THE ELECTRIC WAVE

ALKALINE CHARGER

This circuit was specifically designed to recharge alkaline cells. The unusual connection of the transistor in each charging unit will cause it to oscillate, on and off, thus transferring the charge accumulated in the capacitor to the cell. The orange LED will blink for around 5 times a second for a 1.37V cell. For a totally discharged cell the blinking is faster but it will decrease until it will come to a stop when the cell is charged. You may leave the cell in the charger as it will trickle charge and keep it at around 1.6V. To set the correct voltage you have to connect a fresh, unused cell and adjust the trimmer until oscillations set in, then go back a little until no oscillation is present and the circuit is ready to operate. You should use only the specified transistors, LED colors, zener voltage and power rating because they will set the final voltage across the cell. A simple 9V charging circuit was also included: it will charge up to around 9.3V and then keep it on a trickle charge: the green LED will be off while charging and will be fully on when the battery is close to its final voltage.

A 2.5VA transformer will easily charge up to 4 cells at the same time although 2 only are shown in the schematic. In order to minimize interference from one circuit to the other they have nothing in common except the transformer and, in order to show a balanced load to the transformer, half of the charging units will use the positive sinewave and the other half the negative sinewave. Make sure to use high beta transistors such as BC337-25 or better BC337-40. Type BC337-16 might not work all the time.

All types of alkaline cells can be recharged: it will take around 1 day for a discharged AA cell or 9V battery and up to several days for a large D type cell. The best practice is not to discharge completely the cell or battery but rather to give a short charge every so often although admittedly this is not easy to achieve. Do not attempt to recharge a totally discharged cell or a cell showing even the slightest sign of damage.

5W  INVERTER

A single transistor is all you need for this simple inverter. The main aim of this circuit is to provide a suitable supply for all kind of low power battery chargers that normally connect to the mains such as mobile phones, electric shavers, etc, even an electronic neon light rated at 5W was successfully connected. Only easily obtainable components are used. The transformer is a standard 10VA mains transformer with two 6V windings connected as shown in the schematic. Frequency of operation is between 70 and 190Hz depending on the nature of the load. This frequency is acceptable by most devices but obviously it is not suitable to drive frequency dependent appliances such as clocks or small motors that depend on the mains frequency in order to operate reliably. The transistor will not require any additional heatsink if it is assembled on the metallic case provided for the inverter. The neon glow light will give a useful indication, and warning, on the presence of a dangerous voltage at the output. A 2.5A fuse on the input supply line would be a useful addition. Operation is simple: switch on the unit and connect the load keeping an eye on the neon glow light which should be always on: certain switching chargers demand an initial peak current effectively shorting the output and switching off the neon: in this case you have to try repeatedly to connect the load until it works. A temporary short at the output and a temporary voltage reversal at the input will not damage the unit. Efficiency was not a design parameter however it was measured to be between 50 and 60%. If you have a 110V mains transformer and consequently a 110VAC output you should change the 0.1mF capacitor to 0.22mF, 400V. The waveform is only vaguely sinusoidal. Invert the connection of one of the 6V windings if oscillations do not set in. 

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