As TomGeorge kindly pointed out, I made an sketch of it:
-I call them modules, as each is in charge of doing a specific function
-The modules 1, 2 and 5 are resistive loads in conjunction with small inductive loads (ventilators)
-In module 3, all of them are inductive loads
-Module 4 is a resistive load
Any inductive load needs free-wheel diode across it - with a pulse rating adequate for the load current.
-As it is a 12 V system:
Module 1: 6,1 A
Module 2: 1 A
Module 3: 3 A max. Between 0,3-0,5 A per unit
Module 5: 0,7 A
These current values decide the on-resistances needed for the mosfets, which determine the
heat dissipation (and thus whether heatsinking is needed). Heat dissipation = I^2 R
(So for instance 6A with 20milliohm device dissipates 0.72W, which is borderline for needing
If controlling direct from 5V logic the MOSFETS need to be logic-level, this is vital.
-The power supplies would be 12 V wall adapter/s. As asked, I might need 1 or more.
One for the arduino supply, one for all the mosfet modules is fine - you won't find a 12V wall wart for
that current level (you omitted module 4's current requirement BTW, but its over 11A for the others).
Make the supply capable of at least 25% more than the total current rating, never a good idea to
stress things to the limit.
-Capacitor: I am unfortunately no expert (hence asking). I have read and being advised that working with several MOSFETs can cause disturbances in the system (ground bounce), that would prevent the system from working correctly.
Yes supply decoupling of 100µF or more would be good at each module. That will substantially reduce
spikes in supply and ground on switching. 16V rated or 25V rated electrolytics are suitable.
Therefore, my questions are:
-Should I really use 2 power adapters (one for Arduino, the other for the modules) (please see sketch)?
-How can I minimize the "ground bounce" phenomena? How big, where and how many would I need? For this, I asked for a calculating formula so I could calculate it from the data supplied.
Decoupling capacitor sizing is usually very imprecise, more is always better, but diminishing returns eventually.
Without the datasheets for power supplies, details of the wiring length and resistance, its a rough guess.
The wiring between arduino and mosfet gates is fairly critical - this should be short, a twisted pair direct to
gate and source of the device. 120 or 150 ohm resistor in series with each Arduino pin will limit current spikes
from the Arduino pins. 10k or so resistors between gate and source will prevent the MOSFETs randomly
switching on at system powerup, which is normally needed.