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I've added four 12v DC geared motors using motor shield in Arduino.

I tried giving 9v to motor shield connected with these four 12v DC battery and I observed with Multimeter that each motor connection was having approx 4v.

Since, each motor requires 12v to run well. So, I wanna know how much voltage should I give to motor shield to run all four 12v DC battery at full speed?

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2 Answers 2

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It sounds like whatever motor driver is used on your shield is wasting some power. It's either that or your 9V supply was not capable of delivering the required current.

You should be able to get a quick idea by measuring both the input voltage and the output voltage from the motor drivers under load.

If the input voltage drops under load, it's likely that your power supply isn't capable of delivering the rated current. If the motor output voltage is lower than the input voltage, it's likely the motor driver is wasting power internally.

If it's the former, you'll need a beefier power supply that can deliver the needed current. If it's the latter, you need to check the datasheet of the motor driver to see how much power it wastes at certain operating points to figure out what voltage you need to drive it at to get 12V at the output.

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  • \$\begingroup\$ My 9v battery is giving 8.5v approx and on my motor shield's +/- slots it's measured 4v approx. I wanna know, generally, for operating four 12v dc motors with shield is 12v battery fine? \$\endgroup\$ Commented Apr 4, 2017 at 9:00
  • \$\begingroup\$ Well it depends on a few things, I.e. whether the battery can deliver the current that the motors need and whether the motor drivers are rated to handle that much current \$\endgroup\$
    – tangrs
    Commented Apr 4, 2017 at 22:31
  • \$\begingroup\$ For example, your motor drivers seem to be dropping around 4.5V which is quite inefficient (you're wasting over 50% of your input power). You didn't mention how much current the motor is drawing but the drivers could get quite toasty at higher currents. Does the shield have appropriate heatsinking to get rid of all the excess heat? \$\endgroup\$
    – tangrs
    Commented Apr 4, 2017 at 22:37
  • \$\begingroup\$ The best way you'll find out whether it's fine is to check the specifications of your shield or the datasheets for the motor drivers. \$\endgroup\$
    – tangrs
    Commented Apr 4, 2017 at 22:40
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To run a 12V motor from a battery, you need a nominal 12V battery.

You also need to think about current. For example, A 9V PP3 cannot supply much current. On the other hand, a typical 150 Ah 12V car battery can supply quite a lot of current. You should check the current or wattage ratings of your motors, particularly the start-up current required based on the torque you need to move the expected mechanical load on the motor.

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  • \$\begingroup\$ can i use a 12v battery if i connect a 6v motor to the shield? how does it determine how much voltage needs to be applied to the motor \$\endgroup\$
    – vikrant
    Commented Jun 4, 2020 at 10:20
  • \$\begingroup\$ @vikrant: To run a 6V motor from a battery, you need a nominal 6V battery. \$\endgroup\$ Commented Jun 5, 2020 at 8:24

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