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Author Topic: Motor Shield Power HELP!!  (Read 704 times)
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Hello,
I really hope someone can help. I have recently just brought the adafruit motor shield as it can run 4 DC motors which is what I need. However it will be for a robot which means I will need external power basically I will need to power the arduino UNO and adafruit motor shield with batteries but what I want to do is power the motor shield separate to the arduino so that there will be no damage to the arduino or motor shield board but will still run deficiently. The motors I will be running are just small 4.5V DC motors. I hope someone can give me a good explanation on how to do this.

Many Thanks

Jamie
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Well you could use a 4.8V battery pack (4 NiMH) or 3 1.5V standard batteries.
I think you could also use a much higher voltage pack and use the pwm to limit the output voltage (for example if you use a 12V battery you should be ok if limiting the speed to 95 because the pwm should chop the 12V to about 4.5V) but you better make some tests to make sure you get the right voltage.
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Hello,

Thank you for your reply. So to power the just the arduino what battery pack would i need juat to clarify. To just power the motor shield what battery pack would i need just to clarify again because im kinder new to all thus.

Many Thanks

Jamie
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Don't forget to remove the jumper from the shield if you want to use separate power supplies smiley-wink  you could always do some tests with a multimeter, wall wart/bread board and such to get a better idea of what to expect before you drop money on a battery pack, in the end your going to loose a little voltage from whatever batteries you choose after running through the shield (ie. 5 volts won't be 5 volts). A normal 9v battery should be good enough for just the arduino and a sensor.
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Hello,

Thank you for your reply and sorry for all thw questions. So to clarify a 9V battery will be fine for just the arduino. So what type of batteries would i need for the shield. Would i need just normal off the shelve batteries or will they have to be like rechargable packs as i would prefer to put a few AA or AAA batteries together in a pack if possible just to power the shield

Many Thanks

Jamie
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Hello,

So will 4 AA batterys be efficient enough to power at least 3 4.5v - 5v dc motors.

Many Thanks

Jamie
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you haven't posted a link or anything for the motors your using, so I'm just assuming your using the yellow ones with the black tires.

4x1.2v will give you 4.8v total, it will be less than that once you run them through your shield but you still should be good. The good thing about the single AA batteries is if you did find that the volts dropped too much (around your minimum 3.5v) you can add another battery and switch to a 5AA holder(or less for other bots and stuff) without having to worry about a whole new battery pack for each different build.

I have 5 fully charged AA's(6 volts) hooked up to my adafruit shield and my multimeter is telling me that the batteries are 6.5 volts and the output of the shield where the motors are connected reads 4.92 volts (two motors at full speed running in the air), so it dropped around 1.5 volts, that's with fresh batteries so the output reading may change after running it for a short while. You'll need to try your own experiments.

The "23000mAh or greater" will determine how long you can run the motors before they drain to a point where you need to recharge them again, if you are running four motors the batteries will drain faster than a robot that uses two so look for batteries with high mAH, for the most part if your just turning on your bot for short periods of time you should shouldn't really have worry too much about them dying anyways.  You can always have two sets, one charges while you use the other if you needed to.  I mentioned the Energizer 23000mAh because that's what I use and they do the trick there may be something better?



ps: the mAh label is really small and on the top and side of the battery, not too sure if it's advertised on the package or not? so stay sharp smiley-grin
« Last Edit: July 02, 2013, 11:20:55 am by whiskey » Logged

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The chip used loses about 2 to 3V due to darlington output stages at nominal rated current, so a 4.5V motor
and 7.2V battery (6AA NiMH's or 2S LiPo) pack would be a good combination.  6V is perhaps OK, but I'd
recommend having a little more, remember that battery voltage drops with load and discharge...

If the battery can handle the max (stall) current from all motors simultaneously with ease (ie its a LiPo),
then you could just connect it to Vin as well as the motors.  For LiPo batteries you should have
a fuse or over-current protection circuit (they can push hundreds of amps into a short).

If the motor battery pack can't withstand 4 lots of stall current then use a separate supply for the
Arduino or it'll probably reset every time you load the motors sharply...
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