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, 03:39:47 pm ---I think its possible to cobble together a working prototype of this in a month if you approach it seriously, have a basic understanding of the design issues (especially switching transients destroying things), and can get the magnetics close enough for a 30 second weld.

--- End quote ---
30 seconds is plenty considering i will be welding car panels and anything more than a couple seconds will warp the panels and ruin my day.


--- Quote from: cur8xgo on June 22, 2019, 03:39:47 pm ---
Can we organize the design plan a bit?

Topology: Is this a 115VAC rectified to DC switched into xfrmr for 24V out or something like that?
A: 230 VAC

Magnetics (transformer): What is the proposed design? Core and number of turns of what material? How hot will the core and windings get? What is the operating frequency?
A: I'll unwind a couple SMPS transformers to get my numbers in the right ballpark and go from there.

Switches: What IGBT? Why IGBT? What temperature will they get to?
A: H20R1203, IGBT because all the cool kids do it.

Heat sinking: How much power needs to be dissipated and how will it be done?
A: P4 heatsinks should be fine i think, with a fan of course.

Switch control: Can't use the existing IGBT control circuit?
A: ATX PSUs use BJTs, i doubt that would work.

Current control: So does this need some kind of current feedback servo loop or not? And how will that be done?
I'll use the existing comparator, they have a crowbar circuit to latch so i'll just make it not latch.

Switching transients: How will these be snubbed?
A: diode+resistor+capacitor

Full bridge: What diodes and how hot will they get? What sort of capacitance and inductance will be used to smooth the DC for the torch?
A: two secondaries for two half bridges each with two 150EBU04 diodes in parallel, full bridge would double the losses = double the heat.

Bussing: How will high current be routed as far as bus bars while keeping things very short and balanced?
A: lots of thick wire i guess.



--- End quote ---


--- Quote from: Siwastaja on June 22, 2019, 04:34:22 pm ---
--- Quote from: cur8xgo on June 22, 2019, 03:39:47 pm ---I think its possible to cobble together a working prototype of this in a month if you approach it seriously

--- End quote ---

Yes I agree, but using a degaussing coil as a core material might not be a good start.  :clap:

Nevertheless, do it! It will be fun.

--- End quote ---

Do you mean the XY deflection core? The degaussing coil does not have a core it's just a very long coil with lots of thin wire, basically litz wire if you cut through it.

T3sl4co1l:
The deflection yoke core BTW is some horrible kind of material, not sure what.  Seems to have lower permeability, Bsat and higher losses than the usual stuff.  Maybe stability of permeability is the tradeoff?  Dunno.

A stack of four FBT cores isn't bad.  There's plenty of room to get all the wire you need in there, and while the core area could be higher, you aren't using that much more wire in exchange.

You will want to pay careful attention to how much interleaving is done on the transformer windings.  Primary and secondary need to be as close as possible*.  Probably you'll need many sections of primary and secondary in parallel, to get the total current rating up, while using fine-ish stranded wire (degaussing coils are probably okay, but you'll need a lot of them to finish the transformer).

*And I really mean as possible here, not just a wave-of-the-hands "probably good enough".  You could wind a thousand twisted pairs and connect them in parallel, and get about the right transformer impedance here (<< 1 Ω!).  Anything else you do will have a higher impedance, and therefore more leakage inductance.  Foil windings, and multifilar (flat cable, lots of strands in parallel, broadside) are your friends here.

Tim

cur8xgo:
IGBT because the high voltage right? Otherwise wouldn't MOSFETs be less loss and easier to drive?

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.

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

Can you elaborate on the SMPS transformer reusage plan?

Can you also talk about frequency of operation? I am actually really interested in how you are going to get the transformer right.

Can you draw up a basic schematic so we can all talk about it? This is a cool project






cur8xgo:
Mig wire feed system $19
https://www.ebay.com/itm/Black-24V-DC-10W-Mig-Welder-Wire-Feed-Motor-Mig-Wire-Motor-Mig-Wire-Feeder/153325626788

Mig torch + cable/connector $64 (oops I mean mig "touch" apparently)
https://www.ebay.com/itm/MIG-Welding-Gun-Torch-Stinger-Replacement-Miller-169598-250-Amp-M-25-15FT/392266137032

Refrigerator:

--- Quote from: T3sl4co1l on June 22, 2019, 04:58:59 pm ---The deflection yoke core BTW is some horrible kind of material, not sure what.  Seems to have lower permeability, Bsat and higher losses than the usual stuff.  Maybe stability of permeability is the tradeoff?  Dunno.

A stack of four FBT cores isn't bad.  There's plenty of room to get all the wire you need in there, and while the core area could be higher, you aren't using that much more wire in exchange.

You will want to pay careful attention to how much interleaving is done on the transformer windings.  Primary and secondary need to be as close as possible*.  Probably you'll need many sections of primary and secondary in parallel, to get the total current rating up, while using fine-ish stranded wire (degaussing coils are probably okay, but you'll need a lot of them to finish the transformer).

*And I really mean as possible here, not just a wave-of-the-hands "probably good enough".  You could wind a thousand twisted pairs and connect them in parallel, and get about the right transformer impedance here (<< 1 Ω!).  Anything else you do will have a higher impedance, and therefore more leakage inductance.  Foil windings, and multifilar (flat cable, lots of strands in parallel, broadside) are your friends here.

Tim

--- End quote ---

Damn, i thought i hit jackpot when i found that core, turns out not. I really wanted to use it because it had a lot of space for windings.
Also i counted my FBT cores and i have 5x132mm2, 3x143mm2 and 2x176.6mm2 cores.
Meanwhile a typical 350W ATX PSU core has a 95mm2 area.

I also wanted to find a picture of the one done with a deflection yoke but couldn't find it, i did, however, find one that used two FBT cores for an inverter stick welder/plasma cutter:
https://www.edaboard.com/showthread.php?374338-Homemade-Arc-inverter-welder-And-Plasma-cutter-power

The FBT cores might be a bit of a squeeze form my welder transformer but i'll try.


--- Quote from: cur8xgo on June 22, 2019, 05:30:09 pm ---Mig wire feed system $19
https://www.ebay.com/itm/Black-24V-DC-10W-Mig-Welder-Wire-Feed-Motor-Mig-Wire-Motor-Mig-Wire-Feeder/153325626788

Mig torch + cable/connector $64 (oops I mean mig "touch" apparently)
https://www.ebay.com/itm/MIG-Welding-Gun-Torch-Stinger-Replacement-Miller-169598-250-Amp-M-25-15FT/392266137032

--- End quote ---

I've already found a MIG torch for 30€ locally (by locally i mean in my country) and i'll use a windshield wiper motor for my wire feed for maximum DIY points.
The torch i'll be using: http://irankiai-fb.lt/lt/suvirinimo-irangos-dalys/14708-suvirinimo-zarna.html
There are other ones for 30€ as well but this particular one should be easier to hook up without having to order a socket.

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