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.

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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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    8 Discussions


    4 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.

    2 replies

    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.

    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.


    Question 1 year ago

    i have four 75hq035 diodes would they possibly work?


    2 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.


    4 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!

    1 reply