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I'm using a deek-robot motor shield that has a L293D chip (http://www.deek-robot.com/productShow.asp?id=17). I've connected a 12 volt (4A) power back to the VCC input and IN pints to an Arduino Leonardo board as well as VIN power from the arduino.

I have a motor from a 3.6v cordless drill (comes with a 3.6v batter 1300mamps) that I want to power.

The problem is that the motor driver doesn't seem to be suppling enough power to the motor.

If I hook up a little tiny motor I can get it working but the 3.6v based motor just hisses but won't actually turn.

Additionally I combined outputs A and B into one as each are rated to 600mha so I was hoping to draw enough power this way. That still didn't work.

The voltage output from the A+ and A- terminals are 12 volts.

Not sure what is happening here. How can I get this motor to turn?

Thanks

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  • \$\begingroup\$ You can use another L293 and quadruple drive it. \$\endgroup\$ – StainlessSteelRat May 5 '15 at 1:20
  • \$\begingroup\$ Without more information about the motor's actual characteristics, I'm going to assume you don't know how much it actually takes. Please do what you can to locate identify the motor. Also note that the motor being rated for 3.6 volts may or may not make putting 12 volts on its leads an incredibly bad idea. \$\endgroup\$ – Sean Boddy May 5 '15 at 5:10
  • \$\begingroup\$ An L293 is unquestionably the wrong tool for that job. An L298 might be closer to working, but still dubious. You really want an FET based driver. But as you have seen in comments, work out the current first. \$\endgroup\$ – Chris Stratton May 5 '15 at 5:37
  • \$\begingroup\$ why is the L293 the wrong job? because it can't provide enough current for the motor? \$\endgroup\$ – space_balls May 5 '15 at 7:12
  • \$\begingroup\$ This explains why the L293D is sometimes a very poor choice electronics.stackexchange.com/questions/108686/… \$\endgroup\$ – Andy aka May 5 '15 at 9:37
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Most cordless drills have powerful motors that draw a lot of current. At start up the only thing limiting motor current (apart from the power supply and/or controller) is the resistance of the motor brushes and armature. As a typical example, the Mabuchi RS-380SH-4535 has a resistance of about 0.25 Ohms, so at stall it draws ~14A @ 3.6V. At 12V it would draw over 3 times as much, almost 50A! It would also try to spin 3 times faster, which would cause extreme brush arcing and could cause it to throw a winding.

Current will drop as the motor gets up to speed, but if the power supply and/or controller shuts down due to current overload then it won't even start spinning. If you want to use the L293 and a 12V supply then you need a motor which is rated at 12V or higher, which should draw much less current. For example the Mabuchi RS-385SH-2270 only draws 4A at stall on 12V.

If you want to use your 3.6V drill motor then you need to use a much lower voltage, and you may also need a power supply and controller which can handle higher current. The L293 drops about 2.4V internally at 1A, so with a 6V power supply the motor would only get ~3.6V. However if the stall current is too high then the L293 may not pass enough current to start the motor, and even if it does it will run hot.

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  • \$\begingroup\$ so if I put a standard 1.2 volt batter onto the 3.6v motor it manages to spin at quite a reasonable speed. Probable enough for what I need it to do. So I'm confused as to why it won't spin with the dual drive l293 \$\endgroup\$ – space_balls May 5 '15 at 5:10
  • \$\begingroup\$ What's a 'standard' 1.2V battery? Do you have an ammeter? If so then measure the current draw when your drill motor is powered by this battery (both free running and with the shaft held stationary). Multiply by 10 to get the current your 12V system must supply. \$\endgroup\$ – Bruce Abbott May 5 '15 at 5:19
  • \$\begingroup\$ 1.2 volt battery as in a AA. No, don't have an ammeter. Only a multi meter but I don't think that will help in this situation \$\endgroup\$ – space_balls May 5 '15 at 7:11

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