Automatic Battery Charger Wiring diagram Schematic

Normally, chargers available in the market do not have any sort of control except for a ro-tary switch that can select different tap-pings on a rheostat, to vary the charging current. This type of control is not adequate because of the irregular fluctuations in the mains supply, rendering the control ineffective.  A simple schema intended for automatic charging of lead-acid batteries is presented here. It is flexible enough to be used for large capacity inverter batteries. Only the rating of transformer and power transistor needs to be increased.

Circuit diagram :

Automatic Battery Charger Circuit Diagram

 

The schema has been basically designed for a car battery (about 40 Ah rating), which could be used for lighting two 40W tube lights. The schema includes Schmitt trigger relay driver,float charger,and battery voltage monitor sections.  The Schmitt trigger is incorporated to avoid relay chattering. It is designed for a window of about 1V. During charging, when the battery voltage increases be-yond 13.64V, the relay cuts off and the float charging section continues to work. When battery voltage goes below 11.66V, the relay is turned on and direct (fast) charging of the battery takes place at around 3A.  In the Schmitt trigger schema, resistors R1 and R2 are used as a simple voltage divider (divide-by-2) to provide battery voltage sample to the inverting input terminal of IC1. The non-invert-ing input terminal of IC1 is used for reference input derived from the output of IC2 (7806), using the potentiometer arrangement of resistors R3 (18 kilo-ohm) and R4 (1 kilo-ohm). 

LED1 is connected across relay to indicate fast charging mode. Diodes D3 and D6 in the common leads of IC2 and IC3 respectively provide added protecion to the regulators.  The float charging section, comprising regulator 7812, transistors T3 and T4, and few other discrete components, becomes active when the battery volt-age goes above 13.64V (such that the relay RL1 is deenergised). In the energised state of the relay, the emitter and collector of transistor T4 remain shorted, and hence the float charger is ineffective and direct charging of battery takes place. 

The reference terminal of regulator (IC3) is kept at 3.9V using LED2, LED3, and diode D6 in the common lead of IC3 to obtain the required regulated output (15.9V), in excess of its rated output, which is needed for proper operation of the schema. This output voltage is fed to the base of transistor T3 (BC548), which along with transistor T4 (2N3055) forms a Darlington pair. You get 14.5V output at the emitter of transistor T4, but because of a drop in diode D7 you effectively get 13.8V at the positive terminal of the battery. When Schmitt trigger switches ‘on’ relay RL1, charging is at high current rate (boost mode). The fast charging path, starting from transformer X2, comprises diode D5, N/O contacts of relay RL1, and diode D7. 

The schema built around IC4 and IC5 is the voltage monitoring section that provides visual display of battery voltage level in bar graph like fashion. Regulator 7805 is used for generating reference voltage. Preset VR1 (20 kilo-ohm) can be used to adjust voltage levels as indicated in the schema. Here also a pot meter arrangement using resistors R7, R8, and R9 is used as ‘divide by 3’ schema to sample the battery voltage. When voltage is below 10V, the buzzer sounds to indicate that the safe dis-charge limit has been exceeded.

Author : Yash Deep - Copyright : EFY Mag

Automatic AC Power Switch

Electrical appliances accidentally left on  in (holiday) homes left unoccupied for a  short or a long period consume power  unnecessarily and can present a fire hazard. Everyone will be familiar with those  nagging thoughts, a few miles down the  road from the house: “Did I remember  to switch off the coffee machine? The  lights? The oven?” 

Automatic AC Power Switch Circuit Diagram

Hotel rooms are often equipped with a  switch near the main door which enables the power supply to everything in  the room only when the plastic card (which  might contain a chip or have a magnetic strip  or a pattern of holes) that serves as the room  key is inserted. The schema idea given here  to switch off lights and other appliances is  along the same lines. The solution is surprisingly simple. 

A reed contact is fitted to the frame of the main entrance door, and a matching magnet  is attached to the door itself such that when  the door is closed the reed contact is also  closed. To enable power to the house, press  S1 briefly. Relay RE1 will pull in and complete  the schema for all the AC powered appliances in  the house. The relay will be held in even after  the button is released via the second relay contact and the reed contact (‘latching’ function). 

As soon as the main entrance door is  opened, the reed contact will also open.  This in turn releases the latch schema and  consequently the relay drops out. The  various connected appliances will thus  automatically and inevitably be switched  off as soon as the house is left. The schema is principally designed for  small holiday homes, where this mode  of operation is particularly practical. Of course, for any schema that deals in AC  powerline voltages, we must mention  the following caution. 

Caution:

shock hazard! Construction and connection of this schema  should only be carried out by suitably-qualified  personnel, and all applicable electrical safety  regulations must be observed. In particular, it  is essential to ensure that the relay chosen is  appropriate for use at domestic AC grid volt-ages and is suitably rated to carry the required  current.