Looking for diodes for montgomery ward welder

[Treemonkey1000]

You should replace all 4 of them.

 

[Steve Bosshard]

Ditto - replace all four. (Caveat - provided they are the same part # and part of the same circuit).

 

[Samshine]

The tech support man i talked to over the phone, told me the diodes with the part number he gave me, is the same ones that are in the welding machine now.
samshine

 

[Treemonkey1000]

The tech support man i talked to over the phone, told me the diodes with the part number he gave me, is the same ones that are in the welding machine now.
samshine

So there you go. You will have to scrape up the money it sounds like for all 4. You can not be sure which ones are damaged completely or weak. No sense in taking any chances by not replacing them all. Too bad he didn't give you some more spec's to see if they could be cross referenced. As all have said in this long thread. Good heat sinking, use thermal compound when mounting them, good clean connections to the diodes, and make sure the fan is working correctly..

 

[Transit]

150 amps is less than I had thought, that defiantly says that the diodes are cooked. To bad you did not get the voltage ratings. I would not bother replacing the diodes with the same 150 amp rating, I would be looking at a 200 amps minium and perfer 250 + amps.
640-200UF60 200UF60 Ruttonsha Diodes - Standard Recovery 200 Amp 600 Volt Power Diodes
640-200UF10 200UF10 Ruttonsha Diodes - Standard Recovery 200 Amp 100 Volt Power Diodes

640-250UF80 250UF80 Ruttonsha Diodes - Standard Recovery 250 Amp 800 Volt Power Diodes
640-250UF60 250UF60 Ruttonsha Diodes - Standard Recovery 250 Amp 600 Volt Power Diodes

640-300UF80 300UF80 Ruttonsha Diodes - Standard Recovery 300 Amp 800 Volt Power Diodes 800 V 300 A 5000 A 1.35 V
640-300UF100 300UF100 Ruttonsha Diodes - Standard Recovery 300 Amp 1000 Volt Power Diodes 1000 V 300 A 5000 A 1.35 V
640-300UM120 300UM120 Ruttonsha Diodes - Standard Recovery 300 Amp 1200 Volt Power Diodes 1200 V 300 A 5000 A 1.35 V
640-300UF140 300UF140 Ruttonsha Diodes - Standard Recovery 300 Amp 1400 Volt Power Diodes 1400 V 300 A 5000 A 1.35 V
640-300UF10 300UF10 Ruttonsha Diodes - Standard Recovery 300 Amp 100 Volt Power Diodes 100 V 300 A 5000 A 1.35 V
640-300UF20 300UF20 Ruttonsha Diodes - Standard Recovery 300 Amp 200 Volt Power Diodes 200 V 300 A 5000 A 1.35 V
640-300UF60 300UF60 Ruttonsha Diodes - Standard Recovery 300 Amp 600 Volt Power Diodes 600 V 300 A 5000 A 1.35 V


Other things to keep in mind is how wires are connected to the center pin of the diode, soldered or terminal with pigtail.
If the wires are soldered to the center take care not to over heat the diode.
The diode-heat sink must be electrically isolated from the other diode-heat sink and the welder case. This means that there are insulating hardware to keep the heat sinks from shorting to each other.
I would take pictures and make notes, trust nothing to memory.

 

[BrentD]

This Diode on ebay would be a perfect replacement part. Not sure of the stud size of that diode, but if it's smaller or larger than current, you can always a washer or drill new mounting holes in the heatsink.

You would need 4 of them.

If you're going for a serious upgrade you could go with This 400A diode which is the same price as the one above and more than double the capacity of your existing diodes.

(I build tesla coils for a hobby so I'm used to dealing with high-voltage and high current circuitry.)

 

[Transit]

Brent, good find. The 250 amp meets my minium requirement with a 66% gain in current rating. The 400 amp stud is very attractive, however the used condition gives me concern. If the heat sink needs to be drilled to accept the diode so much the better. Drill and tap the hole, the thread will increase the contact area between the diode and heat sink making the heat flow more efficient.

 

[Samshine]

True it might be 150amp. But if i got four (two above and two below).
That means i get 300 amps. out of it right?
samshine

 

[Samshine]

I took a look at he diode Brent sent me off of e-bay. My diode looks just like that one, except were the copper braid wire is connected to the big end. On this one it looks like it has about a 3/4 inch connecting. Were mine only has a 1/4 inch connecting. Looking at the ruler it looks like it has a 5/16 inch stud. That is what mine is. I like transit's concern. I dont want to put used parts in the welder.
My only concern, me not knowing what the voltage is on my diodes. How do i know if i am picking the right diode for my welder?
I know i sure liked the price on the one on e-bay.
But will this diode work, not knowing the voltage rating of the diodes in the welder now.
Thanks for all your help.
samshine

 

[BrentD]

My only concern, me not knowing what the voltage is on my diodes. How do i know if i am picking the right diode for my welder?

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.

Someone earlier mentioned the inductor. For those that don't know, and inductor is just a coil of wire wrapped around a ferro-magnetic core. It's used in welders to help smooth the DC arc because one of the rules of electricity says that current traveling through an inductor can't change magnitude or direction rapidly due to the magnetic field induced in the core by the current flowing through the coil of wire. When the current starts flowing, that magnetic field stores up part of the energy from the current up to a certain point and then if the current starts to drop, the magnetic field dumps energy back into the coil momentarily boosting the current. When the current starts to rise, the magnetic field in the core will grow again and absorb some of the current and slow the currents rise up to the point where everything is back in balance.

The downside to this is that when the arc is broken the magnetic field in the inductor collapses rapidly. The speed of the collapse creates a spike of high voltage much higher than the initial voltage in the circuit and the welder has to handle it somehow. (This phenomenon, called "inductive kickback" is true for any inductive coil, be it a motor winding or a relay coil.) Fortunately, that voltage spike will produce current flowing in the same direction as the original circuit.

On DC welders, the inductor is placed after the diode rectifier bank, so the kickback from breaking the arc can't flow back toward the diode bank. It is just dissipated (again through physical laws too involved for this discussion.) The only way you would get serious inductive kickback across the diode bank would be if you killed power to the welder while a rod was stuck.

So what this little physics lesson is saying is that 600V diodes should be more than sufficient for your welder, unless you intentionally abuse it by repeatedly sticking rods and killing the power while they're stuck or deliberately connecting the two welding leads together, cranking the power way up, and flip the switch on and off a bunch of times.

 

[Samshine]

Brent thinks for helping me to understand the voltage better.
Could you please point out the diode with the 250amp. 600volts?
The one i was looking at on e-bay has a rating of 1600 volts.
Thanks, samshine

 

[Samshine]

I think i am catching on now. tell me if i am wrong?
I need the four diodes with part number Semikron SKR 130/6
which is sold by Semikron who advertised the diode Semikron part number. SKR 130/16 on e-bay which has a item number 350238374298
thanks, samshine

 

[patrick_g]

Thanks for the help.
I called tech surrport of the welder, number century gave me. He said all the information he had is that i have four diodes. And they are 150 amps. each.
Question is?
Can i just upgrade two of the diodes or do i have to upgrade all four diodes at the same time?
Thanks again for your help. Hope to hear from you soon.

All because of weak link in the chain.

 

[Steve Bosshard]

Semikron SKR 130/6

SEMIKRON - IGBT, Diode, Thyristor, Power Semiconductor Modules, Chips, Assemblies

Now we are getting somewhere.

This may be a generic cross NTE Cross Reference

or Tiny URL - NTE Cross Reference

Sounds like you are on the road to recovery. I would use the OEM part unless there was a substantial reason not to.

Now, wonder what made the diodes fail to begin with ? Just time ? Shorted something? power spike while welding ? Fan quit cooling ? Covered with dust / thrash blocking airflow ?

Sure don't want to let the smoke out of the new diodes.

steve



steve

 

[Transit]

Sam, this is the one you want, This Diode on ebay
Semikron SKR 130/16 250A 1600V Rectifier Diode DO-8 - eBay (item 350238374298 end time Feb-06-10 04:47:44 PST)
As for the 300 amps? NO! components connected in series have a common current with the voltage of each element added. One 150 amp diode or ten connected in series = 150 amps.

 

[oldmech]

Hi! Ac-Dc 250 amps welder can work with 150 amps on DC so I think if you put 300 amps diodes ,You can burnt the transformer supply a lot more expensive than diodes. My small Lincolh welder use 40 amps diodes for 70-80 amps dc. I change or burnt two diodes in four years. I replace it $40 each. No necessary to change all. I test the diode with VTVM. Good luck Oldmech

 

[BrentD]

Brent thinks for helping me to understand the voltage better.
Could you please point out the diode with the 250amp. 600volts?
The one i was looking at on e-bay has a rating of 1600 volts.
Thanks, samshine

My bad... I missed the 1 in the 1600 and saw it as 600. So the 1600V diode is even better. With 2 in series they can withstand a reverse surge of around 3200V. That should be way more than adequate for a welder. Those diodes will probably outlive all of us.

 

[Samshine]

I want to change all four of the diodes. I want to go the right way out, along with the cheapest way out in case if something else is wrong with the welder.
I want feel do bad if i have to junk it.
The diode that is on e-bay. If i decide to go this way, should i get two diodes like this?
Semikron SKR 130/16 250A 1600V Rectifier Diode DO-8 - eBay (item 350238374298 end time Feb-06-10 04:47:44 PST)
And two like?
Semikron SKN 130/16 250A 1600V Rectifier Diode DO-8.
Other words two SKR and two SKN diodes with the same rating.
Thanks again for all your help. samshine

 

[BrentD]

I want to change all four of the diodes. I want to go the right way out, along with the cheapest way out in case if something else is wrong with the welder.
I want feel do bad if i have to junk it.
The diode that is on e-bay. If i decide to go this way, should i get two diodes like this?
Semikron SKR 130/16 250A 1600V Rectifier Diode DO-8 - eBay (item 350238374298 end time Feb-06-10 04:47:44 PST)
And two like?
Semikron SKN 130/16 250A 1600V Rectifier Diode DO-8.
Other words two SKR and two SKN diodes with the same rating.
Thanks again for all your help. samshine

This depends on how your welder is wired. The welder should have 2 metal plates, each with two diodes mounted to it. What you are looking for is how the wires going to the positive and negative lead jacks are connected. If the positive wire is connected to one plate, and the negative wire connected to the other plate, then yes, you would need 2 SKR's and 2 SKN's. If, however, one jack is connected to a heat sink plate and the other to the diode pigtails then you would need 4 identical diodes. If that is the case then which lead is connected to the plate would determine which type you would need. (If the positive lead is connected to the plate and the negative to the pigtails, then you'd need SKR's, but if the negative was connected to the plate and the positive to the pigtails then you'd need SKN's.)

If, neither welding lead is connected to a plate but rather the main transformer is connected to the plates and the welding leads are connected to the pigtails, then you definitely need two of each type, but would have one of each type on both plates and the pigtails of the two common types from each of the two plates would be tied together and go to one welding lead, while the other two pigtails would be connected together and go to the other lead.

In any case you could get by with using 4 identical diodes of either type, but that would require changing some wiring around inside the welder.

 

[Samshine]

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