welding inverter 100a

Welding inverter 100A

Welding inverter is an alternative to conventional welding transformer. Modern semiconductors allows to replace thetraditional mains transformer with a switching supply, which is much lighter, smaller and allows easy current control viapotentiometer. The advantege is the fact that the output current is DC. Direct current is less dangerous than AC and preventsarc extinction.

For this inverter i chose topology, which is the most common in inverters - forward inverter with two switches. In myarticle about switchning supplies it is a topology II.D. Input line voltage passes through the EMI filter and is smoothed withlarge capacity. Since the switch-on pulse would be intolerable, there is a softstart circuit. After switching ON the primaryfilter capacitors charging through the resistors, which are subsequently eliminated by switchning ON the relay. As aswitches the IGBT transistors are used. These are controlled through a forward excitation transformer TR2 and formingcircuits with BC327. Control circuit is UC3844. It's similar to UC3842, but equipped with pulse-width restriction to 50%.Working frequency is 42kHz. Control circuit is powered by an auxiliary source of 17V. Current feedback, due to highcurrents, is using current transformer TR3. Voltage accros the resistor 4R7/2W is approximately proportional to the outputcurrent. Output current can be controlled by potentiometer P1, which determines the threshold of feedback. Thresholdvoltage of the 3rd pin of UC3844 (sensor current) is 1V.

Power devices require cooling. Most of the heat is dissipated in output diodes. Upper diode, consisting of 2x DSEI60-06A, must in worst case handle the average current of 50A and the loss of 80W (both diodes). Lower diodeSTTH200L06TV1 (doube diode with both internal diodes in parallel) must in worst case handle the average current of 100Aand the loss of nearly 120W. Maximum total loss of the secondary rectifier is 140W. The heatsink must be able to handle it.To the thermal resistance you must include the junction-case Rth, case-sink Rth and sink-ambient Rth. Diodes don't haveinsulation, the cathode is connected to the heatsink. Output choke L1 is therefore involved in the negative rail. It isadvantageous because in this case there's no high-frequency voltage on the heatsink. You can use another type of diodes, forexample the parallel combination of a sufficient number of the most accessible diodes, such as MUR1560 or FES16JT. Notethat the maximum current of the lower diode is twice the current of the upper diode. Calculation of the loss of IGBTs ismore complicated because in addition to conductive losses there are switching losses. Loss of each transistor is up to about50W. It is necessary to cool the reset diodes UG5JT a rectifier diode bridge. Power loss of the reset diodes depends on theconstruction TR1 (inductance, stray inductance), but is much smaller than the loss of IGBT. Rectifier bridge has a maximumloss of up to about 30W. UG5JT bridge and were placed on a common heatsink with IGBT. UG5JT diodes also can bereplaced with MUR1560 or FES16JT. During construction it is also necessary to decide the maximum loading factor of theinverter, according to size of heatsinks, winding gauges and so on. It is also good to add a fan.

Switching transformer TR1 is wound on two ferrite EE cores, each with a central column section 16x20mm. The totalcross section is therefore 16x40mm, core must have no air gap. 20 turns primary winding is wound using 14 wires with a 0.5mm diamater. It would be better to use 20 wires, but they didnt fit to my core. Secondary winding has 6 turns of copper strip36x0.5mm. Forward excitation transformer TR2 is made with an emphasis on low stray inductance. It is trifillary wound,using three rolled up insulated conductors of 0.3 mm, and all the windings have 14 turns. Core is made of material H22,middle column has a diameter of 16mm, with no gaps. Current transformer TR3 is made from suppression chokes on thetoroidal core. The original winding with 75 turns of 0.4 mm wire works as a secondary Primary has 1 turn. Orientation of allthe transformer windings must be respected (see dots in schematic)! L1 is ferrite EE core, middle column 16x20mm. It has11 turns of a copper strip 36x0.5mm and the total air gap in the magnetic circuit is 10mm. Its inductance is cca 12uH.

Auxiliary switched supply, including TR4 is described in more detail here. Simplest inverter on Pic 1 has no voltagefeedback. Voltage feedback does not affect the welding, but affects the consumption and heat losses when idle. Without theoutput voltage feedback there is quite high output voltage (approximately 100V) and PWM controller running on max dutycycle, thereby increasing consumption and heating components. Therefore, it is better to implement the voltage feedback.You can inspire on Pic 2. The feedback can be connected directly because the driver is isolated from line. The referencevoltage is 2.5V. Select the R2 to set the open circuit voltage. You can find useful info in datasheet of UC3842, 3843, 3844,3845 or in another datasheet. Inspiration for modifications you can also find in 3-60V 40A supply.

Interesting links from which I drew:http://svarbazar.cz/phprs/index.php?akce=souvis&tagid=3http://leo.wsinf.edu.pl/~leszek/spawarki/http://www.y-u-r.narod.ru/Svark/svark.htmhttp://www.emil.matei.ro/weldinv3.php

Plug & Play IGBT Drivers Concept Pin Options IGBT Drivers w/ Low Lead Times. Contact Us Today! www.agileswitch.com

Battery Welder Machine AC Pulse Spot Welder Machine & Capacitive Discharge Spot Welder www.BatterySpace.com/WelderMachine

DataVox APC Power & UPS for Houston Based -881-7407 www.datavox.com

of 16Welding inverter 100A

10/21/2011http://www.danyk.wz.cz/svar_en.htmlCreate PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer

http://svarbazar.cz/phprs/index.php?akce=souvis&tagid=3

http://leo.wsinf.edu.pl/~leszek/spawarki/

http://www.y-u-r.narod.ru/Svark/svark.htm

http://www.emil.matei.ro/weldinv3.php

http://www.agileswitch.com

http://www.BatterySpace.com/WelderMachine

http://www.datavox.com

http://www.go2pdf.com

http://www.danyk.wz.cz/svar_en.html

http://nexor.electrik.org/svarka/barmaley/kosoy/shema.gif and a little modified:http://nexor.electrik.org/svarka/barmaley/kosoy1/shema.gif

Warning: Inverter circuits are electrically connected to the mains. Inverter contains large capacitors that remaincharged even after turn off. Some components (electrolytes, IGBT, ...) can explode at fault. Inverter output voltage isdangerous. If defective or poor construction at the output can get the mains voltage or voltage higher than required.Inverter can cause electric shock, burns and fire. The arc creates a very intense light (with a large proportion ofultraviolet), from which the personnel should be protected. It can cause permanent eye damage and skin burnssimilar to solar. Weld evolve toxic gases to be ventilated.

Pic 1 - Homemade inverter welder (welding inverter) schematic (click to enlarge)

Pic 2 - Voltage feedback.



http://nexor.electrik.org/svarka/barmaley/kosoy/shema.gif

http://nexor.electrik.org/svarka/barmaley/kosoy1/shema.gif



Tr1 Secondary made of a copper strip





Secondary and a half of a core

Tr1 with wound primary





switching transformer Tr1 with core

Old Czechoslovak switching supply from the mainframe (5V 50A DBP 236 Kosire ZPA). From two such supplies I





salvaged parts for the construction of the inverter (ferrites, coolers, distance posts, spools, inductors, copper strip ...)

Diodes STTH200L06TV1 and DSEI60-06A on the heatsink





heatsink with diodes, TR1, L1, copper tape

Gate drive transformer TR2 with trifillar winding (GDT)





Tests of the exciter UC3844, TR2 and shaping circuit

Shaping circuit for gates





Ready to first start :).





Short-term test for 150A - all survived:).





IGBT, bridge, reset diodes, forming circuits, GDT TR2 and the UC3844 driver.

Current transformer TR3





It is welding :)





Measurement of arc voltage - long arc

Measurement of arc voltage - short arc





The first test (the short-circuit current).

The second test, half the mains voltage, output voltage is too low to hold the arc. At the end you can se PWM on anoscilloscope.





Third test - it is allready welding.

Welding and safety at work - how it should never look like:).





home

Super New Welding Machine Super New Technology Plasma Welder All in One to Weld,Cut,Braze,Solder www.multiplaz.com

Official Digi-Key Site Search Our Huge Selection of Quality Electronic Components Here! www.digikey.com

Voltage Converter 110/220 Heavy Duty Voltage Transformers for 110V/220V volt Voltage Conversion www.220converters.com



http://www.multiplaz.com

http://www.digikey.com

http://www.220converters.com



welding inverter 100a

Documents

welding inverter 100a

current transformer tr3

copper strip 36x0

switching transformer tr1

worst case handle

copper strip

output current

control circuit