Looking for diodes for montgomery ward welder

[Transit]

Larry, what you are describing is more in tune with a mig power supply. I am not aware that this welder has a filter capacitor in the diode circuit. There may be a power correction cap but that would be elsewhere in an AC circuit.
Being that no one has brought up a capacitor, it is unlikely there is one.
Your point is noted, but I do not think it applies.

 

[SPYDERLK]

Larry, what you are describing is more in tune with a mig power supply. I am not aware that this welder has a filter capacitor in the diode circuit. There may be a power correction cap but that would be elsewhere in an AC circuit.
Being that no one has brought up a capacitor, it is unlikely there is one.
Your point is noted, but I do not think it applies.

Capacitance can be present where there are no capacitors per se', but it would be of low value and should not be able to deliver much reverse current. The issue with a capacitance is real altho I think not a problem here. Still, it costs little to go for diodes that have the required safety margin to deal with transients that can be foreseen. Back biasing to the point of conduction will damage a diode. I think the conduction threshold for damage is a fairly small current and the effects are cumulative. ... The previously introduced C across the diode helps against these transients.
larry

 

[Transit]

Yes, but there is a world of difference between a 0.01 uF and 100,000 uF.

 

[SPYDERLK]

Yes, but there is a world of difference between a 0.01 uF and 100,000 uF.

Capacitance can be present where there are no capacitors per se', but it would be of low value and should not be able to deliver much reverse current. The issue with a capacitance is real altho I think not a problem here. Still, it costs little to go for diodes that have the required safety margin to deal with transients that can be foreseen. Back biasing to the point of conduction will damage a diode. I think the conduction threshold for damage is a fairly small current and the effects are cumulative. ... The previously introduced C across the diode helps against these transients.
larry

There is a world of difference between a 0.01 uF and 100,000 uF.
larry

 

[Samshine]

Thanks everyone for trying to help me. But you are way above my head.
I really like to learn all i can about this welder.
I uderstand about the duty cycle. When i said this machine was used for 10 hours straight thats what i mean. Sometimes it was 7am until 2am, but most of the time it was 7am until 9 pm. A 50 lb. can of rods would be burnt in a day and ahalf.
This welder only has two transformers, four diodes and a fan with a sorral that pushes or pulls air on everthing. I believe the diodes was overhead by welding for such long period. Even if something else cause the diodes to short out. I dont believe it would have caused it if the welder hadn't been welding for along period of time.
I just want to find what size diodes i need, then if the welder dont work, i will just use the ac side of it, if it still works when i get through with it. When i throw it in the corner, then i will pull out the how to build manual.
Thanks samshine

 

[Samshine]

Hey i am sorry everybody i didn't mean to run you off.
I really miss reading what everyone wrote.
Thanks to everybody for trying to help me.
I still need help.
I am going to try to call and get the specs. of the diodes of the part number
that i was giving over the phone.
I will get back and post what i was told.
Thanks again everyone. Hope to hear from you soon.
samshine

 

[patrick_g]

If you always do what you always did you will always get what you always got.

HUH??? If you just replace the diodes with the same type it came with (and no other circuit components are defective) then it should be as robust as new (like stock except for cosmetics.) Unfortunately it burned up in the stock configuration. Most likely from exceeding the duty cycle limitations. If you replace the diodes with the ones the company offered AND you don't exceed the duty cycle limitations you should be good to go. Upgrading the diodes and or heatsink would give you a little margin of insurance against failure.

It is always possible that over time heat stress was a diode killer (surpassing the duty cycle limitations) and maybe there was a little flaw in a diode which finally led to failure. You will never know.

Do what you like, it is your welder BUT... if it were me I would either replace the diodes with the ones the company offered or go for an upgraded part, most likely the former than the latter due to difficulty in getting specs for OEM parts. The easiest upgrade is to use the OEM parts the company offered and use larger heatsinks.

Pat

 

[Transit]

There is a strong likelihood that over the years the diodes have improved over the originals and the replacement components are better able to deal with the stress. The web site I posted a link too should at least have the equivalent if not better diodes. I would be looking at diodes in the 400+ amp range, and if possible upgrade the heat sinks. Or if all else fails just wing it and choose something overrated.

 

[patrick_g]

Transit, GOOD ADVICE. Something for the OP to consider that some of us electronic types sort of assume that since we know everyone knows:

Transformers and other similar devices tend to average out their heating such that brief overloads followed by less than max loads just sort of all gets averaged in and the temperature of the component doesn't accurately follow the instantaneous load's heating input.

On the other hand with a solid state semiconductor (his diodes) you only have to exceed any of the max ratings for just an instant to do irreversible damage which if not catastrophic in that one instance IS CUMULATIVE and can lead to catastrophic failure after sufficient repetitions.

Pat

 

[Samshine]

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.