I have a modem which runs at 12V 1A, also I have an UPS battery of 12V 7Ah. I need to design a circuit so that during power outages my modem works from the battery.
Also, a circuit to charge the 12V 7Ah battery with full charge cut off so that I can connect these circuits so that there is no need to look after it after connecting everything like need to recharge the battery every day. So please help me to set up a circuit.
- To connect the 12V 7Ah battery to the modem 12V 1A safely without causing damage to the modem.
- A circuit to charge the 12V 7Ah battery with auto cut off on full charge.
- Automatically change over to battery so that the modem works on power outage with out disconnection.
Also one thing, the battery can't be connected directly to the modem because the modem is 12V 1A and the battery is 12V 7Ah; also the battery when fully charged will show 13.4V on multimeter, the battery is of type lead acid.
sample battery image http://img3.tradeee.com/up/lilian2010/74108.jpg