A superior design than the battery chargers sold in the market for 2..3k as 12V 1XX amp industrial chargers. Automatic battery charger is a versatile circuit for charging 12V lead acid batteries, can provide current up to 10A and has a number of special features:
Battery Charger Features
- Adjustable upper voltage cut.
- Adjustable lower voltage cut.
- Reverse battery connection protection.
- If the battery is not connected, the power at the charger output is cut off.
- LED indicators, charging, full, error or reverse battery.
Automatic Battery Charger Circuit Diagram
The main integrated circuit that controls the disconnection and connection processes, respectively, according to whether the battery is charged or not, is the LM358 opamp. All resistances not specified in power are 1/4W. The bridge diode must be at least 15A (a cooler would be good). The relay operating voltage is 12v and its contacts must support a minimum of 15 amps.
The points marked as P2 on the source part and on the relay are the same point, the specified point should be combined and reinforced with solder filler since it is where the battery current will pass.
The transformer used can give an output of approximately 10A taken from a UPS (uninterruptible power supply) device between 500VA and 600VA, it generally has a 2X7V AC output.
CHARGER SETTINGS
Using VR1, the upper voltage cut-off is set. It can be set between 13.8v and 14.2v.
Note: If the load is constantly connected, it is better to keep it in 13.8v float charge to extend the battery life.
Using VR2, the low voltage charge point can be set. This is the point at which you want the battery to reconnect to the charging system when it is discharged. It can be 11.5v or slightly lower, but it is always recommended to be above 10.5v. This will keep the battery charged in case the load is permanently connected to the battery.
To make these adjustments, let the battery charge to the desired stop point and turn VR1 until the charge LED lights up and you hear the relay click. Then, check that it is cut off once more at the same voltage and it will work, it will always stop charging at this voltage.
Then let the battery discharge or drop to the minimum voltage we want, so that when it reaches that voltage it starts charging again. We do this by turning VR2 until the charge LED lights up when the voltage is reached. Initially the potentiometers VR1 and VR2 are set to minimum and then scaled one by one.
CHARGE CIRCUIT OPERATION
The LM358 measures the voltage levels at the battery in receiver mode by operationally measuring A1, R2 and R3; this is the reference voltage; the drop across R3 is then connected to R1 and VR1 to form a voltage divider across the battery; the voltage to be compared is the drop across VR1; when this is greater than the voltage drop across R3 it increases the opamp output to about 10V; this causes Q1 to reverse bias and the relay (RL1) to close.
Then the second opamp with LM358 marked as U1B is responsible for monitoring the minimum level of the battery, just like before, R8 and R9 form the divider for its reference voltage, this is the value of the drop in R9, then R7 and VR2 form a divider connected to the battery, when the battery voltage drops below a certain point (preset), the output is set to 0v, this causes U1A to bring its output to 0v and Q1 to be triggered again, thus opening the relay.
After the charge starts, the output of U1B rises again, so when U1A closes Q1 again, it gives current to its positive input, which causes it to wait for the minimum step level to be able to start the charge again, when the maximum charge is triggered, all this is done with the help of one of the closed contacts of RL1 .
The Q3 TIP32 transistor is used to control the on and off of the cooler 12v fan while the charger is running.
Transistor Q2 is used to sense when the battery is connected to allow the relay to connect, thus preventing the output wires from being energised and this provides protection against short circuits etc. at the charger output before connecting the battery for charging. The fault LED will illuminate when the battery is reverse connected.
source: electronicabasica00.blogspot.com/2014/05/cargador-automatico-de-baterias-12v-10a.html
