selfmade welding equipment (MIG/MAG/MMA/TIG )

[plasmacut]

Dear sirs
I'm from Ukraine.
first of all I'm sorry for my bad English.
I'm looking for a community of the people who is interested in design, technical solutions and schematic diagrams of different welders (MMA,TIG, MIG/MAG).
I have wide experience in welding equipment fixing and design. Maybe somebody can help me to find people who has the same interests.
Please give me right links.

 

[shenion]

THere is the Amptramp group in Yahoo Groups. Many build their own arc welders.

In my sig there is a link to my DIY arc/MIG/TIG welder.

 

[SirDick Diodenob esquire]

Plasmacut , I am interested in the same having spent 30 years in the power electronics field and finally getting a well deserved redundancy earlier this year , I am bored and now looking to make some money and my current focus is on welders and other similar equipment such as battery/boost equipment . I am qualified in electrical electronic and control engineering but to be honest I never excelled at the really intelectual stuff and have always been far happier hands on but I recently spent a week redesigning and replacing the diode stack on a commercial battery charger which was fitted with those crappy button diodes with good quality IR units . The mod cost me £10 for parts and has made the charger bulletproof ( we shall see ) so I figure that if there is so much crap around being marketed by so called reputable manufacturers that I can do better than them , thats my theory for today . The company concerned fitted an excellent transformer capable of 150amps then spoiled it with cheap diodes , a badly designed heat sink followed by a taiwanese thermal cut out which failed to cut out , they could have completely avoided the damage to their reputation by employing a 12 year old with no design experience and spending an extra £10 on good quality components . I am hoping to find the same thing when I look into welders although the Murex/Butters/Lincoln stuff is obviously excellent . Will also follow the link by shenion to see if it is more appropriate for design/builders .

 

[bill_gj]

shenion & SirDick - I was looking for BIG rectifiers for my old AC arc welder a while ago and came across 'synchronous rectifiers' as a possible much cheaper way of getting DC than trying to buy 150A diodes/SCRs at a reasonable price.
The 'synchronous rectifier' seems to be a way of using cheap-ish MOSFETs in a full bridge arrangement. do eithe of you have any ideas like that? Not being an electronic engineer (just a dabbler) it's beyond me.

 

[SirDick Diodenob esquire]

Bill , I take my hat off to you , you are more than a dabbler if you can get your head around the control circuitry for a synchronous rectifier , I know these are being used for logic power supplies but I am not familiar with it being used at welder level power . Personally I am not an innovator , I use circuits and components tried and tested by other people , I admire the innovators and enjoy reading about the latest thing but would never try anything new myself I have just learned the hard way to let someone else iron out the gremlins which always come with new electronics . You can sometimes buy good quality diodes end of line from suppliers like Farnell , normally they charge an arm and a leg but when they want to introduce a new range they get rid of old stock , nothing wrong with it they just sell it for 75% discount off normal prices , eg line no 366195 85amp 200V Vishay(IR) diodes , they were £2.34 each but have noticed they put the price up recently , have been using the same spec diode for ten years , I noticed a bod selling these for £8.50 each on ebay , made me laugh . I always make my own heat sink using scrap copper busbar , works better than anything you can buy commercially .

 

[pidgeon chit welder]

Dear sirs
I'm from Ukraine.
first of all I'm sorry for my bad English.
I'm looking for a community of the people who is interested in design, technical solutions and schematic diagrams of different welders (MMA,TIG, MIG/MAG).
I have wide experience in welding equipment fixing and design. Maybe somebody can help me to find people who has the same interests.
Please give me right links.

Plasmacut your english is as good , if not better than quite a lot of posters on this site .
Welcome aboard, may your joining help many .

I am interested in electronics and playing with things that can be come part of a bigger set up .

I have a basic qualification in electronic engineering and several as a vehicle orientated mechanical engineer. ( And many others, perhaps not relevent here .)

I gave up trying to repair things years ago when surface mount technology became the norm and I could buy new machinery for less than the repair cost.

Now I'm retired I too am keen to expand my mind and skills by seeing if I can build my own quality multi purpose welder that is just a bit better than the top end of the domestic ones using standard universally available parts.

I look forward to travelling this thread with you all

David

 

[pidgeon chit welder]

Bill , I take my hat off to you , you are more than a dabbler if you can get your head around the control circuitry for a synchronous rectifier , I know these are being used for logic power supplies but I am not familiar with it being used at welder level power . Personally I am not an innovator , I use circuits and components tried and tested by other people , I admire the innovators and enjoy reading about the latest thing but would never try anything new myself I have just learned the hard way to let someone else iron out the gremlins which always come with new electronics . You can sometimes buy good quality diodes end of line from suppliers like Farnell , normally they charge an arm and a leg but when they want to introduce a new range they get rid of old stock , nothing wrong with it they just sell it for 75% discount off normal prices , eg line no 366195 85amp 200V Vishay(IR) diodes , they were £2.34 each but have noticed they put the price up recently , have been using the same spec diode for ten years , I noticed a bod selling these for £8.50 each on ebay , made me laugh . I always make my own heat sink using scrap copper busbar , works better than anything you can buy commercially .

An electronic components guy I know of stocks all sorts of hard to find /out of production / end line stuff . he can be found during working hours at

Harry Donner , Lincoln Road , Peterborough Cambridgeshire UK

He has " Saved my bacon " on many occasions in the past.

 

[GeorgeB]

I recently spent a week redesigning and replacing the diode stack on a commercial battery charger which was fitted with those crappy button diodes .

Do you or anyone know which type of rectifier this is (photo below) as fitted to my Sealey MIG welder? Good or bad? Taking some of the more expensive brands of MIG welder, how do they do better? Leaving aside capacitors and any additional circuitry, can the type of diodes make much difference?

I expected to find 4 diodes if this is some sort of bridge. But there are 8 diodes, so what's this type of array called, and how does it work?

Are these button diodes?

 

[Omniata]

It looks like 8, setup as two sets of 4 in parallel to split the load?

 

[GeorgeB]

It looks like 8, setup as two sets of 4 in parallel to split the load?

That's what I thought but many sources say it's bad design. Perhaps it is! See here, for example:

http://wiki.answers.com/Q/Can_you_put_two_diodes_in_parallel_in_order_to_obtain_the_double_load

Or perhaps it's an insurance, so that either diode can fail on any of the 4 arms of the bridge, without if affecting anything.

 

[Omniata]

If one out of a pair were to fail, the other of the pair would as well, as it would be carrying more than its accepted capacity...

Doing it this way is a good way to make cheap rectifiers as you use more cheaper components, sometimes substantially cheaper, than a few remarkably more expensive individual ones...

 

[shenion]

Yes paralleling them is not a real good idea.

It does work. You don't get 2x the current capacity though due to differences int he diodes. Using two from the same lot will help and is probably what they do. To get near 2x the current they must be exactly matched (more than just the same lot.)

It does spread the heat out allowing better cooling. A single diode would need a heavy heat sink, just the thin plates would be real hot near just one diode. High-power diodes usually have heavy, extruded heat sinks.

I would say it is an OK design. I have seen worse with leadless diodes sandwiched between two plates. Causes uneven contacts.

 

[GeorgeB]

If one out of a pair were to fail, the other of the pair would as well, as it would be carrying more than its accepted capacity...

No, I meant as a QA measure, rather than for cost-cutting. e.g. if the rectifier needs to handle 150A, then you need 4 diodes capable of handling 150A. But instead of dropping down to 2 x 75 you use 2 x 150 as an insurance against failure and to spread the heat, perhaps.

If this is an OK design from Sealey what do Portamigs use?

 

[Omniata]

No, I meant as a QA measure, rather than for cost-cutting. e.g. if the rectifier needs to handle 150A, then you need 4 diodes capable of handling 150A. But instead of dropping down to 2 x 75 you use 2 x 150 as an insurance against failure and to spread the heat, perhaps.

If this is an OK design from Sealey what do Portamigs use?

For low end diodes that wouldn't be too bad an idea but unnecessary and if one were to fail the unbalance would dramatically affect the one in the pair left behind...
Also diodes don't take too kindly to working in this kind of environment without clever electricery to watch for failure...

High end diodes on the other had are more expensive on an exponential scale, that is, from a point the cost goes up a larger amount for a smaller change in current carrying capacity...

I can see where your coming from but this sort of thing would only be done in a very high end power supply with two or more "backup sets" capable of switching in to prevent downtime through failure.
For the majority of the time the backups would be effectively redundant, so in the instance of a welder unless it was a seriously heavy duty piece of kit under constant use te backups would be too greater cost to be necessary...


Good thinking though...

 

[GeorgeB]

I also see that the diodes have numbers which appear to be in a series, so perhaps they are a matched set. But various articles say the diodes can change over time meaning that 150A could end up going through a much lower capacity diode after a few months or years. It just seems too risky. How do they get away with it?

I remain interested in hearing about superior solutions used on superior MIG welders, with photos if possible. What do Portamigs, Lincolns, Murex, etc use for a rectifier?

 

[shenion]

GeorgeB, they use higher-end rectifiers. Usually stud mount.

My Miller and Airco have huge, stud mount rectifiers. I'll post a pic of one when my camera charges up. The stud on the ones I have are 10mm bolts:

Replacements for my Airco are about $120 each. That is OEM from International Rectifier, not a price from a repair shop.

 

[R Kraft]

The big diodes are kind of expensive, but you can make a really bullet proof welder.
But there are about three or four package types that would work well
Robert

 

[GeorgeB]

I like the idea of DIY welders because you can specify generally higher quality components than all but the most top end (transformer based) MIG welders. How many MIGs have diodes like those in pictures posted by Shenion and R Craft? There's a 2006 thread here from a member who faced a bill of well over £100 to replace the low quality rectifier assembly on his MIG welder.

See: http://www.mig-welding.co.uk/forum/showthread.php?t=486

Yet for 4 x £14.74 one could buy 150A rectifiers from RS Components.
That's Rectifier diode 150KR20A 150A 200V
RS Stock No. 357-4598 £14.74

I trust these would be much better and longer lasting than fitted to my present Sealey machine.

Any advances? Anything better and/or cheaper (new)?

 

[R Kraft]

The amperage would be distributed among 4 diodes (600A), so you would have a lot of overkill for almost any small welder.
Robert

 

[GeorgeB]

The amperage would be distributed among 4 diodes (600A), so you would have a lot of overkill for almost any small welder.
Robert

Ah, that's good news then because diodes of around 50A (allowing a bit of headroom above 150A) should be cheaper. I assumed that each of the 4 diodes in the bridge configuration needed to be at least 150A for a 150A MIG welder.