# Looking for new diodes for my welder.



## heimlaga (30 Dec 2015)

My trusty old Unitor SL-22 which is a 200 ampere rectifier stick welder broke down last week. Two diodes out of four are out of order. The welder is probably from the 1960-ies but it is well made and in good condition and produces a surprisingly good welding current for it's era.

Now I need new diodes. The type S3AN125 and they look like this





I got the last diode of this type from Partco in Helsingfors. Unitor in Norway do not stock spare parts for this welder any more. I have only found one supplier who still have theese in stock and that is americanmicrosemi.com. They ask 426 dollars plus custom fees that is over 400 euros plus sales tax makes 500 euros for a minimi order of four diodes. That would be quite a hard blow to my finances. A new welder of similar size and quality would cost around 1500 euros so that is totally out of question.

Does anybody know a supplier who has this kind of diodes for sale?


Edited to correct the figures. I had misscalculated the numbers.


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## CHJ (30 Dec 2015)

I would look for alternate manufacture 150amp/240volt silicon diodes and make up a new bridge rectifier.


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## heimlaga (30 Dec 2015)

Aye....that would be a reasonable solution......... My whole plan for setting up a joinery business hangs on this old welder...... lots of guards and parts to be made and very little money on hand.


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## mindthatwhatouch (30 Dec 2015)

Any good? http://www.weldmart.com/store/diodes.htm


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## heimlaga (30 Dec 2015)

If screwed into a threaded hole in a piece of flat copper or brass bar they would become substitute flat bottomed diodes.

Does this solution make sence?


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## imageel (2 Jan 2016)

Hi, as well as woodworking I do a fair bit of electronics work, and whilst that diode only looks available from American Microsemi you could easily replace it with an equivalent - a quick look at Digikey shows this one that looks suitable.
http://www.digikey.co.uk/product-detail ... A-ND/78837

they do have a Finish site too :lol: 

Personally I would replace all 4 (assuming it's a bridge configuration) - only thing to be aware of is whether the diode case is the anode or the cathode (the diode above is cathode stud). I can't see the spec for this on the Microsemi website, but since you have (I assume) 2 working diodes you could measure them and confirm what type you need (I assume the heatsink onto which they are bolted is live and forms part of the bus feeding the welder output leads/control gear.
They are only £18.25 each, and orders over £50 get shipped from the US for free (UPS/FedEx)

They are based somewhere in the mid-south however I have always had brilliant service from them with deliveries usually taking only 3 days from the point of order
Cheers
Ed


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## heimlaga (4 Jan 2016)

That is exactly the type of diodes I am trying to find as a substitute. The base should be cathode.


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