The mosfets controlling the solenoid valves are N Channel and need to be logic level.
N channel – switching low side (ground)
Logic level – saturated at 3v-5v. Typically 4.5v.
Also need as low a RDSon as possible.
I am currently using IRL540s but these are end of life and there are now better options available (perfectly fine if this is what you have though). Once I find a replacement I will add a comment to the post.
When looking for a suitable mosfet. Look for one that has a logic level voltage stated in the data sheet. It needs to give the RDSon value (in ohms) for 4.5v or 5v. If it only says 10v or 20v then its not logic level.
For the IRL540
Drain-Source On-State Resistance
Symbol = RDSon
VGS = 5.0V. ID=17A, resistance=0.077 ohm
VGS = 4.0V. ID=14A, resistance=0.11 ohm
This reply was modified 3 years, 3 months ago by Martyn.