Me and my friends are making a UPS model. So far we have established a battery charger circuit from mains and over charging protection for backup battery. We are working on charging indication using arduino, but we can not figure out a few things - firstly, when mains supply is on the battery supply should be off, second, after power is restored it should go back to power supply, third, if power is low battery supply should start.
We are basically not able design something for this logic. Please guide us!

 

Welcome to AAC.

First, is this school work?

What you are trying to design is an ATS (Automatic Transfer Switch). We‘ll need some more information to be able to help.

There are two broad topologies for a UPS: Line Interactive and Online.

A Line Interactive (LI) type switches between commercial and battery power as required. When the battery isn’t supplying the power, it is being charged. When the commercial power fails (or sags sufficiently) the power source is switched to the battery—when restored, it switches back.

Depending on the particular LI topology selected, there will be a switchover time from 2ms to 10ms or so when going between sources.

An Online (OL) topology eliminates the switching time because unlike the LI type, the OL always supplies the power through the inverter. If the commercial power fails or sags, the battery stops charging (being a power sink) and becomes a power course. There is no delay since there is no switching.

The OL topology is better if cost is no object, but might not be the best option if you are cost sensitive.

Please tell us—
How much do you have to spend?
How much power will you need? (This will be in both Volts and Amps, and Watt hours (Wh)—that is, what kind of runtime do you need?
What will this be powering?
How much experience do you have in electronics design and construction?

 

Welcome to AAC.

First, is this school work?

What you are trying to design is an ATS (Automatic Transfer Switch). We‘ll need some more information to be able to help.

There are two broad topologies for a UPS: Line Interactive and Online.

A Line Interactive (LI) type switches between commercial and battery power as required. When the battery isn’t supplying the power, it is being charged. When the commercial power fails (or sags sufficiently) the power source is switched to the battery—when restored, it switches back.

Depending on the particular LI topology selected, there will be a switchover time from 2ms to 10ms or so when going between sources.

An Online (OL) topology eliminates the switching time because unlike the LI type, the OL always supplies the power through the inverter. If the commercial power fails or sags, the battery stops charging (being a power sink) and becomes a power course. There is no delay since there is no switching.

The OL topology is better if cost is no object, but might not be the best option if you are cost sensitive.

Please tell us—
How much do you have to spend?
How much power will you need? (This will be in both Volts and Amps, and Watt hours (Wh)—that is, what kind of runtime do you need?
What will this be powering?
How much experience do you have in electronics design and construction?

Thanks for replying!
I am actually a first year electronics engineering student and this is an activity for the semester.
We were planning to use variac as 220V power source. We haven't yet planned on what it will be powering. This is kind of our first time designing such kind of circuit.