Motor Shield Brownout Issues

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snaggletooth
 
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Motor Shield Brownout Issues

Post by snaggletooth »

Hi,
I have a motor shield soldered to an Arduino Mega 256k. I am trying to run two of these stepper motors (http://www.hvwtech.com/products_view.as ... ctID=10948) from the board. I have piggybacked two L293DNE drivers and put a heatsink on top of each piggybacked driver. I run the Arduino off of USB power and the shield from an adjustable DC source 1.5-12 V, 300 mA. I can run one motor just fine at 3 V (i know 3 V motors aren't guaranteed to work but I only noticed this post-item acquiry). My problem is that when i try to run one motor and then the other, the power LED starts blinking and neither motor will work. The blinking LED only starts when the second motor starts to run, the first motor will step fine, and then the blinking will commence. I have a feeling that my source just isn't supplying enough current. Do you think it's that or is there something I am overlooking?

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adafruit_support_bill
 
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Re: Motor Shield Brownout Issues

Post by adafruit_support_bill »

the shield from an adjustable DC source 1.5-12 V, 300 mA.
300mA is really not enough current to run these motors well. With a 1.25 ohm coil at 3v, they are going to try to pull about 2.4A. I'm surprised that you can get even one to run.

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philba
 
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Re: Motor Shield Brownout Issues

Post by philba »

It looks like you are out of spec on two fronts. Those motors look like they pull at least an amp. The specs say 3.1V and 1.25 ohm which ohms laws tells us is 2.48 amps but I'm not exactly sure what to make of the specs since it says coil resistance is 3.1V and rated current 1.25 ohms. Also, the L293DNE datasheet says minimum voltage is 4.5V (or Vcc, which ever is greater).

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adafruit_support_bill
 
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Re: Motor Shield Brownout Issues

Post by adafruit_support_bill »

L293DNE datasheet says minimum voltage is 4.5V
They are also rated at 600mA max. Piggybacked you will probably get close to twice that, but not nearly 2.4A.

Sometimes you can get them to run at lower voltages (as you have seen). But trust me: they won't last long if you exceed the current rating!

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