Mig Welder Upgrade Diode Replacement in Bridge Rectifier

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Introduction: Mig Welder Upgrade Diode Replacement in Bridge Rectifier

About: Lateral thinker, Originator of Inclined Bed Therapy (IBT) Originator of Pocket Full Of Acorns Project. Originator of Operation OASIS.

Inferior diodes often found in cheaper range of mig welders are prone to failure. Once one blows the rest will follow rapidly. Why? Because the type of diodes fitted in the bridge rectifier are linked together so that the sum of all of the diodes covers the amps and voltage generated by welding with the machine. These press fit diodes are the same as used in vehicle alternators.

Obviously installing these enables the welders to be sold at the lower end of the market and for a while they hold out but inevitably fail.

The diodes are installed in a heat sink made from aluminium. In this video, I show how we can remove these inferior diodes from the bridge rectifier and install new Standard Recovery Vishay 70 amp 1600 volt diodes that collectively exceed the workload of these welders and provide a more robust machine with the ability to work at the lower end of the welding scale as well as the higher end with ease.

So instead of having 12 press fit diodes we will install 4 bolt on diodes into the existing bridge rectifier, making the install as easy as possible.

Step 1: The First Image Shows the Original Diodes Removed From the Rectifier and the New Diodes to Replace Them.

Step 2: Full Instruction Video Showing How to Repair and Upgrade a Blown Rectifier in a Mig Welder.

Mig Welder Repair.
Walk through video Upgrading from inferior cheap diodes on a Sealey 180 Mig Welder and many other similar priced welders, which are fitted with press fit diodes that are prone to overload failure.

I used Vishay 70 Amp 1600 volt in parallel pairs, which is two sets of matched pairs, one reverse polarity and one standard polarity. The diodes are clearly marked with arrows showing the current direction.

This modification involves some soldering so you will need a soldering iron capable of heavy duty work. For this I used an old copper iron heated on a gas ring which worked very well.

The repair cost:

2pc Standard Recovery Diode 70HFR160 70A 1600V VISHAY £8.47 plus £3.90 postage

2pc Standard Recovery Diode 70HF160 70A 1600V VISHAY £8.47 plus £3.90 postage

I would not have been able to upgrade this welder had it not been for the people in welding forums who provided photographs and suggestions and reasoning as to why I should not simply replace with another inferior bridge rectifier containing what appear to be vehicle alternator diodes which are not up to the job. So a big thank you to you guys for sharing your knowledge. Category

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    18 Comments

    0
    occilator
    occilator

    7 years ago on Introduction

    agreed. Great work mate.

    I have started to see more and more busted cheap Chinese MIGs popping up recently. You have motivated me to Aquire a suitable MIG and repair it. In your experience, is the rest of the electronics up to scratch?

    I am always reflowing cheapo PCBs from all kinds of electrical equipment. With 100% success.

    0
    AndrewKFletcher
    AndrewKFletcher

    Reply 7 years ago on Introduction

    When buying a spares or repairs welder, you may be able to ask the seller to inspect the rectifier for damaged diodes as shown in the images. You are on to a winner if this is the problem.

    0
    AndrewKFletcher
    AndrewKFletcher

    Reply 7 years ago on Introduction

    The rest of the machine looks ok, the wire feed motor looks inexpensive to replace, and a torch won't break the bank either. What I noticed about working with the new diodes was that the welding of very thin metal appears to be easier and smoother. Keeping in mind I was using C02 instead of argoshield, which tends to spatter and pop and the wire in the machine was a little rusty in places. But the welding didn't spatter and pop which I expected it to.

    0
    aaroninneb
    aaroninneb

    Question 7 months ago on Introduction

    • 70HFR120: Forward
    • 70HF120: Reverse
    • Voltage-DC Reverse (Vr) (maximum): 1200V (1.2kV) I have access to some these diodes and notice they are not the 1600v kind but the 1200v ones and wondered if they will still work good using two of each on a 180 amp welder?
    0
    AndrewKFletcher
    AndrewKFletcher

    Answer 7 months ago

    Add up the total original diodes. Divide by 4 to determine minimum size. Going higher voltage means less chance of blowing one.

    0
    NeilH
    NeilH

    Question 11 months ago on Step 2

    I think I just dont understand enough background...how was it you were able to go from 12 to 4 diodes? For example my MIGs rectifier failed, mine only had one unit with four press fit diodes. So it is a bridge rectifier, having 4 diodes right? A full wave would have only 2...but that requires a center tapped coil correct? And it’s not as efficient as I understand ....so I could see using only two diodes to repair mine but then it’s no longer a bridge as was intended...??

    0
    roy.silva
    roy.silva

    2 years ago

    Great video, what I don't get from the video is if you solder all of the diodes from the same plate to the diode on the that plate, if that make sense. Needed to see some close up pictures of the post soldering. I just purchased the same diodes you mentioned. Please send or post some close up pictures of the finished product.

    0
    AndrewKFletcher
    AndrewKFletcher

    Reply 1 year ago

    Thanks. I didn't solder to the existing diodes, just used the thick wires from those diodes to connect new ones.

    0
    fourier090
    fourier090

    Question 1 year ago on Introduction

    I have a century 180 mig welder. It’s basically a rebranded Lincoln weldpak 175hd. I really like it because it has a thru hole control circuit board and it would be probably easier to desolder components down the road. Anyway I would like to extend the life of it. It seems it has 16 of these type of diodes.
    It works ok, but I was wondering if there really is an advantage to using large diodes in it. I was thinking my design uses many diodes because it is easier to dissipate the heat thru the heatsink, due to the smaller mass and in the the case of a failure the diodes open up and protect the large transformer from being blown.
    Also, the thermostat that is mounted on the heatsink probably would never trip in the case of exceeding the duty cycle and overheating. Here is a pic inside of an older model Lincoln welder that I found on the web. It seems that they did in fact use stud diodes at one time. Mine however is the much more crowded inside the chassis as you can see in the other pic. I would greatly appreciate some help

    96F19C24-8DC7-4496-AEDD-327E2F5C788A.jpeg93FC0143-809A-4FB0-B13F-D51EAE64A3C1.jpeg
    0
    AndrewKFletcher
    AndrewKFletcher

    Answer 1 year ago

    I chose the large diodes based on the logic that these smaller diodes are problematic and the welder is going to find the weakest link and pop the stud diodes. I get what your saying about the small diodes acting as a fuse, but do we really want to keep changing the blown ones and can we afford to have a welder that gives up so readily?

    Your heat exchanger could do with an additional aluminium plate and bolt the diodes through both of them?

    0
    DavidL859
    DavidL859

    Question 2 years ago on Introduction

    Hi Andrew, excellent work.
    My welder has just decided to develop a dead short on 1 of the recovery diodes, not cheap car ones thankfully, but I can't get the correct replacement anymore, so was thinking of doing what you appear to have done some years back.
    How's it held up, is it still going strong?
    Many thanks.
    Dave

    0
    AndrewKFletcher
    AndrewKFletcher

    Answer 2 years ago

    Still working, though haven't had need of it for some time, so can't give a fair analysis, other than it welds much smoother than before the original diodes popped. Thanks for your comment David

    0
    DavidL859
    DavidL859

    Reply 2 years ago

    Thanks for the reply Andrew. I'm thinking it's smoother as there are 1/3 of the original diodes, same forward voltage, so 1/3 the leakage, meaning less modulation and hence a more stable output with slightly higher voltage(up to 6.5v), which would be more noticeable on lower settings. Does that sound about right to you?

    0
    JohnP759
    JohnP759

    Question 4 years ago

    i have four 75hq035 diodes would they possibly work?

    0
    HermanF7
    HermanF7

    5 years ago

    After watching the video a few times I still am unsure as to where to and the arangement of the new diodes. Are one of each polarity installed on each heat sink and if so where do the wires attatch? Additional information about the installation would be very helpful. I have ordered the diodes you recommended. Thank you.

    0
    zikzak1
    zikzak1

    7 years ago on Step 2

    Pretty cool :) I now know what to do with the couple hundred diodes I scavenged out of equipment years ago! Of course the voltages and currents vary, but they all came from AW Sperry and Burroughs equipment that was being junked out. Even have a couple diodes with 6 gauge wire coming off the ends! (I have no idea what to do with those.) I have SCRs and triacs too... Awesome you were able to upgrade that welder... Makes me think I need to score a failed unit cheap and repair it for my shop!

    0
    AndrewKFletcher
    AndrewKFletcher

    Reply 7 years ago

    You could be on to a nice earner Zikzak1