A 7.2V 1C NiCad/NiMh battery charger.

This design uses the Maxim, MAX 713 NiCad/NiMh battery charger IC to control the fast charge time and provide cell voltage monitoring.

Update May 2nd 2011
Added pictures of my prototype design and the PCB layout.
Note: the MAX712/713 device from Maxim semiconductor is now listed as Not Recommended for New Designs (NRND) meaning that the device will be phased out soon.

It charges a battery to approximately 80% charge in 22 or 33 minutes at a current of 2.4 Amps. Once the fast charging has ended, it trickle charges the battery. Power is from a 13.6V, 3 Amp, switchmode power supply. There is also provision to use power from a 12V accessory (cigarette lighter) socket. As there are no transformers inside the case it is lightweight.

Note: You will require a power supply of greater than 13V to operate this circuit. Failure to do so will cuase the fast charge termination to operate incorrectly. I used a car accessory adaptor from Halfords, it provides 13.6V @ 5 Amps, more than enough for this circuit.
The design is based upon the example circuit from the MAX 713 datasheet. Due to the high current, there is a large heatsink on the power transistor, T1 and I also added a small CPU cooler to cool everything down. The cooling fan runs from the 12V supply to the PCB.

This unit is still in use today. It is used as my travel charger for my 'Fun' R/C cars as it is lightweight and works great with the 2000-3000mA NiCAD and NiMH cells I use

Partlist

Part	Value	Device	Package	Description
C1	10nF	C-EU050-030X075	C050-030X075	CAPACITOR, European symbol
C2	10nF	C-EU050-030X075	C050-030X075	CAPACITOR, European symbol
C3	10uF	CPOL-EUE5-6	E5-6	POLARIZED CAPACITOR, European symbol
C4	10uF	CPOL-EUE5-6	E5-6	POLARIZED CAPACITOR, European symbol
D1	1N4004	1N4004	DO41-10	DIODE
H1	MOUNT-HOLE3.2	MOUNT-HOLE3.2	3,2	MOUNTING HOLE with drill center marker
H2	MOUNT-HOLE3.2	MOUNT-HOLE3.2	3,2	MOUNTING HOLE with drill center marker
H3	MOUNT-HOLE3.2	MOUNT-HOLE3.2	3,2	MOUNTING HOLE with drill center marker
IC1	MAX713CPE	MAX713CPE	DIL16	NiCd/NiMH Battery Fast-Charge Controller
KK1	SK104	SK104	SK104	HEATSINK manufacturer Fischer/distributor Buerklin
R1	1K	R-EU_0207/7	0207/7	RESISTOR, European symbol
R2	150R	R-EU_0207/7	0207/7	RESISTOR, European symbol
R3	68K	R-EU_0207/7	0207/7	RESISTOR, European symbol
R4	22K	R-EU_0207/2V	0207/2V	RESISTOR, European symbol
R5	0.1R (5W)	RKH206-8	KH206-8	Power Resistor
R6	150R	R-EU_0207/7	0207/7	RESISTOR, European symbol
R8	1K	R-EU_0207/7	0207/7	RESISTOR, European symbol
Q1	TIP33	TIP33	TO220V	TIP33 vertical mount NPN transistor
LED1		LED5MM	LED5MM	LED
LED2		LED5MM	LED5MM	LED
X1		W237-02P	W237-132	WAGO SREW CLAMP
X2		W237-02P	W237-132	WAGO SREW CLAMP
X3		W237-02P	W237-132	WAGO SREW CLAMP

Schematic (click to enlarge)

PCB and schematic in Eagle CAD format

NICAD.Zip 94 Kb

Prototype unit pictures

The ventilated PSU case is available from Maplin, part number YU32K.

Next inside the case showing the wiring and the placement of the cooling fan.

Finally, detail of the power and LED connections

Updated 02 May 2011