A step-down transformer is one whose secondary voltage is less than its primary voltage. It is designed to reduce the voltage from the primary winding to the secondary winding. This kind of transformer “steps down” the voltage applied to it. As a step-down unit, the transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current.
The primary winding, which doesn’t have to conduct as much current, may be made of smaller-gauge wire.

This dc voltage doubler circuit produces a voltage that is twice its voltage supply. This is useful when a higher voltage level is needed out of a single lower voltage power supply. Since the current consumption levels are low in such cases, the circuit can be built with minimal resources.
The electronic circuit is basically a square wave generator using the common LM555 timer IC. It is followed by a final stage made of transistors T1 and T2. The actual doubler circuit is made of D1, D2, C4 and C5 components.

Modern acid batteries and plates Pb, are embodiment of simplicity in use. Unlike NiCd batteries, they must be recharged by connecting to a constant voltage. In this situation, the loading current will provide a good indication of the state of loading.

Here are two battery chargers using solar cells to capture light energy for battery charging. It converts light energy into electrical energy. Simple and ideal energy saving designs.