Looking for diodes for montgomery ward welder

[Samshine]

Ok here we go again.
I might not can swim, but i can dog paddle.
Sure my head went under, but i can see the shoreline now.
And as long as i can see the shore line, my head is going to be up.
If you got neg. coming in to the heat sink, which has two diodes bolted to it,
and they are tied to a heat sink which ties back into the same heat sink from the the start. They all got to be the the same diodes.
Only question now will my transformer be safe with such big rated diodes?
Thanks again for all your help. samshine

 

[patrick_g]

Only question now will my transformer be safe with such big rated diodes?
samshine

Transformer will only be stressed by the welding load you place on it. Larger/better diodes will not stress the transformer any more than marginal diodes. Transformer tends to average out the heat load (relates to duty cycle and how many minutes out of ten you are welding.)

You can't weld solid for an hour and then let it idle for 9 hours and call that a 10% duty cycle. You can weld for a minute and let it idle for 9 min and call that 10%. Transformer heating (primary failure mode of a transformer) tends to average out over a period of time (not too long but 10 min is reasonable) so you can hit it hard for a few min and let it rest for a few and the heat load averages out. This is what duty cycle limitations are about.

Pat

 

[Transit]

Brent, read the section, "Basic Operation". Diode bridge - Wikipedia, the free encyclopedia

First half cycle:
The current flow is from the AC source left to right, through the UPPER RED path to the +.
The return flow is from the right to left, through the LOWER BLUE path to the AC source.

Second half cycle:
The current flow is from the AC source left to right, through the LOWER RED path to the +.
The return flow is from the right to left, through the UPPER BLUE path to the AC source.

There are always two conducting diodes in series, all the forward voltage and all the reverse blocking voltages are added.
The same current flows through the RED & BLUE diodes.




Grasshopper, when you can take the diode from my hand it is time for you to go.

 

[Transit]

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

I have been doing it for 60+ years. I get out to the field when all else fails, I may kill anyone I wish, but I have to eat the evidence. Pass the stake sauce.

 

[Transit]

Transformer will only be stressed by the welding load you place on it. Larger/better diodes will not stress the transformer any more than marginal diodes. Transformer tends to average out the heat load (relates to duty cycle and how many minutes out of ten you are welding.)

You can't weld solid for an hour and then let it idle for 9 hours and call that a 10% duty cycle. You can weld for a minute and let it idle for 9 min and call that 10%. Transformer heating (primary failure mode of a transformer) tends to average out over a period of time (not too long but 10 min is reasonable) so you can hit it hard for a few min and let it rest for a few and the heat load averages out. This is what duty cycle limitations are about.

Pat

Patrick, you are very close. Welding duty cycle time is based on 10 minutes. Weld 3 min out of 10 and that is 30% at a stated current. Raise the current and the duty cycle will shorten. Lower the current and you may weld longer.
Keep lowering the weld current and at some point the duty cycle will be 100%, once that point is reached you may weld at that current all day long.
Small hobby welders have their 100% point too low to weld anything but thin stock. If you want a welder that can run at the 100% point and do useful work you need $$$$$$.
If you weld past the 100% point and the thermal safety opens, stop welding and keep the machine powered on to keep the cooling fan running. Once the safety resets, the unit must be allowed to cool for the full 10 minutes.

 

[Transit]

Is this correct? I have assigned the letters A, B, C to the heat sinks for clarity, the diode numbers are the same.
You have identified one wire from the transformer to heat sink (C), what is the second wire from the transformer connected to?

You have identified the (-) welding cable from heat sink (C), what is the (+) cable connected to?

Heat sink (C) is insulated from the case?

 

[Samshine]

Transit i'm sorry i need to make a correct. I coundn't get my big head inside the welder.
Correction: The two heat sinks that i though was contacted to the welding
case as a spacer between them, therefore all three heat sinks
are isolated from the case.
I also noticed another wire coming from a different transformer bolted to heat sink number one. This wire comes from the transformer that also has wires running to the thermanl block to make voltage changes. 230 or 208 voltage.
There are three transformers in this welder. There are two up high with the sliding arm between them that moves up and down to make welding amp. settings.
The tranformer below, has four wires coming from it. 2 wires going to the pos. welding lead. And 2 wires going to heat sink which has number 3 and number 4 diodes bolted to it. There is a jumper plate going to the neg. welding lead. from also heat sink with number 3 and number 4 diodes.
Sorry for not giving you full details.
Thanks for all your help. samshine

 

[BrentD]

Brent, read the section, "Basic Operation". Diode bridge - Wikipedia, the free encyclopedia

First half cycle:
The current flow is from the AC source left to right, through the UPPER RED path to the +.
The return flow is from the right to left, through the LOWER BLUE path to the AC source.

Second half cycle:
The current flow is from the AC source left to right, through the LOWER RED path to the +.
The return flow is from the right to left, through the UPPER BLUE path to the AC source.

There are always two conducting diodes in series, all the forward voltage and all the reverse blocking voltages are added.
The same current flows through the RED & BLUE diodes.




Grasshopper, when you can take the diode from my hand it is time for you to go.

So I was right the first time around. That's what I get for thinking about things when I'm up after midnight.

 

[Transit]

There are a few things that do not add up.
If the diode posts are (+) then the heat sinks are (-),
Heat sink (C) has a cable going to the (-) welding cable and at the same time a connection to the (+) welding cable. This is a conflict.

The welding transformer should have two leads, one to the junction of heat sink (A) and post # 3, and one to the junction of heat sink (B) and post # 4, as shown in pages 2 and 3.

Page 1 is what you are describing.
Page 2 is the way a bridge rectifier is wired with the added notations.
Page 3 is page 1 corrected with the information from page 2.

 

[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