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Materiais:

C1_____________14000uF ou 10000uF por 40V eletroltico C2_____________100uF por 50V eletroltico C3_____________.1uF cermico C4_____________.01uF cermicor R1______________5K potencimetro R2______________240 Ohms x 1/4W U1______________LM338k Regulador de 1.2 30V x 5A BR1_____________Ponte retificadora de 50V x 10A T1______________Transformador de 24V x 5A S1______________Interruptor

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Four types of Homebrew 12/20/30 Ampere 13,8volt power supplies:

RE PSF14A12D, PSF14A20D, PSF14A20 and PSF14A30

RE-PSF14A12D

revision 3

By Guy, de ON6MU

This is an easy to make power supply which has stable, clean and protected output voltage. The overal dimensions can be kept (relative) small by using

TO220 darlington BDX-33 transistors. Using 3 BDX-33 darlington transistors is almost 3 times the amount of amps then the power supply delivers,

making it real though to brake ;). Although you could use this design to deliver 20 amps (with almost no modifications and with a proper transfo and a

huge heat sink with a fan), I did not needed such much power. Second reason was the size of the alu box I happen to have spare HI. There was simplynot enough room for the transformer, and surely not enough space to mount a huge heat sink, as the BDX33 transistors can get very hot, and they do

not like that so much.

Although the 7815 power regulator should kick in on shortcircuit, overload and thermal overheating, I build in a very simple secondary overvoltage

protection that's made out of 12 volt relay. The rectified voltage of: 15 volt x SQR2 = 15 x 1.41 = 21.15 volt measured on C1. This is the voltage that

could be on the output if one of the transistors should blow. We need a little calculation to get the exact voltage (or higher) to power the 12volt relay

which should disconnect the output. In this example we use for diode Zd 9v/5watt -> 21v - 9v = 12 volt. To allow the relay to disconnect the output on

lower voltages, use a lower voltage for diode Zd. You could use a different voltage relay too, but diode Zd should be calculated to allow the relay towork just when the output voltage rises over 16 volt + (Zd in the schematic).

P1 allows you to 'trim' the output voltage exactly to 13.8 volts.

Remember to isolate the transistors from the chassis/radiator! This is very important! Use a radiator (heat sink) of appropriate size and surface area;insulating and heat-conducting spacer or at least a thin mica; hot adhesive and thermal paste. Use thick wires.

Just to be sure to prevent HF entering (or going back to the mains) use a ring core to turn the mains a few times around it (see insides pics).

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RE-PSF14A12 Power supply Schematic 1

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Part list PSF14A12D12 Amp BDX33-based power supply:

2 x 15 volt 6+ amps

2 times two MR750 (MR7510) diodes (MR750 = 6 Ampere diode) or 2 times 3 1N5401 (1N5408) diodes.

F1 = 1,5 (2) Amp

F2 = 15 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 two times 4700uF/35v

C2,C5 330uF/35v (revision 2: C5 = 330uF -> improved ripple rejection and stabelisation )

C0',C3,C4,C6,C10 100nF

C7 330uF/25v

C8 47nF

C9 47uF/25v

D1 1N5401

D2 LED

D3, D4, D5 1N4001 IC1 78L15

relay 12 volt 2x5 amp switching

3 darlington transistors: T0,T1,T2 = BDX-33 NPN TO-220 transistor

Zd 8 or 9 volt, 5 watt

P1 1k trimmer

If using a bridge rectifier (like in schematic 2) you do not need 2 x 15 volts 6 amps, but 1 x 15 volt 10+ Amps

Part List PSF14A20D

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 = 3,18 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

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R9 6k8

C1 22000uF/35v

C2, C5 330uF/35v (revision 2: C5 = 330uF -> improved ripple rejection and stabelisation)

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

If using a bridge rectifier (like in schematic 2) you do not need 2 x 15 volts 12 amps, but 1 x 15 volt 20 Amps

The power supply insides

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20/22 Ampere or 30/32 Ampere 13.8 volts power supplyRE-PSF14A20 or PSF14A30

de ON6MU

RE-PSF14A20

Power Supply Schematic 2 (new design)

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Remember to isolate the 2N3055 transistors from the chassis/radiator! This is very important! Use a radiator (heat sink) of appropriate size and surfacearea; insulating and heat-conducting spacer or at least a thin mica; hot adhesive and thermal paste.

PSF14A20 Specs

Heavy duty power supply 13.8 volt, 20 or 30 amps continue

low ripple

short-circuit protection

HF-immunity

Voltage can be set between 12,3 and +/- 15 volts

only 0.35v drop at full load

parts widely available and calculated way over the maximum load

PSF14A20 Parts (30 amp version PSF14A30 in blue)

transformer capable of delivering 20 amps @ 15volt (30 amps)

4 x 2N3055 (6 x 2n3055) (you can also use the 2N3773 transistor)Use a large radiator (heat sink) of appropriate size and surface area; insulating and heat-conducting spacer or at least a thin mica; hot adhesive and thermal paste.

IC 1: 7812 (small heatsink)

D1: MB2504 is used as it is a 25 ampere rectifier bridge and should also be very good cooled. Or you could use 3 times four BYW29 8 amp

diodes (TO220 pinning, cooling).

D2,D3: 1N4001 or simular

D4: 1N5401

C1: 47nF

C2: 22000uF (+ 10000uF) 35volts

C3: 100uF/35volt

C4: 100nF

C5: 4.7uF/35volt

C6: 4.7uF/35volt

C7: 100nF

C8: 220nF

C9: 220uF/25volt

C10: 47nF

C11, C12: 100nF R1: 2k2 / 1W

R2: 10 1/2W (2,2 1/2W)

R3: 6,8 1/2W (2,2 1/2W)

R4': 1 Ohm 1/2W

R5': 0.1 Ohm/10W

R6: 2k2

R7: 10

R8: 2k2

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R9: 22

R10: 1k

R11: 10

P1: 500

F1: 2A (3.18A)

F2: 22A (35A)

P1 allows you to 'trim' the output voltage exactly to 13.8 volts.

Just to be sure to prevent HF entering (or going back to the mains) use a ring core to turn the mains a few times around it (see insides pics).Be sure to use thick braid wires!!! They need to handle 20 (30) amps continues!

Total revision changes:

. highly improved voltage stabilisation

. output voltage feedback circuit stabilisation

. BDX-33 removed

. Cap after 7815 changed from 1uF to 4.7uF

. Resistors before the input of the 7815 changed

. reverse diode (between collector and emittor of 2n3055) removed

. voltage can be set exactly to 13.8v (P1)

. minor HF-immunity changes