Author Topic: Homemade IGBT MIG welder with ATX PSU parts. [blown yet again][blown count: 5]  (Read 28575 times)

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Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #25 on: June 22, 2019, 08:50:39 pm »
Found another degaussing coil laying around and this one is huge, only about 5.5mm thick (5-ish mm without the tape) but boy is it long and according to the link below it should be able to handle well over 50A and since i'll be using two secondaries it should be enough.
http://www.jst.fr/doc/jst/pdf/current_rating.pdf

Also i think i'll be doing a modified interleave winding with the primary sandwiched between my secondaries.



Did some calculations with an online calculator and i think i'll settle for a 10T primary and an 8T secondary.

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


Open circuit voltage doesn't matter because PWM. Also because of the way SMPS PSU works you have to divide your 230VAC peak voltage by 2.
A 10:8 ratio would mean about 17% duty cycle at idle to get 22V.
230*1.41 = 324V(peak)
324*8/10 = 259V
259/2 = 130V
22/130 = 17% duty cycle.

Actually 17% duty cycle seems pretty low, i hope my peak current doesn't get too high.
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Offline xavier60

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #26 on: June 22, 2019, 08:55:43 pm »
There happens to be a nice design for a 2 switch IGBT welder in this thread. https://www.eevblog.com/forum/beginners/component-role-in-a-circuit/msg2502276/#msg2502276
It uses the UC3845 current mode controller IC which is better suited than the TL494.

I have a cute little Miller inverter TIG/stick welder that is almost 20 years old (!) and still working great. It is a real work of art inside and uses a phase-shifted full bridge topology; something that was still very much considered "experimental" at the time.
Interesting, I have been keeping alive a few Castolin/Eutectic PowerMax 2 welders that also have the phase shift topology. Maybe the same as the Miller.
https://www.elektroda.pl/rtvforum/topic2554501.html
https://www.mig-welding.co.uk/forum/threads/eutectic-powermax-2-faulty.36400/
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Offline cur8xgo

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #27 on: June 22, 2019, 09:19:40 pm »
Quote
Open circuit voltage doesn't matter because PWM.

There is an output choke right so thats why?

 

Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #28 on: June 22, 2019, 09:36:25 pm »
Quote
Open circuit voltage doesn't matter because PWM.

There is an output choke right so thats why?

That and also some capacitors.

There happens to be a nice design for a 2 switch IGBT welder in this thread. https://www.eevblog.com/forum/beginners/component-role-in-a-circuit/msg2502276/#msg2502276
It uses the UC3845 current mode controller IC which is better suited than the TL494.


Yeah i've found quite a few of those:
https://www.hlektronika.gr/forum/showthread.php?t=53608
https://www.homemade-circuits.com/smps-welding-inverter-circuit/
http://danyk.cz/svar_en.html
 
But i want to make mine my way.
I have a blog at http://brimmingideas.blogspot.com/ . Now less empty than ever before !
An expert of making MOSFETs explode.
 

Offline strawberry

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #29 on: June 22, 2019, 10:54:00 pm »
How about sinhronous rectifier?

modern IGBT can run 50..100kHz not just 20..30kHz

I think, bipolar gate drive is better than unipolar
 

Offline xavier60

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #30 on: June 23, 2019, 01:55:37 am »
I suspect that higher frequency makes the output choke unnecessary. I can't find the choke in the design  linked earlier.
And my old welders don't have a choke. The rectifier output pulses are 100KHz, I think it relies on lead inductance.
« Last Edit: June 25, 2019, 10:34:11 pm by xavier60 »
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline tautech

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #31 on: June 23, 2019, 02:09:41 am »
I suspect that higher frequency makes the output choke unnecessary. I can't find the choke in the design the I linked earlier.
And my old welders don't have a choke. The rectifier output pulses are 100KHz, I think it relies on lead inductance.
Chokes in MIGs are more common in single phase plain transformer types however an old 3 phase unit I had didn't have a choke at all.
Typically the cleaner the DC the better they weld.
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Offline james_s

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #32 on: June 23, 2019, 03:37:16 am »
I get the distinct feeling that you have no idea just how difficult of a project this is going to be. Inverters require meticulous attention to detail, especially high powered inverters. One thing just slightly out from perfect and the whole thing goes bang in an instant.

If you want a welder just buy one, if you are on a budget you can buy used welders, sometimes for not a whole lot of money.

If you want an advanced engineering project then go ahead and try to build one, just realize that you will spend more money on parts and almost certainly get inferior results to the cheapest Chinese welders on the market.

Also how experienced are you at welding? MIG is one of the easier ones to learn but it still takes a great deal of practice to get good at it.
 

Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #33 on: June 23, 2019, 08:11:11 am »

Also how experienced are you at welding? MIG is one of the easier ones to learn but it still takes a great deal of practice to get good at it.

I learned to MIG weld when i was 13, it's basically a hot glue gun for metal.
Assuming the welder is correctly set up it takes about 30 minutes to learn MIG.
I have a blog at http://brimmingideas.blogspot.com/ . Now less empty than ever before !
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Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #34 on: June 23, 2019, 10:06:57 am »
How about sinhronous rectifier?

modern IGBT can run 50..100kHz not just 20..30kHz

I think, bipolar gate drive is better than unipolar

Synchronous rectification would over-complicate things.
I have a blog at http://brimmingideas.blogspot.com/ . Now less empty than ever before !
An expert of making MOSFETs explode.
 

Offline DannyTheGhost

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #35 on: June 23, 2019, 10:28:43 am »

Synchronous rectification would over-complicate things.

Sometimes you need to complicate your design when you don't want to dissipate over 50 watts from rectifier
 

Offline MagicSmoker

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #36 on: June 23, 2019, 11:36:04 am »
Interesting, I have been keeping alive a few Castolin/Eutectic PowerMax 2 welders that also have the phase shift topology. Maybe the same as the Miller.

My Miller was supposedly made by Fronius, but Fronius lost the contract with Miller soon after because it couldn't keep up with parts demand. I opened mine up to poke around inside even before the warranty was up and then again about a year ago to check the ESR of the elkos inside and everything was still within spec. Then again, I probably don't put more than about 10 hours of use on it any given year...


I suspect that higher frequency makes the output choke unnecessary. I can't find the choke in the design the I linked earlier.
And my old welders don't have a choke. The rectifier output pulses are 100KHz, I think it relies on lead inductance.

The "choke" might be the leakage inductance of the transformer, usually by specifying an unusually large gap for a core that really shouldn't have one in the first place (e.g. - forward mode transformers). Note that this definitely falls in the "ugly hack" category, and not something I would personally try to replicate just to save on the cost/volume of a proper choke.

 

Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #37 on: June 23, 2019, 01:10:11 pm »
The transformer is wound, i took care to make sure the primary is properly isolated from the secondary.
Although as much as i tried i could only fit 7.5T in the secondary, no big deal.
I couldn't find appropriate litz wire for my primary so i went outside, screwed to screws into a board spaced about 1.7m apart and made some. In the end it was quite a squeeze but i think it looks pretty ok-ish.

Now i can begin building the primary switching circuit.
« Last Edit: June 23, 2019, 01:18:12 pm by Refrigerator »
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An expert of making MOSFETs explode.
 

Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #38 on: June 23, 2019, 01:15:32 pm »

Synchronous rectification would over-complicate things.

Sometimes you need to complicate your design when you don't want to dissipate over 50 watts from rectifier

A CPU cooler can handle that no problem.
I have a blog at http://brimmingideas.blogspot.com/ . Now less empty than ever before !
An expert of making MOSFETs explode.
 

Offline cur8xgo

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #39 on: June 23, 2019, 02:53:58 pm »
The transformer is wound, i took care to make sure the primary is properly isolated from the secondary.
Although as much as i tried i could only fit 7.5T in the secondary, no big deal.
I couldn't find appropriate litz wire for my primary so i went outside, screwed to screws into a board spaced about 1.7m apart and made some. In the end it was quite a squeeze but i think it looks pretty ok-ish.

Now i can begin building the primary switching circuit.


very interested to see how that performs? so thats just magnet wire and you twisted it to make litz?

how did you decide on litz vs foil?

 

Offline cur8xgo

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #40 on: June 23, 2019, 02:54:32 pm »

Synchronous rectification would over-complicate things.

Sometimes you need to complicate your design when you don't want to dissipate over 50 watts from rectifier

A CPU cooler can handle that no problem.

Ya I dont think you will have an issue getting rid of 50W from TO247

 

Offline cur8xgo

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #41 on: June 23, 2019, 02:55:57 pm »

Also how experienced are you at welding? MIG is one of the easier ones to learn but it still takes a great deal of practice to get good at it.

I learned to MIG weld when i was 13, it's basically a hot glue gun for metal.
Assuming the welder is correctly set up it takes about 30 minutes to learn MIG.

Yep even a poor mig welder can get the job done for simple projects....I've taught people who had zero mechanical aptitude and never even knew what welding really was how to FCAW in about 30 minutes..then they practiced on their own for about an hour and were able to put tubing together to make things. Its motivation that is really key

 

Offline strawberry

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #42 on: June 23, 2019, 03:32:39 pm »
Synchronous rectification is not complicate. Same gate drive sigal for rectifier mosfet gates
 

Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #43 on: June 23, 2019, 04:44:15 pm »
Synchronous rectification is not complicate. Same gate drive sigal for rectifier mosfet gates

I'd have to order new parts and wait for them to arrive = nope.
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An expert of making MOSFETs explode.
 

Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #44 on: June 23, 2019, 04:46:24 pm »

Synchronous rectification would over-complicate things.

Sometimes you need to complicate your design when you don't want to dissipate over 50 watts from rectifier

A CPU cooler can handle that no problem.

Ya I dont think you will have an issue getting rid of 50W from TO247

Don't forget i have two diodes in parallel.
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An expert of making MOSFETs explode.
 

Offline cur8xgo

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #45 on: June 23, 2019, 05:56:55 pm »

Synchronous rectification would over-complicate things.

Sometimes you need to complicate your design when you don't want to dissipate over 50 watts from rectifier

A CPU cooler can handle that no problem.

Ya I dont think you will have an issue getting rid of 50W from TO247

Don't forget i have two diodes in parallel.

Ya even easier

I've been doing it at 125A to 150A through TO-247 50% duty cycle (full bridge) for 30 to 60 seconds at a time dozens of times. The heat sinks arent even that big maybe 5-10 sq inches? There is forced air but its about a foot away and is cooling the switches first. They heat sinks get warm but not hot. I have not yet measured junction temperature or calculated the heat sink efficiency to see if its reaonable but it definitely works so far. 0.54V @ 155A btw (per leg of FB)





« Last Edit: June 23, 2019, 05:59:09 pm by cur8xgo »
 

Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #46 on: June 23, 2019, 07:30:58 pm »

I thought up a pretty good way to get the most out of my diodes.
Basically since the weird TO-247 diodes came in a package that's meant for electrical isolation i decided to solder the diodes straight to a copper plate and then bolt the plate to a heatsink, which i pulled from a Dell Dimension.
This way the diodes will not only dissipate the heat better but they will also pass current through the aluminum heatsink.


« Last Edit: June 23, 2019, 07:36:39 pm by Refrigerator »
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Offline strawberry

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Offline RefrigeratorTopic starter

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #48 on: June 27, 2019, 03:46:35 pm »
After some fiddling i have the rectifier diodes sorted and IGBT gate drive sorted as well, only a few finishing touches left.
Next will be the GDT, but before that i think i'll remake the TL494 board. Keeping the ATX PSU board as a control board seemed like a good idea at first but i might as well go all in and remake it on some proto-board. The TL494 datasheet is a little confusing at first but i think i have it figured out.
I also remembered that i have a Delta fan from a Dell dimension, 1.6A at 12V makes 19.2W so it ought to move some air.  :)

https://www.edaboard.com/showthread.php?57813-SWITCH-MODE-ARC-INVERTER-WELDER-SCHEMATIC/page2&p=862700&viewfull=1#post862700 arc welder with deflection ferrite core
Exactly what i was looking for, but they mention that the core loses inductance after some time, perhaps it's heat related?
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An expert of making MOSFETs explode.
 

Offline strawberry

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Re: Homemade IGBT MIG welder with ATX PSU parts.
« Reply #49 on: June 27, 2019, 07:41:29 pm »
MIG/HF TIG 200A inverter
3phase
UC2834 current mode controller with built-in gate drivers
half bridge 40A IGBT 0.66mJ@150 1.6V heatsink SK442-100
E65 CF297 2 sets in paralel ( dont know if they are good cores)
 


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