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Author Topic: 12v 7AH lead acid+arduino+motor driver =smoke WHAT HAPPENED?  (Read 6760 times)
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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  smiley-eek

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 smiley-mr-green
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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.
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from your motordriver specs
Quote
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 http://www.robotpower.com/products/MegaMoto_info.html. I'm really pleased with it's working but there was/is no library.

Best regards
Jantje
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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.
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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.

smiley-wink
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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!
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http://
For a 7AH.12V battery u need a high current (order of 5-8amps) motor driver.Moreover 2A drivers would just blow off giving smoke and may also damage arduino uno.Instead use a fuse
(4 amp) for limiting current into the motor driver.While navigating the web I found some POLULU motor driver have the same functionalities.Also the l298 can be configured into 4A current to a single motor
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