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Most efficient 12v to 5v battery power supply
Moderators: adafruit_support_bill, adafruit

Most efficient 12v to 5v battery power supply

by Blimey on Tue Mar 19, 2013 5:06 pm

What is the most efficient method of getting a stable 5v power supply from 12 volt lead acid batteries? Note, the battery voltage extremes can vary from 11.8 volts to 15.8 volts while being charged by solar panels.

I have read about voltage regulators, voltage dividers, step-down converters and others etc, but bearing in mind the voltage range, is there one method that achieves what I need best of all?

I have several Arduino Uno and later ATtiny85 projects I'd like to try, but feel I need to get a stable power supply sorted out first...

Can you please help?

(Soldering parts is no problem)
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Re: Most efficient 12v to 5v battery power supply

by adafruit_support_bill on Tue Mar 19, 2013 5:08 pm

One of these will efficiently regulate your battery output to 5v/1A . http://www.adafruit.com/products/1065
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Re: Most efficient 12v to 5v battery power supply

by fuceye on Tue Mar 19, 2013 9:27 pm

Specs (from http://arduino.cc/en/Main/ArduinoBoardUno):

i just plug the uno straight into the 12v cig lighter in my car....

Microcontroller ATmega328
Operating Voltage 5V
Input Voltage (recommended) 7-12V
Input Voltage (limits) 6-20V

Digital I/O Pins 14 (of which 6 provide PWM output)
Analog Input Pins 6
DC Current per I/O Pin 40 mA
DC Current for 3.3V Pin 50 mA
Flash Memory 32 KB (ATmega328) of which 0.5 KB used by bootloader
SRAM 2 KB (ATmega328)
EEPROM 1 KB (ATmega328)
Clock Speed 16 MHz
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Re: Most efficient 12v to 5v battery power supply

by adafruit_support_bill on Tue Mar 19, 2013 9:37 pm

i just plug the uno straight into the 12v cig lighter in my car....

You can do that but...
First of all, most automotive systems are closer to 14v than 12v - and pretty noisy to boot.
Secondly, even at 12v, close to 60% of the power will be dissipated as heat by the on-board linear regulator. Touch the regulator on one that has been running for a while if you don't believe it.

You can run an Arduino at 12v. I would just think very carefully before connecting any additional loads to it.
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Re: Most efficient 12v to 5v battery power supply

by Arctic_Eddie on Wed Mar 20, 2013 6:16 pm

I've used these in a variety of projects.

http://www.ebay.com/itm/1PCS-LM2596-DC- ... 1088690509?
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Re: Most efficient 12v to 5v battery power supply

by ModemJunki on Wed Mar 27, 2013 3:11 pm

adafruit_support wrote:One of these will efficiently regulate your battery output to 5v/1A . http://www.adafruit.com/products/1065


But... for an Uno you want more than 5V for Vin, correct? "Recommended 7-12V" and "Limits 6-12V" is the spec on arduino.cc.

I've been looking at this because I also have an automotive project in mind. I was thinking that if you have any reasonable amount of "extra" stuff drawing power from the pins, 5V won't cut it as Vin.

If you were going to scratch-build a rig or use an Ardweeny I suppose this would be perfect, and indeed I am putting this on my list of Things I Might Need as I may use an Ardweeny for my automotive install. But if I use something else (like an Uno or Nano or Mini or similar) I would probably try and get around 9V @ 1A switchmode regulated in there.
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Re: Most efficient 12v to 5v battery power supply

by adafruit_support_bill on Wed Mar 27, 2013 4:07 pm

But... for an Uno you want more than 5V for Vin, correct? "Recommended 7-12V" and "Limits 6-12V" is the spec on arduino.cc.

Not really. The 7-12v spec is so that the on-board linear regulator can regulate it back down to 5v (and not very efficiently either).

If you have a good regulated 5v source, you can bypass the Uno's regulator and feed 5v directly to the 5v pin. That is exactly what happens when you plug it into a USB port.
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Re: Most efficient 12v to 5v battery power supply

by ModemJunki on Wed Mar 27, 2013 5:31 pm

adafruit_support wrote:
But... for an Uno you want more than 5V for Vin, correct? "Recommended 7-12V" and "Limits 6-12V" is the spec on arduino.cc.

Not really. The 7-12v spec is so that the on-board linear regulator can regulate it back down to 5v (and not very efficiently either).

If you have a good regulated 5v source, you can bypass the Uno's regulator and feed 5v directly to the 5v pin. That is exactly what happens when you plug it into a USB port.


Aha, excellent to know. I was going by the advice on the ruggeduino site (you cannot power a ruggeduino from the 5V pin) and the warning on the Uno page at arduino.cc (5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.). These warnings are probably to keep newbies like me from letting the Magic Smoke out.

I think the key is as you say - a "good regulated 5V source" - and so the buck converter would do the job.

I shall buy one and experiment with it.
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