large torque/powerful motors) and generally easier to do. Plus you won't burn out a power supply, strip gears, or have other nastiness occurring.

:wink:

cr0sh:

MarkT:
Looks like the heatsink on that board would be good for about 2W without a fan.

The L298 can also be configured in a bridged mode to give you 4A of current output into a single motor (you're gunna need a bigger boat - I mean heatsink).

Technically that's paralleled, not bridged... Its already a bridge!

12v 12AH lead acid+arduino+motor driver =smoke
nd if separate power supply is given to motors then how come arduino uno will controll it?

VinsanKH:
12v 12AH lead acid+arduino+motor driver =smoke
nd if separate power supply is given to motors then how come arduino uno will controll it?

The Arduino does not handle the power to the motor. That is the job of the MOSFETs in the driver. The UNO sends a 3.3-5V signal of maybe 0.25Ma to the gate of the MOSFET. This lets the MOSFET pass current from the motor's power supply to the motor. In essence the MOSFET is acting as an amplifier of the UNO's signal.

Discrete MOSFETs can handle 100s of amps and still be triggered by an Arduino. Although, I'd be using some signal isolation in such a case!

What else are you powering from the Arduino 5V and 3.3V pins? 12V input and more than 500mA output at 5V will burn the Arduino's 5V regulator.