mig welder repair procedures

[eddie49]

Maybe those big diodes fell out of the side of a snow-damaged Eurostar locomotive...
They are very impressive. If I had a local scrapyard that would sell 8 of them for a tenner, I'd be round there every day.
The best offer I have found so far is:
http://www.surplussales.com/semiconductors/DiodeSaleStud.html
but that is in USA.

 

[SirDick Diodenob esquire]

Eddie , I think I may have just been lucky on the day that the guy doing the work didnt know what they were but they are the exact same type as I found inside a 450amp old TIG machine and there should be plenty of these being scrapped these days . At the scrapyard they were breaking the ceramic off with a hammer to get at the stud and the braided copper tails so the scrap value I suppose would be very little. Dai these came out of a large rectifier which apparently had dozens of these inside but they had already stripped them completely and mangled the rest of it . Before leaving the power industry I never gave a second thought to the cost of this type of component , panels where regularly removed from service and just dumped for the scrap man , the parts would never be salvaged or reused . I would think that scrapyards near the Chlorine plants in Runcorn would be seeing a lot of this stuff . You could certainly use the old plates in your welder to mount four new diodes.

 

[dai]

Eddie , I think I may have just been lucky on the day that the guy doing the work didnt know what they were but they are the exact same type as I found inside a 450amp old TIG machine and there should be plenty of these being scrapped these days . At the scrapyard they were breaking the ceramic off with a hammer to get at the stud and the braided copper tails so the scrap value I suppose would be very little. Dai these came out of a large rectifier which apparently had dozens of these inside but they had already stripped them completely and mangled the rest of it . Before leaving the power industry I never gave a second thought to the cost of this type of component , panels where regularly removed from service and just dumped for the scrap man , the parts would never be salvaged or reused . I would think that scrapyards near the Chlorine plants in Runcorn would be seeing a lot of this stuff . You could certainly use the old plates in your welder to mount four new diodes.

you havent got 4 spare have you

 

[Kelvin]

what the position that your selector switch put on ?? "0" position ?? i think you better measure you machine output voltage from the torch (+) with respect to earth (-), there should be 17 to 40 volts something, if there have any volts output more than 17,18 and your could be weld in nodoubt! unless the torch worse inside..

 

[R Kraft]

The heat sinks in your machine were not very good , even with the pressed in diodes they were designed for.
There are several different diode packages that would work, in a moderate amperage machine like yours.
Stud,ISOTOP ,DP20,DP34,DP50 and DP70.
You just need to see what you can find at a good price.
Robert

 

[dai]

summat like this

http://uk.farnell.com/semikron/skn240-04/diode-standard-320a-400v-stud/dp/9564462

 

[R Kraft]

summat like this

http://uk.farnell.com/semikron/skn240-04/diode-standard-320a-400v-stud/dp/9564462

Those would work, pricey little things though.
Just will have to fab up a heatsink for them.
Robert

 

[dai]

right guys got a new rectifier but...it hasnt got the resistors(??) on it
do i need to swap the resistors over or will it work ok??
also what are the resistors for??

 

[shenion]

The resistors are to bleed out the charge on the filter caps when you release the trigger.

 

[dai]

The resistors are to bleed out the charge on the filter caps when you release the trigger.

do i need them ??


i seem to remember that when i finished welding that if i touched the torch on the work it would spark for some time after(3-5minutes)

 

[shenion]

Then they were probably bad. They should discharge the caps in a few seconds.

They are a safety issue. Will work without but be annoying. 100 ohm 10 watt is a common value, you could pick them up at places like Farnell (order # 1737303, £0.34/ea).

 

[dai]

not my day today
put the rectifier on started feeding wire through to have a go then a big bang,fizz and a big cloud of smoke

capacitor decided to grenade its self

 

[shenion]

They do that; actually, that looks clean. I have seen shrapnel/confetti/slime all over.

Could be the caps are shorting out and could have contributed to the rectifier going.

 

[dai]

will it still work on 7 capacitors??
i tested the caps a few days ago and they all seemed ok

 

[shenion]

It will work on 7.

If one went, probably the others are not that far behind.

 

[dai]

are they typical like 1 will last 30 years and the next will last 30 minutes

 

[shenion]

They degrade over time.

Most are rated for a certain number of hours, usually 1000 to 3000. They degrade faster at higher temps and there are usually 85c and 105c grades.

Hard to say how long they will last. you might see about replacing them. Keep an eye on ebay for the same size. I picked up a few for my MIG real cheap. 8 will probably cost you near £100.

What are their markings?

 

[dai]

 

[shenion]

40V seems low. Without those bleeder resistors it can spike up while welding.

8 x 10,000uf is 80,000 uf. you can look for a lot of low ESR or "Computer Grade" caps that add up to about the same (preferrably 50V or higher). Something like four 20,000uf.

You would have to assemble them differently as they are usually different sizes. Aluminum bar stock or flattened copper pipe make good buss bars.

 

[dai]

phizically size wise is there any difference in capacitors?

can i say thanks to you shenion you been a big help