AVT 5553 Controller for Resistance Welder Owner's manual

The internet is full of amateur resistance welder

designs for joining small metal parts and attaching

battery terminals. All these designs are based on a

converted transformer from a microwave oven,

which can be bought for a pittance from electronic

scrap or obtained from worn-out equipment.

Transformer from microwave oven have sufficient

power for such applications, approaching 1 kW,

and can be easily and cheaply converted from the

high-voltage version to that required by the

welder.

Features

• ideal for welding battery packs.

• user interface: 2×16 display and buttons

• board sizes:

- controller board: 96×50 mm

- actuating board: 96×45 mm

• complete welder requires a transformer from the

microwave oven

Detailed descriptions of the way in which the

transformer should be reworked are best sought on

the web (photos, videos), while at this point we

propose to make a proven and universal controller for

such a welder, ensuring minimisation of inrush current,

adjustment of tripping time and delay, as well as

guaranteeing symmetry of the transformer supply.

Unfortunately, many of the controllers used to date in

such projects are similar to each other and are more or

less faithful modification of the old concept, thus,

unfortunately, reproducing the serious flaws of the

original concept. The proposed controller is directed

to work with a welder, but in practice it can be used to

work with any medium-power transformer. It has an

output stage matched to an inductive load and turns it

on at the maximum of the instantaneous mains

voltage, the complete opposite of more than half of

similar designs. It is worth replacing your existing

controller with this solution.

The controller circuit is supplied with rectified but

unfiltered voltage from the mains transformer, so that

the controller can detect the mains sinusoid passing

through zero. This is done by a circuit made up of

resistors R1 and R2 with protection diode D2, which

provides a pulsing voltage to the microcontroller input.

The voltage is then filtered and stabilised at 5 V using a

three-terminal stabiliser IC1.

Microcontroller is clocked by a clock signal stabilised

Circuit description

Controller for Resistance Welder

The kit is based on a design of the same title published in

Practical Electronics 10/2016. Full version of the original

manual is available to download here:

http://bit.ly/2mpQd8b

AVT 5553

kits

ASSEMBLY DIFFICULTY

PDF

DOWNLOAD

Fig. 1. Schematic diagram

by a quartz resonator and works with 5 buttons and a

2×16 character LCD display. Buttons S4 and S5 change

the switch-on time of the welder, S2, S3 adjust the

delay of activation, and S5 switches on the

transformer. A buzzer driver with T3, which signals the

welding process, transistor T2, which switches on the

LED in the optoisolator, and T1, which switches on the

optional fan, operate as auxiliary circuits.

The fan control signal is provided by a 10 kΩ NTC

thermistor inserted between the 4th pin of the X1

connector and GND. A mains transformer is located on

the actuating board, along with a bridge, providing the

supply voltage for the controller. There is also a

thyristor switch based on two thyristors and an

optotriac switched on at any time. Capacitor C10 and

resistor R18 suppress surges that could damage the

thyristors.

MEGA8-P

LCD 2x16

10k

1N4007

1N4148

27p

100n 100n

100n

7805

4,7k

10k

100k

10k

4,7k

2,2k

220

BC327

10k

2,2k

BC337

8MHz

100u1000u

BC337

4,7k

10k

100n

GND

+5V

MOC3021

2,2k

330

390

100n

TYN616

1N4007

330

2VA/6V

GND

PB5(SCK) 19

PB7(XTAL2/TOSC2)

PB6(XTAL1/TOSC1)

GND

VCC

GND

AREF

AVCC

PB4(MISO) 18

PB3(MOSI/OC2) 17

PB2(SS/OC1B) 16

PB1(OC1A) 15

PB0(ICP) 14

PD7(AIN1) 13

PD6(AIN0) 12

PD5(T1) 11

PD4(XCK/T0) 6

PD3(INT1) 5

PD2(INT0) 4

PD1(TXD) 3

PD0(RXD) 2

PC5(ADC5/SCL) 28

PC4(ADC4/SDA) 27

PC3(ADC3) 26

PC2(ADC2) 25

PC1(ADC1) 24

PC0(ADC0) 23

PC6(/RESET)

IC2

GND

VCC

CONTR

R/W

DIS1

PR1

3 1

LED1

LED2

C4 C5

GND

IN OUT

IC1

R10

R11

R13

R14

- +

SG1

R12

X1-1

X1-2

X1-3

X1-4

X1-5

X1-6

X1-7

X1-8

X1-9

FIREFANTHERMPOW

POW

SIG

OK1

R18

R17

R15

C10

TY2

TY1

R16

X2-1

X2-2

X2-3

X31

X32

X41

OUT

X42

JP3

TS1

FAN

TERM

ZERO

BUZZ

OUT

S1.1

LCD DISPLAY 16x2

PRI

SEC

Mounting diagram is shown in Figure 2. Mounting is

typical and needs no special discussion. Controller

board contains components on both sides of the

laminate. One side houses the LCD display, control

buttons and LEDs, the other the remaining

components. The display was soldered to the board

using a goldpin connector, and details are shown in

the photographs. Starting up the controller is basically

limited to switching on the power and setting the

contrast with potentiometer PR1. When you press the

release button, the red LED should light up and a

sound should be heard (with jumper JP3 shorted). If

the controller is supplied with DC voltage for testing, it

will not be possible to determine when zero appears in

the voltage supply, thereby determining the precise

moment of release. The controller in such a situation

will refuse to operate and will display an appropriate

error message. However, by attaching a jumper to pins

1-2 in JP1, this message can be bypassed and the

controller can be forced to work 'blindly'. Adjustment

of the tripping time is possible from 20 ms onwards in

20 ms steps, in order to maintain an even number of

grid periods fed into the transformer. Delay can be

adjusted from zero in 10 ms increments. Times from

the top down are basically unlimited. Fan tripping

threshold has been pre-set at around 40ºC, but by

pressing the two buttons responsible for setting the

time and switching on the power at the same time, this

can be changed. It is then necessary to place the

thermistor in an environment with a threshold

temperature and using the delay buttons, change the

position of the switch-on threshold in a wide range.

Start-up of the actuating board is best done without

the welder transformer. Instead, an ordinary 40-100 W

incandescent bulb connected in series with a thyristor

circuit can be used. When all is OK, it will light up when

"FIRE” is pressed for the desired time. Using the

controller for other applications is possible, but

requires thought and careful selection of thyristors and

the R2/C2 suppression circuit. The same applies to

higher power welders, as some people multiply the

power of the welder by combining two or even four

transformers together. Such combinations have not

been tested here.

Fig. 2. Arrangement of components on the PCB. Fig. 2. Arrangement of components on the PCB.

123456789

1 2 3

1 2

Mounting and start-up

List of components

Resistors:

R1, R4, R9, R13:......................4,7 kΩ

R2: ..............................................100 kΩ

R3, R5, R8, R11, R14:............10 kΩ

R6: ..............................................220 Ω

R7, R10:.....................................2,2 kΩ

R12:............................................56 Ω

R15:............................................390 Ω / 0,5 W

R16, R17: ..................................330 Ω / 1 W

R18:............................................2,2 kΩ / 2 W

PR11: ........................................mounting potentiometer 10 kΩ

Capacitors:

C1: ..............................................1000 uF

C2, C3:....................................... 27 pF

C4, C5, C7-C9: ........................100 nF

C6: ..............................................100 uF

C10:............................................100 nF / 250 VAC

Semiconductors:

IC1: .............................................7805

IC2: .............................................ATmega8

T1, T3:........................................BC337

T2:.........................BC327

D1, D3, D4: ........1N4007

D2: ........................1N4148

LED1:....................red LED, 3 mm

LED2:....................green LED, 3 mm

OK1: .....................MOC3021

B1:.........................bridge 0,5 A / 50 V

TY1, TY2:.............TYN616 + heat sink

DIS1: ....................LCD 2×16

Other

S1-S5: ..................button 13.5 mm

SG1:......................buzzer with 5 V generator

TS1: ......................transformer 2-2,5VA/6VAC

Q1:........................8 MHz

X1, X2: .................DG301-5.0/3

X3, X4: .................DG360-7.5/2

Other mounting components

Optional components:

Thermistor NTC 10 kΩ

Fan 5 VDC

ZOOM

AVT SPV reserves the right to make changes without prior notice.Installation and connection of the appliance not in accordance with the instructions, unauthorised modification of

components and any structural alterations may cause damage to the appliance and endanger persons using it. In such a case, the manufacturer and its authorised representatives shall

not be liable for any damage arising directly or indirectly from the use or malfunction of the product.

The self-assembly kits are intended for educational and demonstration purposes only. They are not intended for use in commercial applications. If they are used in such applications, the

purchaser assumes all responsibility for ensuring compliance with all regulations

This symbol means do not dispose of your

product with your other household waste.

Instead, you should protect human health

and the environment by handing over your

waste equipment to a designated collection

point for the recycling of waste electrical

and electronic equipment.

Leszczynowa 11 Street,

03-197 Warsaw, Poland

https://sklep.avt.pl/

AVT SPV Sp. z o.o.