Hi, I want my arduino and gsm shield to be powered even on power failure. I have one 12V 3A acdc adaptor and 6V 4.5 AH lead acid battery. I'm thinking of using a relay or a diode. which one is better? I already have a 1N5822 schotkky diode for lower voltage drop.
Here is the schematic. The LED represents the arduino and gsm shield.
I thought of that too but with the diode it is still draining a very little ampere on the battery even when not in use. Do you think its okay? yes, the gsm shield has on board regulator.
Charging sla's aren't that bad, they are pretty robust(I toture them often with electrically abusive experiments), probably the most effecient way would be a mosfet, a regular diode would only be worth it at low currents, a germanium diode is better but still has current limitations(as well as heat)
Basically for that size battery you will want to charge it @.3-1amp constant current untill it reaches close to 13.8, then you have it constant voltage @13.8
Easiest way is to use a lm317 although @1amp you will need a heatsink