China ACDC TIG, Mitech 160 malfunction

[donald branscom]

I agree with Sundown on this.

Even if you do get the machine to work like it is supposed to ,how long before it breaks again?

Basically the design and values of the components may not match correctly and it was not tested enough under realistic conditions.
I believe products should be well tested before going to market.

If you want to learn about electronics then maybe it is worthwhile.

[donald branscom]

OK. So here is the thing. For anyone who wants to know or anyone who cares.
Never buy an inverter style welder!
Now that I have looked at this in some depth, I cannot understand the stupidity in trying to get away with it for any length of time........Unless your design is absolutely bullet proof and you use only the best components, over engineering the s**t out of it from the get go.

Reason: Take 240v, (Australia) rectify it and drop it to 60v (DC) with the ability to draw 160Amps. This means disposing of 160v at 160 Amps....25000 watts.

No wonder they need two fans.....what they do is use a 'pulse width modulator'
just a fancy way to say they switch it on and off a few times per second and then just add up the ON bits and store it. (integration) so that the average voltage is now much less.
But switching 240v DC on and off at 160 amps takes quite a bit so they use 12 mosfets on a heatsink with a whole lot of filtering and smoothing just to get 60v DC at 160A.

****! a transformer is so much easier and more reliable. My old stick welder is 60v at 160A and it gets a bit hot but is dead reliable......all those little plug packs that power mobile-phones, intercoms, calculators, all run on the switch mode design instead of wire transformers...they have decided that the transformer is old fashioned and too environmentally unacceptable.......
Bl@@dy Greenies!

But I am having a rage....I will just pull this to bits for the parts and go back to my home made DC only TIG that cost me peanuts to build and goes like S**t out of a Shotgun!

Stay away from Chineese inverter cr@p! it is too complicated and unreliable QED!

Cheers.

Thanks for that explanation IRA.
The switching on and off.....is that why they call it a chopper inverter?

If we had more teachers that could give the "hot rod version" of a design explanation, then more people could understand many more things.

[junkweld]

Hi, Yes its a little easier for me because my background is in electronics anyhow.
In the Mitech super 160 there are different sections. As Junkweld says, the left hand side and is 220-240v rectifiers and a regulation system to bring the volts down to 60 volts DC. Then if you want AC, there is a system that converts it back using a switching system and some waveshaping.

I have a problem getting that AC output and I think it is generated from the pulser board behind the front panel, then fed to the wave-shaping circuit so that the 60v can be used in AC mode. Because I had some of the start voltage which is very high, on the pulse board, I think some semiconductors have been damaged. I will change some of them and see......wish I had a circuit diagram. So-called 'Mitech' in China has not assisted me yet......not holding my breath.

I still don't know how I got this arcing effect on the pulse board but I hope to find out soon.

There are some who think we are nuts to play with these things but some of us just can't justify going and spending 2000/3000 dollars Australian for US made goods...even if they are better made.

I got this one really cheap and was using a home made one up until now....I made my own tig welder in 2008.....HV start and all, but only DC operation.

Cheers, Ira

I don't think you will ever get any useful info from Mitech. Just like the USA companies they want you to buy a new board or machine.

Did you ever figure out the arcing problem? What is arcing to what?

You built a TIG box with high voltage high frequency start? Please tell me it isn't one of those microwave transformer and oil burner HV HF start rigs.

[junkweld]

Man I wish I had some PIZZA.......

and BEER! .

[junkweld]

Thanks for that explanation IRA.
The switching on and off.....is that why they call it a chopper inverter?

If we had more teachers that could give the "hot rod version" of a design explanation, then more people could understand many more things.

It is just a switch mode inverter like the power supply in your PC and all kinds of other stuff around the house. The market has moved towards them from transformers because they are more efficient, smaller, and lighter.
Look inside one of those modified sine wave inverters that you power off a 12v battery and you will see what looks like the inside of an inverter welder.

The way they work is this:
220VAC wall input => DC rectifier to 370VDC => MOSFET chopper feeding step down transformers at 20KHz to 100KHz => DC output to weld or to AC chopper => AC chopper using MOSFETs to AC output.

[danzx11c]

enjoyed read this post . thanks