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This will be my first time trying to power my Arduino from an external source rather than an USB port.

I will need to power my Arduino Nano (Rev 3.0) with an external 24V DC power supply (from a 24V, 36Ah lead acid battery), so I was wondering what I could do.

I have three possible solutions:

  1. Connect the 24V power supply to a 24V-to-12V DC buck converter, and supply the 12V voltage to the Vin pin on Arduino Nano to power my Arduino Nano.

  2. Connect the 24V power supply to a 24V-to-12V DC buck converter, and supply the 12V voltage to a voltage regulator (LM7805), and supply the 5V voltage to the 5V pin on Arduino Nano to power my Arduino Nano.

  3. Connect the 24V power supply to a voltage regulator (LM7805) directly, and supply the 5V output voltage to the 5V pin on Arduino Nano to power my Arduino Nano.

Do all of the 3 solutions work theoretically? Will all of them successfully power the Arduino Nano? Which one is better?

EDIT

I will get my 24V DC supply from a 24V, 36Ah lead acid battery, and I will use my Arduino Nano to power a DC motor via L293D and buttons. I am not sure how much output current I will need, but I think it wouldn't be a lot. Will the 24V, 36Ah lead acid battery affect my choice?

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    \$\begingroup\$ A buck converter will almost always do the job (much) more efficiently than a linear regulator, so you're generally better off either avoiding the linear regulator completely, or getting the power as close to what's needed as possible before having the linear regulator do its thing. \$\endgroup\$ – Jerry Coffin Nov 15 '17 at 0:55
  • \$\begingroup\$ How much current is needed at 5V? If it is more than a few mA, you should just use a 5V buck regulator (an option you did not mention). \$\endgroup\$ – mkeith Nov 15 '17 at 3:34
  • \$\begingroup\$ @Natalie: why are you concerned about efficiency when using off-line power supply? I doubt you will notice any difference in electricity bill regardless of how Arduino Nano is powered. \$\endgroup\$ – A.K. Nov 15 '17 at 4:15
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    \$\begingroup\$ @A.K. Since I am getting the 24V from a battery, I wanna make sure the battery lifetime would not drop dramatically. \$\endgroup\$ – Natalie Nov 15 '17 at 4:38
  • \$\begingroup\$ I see, I thought it's a power supply. Anyway, with such a battery your arduino will have power for more than a year. Battery self-discharge will affect the battery life more. Plus current consumption by the motor. Arduino Nano does not have 12VDC input, does it? If it doesn't, a DC/DC buck 24V to 5V convertor is the natural choice. \$\endgroup\$ – A.K. Nov 15 '17 at 5:09
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The most efficient solution would be to use a 24V->5V DC->DC converter.

Adding a 7805 at any point will simply waste power - the 7805 (or any other linear regulator) just acts as a resistor. The current drawn from the 24 volt source will equal the current required by the Arduino (plus a bit for the regulator operation).

With a DC-DC converter, the power drawn (not the current) from the 24V source will equal the power required by the Arduino (plus a bit for the DC-DC converter operation and inefficency).

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  • \$\begingroup\$ We are counting peanuts, but at <20 mA, DC-DC converter loss may be a substantial fraction of total power. For example, the suggested LM2596 has 5mA typ. no-load current. \$\endgroup\$ – A.K. Nov 15 '17 at 5:43
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*7805 has a pretty bad effectiveness

--12->5 will really hot

--24-> 5 don't ever think...

maybe u can try LM2596 to solve it

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Your first choice is the best one imo. The 5 V pin on Arduino nano is intended to be a low current local output supply for projects so not recommended to supply the board via the 5 V pin. It is possible if you have a regulated supply which won't exceed 5.5V. See: https://www.rugged-circuits.com/10-ways-to-destroy-an-arduino/

And https://forum.arduino.cc/index.php?topic=271158.0

Use the 24 V to 12 V convertor and apply it to Vin on Arduino. The Arduino has a built in power regulator that provides the local 5 V on-board voltages. Ie the second part of your choice 2 is already implemented on board the nano.

This way you will have 24 V, 12 V, 5 V and 3v3 sources available for your project. 5 V and 3v3 via the Arduino itself but those are current limited. Eg Entire current for arduino nano is 500 mA max. Cant recall off hand what max current is via 5v or 3v3 pins.

A 12 V 2956 converter would give you up to 3 A. The 24 V supply whatever your battery could provide. A well designed 2956 circuit would stabilise the 12 V input to the arduino if your project suddenly drew a large parallel current from the 24 V supply making the voltage drop due to internal resistance on battery. Similarly if you used the 12 V output from 2956 to power the arduino and the project in parallel.

Vin is 7 V to 12 V. So a 5V supply wouldn't work on Vin.

You could also supply 5 V via the usb connector. But I like to use that for serial comms with PC. Don't like powering projects via computer usb as that can cause power surges on pc especially if there's an unexpected fault during development (accidental shorts can happen!). If you power via USB and Vin simultaneously then i believe the on board regulator selects highest voltage source. So 12 V will win and current isn't drawn via PC.

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