putting voltage through vin pin

hi
currently on a project have been all over the web /youtube ect to find this answer but so many conflicting results ,in a nutshell
i have 4 x 18650 batteries supplying 14.8 v @2900mah per battery i take it this can be put through vin pin with a step down module to take it to 12v
or 3 x 18650 batteries supplying 11.1v @2900mah per battery would connect straight to vin pin without any damage to arduino ,another question is because vin then supplys 5v to arduino would the extra voltage of the batteries make them last a bit longer and not be too much of a drain ,i have an lcd i2c 5v display connected aswell as a 5v relay board which would only be used maybe 4 times per day
colin

i have 4 x 18650 batteries supplying 14.8 v @2900mah per battery i take it this can be put through vin pin with a step down module to take it to 12v

Why bring it down to 12V?
That still means the onboard linear regulator is burning off 7V pointlessly.
Use a switch mode converter and take it down to 5V

Which board? A diagram of your project would make things more clear.

In general. You can put 12V into Vin on most Arduino boards. On the Uno Vin goes into an AMS1117 3v3 regulator that provides 5V to the rest of the board. You are on the upper edge of safe, but some will tell you that this is dangerous. I have been running an Uno with a 12V wall-wart for months and the on-board regulator is barely warm to the touch.

Where is the relay getting power?

Read this.

Take care powering the Arduino through the Vin or the power jack. Powering through Vin or the power jack means that the Arduino and all peripherals that are on the 5V rail are powered by the onboard 5V regulator. The on board 5V regulator is not heat sinked so will supply limited current before it overheats and shuts down. The recommend max power dissipation for the regulator is 1 Watt. With 12V into the regulator the max current is about 140 mA (1W / (12V - 5V)). The Arduino uses around 50ma of that leaving less than 90mA (max) for everything else. I would use a buck converter to drop the 12V to 5V and connect that to the 5V on the Arduino, bypassing the, weak, 5V regulator.

hi apologies ite an arduino uno board ,i thought the 5v was for out putting 5v not in putting,thought the idea was vin in 5v out ,theres a lot of confusion going on (most in my head) colin

You can put 12V into Vin but you must consider how much current that the 5V regulator must supply.

The UNO has a feeble little regulator which can supply the board itself but has trouble if you try to supply too many things via the 5V pin. The high the voltage on Vin the worse the problem gets.

The efficient way is to ignore Vin and the onboard regulator and supply 5V to the Arduino 5V pin and also to any other things that need it.

Steve

Hi Thanks very much for all the help think I'll go from 14v using DC step down converter to 5v and use 5v pin that should leave me bit of space in keeping batteries topped up is my thinking hope that's right if I've got 14v to play with but only using 5v I'm thinking it should last longer do you think that's the case Colin

A very real danger is that the obsolete tutorials on the Arduino site and others misleadingly imply that the largely ornamental "barrel jack" and "Vin" connections to the on-board regulator allow 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 (older) Arduinos, it does not.

Powering via the "barrel jack" or "Vin" connections is asking for trouble. The "5V" pin is not by any means an output pin, if anything a "reference" pin but most certainly the preferred pin to which to supply a regulated 5 V.