Battery powered Arduino - vin vs 3.3v

Hello all,

I have an Arduino Nano that I'm powering through 3 X 1.5V batteries. Measuring "vin" - "gnd" pins gives me 4.3V but measuring "3.3V" - "gnd" pins only gives me 2.8V I'd have expected to see 3.3V there. Any ideas as to what's going on?

The Nano is a Chinese clone and I have a nrf240l radio attached to it.

Thanks in advance.

Yes, Vin connects to a 5V regulator not a 3V3 regulator, this needs at least 6.5V to work correctly and produce 5V out. This is known as head room.

Just connect your 4.5V to the 5V pin.

Thanks Grumpy_Mike for your response but not sure if I understand; isn't the 5V pin an output? My nrf240l does need to be connected to 3.3V, so are you suggesting that if I connect my 4.5V battery to the 5V pin, I can draw 3.3V on the 3.3V pin?


The 5V pin is an output, but many of us use it as a way to power our projects (in fact, I’m working on a new project that powers an Arduino through the 5V pin). If you do so, you will still be able to draw power from the 5V. I’m not sure about the 3.3V pin, but I’d think it’d work

Then you will need a 3V3 regulator to provide this. The one on the Nano is, or should be 5V.

Thank you for your responses. I guess Im just not sure why this voltage drop is.

I know this isn’t my thread, but I had a question that retains to this. Let’s say I’m using an Uno (or any board that has a 5V pin and a 3.3V pin) and I power it with a stable 5V. Will the 3.3V pin give me 3.3V or will it just no work or give me 5V?

Not really. It is more correctly a "reference" pin for 5 V devices, but principally it is the proper way of powering the Arduino since it is a direct connection to the 5 V line for the ATmega chip and the USB interface.

Of course, when you use the USB interface you feed - again , 5 V - into the USB connector and you can get something approaching 5 V from the "5V" pin except that there is a diode in between, dropping some fraction of a Volt and with (generally) a 500 mA current limitation. And if you are not connecting via USB, the USB chip is wasting your battery power; it would be better to use a Pro Mini.

"Vin" should be strictly avoided.

Finally, a Chinese clone may or may not actually have a 3.3 V regulator capable of powering a NRF device.

If you are powering it via 5 V, you have a 3.3 V regulator regulating down from the 5 V line. Except for clones deriving 3.3 V from the USB chip which have a very limited current capability.

Yeah I’m using a Pro Mini to avoid power loss (since I’m using a battery) so I should be able to power an OLED display off the 3.3V line


First you said:-

And now you say :-

Now which is it? The two are very different in regards to power. All my answers have assumed that you were telling the truth in your first post.

No no, I’m not the guy that said I’m using the Nano (I just asked a question since it pertained to the OP’s topic). Mine is a 5V Mini, so it would have worked the same as the Nano anyway

OK, that’s what you get when you hijack a thread.