I am a programmer by trade and I like to mess around with Arduinos from time to time. I recently purchased a BUNCH of 12V 5W DC water pumps (the 3x5 models shown here). I am currently evaluating how to best control these with my Arduino Mega. I found These little control boards that can handle up to a 12V external power supply while using the arduino for control signals. Cool.

I was talking to my friend about buying a bunch of these things when he mentioned that running motors simultaneously in parallel like that (I intend all motors to share the same power supply) will add up the amperage. I did some math (correct me if im wrong please) and If I wanted to run 6 motors at one the circuit would need to be able to handle 2.5 amps

I made a wire diagram to help me (and hopefully you guys) understand: enter image description here

After what my friend told me I am now worried about burning out the control boards and/or my Arduino. The control boards can only handle .8 amps (I think, hard to find info on this thing) and from what Iv'e read the mega can handle .25 (maybe 1 amp? still, much too low). Does anyone know how I am supposed to deal with high amps? Or is my friend wrong, and the amps aren't an issue?

EDIT1: Someone pointed out I should not use the ground pin on my arduino. The controller boards now use the vcc pin for the + end of the power supply and the grnd pins are now hooked up to the - end of the power supply. Updated schematic

  • 2
    \$\begingroup\$ The power to your motors must not go through the Arduino board. It should go directly to the motor driver boards. The Arduino will then need to have a common ground with those. Do you need to be able to reverse the motors? If not you can use a single logic-level N FET and a catch diode each instead of an H bridge... \$\endgroup\$ Commented May 7, 2020 at 2:34
  • \$\begingroup\$ This is a separate issue but AA batteries will not last long if you are trying to pull 2.5 amps from them. Is it possible to tap into mains power with a wall wart DC power supply? \$\endgroup\$ Commented May 7, 2020 at 2:37
  • \$\begingroup\$ It's not a AA battery. that was just the only power-supplyish symbol my circuit diagram software had. The power supply is TBD too but it will be 12V. \$\endgroup\$
    – Rosey
    Commented May 7, 2020 at 2:40
  • \$\begingroup\$ The Arduino ground almost certainly needs to be connected to the negative terminal of the motor power supply - but make that connection from the Arduino directly to the motor supply, so no motor current flows through that connection. \$\endgroup\$ Commented May 7, 2020 at 22:59

1 Answer 1


Each of these devices will have various ratings, and it's important when looking at the whole design that none of the ratings are violated, or you risk something burning up.

Lets start with the motors:

spec, 12V, 400ma

Ok so 400mA each at 12V.

These are connected to the Dual L9110S H bridge Motor Driver. The rating on that is 12V 800mA per channel 12V 800mA

So far so good.

There are 6 motors, and they are all being powered by the 12v power supply.

The power supply will need to supply at least 400mA*6 = 2.4A. The motors will require surge when they turn on, so give yourself some headroom here.

Note that the arduino is only sending low current control signals to the motor drivers. It's not supplying power for the motors. It's like you pushing the gas peddle on a car.

The arduino therefore doesn't have any current requirements. It simply has to send control signals of the correct voltage. The signals from the arduino will be 5V, and according to the datasheet of the L9110s, 5V will work fine.

  • \$\begingroup\$ Yes so after updating the external power supply issue I am no longer worried about the Arduino. I still don't understand if my controller boards are at risk though. Say I did get an external 12V power supply with, for example, the ability to supply up to 15A. If I turn on all the motors at once, will that burn any of the boards? And if it will, how do you avoid that? Do I need more components? \$\endgroup\$
    – Rosey
    Commented May 7, 2020 at 3:04
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    \$\begingroup\$ @Rosey Even if you turn on all the motors at once the ratings will not be exceeded. \$\endgroup\$
    – Drew
    Commented May 7, 2020 at 4:08

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