ac welder conversion

[joel.richeme]

i was looking at a few pages for converting my old miller thunderbolt 225 ac into a dc welder hoping to be able to run my 12vs wire feeder with it. before you say, in the next year im planning to buy a XMT 350MPA for that purpose. in the mean time modifiying my thunderbolt is a cost efficient option. i got three options for the rectifier part of the project. cheapest would be to buy 10X 50A bridge rectifiers and plug them in parallel, and mount them on a big heat sink
in the middle i can purchase a 500A bridge rectifier also mounted on a heat sink.
lastly, more costly buying 4 big 250A diodes just like those we found in miller engine driven welders like my 2E and my big 40.
also for the stabilizer part i was planning on buying an old one from a local welding repair center.

now, can someone point me what they would choose and why ?

[H80N]

i was looking at a few pages for converting my old miller thunderbolt 225 ac into a dc welder hoping to be able to run my 12vs wire feeder with it. before you say, in the next year im planning to buy a XMT 350MPA for that purpose. in the mean time modifiying my thunderbolt is a cost efficient option. i got three options for the rectifier part of the project. cheapest would be to buy 10X 50A bridge rectifiers and plug them in parallel, and mount them on a big heat sink
in the middle i can purchase a 500A bridge rectifier also mounted on a heat sink.
lastly, more costly buying 4 big 250A diodes just like those we found in miller engine driven welders like my 2E and my big 40.
also for the stabilizer part i was planning on buying an old one from a local welding repair center.

now, can someone point me what they would choose and why ?

NOT a viable project

You will throw good money after bad.....

The miller thunderbolt 225 is a Constant Current "Drooper" supply..... MIG wants a Constant Voltage supply

[Aeronca41]

I strongly agree with H80N. Attempting to use a constant current (designed for stick) welder in a constant voltage application (wire) will generate very poor results. Things that don't work are not cost efficient even if they're free. Spend your money on a mig welder, or a constant voltage source to hook your 12vs to.

[Lostone]

We have a 12VS at work. It has a CC/CV selection switch so in theory what you want to do would work but it's going to be a a big disappointment. No mater wat those YouTube videos show, it's not as simple as just poppingany old rectifiers in there and going to town. It's way more technical then I feel like getting into on here but your going to have more money and time into it, a massive heat sink will have to be built, and almost no duty cycle.

it would cost less to buy a 110 used mig welder. And I still think he probably come out ahead with more power

[MAC702]

The 12VS is designed to work with a CC (constant current) source. While big diodes can turn an AC machine into a DC machine, I've not actually seen in done since I was a kid. Our first machine was an old Hobart AC machine the size of a big chest freezer. My dad had a box with four big diodes on it for DC stick welding. Worked great, but used exclusively for SMAW.

Also, feeders operating on voltage-sensing mode for CC use are usually seen on big jobs. I don't know if you'd have the fine control for other jobs that GMAW might be used for.

Your post asked us to help you choose, but didn't give us any of the actual cost numbers that you are looking at. Just factor in what you think your time is worth, and how much of an experiment you are willing to do versus using the same parts actually used in welding machines.

[Lostone]

The loss to heat rectifying to DC will be huge. There a reason that the Thunderbolt AC/DC machine is only rated at 150 amps on the DC side.

12VS is a CC or CV unit. I've used ours on our 301 at work many times. Your issue is going to be Getting the voltage down. Your looking at adding a big expensive step down transformer to the mix. You'll have more into then it's worth.

Can it it be done. Probably. Is it going to be effective. Probably not.

Then in there's still that pesky low duty cycle issue.

[joel.richeme]

The loss to heat rectifying to DC will be huge. There a reason that the Thunderbolt AC/DC machine is only rated at 150 amps on the DC side.

12VS is a CC or CV unit. I've used ours on our 301 at work many times. Your issue is going to be Getting the voltage down. Your looking at adding a big expensive step down transformer to the mix. You'll have more into then it's worth.

Can it it be done. Probably. Is it going to be effective. Probably not.

Then in there's still that pesky low duty cycle issue.

sure the thunderbolt is rated to 150 dc because the rectifier is hooked up to the "low" side of the secondary according to the schematic.

The XMT or INVERTEC is a good option but i dont have that king of money right now. 1500-2000 is a big investment for me.

im looking at about 150$ to modify the thunderbolt. low duty cycle isnt a real problem since its more a hobby than an income.

im just tired of pilling that welder generator outside every time i want to use the feeder, also it cost a fortune tu run the thing all day.

does anyone have a solution or a suggestion if i want a CV power supply to run the 12vs that will be able to run from 220 1ph ???

[joel.richeme]

mac702 here are the cost of each option (rectifier part only)
10x 50A rectifiers 15$
big 500A 1000v bridge rectifier 56$
4x 250A 1600v silicon diodes 100$

connectors 15$
wiring and terminal 25$
choke 40$
2 capacitor 10,000uf 160V 30$.

on a CC power supply the 12vs is bad at short circuit mig, good with globular transfer and works really well for spray transfer. i just dont know if 200A out of the thunderbolt would be enough for a quality result.

i made little research but its difficult to find a good CV power supply working on 220 1ph.

[H80N]

i made little research but its difficult to find a good CV power supply working on 220 1ph.

That is still your best option

some kind of diy kluge will just waste your money

[joel.richeme]

H80N ill also try to call my local welder repair shop and buy a mig machine with a non working feeder to salvage the power supply part

[H80N]

H80N ill also try to call my local welder repair shop and buy a mig machine with a non working feeder to salvage the power supply part

good approach....


The old MM200 has a bulletproof power supply... would be a good candidate

and is BTW a 270 amp supply...

[Aeronca41]

mac702 here are the cost of each option (rectifier part only)
10x 50A rectifiers 15$
big 500A 1000v bridge rectifier 56$
4x 250A 1600v silicon diodes 100$

connectors 15$
wiring and terminal 25$
choke 40$
2 capacitor 10,000uf 160V 30$.

on a CC power supply the 12vs is bad at short circuit mig, good with globular transfer and works really well for spray transfer. i just dont know if 200A out of the thunderbolt would be enough for a quality result.

i made little research but its difficult to find a good CV power supply working on 220 1ph.

My additional 2 cents worth: the "10 diodes in parallel" in my opinion is a possible but not necessarily good design approach and may not be reliable. Unless you pay big bucks for matched diodes, or buy a big box and match them yourself, each will have a slightly different forward resistance and therefore will not share the load equally. It all depends on the consistency of the diodes you get. The ones with a lower resistance will carry more than their 10% share of the load and will not last as long as the ones that are loafing. Then, you have to disconnect them all and measure individually to find the bad one(s). If you happen to get a couple with very much lower forward resistance than the others, they will fail almost immediately.

[xryan]

You're going to spend as much in parts to.modify the Thunderbolt as a new Thunderbolt AC costs...and still end up with something that will be less useful than a new AC/DC Thunderbolt Just sell the Thunderbolt. You've got other big engine drives and making an execise in futility to use a wire feeder on a Thunderbolt....

[ryanjones2150]

Miller makes a DC rectifier for the thunderbolt. Can't think of the model off hand...sc-150 or something. Won't be until Monday before I can get back to the shop and look. But it's still only 150 amps.

[joel.richeme]

ryanjones2150 you refer to the tc-150, they are hard to find. according to the manual they only have 4X 85A 300V diodes, one varistor and a stabilizer. im pretty sure if i beef up the components i can get better output.