13,8 Volt 20A Power Supply

This is power circuit that has maximum current supply 22 Ampere and output voltage 13.8 volt trimmed by P1. Remember to isolate the transistors from the chassis/radiator of power supply box! This is very important!

Part list for 20 Amp BDX33-based power supply:

2 x 15 volt 12+ amps
2 times 3 MR750 (MR7510) diodes (MR750 = 6 Ampere diode) or 2 times 5 1N5401 (1N5408) diodes.
F1= 2 Amp
F2= 25 amp
R1= 2k2 1 Watt
R2= 10k
R3= 1k 0.5 watt
R4,R5,R6,R7= 0.1 ohm 10 watt
R8= 4.7
R9= 6k8
C1= 22000uF/35v
C2= 330uF/35v
C0′,C3,C4,C6,C10= 100nF
C7= 330uF/25v
C8= 47nF
C9= 47uF/25v
D1= 1N5401
D2= LED
D3, D4, D5= 1N4001
IC1= 7815
Relay 12 volt 10 amp switching
Four darlington transistors: T0,T1,T2,T3 = BDX-33 NPN TO-220 transistor
ZD= 8 or 9 volt, 5 watt
P1= 2k trimmer

Source :powersupply.circuitelectronic.net