battery-charginglead-acidsolar cell
I need to have a controller for charging a 12V 7AH battery and provide uninterrupted supply.
The source for charging would be 12VDC from a PSU or if there is a failure in that from a solar panel. I am confused , I found a few such solutions for lipo batteries but cannot find for lead acid batteries. I want to have auto charging and cutoff on full charge.
There are some ICs that provide solution for solar but they have no support for the other source.
Battery University is a good starting point. A vast amount here Battery University
Particularly:
Based on the following, it would SOUND wise to charge fully for "a while" under trickle and then to open circuit the charger until Vbattery fell to approaching 2.1V/cell. A controller to implement this could be extremely simple.
Dangerous in isolation, but, they say:
Most stationary batteries are kept on float charge. To reduce stress, the so-called hysteresis charge disconnects the float current when the battery is full. As the terminal voltage drops due to self-discharge, an occasional topping charge replenishes the lost energy. In essence, the battery is only “borrowed” from time to time for brief moments. This mode works well for installations that do not draw a load when on standby.
Lead acid batteries must always be stored in a charged state. A topping charge should be applied every six months to prevent the voltage from dropping below 2.10V/cell. With AGM, these requirements can be somewhat relaxed.
Measuring the open circuit voltage (OCV) while in storage provides a reliable indication as to the state-of-charge of the battery. A voltage of 2.10V at room temperature reveals a charge of about 90 percent. Such a battery is in good condition and needs only a brief full charge prior to use. If the voltage drops below 2.10V, the battery must be charged to prevent sulfation.
Observe the storage temperature when measuring the open circuit voltage. A cool battery lowers the voltage slightly and a warm one increases it. Using OCV to estimate state-of-charge works best when the battery has rested for a few hours, because a charge or discharge agitates the battery and distorts the voltage.
Firstly, the feed to the cameras: I think, to be safe you should use a low drop-out regulator to feed your cameras - this takes care of slight overvoltages. The KA278R12C is a linear voltage regulator with very low drop out: -
Note that even when the input voltage is at 10V, the device is still able to ostensibly produce 10V at its ouput when delivering over an amp (6 ohm load). I suspect this device will be good enough to feed your camera system but I can't absolutely say because you haven't specified current. There are other higher power devices that would fit the bill.
Can I wire a load to my battery if it is connected in parallel with the charger?
If the battery is lead/acid and the charging current is significantly more than what the camera load takes when attached to the above regulator then yes you can. If the battery isn't lead-acid then we need to know which technology it is.
How can I add a solar panel + controller to the previous circuit?
Playing safe, you can use a relay circuit that activates the relay when the AC power is applied to the charger - the relay contact can switch the battery from solar charger to AC charger in a few milli seconds. Playing a little bit unsafe, it's likely that your solar charger will have a diode in its output that protects the battery from discharge when the sun doesn't shine.
This very same component probably can mean that you can connect the AC charger permanently to the battery (and solar charger) BUT, you may need to add a series diode\$^1\$ in the AC charger's output when AC is off and the solar charger is feeding juice to the battery; the AC charger's output circuits may be activated by the solar charger and it's difficult to say what will happen - worst case it might pop the output transistor in the AC charger - best case no problem.
However, the chances are likely that your AC charger (just like your solar charger) will be protected from reverse voltages when power is down (or sun is not shining). You need to check this.
\$^1\$The diode needs to be a low volt drop schottky type capable of taking the charge current (again, you haven't specified max charging current so it's impossible to say but there are plenty rated for 10A and 20A continuous usage).
Best Answer
A integrated solution for this task is found at Linear Technologies. They have a good white paper to introduce the concept of maximum power point tracking: Techniques to Maximize Solar Panel Power Output. A suitable solution for your application could be the LT3652 - Power Tracking 2A Battery Charger for Solar Power.
The second source you just put in parallel to the solar panel and in each circuit (dc source as well as solar panel) you put a diode. Make sure to use low forward voltage drop diodes (such as a Schottky diode) that are suitable to carry the current in your application.