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Automatic mains/battery transfer and charger circuit ?
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Automatic mains/battery transfer and charger circuit ?

by ImSebastian on Tue Aug 13, 2019 12:46 pm

Hey folks-

I'm developing a product wherein I need a battery backup. It's basically a 12V motor that needs to close in the event of a mains power outage. I use an Arduino to control a daily open/close motor and need to protect the system from the sun in the event of a power failure.

In the past, I used a normal 12V lead acid battery and wall charger, and just tied the (+) on the battery, the (+) on the charger, and the V_in to the arduino. It works, but the battery is huge and I'd like to see a solution that actually transfers power over.

If anyone has any input I'd be greatly appreciative!!

Sebastian

ImSebastian
 
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Re: Automatic mains/battery transfer and charger circuit ?

by adafruit_support_mike on Tue Aug 13, 2019 9:55 pm

You could use a step-down converter like this one:

https://www.adafruit.com/product/1385

Switching converters are more efficient than linear regulators like the one on the Arduino. They use an inductor's magnetic field to convert excess voltage to more current, or vice versa.

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Re: Automatic mains/battery transfer and charger circuit ?

by ImSebastian on Tue Aug 13, 2019 10:31 pm

Thanks for the note! Maybe I typed poorly, but I'm looking for a battery charging setup. I'd like to keep the battery charged when the mains voltage is present, and switch over to the battery voltage when the power drops out. Just the way a computer is charged when plugged in but reverts to battery when unplugged.

As I type this I realize maybe it's a silly question... do I just use a normal charger (either an IC and DIY circuit or a COTS charger) and just attach my project to the (+) and (-) of the battery?

Thanks!

ImSebastian
 
Posts: 10
Joined: Mon Feb 09, 2015 3:43 pm

Re: Automatic mains/battery transfer and charger circuit ?

by adafruit_support_mike on Tue Aug 13, 2019 10:53 pm

Yes, that should work.

Battery backup power supplies are usually easiest to make if you take power from the battery all the time. Then it's just a matter of whether the charger is running or not.

With that arrangement, the charger sees the load connected in parallel with the battery. Most chargers see the load as additional current flowing into the battery, and don't care about the difference.

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Please be positive and constructive with your questions and comments.