Check my work before I buy? 10 DC motors, 5 control boards, 1 MEGA?

Hi, I am making my first large Arduino project and I was wondering if anyone could point out any potential issues with my circuit before I go and buy some components.

I am using:

  1. an Arduino MEGA2560
  2. TEN small dc motor pumps (these 3x5 ones) which run at 12V 5W

I am currently thinking about buying FIVE of these little motor control boards (these) which can handle external power supplies of 12V while using the Arduino to control them.

I have seen people do exactly what I want to do with 1 motor and 1 control board, but I am worried about what might happen when I scale up.

The MEGA seems to have enough pins to control 5 boards but I am worried about the (amperage?) current that will build up by running 10 motors simultaneously in parallel. I intend to use the same single external power supply for all 5 boards. In my researching this board I have noticed people using the ground pin on the Arduino to ground the external power supply as well.

So 2 questions

  1. Do I run the risk of frying the Arduino or control boards by sharing the same ground pin for every circuit?
  2. I am not sure on my math here but the motors running at 12V 5W means the power supply will be giving 0.42A on the input wire. My understanding is that using the same power supply to run 10 motors adds up the amperage. Which means at most my input wires would be at 4.2A. Do I need to worry about wire gauge for the input wires at this high amperage?
  1. You must share the grounds. It is best to use a "star ground" where all the leads connect at one point.

  2. The motors in the link are rated at 3W (so each would draw about 250 mA in normal operation), however the startup current is 5 to 10 times that. The motor power supply must be able to easily handle the expected startup current, for as many motors as will be starting at once.

Use reasonably heavy wire for motor connections (20 Gauge stranded will handle 2.5 Amps max), and solder the connections or use screw connectors. Breadboard tracks will burn at those currents.

Sorry I should have specified I am using the 3mm X 5mm pump model on the page I linked which is 12V 5W. OK so thick wires going into the control boards. Do I need thick wires coming out of the control boards too? Like to the motors?

What were your small projects?

You need thick enough wires, where thick enough depends on the current you want to run through then.

Too thin wires: excessive power loss; in extreme cases potential for fire.

Too thick wires: a mere inconvenience and overspending. The project will work fine. This is always safe, but could cause practical problems (weight, physical size).

OK. What about the chips on the control boards? will those burn out?

I am posting a diagram of my circuit so far. It has a few less motors but the same problem.

rorosentrater:
OK. What about the chips on the control boards? will those burn out?

Only if you try to overload them - either overvoltage or insufficient cooling (a major issue if your motor controller is an ancient L298 or L293).