Powering Arduino efficiently

Hi, I'd like to power the Arduino uno efficiently from a battery.
I figured itd be more efficient to take a 3.7v rechargeable battery, step it up to a regulated 5v and connect the 5v to the USB port.
That is rather then using a 9v battery which doesnt have enough mAh to drive an Arduino for longer than 2 hours.

What is your opinion please?

I have a side question too please.
If the Arduino uno is powered up from the Vin or the Power Jack, can it later be connected to the usb in order to transfer data to the PC, while the Vin or power jack are still supplying the power? Will the USB know it doesn't need to supply 5v in this case and only use the data lines? (Since the power is supplied from the Vin or Power Jack)

Thanks a lot :slightly_smiling_face:

For battery use, I would recommend a 3.3V Arduino of some kind, one with a "low-dropout" regulator so it can run directly from a 3.7V li-ion/li-po or 3x or 4x NiMH cells. Also explore using "low power sleep" library to save power when the Arduino is idle.

Whether you can safely connect an Arduino to usb at the same time as using another power supply including batteries, depends on the model of Arduino. With some models, there is a danger of damaging your pc/laptop, I understand, while others protect the PC. If you chose an Arduino Pro Mini, for example, you can avoid the danger by simply not connecting the Vcc wire from the separate usb-serial adaptor to the Pro Mini.

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Hi Paul,
Thanks so much.

For the moment, we are obliged to use Arduino uno.
For the Arduino uno, can the usb be connected while either the Vin or Power Jack is already connected?

Would you reccomend for the Arduino uno to step up the 3.7v to 5v and power it from the usb port?

Sorry, I don't know enough about Uno to know if it is safe to connect USB and Vin at the same time. I don't like the design of Uno and don't use them.

I would not recommend using a step up converter or an Uno for a battery powered circuit. In fact I would recommend not using them, as mentioned above. You will never get good battery life like this. But if forced to do so, I would connect the output of the step up converter to the Uno's 5V pin.

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Hi Paul
Thanks a lot again for the help.

In Arduino, they mention not to connect the 5v to the 5v pin.
Why would you prefer it over connecting it to the usb port using an old usb b cable from the step module to the usb port?

Could you recommend please a reliable 3.7v to 5v step up module that outputs regulated 5v?


You can power the Arduino by connecting the output from this board to the 5V pin and GND. You will need to solder wires to the 5V, 1A OUT pins on the board.

Hi IceChes,
That's great!! Thanks!!! :slightly_smiling_face:

A question please,
When the 5V output of the booster is connected to the 5V pin of the Arduino uno,
Will it still be possible to connect the PC to the Arduino uno through USB port?


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Adafruit Micro Lipo - USB LiIon/LiPoly charger

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The best ways to reduce power consumption are:

  1. Construct a bare bones project with no unnecessary LEDs on the board, no programmer on the board, and no power supply components on the board. Obviously you will need to use an external programmer, but that's not too difficult.

  2. Use the various powerdown modes as much as possible, and interrupts to wake and run the processor only when needed.

  3. Unless you absolutely have to have 16MHz, then you can use two AA cells and run at 3V

For example, my current project involves a bare bones setup, which will wake up every few minutes, take a measurement, then go back to sleep. As the current consumption in power down mode on the Watch Dog Timer is only a few micro Amps, two AA cells should last for a year or two.

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Forgot to say. You can use the Calibrated Internal RC Oscillatior. It runs at 8Mhz, so if you use a division of two then you can run at 3V with 4Mhz. That way you wouldn't even need a crystal on your bare bones project. And based on my previous measurements, the Internal RC Oscillator is typically very accurate.

Thanks a lot!!

By the Arduino uno schematics,
The T1 Mosfet decides whether to shut off the USB Vcc or not.

In our case, the Vin is 0V, meaning, the Gate voltage of the Mosfet is LOW, right?
And then, both Drain and Source of the Mosfet are 5v.

Won't there be a collision?
arduino-uno-schematic.pdf (32,7 KB)

I'm not sure. if you want to make sure, power the board on 5V while you are programming/debugging and switch over later.

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Your post was MOVED to its current location as it is more suitable.

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Why the Vin debate?
Using an UNO, a NEO-6M, a 4x20 LCD and a 6000 mAh power pack connected to the USB there's no need for any Vin.
When developing the code, computer USB power is used. When using the build as mobile the power pack does the job.
I think I calculated the life of that pack to be more than 48 hours, well enough for a portable speedometer...

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Thanks a lot
the thing is i need to use the usb to download data from the Arduino uno while it is powered and working

Me too!

But USB and the basically useless "Vin" are safe together FWIW.

Very misleading piece of advice. :-1:

Yes and no.

OK, here's the situation.

The "5V" pin is the direct connection to the supply terminal of the microcontroller, so that is the correct place to supply a regulated 5 V.

The concern is that if you are also connecting via USB to a PC which will provide 5 V, then if your 5 Volts supplied to the "5V" pin is slightly higher than the USB 5 V, it will feed current back into the PC USB hardware and that may - particularly on laptops - cause the USB interface to malfunction (requiring a full power down) or even be permanently damaged.

This risk is dubious since the majority of "powered" USB hubs on the market do exactly that and you do not seem to see reports about a problem, but it has been reported including by some contributors here in regard to the UNO. So the rule is, you disconnect the "5V" pin whenever you are going to connect the USB port to a PC. If you need to run the system like that - obviously you do not just for programming - then you supply 5 V to all the other devices requiring it from your separate supply, but not the UNO itself.

Since the Nano includes a diode between USB and "5V" pin, it has no such problem.

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Can't that down load device also provide power via the USB? Odd receiver?

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Thanks a lot

Well i want to power the Arduino uno without depending on the USB. It needs to be mobile.
The USB is just for programming and download data.

Great answer. Thanks a lot