I'm using an arduino nano ethernet shield like the one robotdyn sells (https://robotdyn.com/nano-v3-ethernet-shield-w5500-v2.html). However, I'm using 12v to power everything through the Nano's Vin pin, but everything is getting hot and the ethernet shield stops working after a short amount of time. When I use the USB port this stops happening, so I think the current draw from the ethernet shield and the sensors is too high for the Nano's regulator. I have a couple of Nano IO shield (https://images.app.goo.gl/Pw515G9n2EnTcxS49), and wanted to know of they have an onboard regulator that can supply more current than the Nano when using the 12v jack.
Connect a well regulated 5V supply (cell phone charger) to the 5V input on the Nano. That bypasses the weak on board 5V regulator.
I'm using 12v
so I think the current draw from the ethernet shield and the sensors is too high for the Nano's regulator.
The reason for the heat is that the onboard 5V regulator is only good for about 1 Watt of dissipation. With 12V input the regulator must drop 7V. To stay under 1W, the current from the regulator must stay under about 140mA (12V - 5V = 7V, 1W / 7V = 143mA). The Nano uses about 50mA so there is less than 90mA left for other uses. Pulling more current than that causes the regulator to heat up and go into thermal shutdown.
Thanks for that breakdown. We were hoping to not have to use a charger, but if the IO board doesn't have a better regulator, that's what we're going to do.
I see a regulator in the IO shield, but doesn't look to be any better heat sinked than the one on the Nano so I would not trust it to be able to dissipate heat any better or deliver much more current.
groundFungus:
Connect a well regulated 5V supply (cell phone charger) to the 5V input on the Nano. That bypasses the weak on board 5V regulator.
I assume this is via the VIN pin?
Cheers
Les
Lesthegringo:
I assume this is via the VIN pin?
Dead wrong! 
See where he said:
groundFungus:
Connect a well regulated 5V supply (cell phone charger) to the 5V input on the Nano.
Find a pin marked "5V". And connect the negative to "GND"
Ok, thanks
So that I understand, what exactly is the VIN pin for, and what voltages would you use with it? If you check my other post re RS485 networks, it may be related to issues I'm having with that
Cheers
Les
The "Vin" or "RAW" terminal is essentially a legacy part, though some UNO "clones" such as the "RoboRed" and more sophisticated Arduinos do incorporate an actually functional switchmode regulator, it should simply be ignored on the older designs. 
The obsolete tutorials on the Arduino site and others imply that the largely ornamental "barrel jack" (UNO) and "Vin" connections to the on-board regulator is a usable source of 5 V power. This is absolutely not the case. It is essentially only for demonstration use of the bare board back in the very beginning of the Arduino project when "9V" transformer-rectifier-capacitor power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes. And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.
If you are asking this question, it is highly likely that you will wish to connect something else. In which case, the answer is regulated 5 V.
This is because the on-board regulator is essentially capable of powering only the microcontroller itself and no more than a couple of indicator LEDs. The on-board regulator might be able to power a few other things if it had a heatsink, but on the Arduinos, it does not.
Powering via the "barrel jack" or "Vin" connections is asking for trouble.
Fantastic, thanks for the explanation.
All I want from my arduinos is the signal to the particular module (stepper driver, LCD display, LED), and as in the case of the stuff that requires extra power (e.g. stepper driver) then I would prefer to power that separately. I suspect you have answered my question from the other thread.
I have an old Nokia phone charger in the garage, think I'll go dust it off
Cheers
Les
I have an old Nokia phone charger in the garage
Measure the no load output before you hook it up to your Arduino to be on the safe side. Make sure that the output is under 5.5V.
Just checked, 5.17v.
Thanks again
Les