Low-cost solution for the shipment of each of nickel, cadmium, and NiMH batteries

Low-cost solution for the shipment of each of nickel, cadmium, and NiMH batteries
Here is the schematic 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 for the charger. This can be used to recharge cell phones, toys, video batteries, MP3 players, ... and is selectable charging current. A LED is located in the circuit to indicate charging. Can be built on a breadboard or a general purpose PCB. Hope you like it.


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:

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.