Looking for diodes for montgomery ward welder

[Transit]

Irving missed a few things.

The diode may be shorted, a low resistance in both directions.
The diode may be open, high or infinite resistance in both directions.

Most digital volt ohm meters have a Diode setting, this is a go, no-go test. With the meter set to the diode test, a diode symbol. Touch the meter leads together and you should hear a beep.
Connect the RED and BLACK probes to an isolated diode and then reverse the connection. You should hear the beep one way and no beep the other way. All beeps or no beeps and the diode is toast.

Right now we are taking general educated guess of what should be or not. If you can, take some pictures and not too close or they may be out of focus. We will be able to see what these heat sinks and fan look like and make better judgments.

BTW, it is not how many hours a day the welder is used, it is the duty cycle rating that counts. A 30 % duty cycle means, weld for 3 minutes and let it cool for 7 minutes with the fan running. The duty cycle is inversely liked to the welding current, high current welding=short welding time and low current welding= long welding time.

 

[Treemonkey1000]

This poor guy is going to give up and go buy a new one with information overload here. All of these guys are very knowledgeable and a great resource. One more bit of information if you do use a meter to test them out is to disconnect one end of the diode from the other part of the circuit. This will help to prevent reading resistance from the transformer or other components in that circuit. Those large diode junctions might not read correctly with a Diode test function. That's where I like my old Simpson 260 meters. As an electronic Geek here at a company that makes all of the large passenger jets and military products it would be fun to poke around in that welder.

 

[patrick_g]

Irving missed a few things.

The diode may be shorted, a low resistance in both directions.
The diode may be open, high or infinite resistance in both directions.

Most digital volt ohm meters have a Diode setting, this is a go, no-go test. With the meter set to the diode test, a diode symbol. Touch the meter leads together and you should hear a beep.
Connect the RED and BLACK probes to an isolated diode and then reverse the connection. You should hear the beep one way and no beep the other way. All beeps or no beeps and the diode is toast.

Yes but... There are more than just these three possibilities, open, shorted, or good. As a previous poster mentioned your digital meter's diode test (or a conventional analog $3 meter will find a bad diode if the diode is shorted or open but... it will not find a diode that only has symptoms when it is hot or conducting a good fraction of its rated current or only leaks in reverse at near its PIV. Your suggested test will find SOME bad diodes, the ones good and truly shorted or open but will not find ones that leak when hot or current or voltage stressed. What do we know for sure? If your test says it is bad IT IS BAD. If your test says it is good it may still be bad.

Oh, and RIGHT ON TREE MONKEY!!!!

Pat

 

[Transit]

All valid points, it is very easy to fix problems when you have $100,000 in test equipment, so let us keep it simple. The OP has what he has to work with, lets make the best use of it. 99.99999% chance that the diodes are open from the current stress. If the diodes were ever shot circuited for an instant the high current output of the welding transformer would have burned them open.

 

[mitch becton]

if you have a local alternator starter rebuilder give him a call and ask if he can you the repair diodes for a powerline alternator or can he get you the specs as far as what might match your diodes. this powerline company produces only high hard duty alternaors for emergency and military applications and the diodes can be bought as a kit. if you cant find local rebuilder to help please-mail me wmbecton@comcast.net or call my cell number is 678-478-7427 i amin the speciality alternator and starter business and have many rebuilders who use these diodes in repairing battery chargers so i think they might work for the welders also.

thanks

mitch becton

 

[Transit]

if you have a local alternator starter rebuilder give him a call and ask if he can you the repair diodes for a powerline alternator or can he get you the specs as far as what might match your diodes. this powerline company produces only high hard duty alternaors for emergency and military applications and the diodes can be bought as a kit. if you cant find local rebuilder to help please-mail me wmbecton@comcast.net or call my cell number is 678-478-7427 i amin the speciality alternator and starter business and have many rebuilders who use these diodes in repairing battery chargers so i think they might work for the welders also.

thanks

mitch becton

Interesting, is there a web site to learn more? 2 and 300 amp diodes are hard to come by.

 

[mitch becton]

transit and others
being doing this for over 20 years and do not know of any website that you can go to and find out the specs that are availaable. i can fax the catalog pictures with specs that i have access to and can research anything that goes along with these train of thought
back to original post the ones i was thinking about pos and neg they are rated at 150amp and up to200volts they are threaded with a 3/8-24 post with a 6inch sleeve that is colored coded for pos or neg. they are other that i can get that will possibly get above the 200amp. i also have access to a70amp 200v with a 1/4-28 post with a eyelet to hook up a wire to and cannot tell exactly today what cost would be on these 2 but i can assure you all they wont be $30.00 each and as i stated before theywork great for battery chargers.
my e-mail address is wmbecton@comcast.net my cell number is 678-478-7427 i willbe able to supply more exact cost etc on monday.
hope this helps.

thanks

mitch becton

 

[mojoinco]

Well, something else. While you are in there, look for any terminal blocks and connectors. Look for the obvious corrosion, then take the nuts loose and clean the corrosion you don't see (small wire brush, etc). A little battery terminal anti-corrosion spray should also help when you are done. You should also consider using some conductive grease on the diodes too. They may have the old beryllium grease on them. Don't lick your fingers after you clean it off. That would be bad. You can't buy it anymore due to it being poisonous.

re: beryllium is a Group 2 (IIA) element. It is a metal and has a high melting point. At ordinary temperatures, beryllium resists oxidation in air. Beryllium compounds are very toxic.

And look at the slider for the transformer (the current adjuster). Just check the contacts and the contact points across the transformer coils. All signs of wear, probably okay, but check them out.

I'd guess (per suggestion of looking for the cause of the failure -- besides wear) that your cooling fan could use a little lube (verify that it blows the correct direction -- really).

 

[Transit]

Rereading everything from the top, samshine had the unit checked by two repairmen and the opinion is the diodes are shot, we do not have to cover that ground again. We need to concentrate on finding suitable replacements and not get caught up on the chatter.
Try here. hilite the foward current say 250 to 350 amps and click on APPLY FILTER.
Electronic parts, Electronic Components, NTE replacement Parts, transistors, capacitors, and more!!!

 

[SPYDERLK]

It has been my experience that exceeding the current or heat ratings have always caused diodes to fail. In a full wave bridge two blocking diodes are always in series adding the PIV limit. One cannot always guarantee that the impressed voltage will be equally divided, however the total PIV should be adequate. A small 0.1 uF cap across each diode should suppress any transient spikes. The other alternative solutions are expensive.

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