Hi, currently i need to do my finall year project that i choose whoch is UPS offline 500/600va and could anyone help me or send the circuit diagram to me. Thanks

 

Why would you choose a project you know nothing about? Search for existing UPSs and interrogate the data sheets.

 

It's also cheaper just to buy a UPS.

 

The problem that I see with this design is that the batteries are being continually drained while they are being charged, therefore, the charger never gets to fully charge the battery bank, unless you shutdown all your loads. For continuous operation, you would be going thru batteries like mad! I would never design a UPS system like this for continuous operation! Its no wonder you had to invest in an automated battery watering system. A marginal design...at best.

The way I see around this problem is to use a battery bank (12Vdc x 4) parallel connected with a battery charger permanently connected, and then an inverter (12Vdc-115Vac) of the VA size you need connected to the battery bank. Now here is where you need something to sense AC mains power failure. I would use a current transformer around the AC mains circuit with a 12 VDC meter-relay with adjustable setpoint connected to the current transformer secondary. When AC mains power fails, the meter relay contacts switch, enabling the inverter's output to switch on (by contactor or solid state relay). When AC mains power returns, the meter-relay contacts switch state disabling the contactor or SSR. The advantage of the meter-relay is two-fold; you have a positive indication of AC mains current (or lack of) and a reliable method of keeping your battery bank always 100% charged and ready for action.

Around here, we never shutdown our computers.

Regards, DPW [ Everyone's knowledge is in complete...Albert Einstein]