Electronics > Projects, Designs, and Technical Stuff
Homemade IGBT MIG welder with ATX PSU parts. [blown yet again][blown count: 5]
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Refrigerator:

--- Quote from: cur8xgo on June 22, 2019, 05:15:46 pm ---IGBT because the high voltage right? Otherwise wouldn't MOSFETs be less loss and easier to drive?

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Driving them would be pretty much the same because they both have a gate, MOSFETs would have lower losses but i have CPU heatsinks to spare so it won't be too big of a deal to get rid of the heat.


--- Quote from: cur8xgo on June 22, 2019, 05:15:46 pm ---I'm interested in exactly how current will be limited to allow sheet metal usage. It might actually be easier to make a welder which welds thicker material than thinner material in this respect.

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I could add a timer to the welder for short welds, current will be handled through a current transformer.


--- Quote from: cur8xgo on June 22, 2019, 05:15:46 pm ---
Torch + feed drive systems are available from communist china on aliexpress and ebay FYI

That diode is about 0.8V @ 100A. Wouldnt a single secondary with a full bridge and four of these 0.5V @ 80A (parallell) waste less power? https://www.digikey.com/products/en?keywords=DSSK%2080-0045B

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That's assuming 100% duty cycle (in welding terms) on some thick metal, if i remember right MIG welders work in the 60-ish amp range.


--- Quote from: cur8xgo on June 22, 2019, 05:15:46 pm ---Can you elaborate on the SMPS transformer reusage plan?

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I'll unwind it to see how the boys at chinatown do it and toss it away.


--- Quote from: cur8xgo on June 22, 2019, 05:15:46 pm ---Can you also talk about frequency of operation? I am actually really interested in how you are going to get the transformer right.

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I looked online and it seems like 22kHz and 33kHz are are the most common switching frequencies, my board being from a 350W supply i expect the latter.


--- Quote from: cur8xgo on June 22, 2019, 05:15:46 pm ---Can you draw up a basic schematic so we can all talk about it? This is a cool project


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Not much to draw except the gate drive, for SMPS schematics you can check out this:
http://danyk.cz/s_atx_en.html
^^^^excellent source for anyone tinkering with ATX PSUs.
I'll also include a my gate drive schematic.
cur8xgo:
Okay dumb question....why an inverter? Why not just drive a 60hz transformer and full bridge the output?

Or go totally bare bones and just have a transformer in a box like harbor freight does with their 125amp 110v mig welder

I guess now I am wondering why AC powered inverters exist at all....is it just because switching faster could reduce transformer size vs 60Hz?



Refrigerator:
So far i've unwound two ATX transformers and they're pretty much the same, i only counted turns on primaries and the 5V secondaries since those were the main windings so to say.
Transformer consists of two 19T primaries, while 5V secondaries are 4T each sandwiched between the two 19T primaries.
Let's say i use four of my smaller 132mm2 cores for one 528mm2 transformer core, that means it's got about 5.3 times more cross sectional area than the ATX PSU core.
So basically my primary will now be 19T/5.3 = 3.58 ~ 4T and secondary (because i need 22V, 22/5=4.4) 4T*4.4/5.3=3.32 ~ 3T.
I'm pretty sure those numbers i just came up with are a pretty good recipe for some magic smoke, but that winding ratio should mean about 25% duty cycle.


--- Quote from: cur8xgo on June 22, 2019, 07:26:36 pm ---Okay dumb question....why an inverter? Why not just drive a 60hz transformer and full bridge the output?

Or go totally bare bones and just have a transformer in a box like harbor freight does with their 125amp 110v mig welder

I guess now I am wondering why AC powered inverters exist at all....is it just because switching faster could reduce transformer size vs 60Hz?


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I have a german made AC buzzbox and it's so heavy that you need two people to carry it, you can still pick it up by yourself but it's dangerously heavy.
Meanwhile inverter welders are small, easy to carry and have all kinds of features.
Edit: i could add a full bridge with SCRs with some control circuitry to control the output current and voltage but for above mentioned reasons i won't, also with a CO2 cylinder it would be even heavier and more awkward to carry around, not to mention the wire feed and spool, i would be well over 100kg.
Refrigerator:
Did some calculations with an online calculator and i think i'll settle for a 10T primary and an 8T secondary.
cur8xgo:

--- Quote from: Refrigerator on June 22, 2019, 07:55:23 pm ---Did some calculations with an online calculator and i think i'll settle for a 10T primary and an 8T secondary.

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What kind of open circuit voltage do you get with a 10:8 ratio on a 240VAC rectified input?


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