Low Cost Universal Battery Charger Schematic

Here is the circuit diagram of a low cost universal charger for NiCD - NiMH batteries. This circuit is Ideal for car use. It has ability to transform a mains adapter in to a charger . This one can be used to charge cellular phone, toys, portables, video batteries, MP3 players, ... and has selectable charge current. An LED is located in circuit to indicate charging. Can be built on a general purpose PCB or a veroboard. I hope you really like it.

Picture of the circuit: 

 A Low Cost Universal Charger Circuit Schematic

Circuit diagram:

A Low Cost Universal Charger Circuit Diagram

Parts:

R1 = 120R-0...5W
R2 = See Diagram
C1 = 220uF-35V
D1 = 1N4007
D2 = 3mm. LED
Q1 = BD135
J1 = DC Input Socket

Specifications:

• Ideal for in car use.
• LED charge indication.
• Selectable charge current.
• Charges Ni Cd or NiMH batteries.
• Transforms a mains adapter into a charger.
• Charge cellular phone, toys, portables, video batteries …

Features:

• LED function indication.
• Power supply polarity protected.
• Supply current: same as charge current.
• Supply voltage: from 6.5VDC to 21VDC (depending on used battery)
• Charge current (±20%): 50mA, 100mA, 200mA, 300mA, 400mA. (selectable)

Determining the supply voltage:

This table indicates the minimum and maximum voltages to supply the charger. See supply voltage selection chart below.

Example:

To charge a 6V battery a minimum supply voltage of 12V is needed, the maximum voltage is then 15V.

Voltage selection:

Voltage Selection Chart For Low Cost Universal Battery Charger

Determining the charge current:

Before building the circuit, you must determinate how much current will be used to charge the battery or battery pack. It is advisable to charge the battery with a current that is 10 times smaller then the battery capacity, and to charge it for about 15 hours. If you double the charge current , then you can charge the battery in half the time. Charge current selection chart is located in diagram.

Example:

A battery pack of 6V / 1000mAh can be charged with 100mA during 15 hours. If you want to charge faster, then a charge current of 200mA can be used for about 7 hours.

Caution:

The higher charge current, the more critical the charge time must be checked. When faster charging is used, it is advisable to discharge the battery completely before charging. Using a charge current of 1/10 of the capacity will expand the lifetime of the battery. The charge time can easily be doubled without damaging the battery.

Note:

• Mount the transistor together with the heatsink on the PCB, bend the leads as necessary. Take care that the metal back of the transistor touches the heatsink. Check that the leads of the transistor do not touch the heatsink. 

Simple Smoggy Circuit Schematic

Even if your good old (Sony) Walkman  sees little use nowadays it would be a  shame to get rid of it altogether. The more  so when just removing the tape head  would allow the built-in audio amplifier  to become an outstanding electrosmog  detector for a variety of purposes. Looking at the schematic, readers with RF  experience will have no difficulty in recognising the diodes and coils of the two  detector-receivers, which serve to capture and demodulate RF signals. With its  coil of four turns (L2) one receiver covers the higher frequency range of the  electromagnetic waves, whilst the sec-ond detector takes care of the lower frequency range. 

Circuit diagram :

Simple Smoggy Circuit Diagram

For this reason a coil with a  greater number of turns is required: L1 is  an RF choke of about 250 µH. The precise  value is not critical and it could equally be  220 µH or 330 µH. The outputs of both detector-receivers  are connected to the cables disconnected  previously from the tape heads, feeding the  right and left channel inputs to the Walk-man’s audio amplifier. Please note here that  the screening of the tape head cable does not  have to be absolutely identical to the ground connection of the amplifier circuitry. As  we are dealing with a stereo amplifier,  we are listening into both channels and  thus both RF ranges at the same time.

One channel of the amplifier can also be  used to demodulate low-frequency magnetic alternating fields  via a capacitor  (C3) bypassing diode D1 and connecting either a third coil (L3, for instance;  a telephone recording adapter) as the  pickup device or else a long piece of wire  for acquiring low frequency AC electrical fields. Sources like this are discernible mainly by a distinct 50 Hz (or 60 Hz)  humming in the earphones. Predicting what you may hear down to  the very last detail is difficult, since every  locality has its own, individual interference sources. Nevertheless, with practice  users will succeed in identifying these  interference sources by their particular  audio characteristics. 

To sum up, four different ‘sensors’ can be  connected to the inputs of this circuit:  ANT1 (approx. 50 cm long whip antenna),  ANT2 (3.5 cm short stub antenna), ANT3  (approx. 1 m long wire antenna for low frequency electrical fields) and a coil for magnetic fields. Finally, two more tips:

1. Use only ‘good old’ germanium diodes for  D1 and D2. Sensitivity will be much reduced if  silicon diodes are used, as these have a higher  threshold voltage.
2. Smoggy does not provide an absolute indi-cation of field strength and even more so can-not provide any guidance whether anything  it detects might be harmful. Its function is to detect electromagnetic signals and compare  their relative magnitude.

Author : Tony Ruepp  - Copyright : Elektor