My motor shield is (almost) on fire!

[madfish]

Hi there!

Iam quite a newbie if it's about electronics so maybe i'm about to describe something very bad!

Here is what i use:
- Arduino Mega
- Adafruit Motor Shield
- stepper motor with included gearbox (this one: http://www.stepperonline.com/gear-1001- ... -p-36.html )
- power supply: 2 different possibilities: 1. classic USB from my laptop OR 2. a lipo 7.4v battery (2200mAh)

First, when i was coding my sketch and testing it, the arduino was plugged to my computer, the motor shield stacked on it, with the little power jumper on, to transmit the current to the stepper motor, and everything was ok.
Then, i decided to release it from the computer, and to use a USB-equivalent power supply, like this one http://www.adafruit.com/products/501 but mine actually supplies a 2A current, and still, everything was working great.
Finally, i decided to make my device totally free and to use the lipo, and now, there are some symptoms:
- the motor is very noisy (big "clack" for each step, whereas it was almost impossible to hear it on usb)
- the L293D chip is hot like crazy after 1 minute (i can't even touch it with my finger!)
- the bottom of the motor (where wires arrive) is also very hot!

I tried different ways to supply my system with the lipo:
- using a 5.5mm/2.1mm plug on the arduino, with the power jumper on
- with the lipo naked wires to the motor shield dedicated to power input, power jumper on
- both, with power jumper off

All those 3 ways are giving the same symptoms...

I though about lowering the voltage because my motor is supposed to work at 6.2v, but then, i've seen the need of a 1.2 additional volt because of using the L293D chip...

I have no more idea and i think that using a heatsink may be a patch but is not really a solution.
And you, do you have any fix to my problem?

Thanks in advance!

(ps: excuse my English, iam actually from France)

[adafruit_support_bill]

Finally, i decided to make my device totally free and to use the lipo,

Your LiPo battery is a higher voltage than your 5v USB supplies. If you increase the voltage to the motor, it will draw more current. The more current drawn by the motor, the hotter the motor and the L293D chip will get.

my motor is supposed to work at 6.2v, but then, i've seen the need of a 1.2 additional volt because of using the L293D chip...

Your motor will draw 0.67A at 6.2v. The L293D in the motor shield can only supply 0.6A continuously.

For options to increase power output of the shield, see the section called "I Need More Power" in this post: http://forums.adafruit.com/viewtopic.ph ... 73#p137823

[madfish]

Thanks for your quick answer!

actually, the power supplied by the USB produce enough torque with my stepper, is that possible to lower the lipo input current? For example, is it possible to lower from 7.4v to 6v by pluging something between the lipo and the arduino? (something that produce stable 6v)
If possible, is this "something" going to heat?

[adafruit_support_bill]

If 5v produces enough torque, you can use something like a UBEC DC/DC converter to reduce the output voltage of your LiPo. Unlike linear voltage regulators, these are very efficient and will not produce a lot of waste heat.
http://www.adafruit.com/products/1385

[madfish]

ok, great! and it's not as big! I will try it!
Thanks very much for your support and reactivity!