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seperate power supplies on motor shield
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seperate power supplies on motor shield

by derFloh on Tue Feb 14, 2012 5:49 am

hello,

i have a general question about seperate power supplies on a motor shield...
in case i power the arduino with a 7.2v battery but need a higher voltage for 4 dc-motors (up to 12V),
is it possible to plug a 12V battery to the PWR_EXT block on the shield? so: do i get 12V as max output?!

a second question: what kind of gear-motor do you recommend for driving in a wide range of speed (0-255)
i found this one (with a wide operating range of 3-12v and low current) http://servocity.com/html/101_rpm_gear_motor.html

thank you so much!
flo
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Re: seperate power supplies on motor shield

by adafruit_support_bill on Tue Feb 14, 2012 7:59 am

You can connect your 12v supply to the external power terminals on the shield. :!: Be sure to remove the adjacent power jumper. The maximum output you will get at the motors with a 12v supply will be about 10.8v. (There is a 1.2v drop through the H-Bridge chips).

A 12v motor should give you a good range of speed. Lower voltage motors (e.g. < 6v) are difficult to control at lower speeds. The motor you linked looks like it should work well - although they do not mention the stall-current.

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Re: seperate power supplies on motor shield

by derFloh on Tue Feb 14, 2012 9:09 am

thank you very much!
thats what i needed to know! :)

cheers
flo
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Re: seperate power supplies on motor shield

by taucrit on Wed Mar 21, 2012 2:48 am

A follow up question, since I too am powering a pair of 12 volt stepper motors via the external power terminal on the motor shield. You say it is necessary to remove the jumper next to the terminal blocks when running external power to the shield. I assume this is because 12V is too much for the Arduino - is that correct? I am planning to run the motors outside and it would be great to only need one power supply. Ideally I'd like to run the arduino and the motors off the same external 12V battery pack rather than carry a separate 9V battery for the arduino. Is there any way to achieve this?
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Re: seperate power supplies on motor shield

by adafruit_support_bill on Wed Mar 21, 2012 6:19 am

You say it is necessary to remove the jumper next to the terminal blocks when running external power to the shield.

That statement applies to the case of using separate supplies. It is not a good idea to have two power supplies connected in parallel.

If you have only one supply (presumably one that is compatible with both the motors and the Arduino), you can leave the jumper in place. The supply can be connected either to the Arduino DC jack or the external power terminals on the shield.

The Arduino is rated for 7-12v DC input, so it will work with your 12v supply. The other concern is possible electrical noise from the motors interfering with the Arduino. If you see any erratic behavior or resets on the Arduino, you should go to separate supplies.

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Re: seperate power supplies on motor shield

by taucrit on Wed Mar 21, 2012 11:23 am

Thanks!
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