Uno running off mains power supply with back up 12v battery?

Hey there

I want to run my arduino off the mains with a 12vdc adapter. But does anyone know can I also t off to a 12v battery so the arduino keeps running when there is a power cut? (which we get a lot of in South Africa).

Anyone know if I can run this without charge regulator or anything?

The way I would do that is to use a trickle-charger to keep the battery charged and run the Arduino off the battery. The Arduino will just keep working if the mains power fails.

mains --- charger --- battery
|
---- arduino

...R

Ok that makes sense. Do you know what kind of charge regulator I need?

Yes. For a 12V Gel-cell, you want a regulator (such as an LM317) set to 13.4V but with a series diode on the output (so it actually needs to be 14V before the diode) to prevent current flowing back into the regulator when the mains goes off.

Secondly, your battery capacity is valuable, so you need to power the UNO via an efficient switchmode regulator to drop the ā€œ12Vā€ down to 5V and feed it directly into the Vcc connection.

Sounds complicated!

You would also need a current limiting circuit for when the battery is discharged and would like to draw more current than the wall-wart and LM317 can handle.

You should be able to buy a suitable charger in an auto-accessory shop. Just make sure that you do NOT get a fast charger. You need one that is safe to leave connected all the time.

The Battery University website has lots of useful information

...R

Cool thanks Robin

How much current will your arduino thing draw? If it is below 1Amp I would take the easy option and use a USB car charger to step down from 12V to 5V. Most are based on a switchmode supply these days which gives you 80-90% efficiency.

Also if you are using a gel/lead acid battery they don't last long if you take the full rated current. E.g. a 1Amp hour battery will only last 20 min or so if you take 1Amp but will last 20 hours at 1/20Amp.

chopsuwe:
use a USB car charger to step down from 12V to 5V.

The Arduino already has a voltage regulator

Also if you are using a gel/lead acid battery they don't last long if you take the full rated current. E.g. a 1Amp hour battery will only last 20 min or so if you take 1Amp but will last 20 hours at 1/20Amp.

This is quite true - I had been assuming the OP would be using a big lead-acid battery.

...R