Looking for diodes for montgomery ward welder

[Transit]

I know there is two diodes bolted both ends to the same heat sink. (I assume these are negative diodes). Diodes running east and west.
While the other two diodes are bolted to the other heat sink with a plate running from one of the welding connecting jacks connecting the two pig tails on a stud which the stud is bolted to the same heat sink. Diodes are running north and south.
I hope you can tell by my description, which type of diodes i need.
Thanks for all the help. samshine

What you are saying is that you have two separate heat sinks, each heat sink has two diodes bolted to it.
Does it look like this? Tell me where the wires go from the heat sink and posts.
The reason i ask about the wires is because all four diodes MAY be the same or a set of two may be +/- and the other set may be -/+ and this will effect how things are wired. A photo would be a big help.

 

[SPYDERLK]

With regard to the AC input, one of the "blocking" diodes is forward biased so the inverse or back biased flow is resisted by only one diode. Also note that where there is capacitance on the DC output the stored charge can add to the back bias causing the diode to see the full peak to peak AC PIV. Most welders are 80VAC RMS, or less, open circuit on the secondary winding. This says the diodes can see as much as 80x2x 1.414 = 226V [peak to peak] reverse bias. You want the diode PIV ratings above that to be safe.
larry

Like somebody said before a diode is (basically) to electricity what a check valve is to water or air. It allows voltage to only flow in one direction. Just like a check valve, there is a limit to how much backwards pressure (i.e. voltage) it can block before it breaks down. (Forward voltage doesn't matter unless it is astronomically high.) Where things get a little different with electricity is that you can put two diodes in series and their "peak inverse voltage" adds up. These diodes in question are 600V diodes so putting two of them in series would give you a diode rated roughly 1200V (more or less based on some unpredictable technical factors that are mostly irrelevant here)

The primary transformer in your welder steps voltage down from 220V to a lower voltage, usually no more than 80-90 volts in "standby". When you strike an arc that voltage will drop by as much as half.

So if you consider that, then the 600V diodes are more than enough to handle that voltage.

[I tried to get the "series" thing out of the consideration earlier, but it seems to sneak back in]... However, the 600PIV you would get from these in a full wave 4 diode bridge is well above what you need.
larry

 

[BrentD]

I know there is two diodes bolted both ends to the same heat sink. (I assume these are negative diodes). Diodes running east and west.
While the other two diodes are bolted to the other heat sink with a plate running from one of the welding connecting jacks connecting the two pig tails on a stud which the stud is bolted to the same heat sink. Diodes are running north and south.
I hope you can tell by my description, which type of diodes i need.
Thanks for all the help. samshine

What about the other other welding jack? Is it connected to the other heatsink or to the other two diodes's pigtails? If it's connected to the plate then all 4 of your diodes are exactly the same and in that case which plug, + or - , is connected to the heatsink will determine which type of diodes you need.

 

[Transit]

What about the other other welding jack? Is it connected to the other heatsink or to the other two diodes's pigtails? If it's connected to the plate then all 4 of your diodes are exactly the same and in that case which plug, + or - , is connected to the heatsink will determine which type of diodes you need.

Brent, if Sam fills in the information in my illustration I will update it so we are all looking at the same page.

 

[Treemonkey1000]

Samshine take some pictures of the inside with enough detail if you can might save some questions.

 

[Samshine]

I am sorry i dont have the tools to post on here. But i did take some pics. from my cell phone. I can send them to anybody that calls me.
My number is 1-912-258-4494

The postive welding dc jack is hooked to the dc transformer. The other end of transformer is connected to the isolated heat sink, which has two diodes bolted to it. the pigtail is bolted to the other heat sink. The heat sink has a isolater keeping the heat sinks from touching.
The negitive welding dc jack is connected to ac transformer, along with a plate connected to dc neg. jack, which runs to a stud that is bolted to the heat sink along with pig tail of both of the other two diodes. These two diodes is bolted to the other heat sink. This heat sink is not isolated from welder case. The only isolater is located between the two heat sinks.
I hope this clairifys it.
There is four diodes. two on each heat sink with all pig tails bolted to opposite heat sink with isolater between the two heat sinks.
Thanks for all your help. samshine

 

[Transit]

I am sorry i dont have the tools to post on here. But i did take some pics. from my cell phone. I can send them to anybody that calls me.
My number is 1-912-258-4494

The postive welding dc jack is hooked to the dc transformer. The other end of transformer is connected to the isolated heat sink, which has two diodes bolted to it. the pigtail is bolted to the other heat sink. The heat sink has a isolater keeping the heat sinks from touching.
The negitive welding dc jack is connected to ac transformer, along with a plate connected to dc neg. jack, which runs to a stud that is bolted to the heat sink along with pig tail of both of the other two diodes. These two diodes is bolted to the other heat sink. This heat sink is not isolated from welder case. The only isolater is located between the two heat sinks.
I hope this clairifys it.
There is four diodes. two on each heat sink with all pig tails bolted to opposite heat sink with isolater between the two heat sinks.
Thanks for all your help. samshine

Sam, I do Tech Support work all day by phone. I ask specific questions in a specific order. Please open the pdf file in post #81 and tell me what goes where and I will redraw the diagram to indicate the additions and changes.

 

[BrentD]

Sam, I do Tech Support work all day by phone.

Ick! Have you qualified for sainthood or insanity yet? Stick with that job long enough and you'll eventually make one of the two.

 

[Samshine]

Transit sorry for the confussion.
I have three heat sinks. Diode one is bolted to one. Diode two is bolted to one. And diode three and four is bolted to the third heat sink.
Post 1 and post 2 connects to the heat sink that diodes 3 and 4 is bolted too.
Transformer and neg. welding cable is connected to heat sink with the number three and four diode.
Post 3 is bolted to the heat sink that diode one is bolted too.
post 4 is bolted to the heat sink that diode two is bolted too.
Note: heat sink one and two is bolted to welder bottom without insulater.
thanks for all your help. samshine

 

[BrentD]

[I tried to get the "series" thing out of the consideration earlier, but it seems to sneak back in]... However, the 600PIV you would get from these in a full wave 4 diode bridge is well above what you need.
larry

I've been thinking about this today and just realized you're right. In a full-wave bridge rectifier, you never really have two diodes acting in series. At any point in time you will only have 2 diodes forward (or reverse) biased, but in different directions. Guess I've spent too much time with long strings of multiple diodes under oil in Tesla Coil supplies. Skews my thinking.