Actually, the Nano can apparently draw up to 1A from the 5V pin. My problem is that I can only get 500mA through the USB mini B port.
Please explain.
Where would that 1A initially come from.
I hope you're not thinking of the 5volt regulator.
Because it's thermal restrictions set in before it's max current restrictions.
Leo..
My bad, it was 0.8A:
https://docs.arduino.cc/learn/electronics/power-pins/#3v35v-pin
The maximum current that can be drawn from the 3V3 and 5V pins when working as power outputs are summarized below.
...
Board 5V Pin Output Current (A)
Nano 0.8
No, it's not.
The sales idiot who wrote that just took the absolute max current rating from the regulator's datasheet without thinking there could be more to it.
Say you would connect 9volt to Vin.
There would be a drop of 9 - 5 = 4volt across the regulator.
That would generate 4volt x 1Amp = 4watt of heat in the linear regulator.
Enough to melt the solder or send the regulator to silicon-heaven.
Remember that that regulator is only cooled with a square inch of circuit board copper.
I would say it's wise to keep power in the regulator below 1Watt.
Now do the math with different input voltages and current draws.
Leo..
So I think I'm all good for the 5V power supply. I'm still a little unsure about the 3.3V though.
@jim-p could you please point me to more information on this? Most websites don't say much about where that 3.3V actually comes from, or they say something like "generated by on-board voltage regulator", so I'd like to be sure that it works when powering the Arduino solely through the 5V pin (no USB connected, nothing going to VIN).
Ah I see, and that was the FT232 jim mentions. I can see it in the schematic. I had noticed it before but wasn't sure it was the actual 3.3V supply as it seemed strange that it would be coming from a USB chip and not a voltage regulator.
That is the purpose.
It's not there to prevent the LED from being powered from USB as @stitech describes. There is also another diode on the board that prevents the external 5V supply from feeding into the USB connector, so you are protected both ways
You are fine for both the 5V and 3.3V power.
so I'd like to be sure that it works when powering the Arduino solely through the 5V pin (no USB connected, nothing going to VIN).
You will have the 3.3V in both cases, when USB is connected and when 5V is applied or when both are connected.
As I explained in post #14 the 3.3V comes from the FT232 chip, not a dedicated regulator. It is Arduinos cheap way of giving you 3.3V but not with a lot of current.
Actually. there is nothing to limit the amount of current from either the USB connector or the 5V pin, so you need to be very careful with your wiring and make sure you do not create any short circuits.
Most USB ports will turn off if you try to draw more than it can supply but I don't know if your 5V supply has any protection. You may consider using a fuse just to be safe.
The Nano is a cheap barebones design without a fuse or 3.3V regulaor like the Uno.