The circuit presented slows down a small motorcycle or car battery, or a set of Nicad batteries, and when the power fails, it automatically feeds one or more small emergency lamps. Simple to assemble it uses low cost material.
The transformer has a dual purpose: supplying power for the slow charge of the battery whose current is given by R1 and, at the same time, keeping the relay K1 which turns the emergency light off.
When there is no voltage on the primary of the transformer, the relay opens its contacts, interrupting the charging circuit and attaching the battery to a small bulb. If the battery is 12 V, internal car lamps can be used. In Figure 1, we have the complete diagram of the device.
The arrangement of the components and the welding of the small parts on a terminal strip are shown in Figure 2.
The recommended relay is 6 V with 100 mA coil (Metaltex) and the transformer has 6 + 6 V secondary with 1 A current. The other components are common.
Material list
D1, D2 - 1N4002 - silicon diodes
C1- 100 uF x 12 V - electrolytic capacitor
K1- 6 V Relay
R1- 47 ohms x 2 W- resistor
B1- 12 V battery
T1- Transformer - see text
F1- 1 A - fuse
Miscellaneous: socket for lamp, fuse holder, terminal bridge, power cable, wires, welding, etc.
