Need some help with my electronic schematic (battery backup)

[Michel]

Hello,


I would like to build my own DIY battery backup system.
I had some basic schematics in my head and it would be appreciated if I could get your thought about this.
I have the normal power supply relay terminals wired as N/O and the battery relay terminals connected as N/C.
When the power adapter got power, the main power supply will be connected to the 24V output, and the battery terminals will be disconnected.
When the power fails, the power adapter will disconnect and the battery terminals will connect to the 24V output.


Do you all think this will be a good solution or are there some flaws in the schematics?
My consern right now is the battery relay powered 24/7 until a power failure accures (which might happen the next month, or maybe after a year?)
Is it oke to keep the relay powered on for such a long time?

Any tips on improving my schematic are highly appreciated.

It will only be used to power two 24V-20W powerheads so I guess the total output will be about 24V 2-3A

 

[Subsea]

To address your UPS system schematic: it’s fine as is.
Once a month, you should unplug the ac supply and monitor voltage on batteries for one hour. Document voltage drop and note changes over time.


I have a diy UPS system that runs two 70W pumps for 48 hours. I choose to operate pumps with inverter output from batteries which are maintained with a smart battery charger. There are no switches which I consider to be a weak link.

 

[Reefering1]

Sure, but I would skip the diodes(a capacitor can be used if your concerned about inductive kick, but not necessary and has consequences), and aren't you half using the dpdt relays? I suggest:

(Sorry for the crude sketch)

 

[Reefering1]

The only place for diodes, imo, is between the charger and battery. That way the charger isn't being back fed when not powered.

 

[Michel]

Thanks for the replies! The reason I had the diodes was because I was afraid the relais might not switch exactly the same time and I did not want one power source feeding the other power source when both turned on at the same time.

The schemetic you made with 1 big relai instead of 2 kinda fixes this issue I guess. So I think that is the way to go!