schema and assembly of a battery charger lead

We chose to supply electricity to our telescopes with small lead-acid batteries of 12 volts / 6 amps-hours for training in right ascension or 12 Volts / 2 Amps-hours for training in declination. You can purchase these accessories to a specialist in batteries, from a vendor of spare parts for models or a supplier of electronic components. This type of sealed, maintenance-free battery is very fragile, do not load it with a car battery charger (in this case his life would be very short).

We suggest making a charger for these batteries to delicate health. It may be separated from the drive, but if you want you can integrate it into the casing of it, possibly with the battery.
In the latter case, if you use the drive when the charger is on, you may experience a particular problem. Indeed, if a power supply transformer in the same housing as the drive, it can be influenced. Therefore, the frequency of the current generated by the drive may be erratic. To avoid this, care must be taken to isolate (or remove!) Drive the power transformer and the son whom he is connected.
The voltage supplied by a lead-acid battery is 2 volts per cell (a 12V battery is made ​​up of six elements). The voltage used to recharge its not exceed 2.3 volts per cell (for an ambient temperature of 20 ° C). A lead-acid battery should never be stored flat. The minimum voltage of a discharged lead-acid battery should not fall below 1.75 volts per cell under threat of irreversible damage.
The maximum current load must not exceed 0.3 x Ca
with: Ca = Rated capacity of the battery.
Example: A 7 AH battery should not be charged with a current greater than 7 x 0.3 = 2.1 A

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Figure 1: Block diagram and location of the battery charger

This is a regulated supply voltage with output current limited to 450mA or so, accompanied by a visual inspection of the load. The maximum output current varies with R3 as described in the data sheet L200.
The diagram is explained in Figure 1. When we connect the battery to be charged to the live circuit, the red LED D4 is illuminated. When charging is finished it off and the green LED lights turn D3. The buzzer will sound when we inadvertently connect the battery backwards. This does no damage.

 

Figure 2: Printed circuit board battery charger lead seen from the side components. Size = 41x76mm.

The arrangement poses no particular problem. The circuit IC1 requires a finned radiator. The thread of connection with the battery can be equipped with terminals or crocodile clips. Before mounting the circuit in a case, we must adjust its output voltage (no load) with Aj the value of 14 volts (0.2 volts to close). And set the charger may be permanently connected to a lead acid battery of 12 volts without it can suffer from overload, even when the load is complete.