Looking for diodes for montgomery ward welder

[Samshine]

Ah, but you have to remember that we are dealing with 2 parallel strings each with 2 diodes that are in series with the arc between them. (The two parallel strings just happen to be connected to separate transformer legs.)

If the forward diodes are in series then the reverse-biased diodes are also in series. Take a look at the attached schematic for a better view.

Colored lines and arrows indicate current flow during each transformer phase. (I.e. Blue lines, left side of transformer is - right is +. Red line, Left is + Right is -.)

You can see that at any point in time the diodes in the green box will always be in series and the diodes in the turquoise box will also always be in series.

Originally Posted by Samshine
Transit after looking at the drawing. The diode hook up looks good.
The only problem i see is the transformer hook up.
This transformer has 4 wires coming from it.
Two wires hook up to the dc pos. welding lead.
Two wires hooks up to the number C heat sink. Also another hook up hooks from the same number C heat sink and runs to the dc neg. welding lead.
Like i mentioned earlier this welder has three transformers. I was told one was a secondary transformer. These other two tranformers are the ones at the top. The slider bar runs up and down between the transformers to change the amp. There is two wires running from one of these transformers and hooking up to the dc neg welding lead as well. Also there is just one wire running from one of the transformers up top and hooks up to number A heat sink.
Thanks for all your help. samshine

 

[Gary Fowler]

Collect $.10 from each poster on this thread and go buy a new machine.

 

[Treemonkey1000]

Ok about a 1 minute search for DC welder schematics gave me this.. Let's get this show on the road. Scroll down to section 6 and it shows the schematic for the AC and DC portion of this particular welder. Your results may vary.


http://www.millerwelds.com/om/o321n_mil.pdf

 

[BrentD]

Ok about a 1 minute search for DC welder schematics gave me this.. Let's get this show on the road. Scroll down to section 6 and it shows the schematic for the AC and DC portion of this particular welder. Your results may vary.


http://www.millerwelds.com/om/o321n_mil.pdf

The problem isn't the schematic. All DC welders use the same basic schematic or a variation thereof. The problem is with the parts. Stud diodes are made in 2 versions. One with the metal case being the anode and the pigtail being the cathode and the other variation is exactly opposite.

If Samshine's welder uses 2 of each and we tell him to buy 4 of 1 kind and install them exactly as the originals were installed, then we've just told him how to blow those diodes he just bought. I prefer to be relatively certain I'm giving good advice, particularly where there is an obvious electrical novice involved. (Truth be told, there must be a few of us who obviously like solving problems or the best thing for us to do would be to tell Samshine to find an electrician to take a gander at the welder and tell him how to hook everything up.)

 

[SPYDERLK]

Ah, but you have to remember that we are dealing with 2 parallel strings each with 2 diodes that are in series with the arc between them. (The two parallel strings just happen to be connected to separate transformer legs.)

If the forward diodes are in series then the reverse-biased diodes are also in series. Take a look at the attached schematic for a better view.

Colored lines and arrows indicate current flow during each transformer phase. (I.e. Blue lines, left side of transformer is - right is +. Red line, Left is + Right is -.)

You can see that at any point in time the diodes in the green box will always be in series and the diodes in the turquoise box will also always be in series.

The arc has nothing to do with it. When the output is open circuited is when the full peak AC is applied across 2 // reverse biased diodes [that are each in series with a forward biased diode]. When the arc is present the AC voltage is just less. I believe the WIKI diagram is easier to understand and is correct and shows this clearly. I will take a harder look at yours later when I have more time.
larry

 

[Transit]

Ok, I知 back. Reading all the posts I see you guys are all over the place.
The question of all four diodes being the same was answered by Lincoln/Century and by the fact that the diodes are mounted on three heat sinks. If the original diodes were PN and NP, then they would/could be mounted on two heat sinks.
Researching the net for information about the Ward/Century welder, its very thin, others are looking for information too. The only way to get a manual would be direct from Lincoln/Century if they are available.

The diagram is as close as I can make it with sams description. I do not think there are three transformers. The two transformers that Sam describes with the slide control in between is most likely one transformer with the primary and secondary split. The slid moves part of the core to control the current output of the transformer. The third transformer may be an inductor to smooth out the current.
Being that we are not 100% sure how the transformers are connected, I would work on replacing one diode at a time on each of the heat sinks, wire for wire, being careful to keep everything in order.
I do not understand why Sam keeps asking if the diodes we have been talking about are correct, that was settled long ago.
Lincoln

 

[jimmysisson]

Sam, can,t you get a photo of your welder's innards to these guys, the suspense is killing me!
Jim

 

[Transit]

I found a very good and simple expiation about semiconductors.

Full-wave Rectifier

 

[oldmech]

Hi! Thanks TRANSIT for info. My small DC Lincoln welder use Full wave rectifier with Capacitor.
I remember Forty years ago A lot DC power supply use CHOKE (look as a transfo) for DC filter. Old diodes was less efficients New Diodes are better now. May Be Old welders can use one main transfo. with diodes and chokes for better Dc voltage. Good luck! Oldmech

 

[tundrawolf]

What happened to Samshine?? Did he get his welder to work? I am replacing the diodes (Of unknown current) in my Westward welder and have read this thread intently.