Hello Readers,

I want to design a circuit that will perform the following:
> if 220V AC on
>> LAMP off
>> if battery >12 v
>>> disconnect from mains
>> else
>>> connect and charge from mains

> esle if 220V AC off
>> LAMP ON

this is the final circuit, pls feel free to comment or provide new am improved circuit.

 

It looks like it could (almost) work on paper but there are a few points to consider:
1) The same function could have been achieved without relays
2) D1 and D4 should be across the relay coils
3) There isn't any current limiting on the battery charging circuit
4) It is very likely that RL3 will buzz and chatter. e.g. the charging circuit will pull the battery voltage high, Q1 will switch on and disconnect the charging feed, the battery voltage will then fall, Q1 will switch off........and around it goes....
5) There is also the problem that the "battery charged" threshold will be very poorly defined

 

Here's a simple, relay-free, solution....

 

Is the AC input in the schematic in post #1 220 VAC? Perhaps not good for the LM317.

 

I need to also ask for clarification on the AC input voltage. Is it direct from the 220 VAC line voltage, or it is from the secondary of a step-down transformer?

 

Thank You all for your contribution. AC input is from Secondary transformer 220 VAC to 25-20 VAC.

Original Circuit: