Power supply

I need to use a compact power supply for my project. It is safe to run an Uno on 9V 400mA ? my setup will draw max 200mA but I note than 1A is recommended for the supply. Why is this?


“ I note than 1A is recommended for the supply”

Where did you read this ?

Depends on what the rest of the load is - the Uno takes some 80n mA by itself, and is not capable of supplying another 120 mA out of its 5V pin. An Arduino is NOT to be used as power supply for anything more than some basic sensors and maybe an LED. At 200 mA and a 9V supply the regulator will overheat!

I assume the rest of your load is also 5V. If so, grab an old mobile phone charger that can do 0.5A or more (most newer ones will do 1-2A) and use that. Power the Arduino through the 5V pin, the rest of your project can get power directly from the power supply.

200mA is just... within the limit of drawing from an Uno on an external 9volt supply.
Anything more and the 5volt regulator will overheat and shut down/reboot (if you're lucky).
Making a 9volt/400mA regulated supply already overkill.

Better to power the Uno with a 5volt cellphone charger on the USB socket.

200 mA * (9-5)V = 800 mW. May or may not work long term. I normally use 700 mA as limit when calculating heat dissipation of such small packages, and have the feeling that's pushing it already.

If that 9volt supply is connected to the DC socket, then dissipation is 200mA * (9 -0.7 -5) = 660mW.

However you look at it, encouraging anyone to use the "Barrel Jack" or "Vin" on a UNO/ Nano/ Pro Mini/ Leonardo/ Pro Micro is setting them up for trouble, future if not present. :roll_eyes:

(Because sooner or later, something will be added. :astonished: )

Thanks everyone for your replies

I noted that a charger (wall-wart) targeted at the Arduino is 9V 1A, hence my (poor) assumption. I will eventually build out the design on a PCB and was planning on leaving the USB out so was keen on using a barrel jack. From what I've read 5V at the barrel jack is not enough. Is this true?

Do you think a 5V 600mA supply like this directly powering around 200mA of components + the Arduino via the barrel jack would work?
https://tinyurl.com/ycwckhfh (link to ebay item)

Just forget about that barrel jack! Cut it off, grind it away, burn it, whatever. Forget about it.

Your Arduino is equipped with a 5V pin for a reason, which, contrary to popular belief, should NOT be considered a power source for other things (though it definitely can be used that way as well).

If you're making your own PCB , you can use a barrel jack connected to your MCU's Vcc pin and plug the MCU's voltage (5V or 3.3V) into it.

Looks like I'll be sticking to the USB then :slight_smile: at least until I get to a PCB

I have to agree with #8.

Even the USB port is limited as it has "protective" components between it and the real 5 V line.

You have 5 V? (you should.) Connect it to the "5V" terminal. Connect it also to all other components that require 5 V.