Power Outage Detector with SMS-alarm - circuit idea

Hi everyone. I'm a somewhat newbie with circuits, did well in school though :) Have been programming for a couple of years with different languages, so I'm comfortable with code.

Anyway, I have this idea for setting up an power outage detector. I've read a number of threads on the topic, but never seen a solution like mine. I think the image provided will explain most of it.

Would this work or am I getting something wrong? Very grateful for any advice :)

Short explanation: The three power inlets from the house would naturally die at a power outage, leaving the battery to power the arduino. The charger is a normal one from any store, keeping the batteries constantly charged. About logic: A very short log would be saved to the EEPROM, like if power is coming from batteries or from mains (+ time). This way I don't have to care about the board resetting by the switch, and could send appropriate SMS anyway.

Hi, welcome to the forum,

1. You will probably need a trickle charger to prevent damaging the batteries, it's on constantly.

2. Would you really need 3 main power supplies for your project to work ?

Looking at the picture you have an DC power-supply connected to the battery-charger. You only need to check whether the input of the charger is powered, to get the info you want.

Since the voltage feeding the charger probably is higher as 5 volts you need a voltage-divider, which you can make using 2 resistors.

If the purpose of the second power supply (the lower right one in your diagram) is to indicate a power outage to the Arduino it is not necessary.

If you have a diode between the charger and the battery (to prevent the battery back-feeding to the charger) the Arduino just needs to monitor the voltage upstream of the diode.

...R

Thanks for the input guys!

Robin2
The power supply you are talking of is the arduino power supply while power is still on. When there is a current into the relay (the third DC power supply, lower left in picture), the arduino will take power from the lower right DC. When no current into the relay (i.e. power outage), it will take power from the battery. So the relay controls whether the arduino takes power from the battery or the mains.

Are you saying that I could just feed the arduino directly from the battery, while it’s being charged? Only that I put a diode between the charger and the battery? And then something to monitor voltage between diode and charger? No need for a relay?

Simpson_Jr
Thanks for the welcome!

1. I’m looking at a common cheap battery charger for 9V batteries. It has built in circuitry for detecting whether it’s is full or not.
2. Yeah I know, I also think it looks like it should be possible to skip one or two?
The DC source for controlling the relay could maybe be the same that feeds the arduino?

techio: Are you saying that I could just feed the arduino directly from the battery, while it's being charged? Only that I put a diode between the charger and the battery? And then something to monitor voltage between diode and charger? No need for a relay?

Yes.

In a way I am doing that 24/7. I have an Atmega328 running from a large (200Ahr) 12v battery (via a 7805 regulator) which is put on charge a couple of times a day. The '328 never notices.

...R