Lead Acid backup battery charging and switching.

[Astrid]

Need in case of power failure (AC) power to automatically attach the backup battery (12V Lead Acid 7-30Ah) current 2.5A max. It is probably not a problem P-MOSFET + diode.
But I would like the device to recharge the battery and watched her status with regard to maximum durability and energy savings.
For charging a 14V +, but sometimes that can be 17V +.
The devices have a processor, looking for some inspiration for the scheme, or suitable circuit for supervision

 

[BradtheRad]

It sounds as though you have a 12V power supply. It provides power continually to some device. Is this correct?

So suppose you were to hook up to the battery in the middle. You regulate the power supply to 13.8 V (a normal constant condition for a 12V battery). Perhaps as low as 12.8 V.

The battery would trickle charge, yet not overcharge. Its power would be available immediately if there is a blackout.

 

[Astrid]

Describe those going slightly more accurately
Power is
either AC 16V => DC 17V
or
switching power supply DC 13.8V max 2.5A
device is 7/24
If the power fails I want to add a backup battery 12V 4-30 Ah
I like taking the battery attached so as not to constantly recharged, because it costs money and, second, shorter battery life.
Therefore, we need either a controllable current source 0-1A
or switched current source, for example, 0, 100 mA, 700 mA (not charging, slow and fast charging)

 

[carpenter]

For example
R1 current shunt resistor
U2A amplifi voltage on R1 Vout= R1*I* (1+R3/R2)=R1*I*10
U2 drive PMOSFET Q1 so that V3=10*R1*I for V3=2V I over R1=2A
In real V3 is DAC
During power failure (V1 = 0) the device is powered from batterie across the diode in Q1.
ADA4661 not completely cheap amp, but need to find a cheaper precise Rail to Rial Amp.
What do you think?