Diode upgrade in welder

Thread Starter

Wasoofa82

Joined Jan 24, 2021
41
Hello everyone I was thinking of hotrodding (upgrading)the diodes in my mig welder to better quality stud diodes. The welder does work ok, I heard that you could get a much better sizzle and control of heat especially when welding with thin gauge sheet metal. For instance I notice the much higher end machines like Millers seem to have a better crisp sizzle,
I assume this can be attributed to the better quality diodes. The problem is I I think this heat sink won’t accommodate larger diodes not because the size but rather the heat dissipation would be more difficult because of the larger stud size( thermal junction junction max of the diodes was matched to the heatsink. I’m guessing 4 stud diodes would replace the 12 smaller diodes that are in there now. Here are some pics1395E933-4517-4F0D-91DE-F9202D45A1A6.jpeg97CA56E2-CFA2-45A4-B841-DE1F7A584BE2.jpeg
 

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Thread Starter

Wasoofa82

Joined Jan 24, 2021
41
I forgot to mention that I’m guessing the reason behind using more small diodes is to distribute the heat more evenly over heatsink so it could dissipate much better through the use of the fan. I mean a larger mass of a stud diode is going to be harder to remove the heat and it’s also pretty cramped inside the chassis in fan also probably has to also cool the large transformer
 

Papabravo

Joined Feb 24, 2006
16,809
Hello everyone I was thinking of hotrodding (upgrading)the diodes in my mig welder to better quality stud diodes. The welder does work ok, I heard that you could get a much better sizzle and control of heat especially when welding with thin gauge sheet metal. For instance I notice the much higher end machines like Millers seem to have a better crisp sizzle,
I assume this can be attributed to the better quality diodes. The problem is I I think this heat sink won’t accommodate larger diodes not because the size but rather the heat dissipation would be more difficult because of the larger stud size( thermal junction junction max of the diodes was matched to the heatsink. I’m guessing 4 stud diodes would replace the 12 smaller diodes that are in there now. Here are some picsView attachment 232181View attachment 232182
The problem with assuming things, and acting on those assumptions, may or may not produce the expected results. It is not altogether clear what you mean by "better quality diodes". A bigger size does not imply better quality.

It sounds like surface area may be the prime determinant of heat sink efficiency. You could also consider convection or forced air cooling. Last but not least, make your heatsink out of black anodized aluminum for an improvement in heat radiation.

I have no idea what factors affect "crisp sizzle" and I suspect you don't either. By all means knock yourself out with the hotrodding, but don't be disappointed if you don't get the results you expect.

It will surely help if you know how to read a diode datasheet, so you have some idea of what you are getting. We can help you with that. Ask all the questions you want.
 

Thread Starter

Wasoofa82

Joined Jan 24, 2021
41
Well I guess with wire feed mig welders what I mean by “crisp sizzle” is that spatter is much less when welding and there is almost like a higher pitched chirp sound almost like a squeal when compared to some other cheaper welders which almost sound more like a rapid bacon frying sound. This is probably also attributed to the smoother wire feed mechanisms. Sorry if I may sound kind of silly, in fact I did look at some videos of much newer machines that are like mine. Mine is essentially a rebranded Lincoln Weldpak 180 about 12 years old. The new ones that they sell at Home Depot for instance, seem to have the same kind of sound that I’m after. I also did manage to look under hood on one of them and they use the same kind of ceramic diodes that are in my machine. Maybe it’s just a moot point, but also would I improve the welding duty cycle. I guess I got some homework to do here is a video of guy performing this modification
 

Papabravo

Joined Feb 24, 2006
16,809
Well I guess with wire feed mig welders what I mean by “crisp sizzle” is that spatter is much less when welding and there is almost like a higher pitched chirp sound almost like a squeal when compared to some other cheaper welders which almost sound more like a rapid bacon frying sound. This is probably also attributed to the smoother wire feed mechanisms. Sorry if I may sound kind of silly, in fact I did look at some videos of much newer machines that are like mine. Mine is essentially a rebranded Lincoln Weldpak 180 about 12 years old. The new ones that they sell at Home Depot for instance, seem to have the same kind of sound that I’m after. I also did manage to look under hood on one of them and they use the same kind of ceramic diodes that are in my machine. Maybe it’s just a moot point, but also would I improve the welding duty cycle. I guess I got some homework to do here is a video of guy performing this modification
As I see it you have two immediate problems:
  1. Identify potential diode replacement candidates
  2. Identify a vendor with suitable price and availability
Parts like diodes are available from online vendors like Digi-Key and Mouser
https://www.digikey.com/
https://www.mouser.com/

Both site have selection guides to help you narrow the search to parts that meet your requirements, are priced within your price range, and available. These sites will also allow you to download datasheets so you will have some idea of what you are getting. Datasheets also have mechanical and mounting information which you may need to fabricate a new home for them.

Tell me if the guy in the video has any useful recommendations, or if there are things that are still a bit confusing. If you give me timestamps in the video I won't have to watch the whole thing.
 

Thread Starter

Wasoofa82

Joined Jan 24, 2021
41
At 3:45 he mentions this data sheet. https://www.mouser.com/datasheet/2/427/vs_70hfrseries-1769215.pdf
So altogether I would need 2 standard polarity and 2 reverse polarity diodes. He has a 180amp mig welder in the video which is what I have. Here are some pics of a comparison of the wire drive mechanisms between a very new model of welder vs a an older one which mine
 

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Thread Starter

Wasoofa82

Joined Jan 24, 2021
41
I’m just trying to improve the life of my machine it kind of has sentimental value to me, as in I repaired a lot of cars with it and it was purchased the same time when my nephew was born. I already successfully repacked the wire drive mechanism with Mobil 1 red synthetic grease vs the fishing reel grease that was in it already
 

Papabravo

Joined Feb 24, 2006
16,809
Those diodes are 70 amp diodes, and you have a 180 amp machine. something does not compute. They also come in a variety of Repetitive Reverse voltage models which is important for you. They will be used in a bridge rectifier and be subjected to the peak revers voltage of your AC waveform. Are you running off 120 VAC or 240 VAC? Do you know how to compute the maximum reverse voltage you will require? The standard and reverse polarity models refer to which part of the diode is connected to the case. I did not find any in stock when I looked.
 

michael8

Joined Jan 11, 2015
184
Keep in mind that the voltage drop on the diodes goes down as their temperature goes up up. Cooling them
raises the diode voltage drop. Too hot, of course, is bad.
 

Thread Starter

Wasoofa82

Joined Jan 24, 2021
41
Or maybe a little less current rating since these are pretty heavy duty themselves. I don’t think I could get stud diodes to fit in there
 

MisterBill2

Joined Jan 23, 2018
9,274
It does not seem reasonable that what is making the diference is the diodes. Probably the better welder provides a different current/voltage slope and possibly has a faster response time in some control loop. Somewhere in the literature they may mention why the one welder is better than others and that should be your answer about what to change. And my guess is that it is not the diodes.
 
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