This is the circuit I have designed. I want to be sure whether I have designed it properly or not.
Here is the Purpose:
I am trying to power a Network device 24 hours which requires 9v (600ma). I have a 12 Volts 9AH (SLA) battery and a 12-0-12 (2 ampere) center tapped transformer. When there is mains available this circuit should charge the battery, auto cut off when full charge state is achieved and protect the battery from over discharging.
Circuit: When battery voltage reaches 13.8 V then the T1 (Transistor BC547) goes on, making relay K1 on so the default connection between point 'a' and 'b' breaks and the charging stops. Similarly when battery voltage drops below 10.8v then T2 goes off so is the relay, Hence the over discharge is prevented.
Problem: This circuit is working to some extent, but as mains go off this circuit will provide power for only 50-55 minutes. I don't have any idea why this battery drains so fast. Also the relay bounces back and forth for a while near to the cut-off voltages.
So my point is how do I stop this battery from draining so fast. I am using a brand new battery and there is no problem with the battery. Is relay drawing so many power or may be the linear regulator 7809. Also how do I make it more efficient. Any suggestion would be appreciated.
This is what is written on battery:
Cycle use: 14.4-15 Volts
Stand By use: 11.5-13.8 Volts
Initial Current not less than 2.7 ampere
1. Moreover, At what current and voltage should I charge this battery?
2. Suppose I am charging the battery at 2 ampere current and lets say, I do not apply any current regulator (meaning, Once I have started charging I do not regulate the current there after) , does current gradually decrease as the battery charges up or do I have to reduce the charging current after 70% charge of state?
3. How important is the float charge in my case? Battery is frequently drained lets say once in a two day period.
4. How can I cut down the components and ultimately the price?