You could use the higher on-resistance P-MOSFETs for the lower current devices and use Mike's circuit just for the high current ones.
Or you could put the high current P-MOSFETs on a heat-sink.

 

I took one last look before I crawled into bed. How about this one? Check it out, the FQP27P06.

 

The best I found was the IPP120P04P4L03AKSA1 with an on-resistance of 2.9mΩ.
That should be good for about 18A without a heatsink.

 

Ok thanks ill give it a shot, i wasn't aware the arduino could accept that kind of voltage.

Which Arduino are you using? There are tons of very different Arduino and Arduino compatible devices, and they have different acceptable supply voltage ranges. The advice that's been given so far sounds appropriate for an Arduino Uno, but not for certain other models.

 

You could also parallel two or more MOSFETs to get the desired output current. For example, three 10A MOSFETs in parallel to get 30A capability.

PS Use heat sinks.

 

Hey @Mr. Incredible,

I'm designing a arduino setup for the exact same use case as you. Got my touchscreen arduino code just about done but running into mosfet current issues too. Did you ever get the PCB figured out? I'm very interested and could really use your help. And I'm interested in sharing our code and designs.

Thanks,
Steve
stevep@orm19823.com

 

Do you really need to switch the positive supply? The job gets an awful lot easier if you switch the negative supply

 

i don't know what PCB settings are capable of withstanding the high currents. Anyone able to help out on the circuit design process would be much appreciated.

so you didn’t get the Digikey freebie ruler?(The one where they got their own web address wrong) It has the current carrying capacities of copper tracks listed.

 

Hello,

Adafruit also has some one like it:


Here is also the datasheet for the digikey ruler, with some extra info.

Bertus