If I were to implement a simple battery backup system like this to power several WiFi radios in a field situation, how would the battery handle it? Would trickle charging it like that wear it out after several months? Or years?
For example, the system could have power for perhaps three or four months, and then need battery backup for half an hour if the mains power went out.
I have seen some battery systems that monitor the battery's charge, and when they do charge it, they use a pulse system.
Do I need something like that? Or will this simplistic approach be effective?
BTW, this is a standard 12v Lead-Acid battery like from a UPS.
simulate this circuit – Schematic created using CircuitLab
Best Answer
As Mrs Beeton would say - first catch your battery. The sealed lead acid type used in a myriad of long term applications such as UPS and alarms. Generally this battery is designed for exactly this type of application and will maintain its charge losing something in the region of 40% over a period of 1 year. (Some do better, some do worse - check manufacturer's specs. It also depends on other factors such as temperature etc. etc.) You should expect a few years of service before changing the battery. As your running a wifi system why not send data about battery condition.
The trickle charge only needs to keep the battery topped up. Overcharging is always a potential problem so the trickle charger should have limited voltage.
The circuit you have shown would not work as it does not switch between the normal supply and the battery backup. You need something like this. Reg 1 limits the charge voltage and R(trickle) the charge current. The LED indicates the supply is on (and ok) Reg 2 is the normal regulated supply controller. The diodes allow the battery to take over if the supply fails. (switchover)