# DC Polarity for a Wire Feed Welder



## Be_Zero_Be (Oct 30, 2018)

I have a Multi-Mig wire feed welder model 90065-66 (sold by Costco a long time ago).
It is a DC welder with gas capability (not currently implemented).
The output is unfiltered Full Wave Rectified DC.
The factory set up is for the DC Positive to be connected to the Torch and  the DC Negative is connected to the Ground Lead.

Is this the best setup for Flux wire and gas?

I am also considering adding a 48,00 uF filter capacitor to the output.
Is this advisable?

Any advice is appreciated.


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## pontiac428 (Oct 30, 2018)

Hmmm, are you certain it's not DCEN (DC, electrode negative)?  That's what you want for solid wire with gas.  AC works with flux core, but DC is cleaner if you have good control over your feed and heat.  Flux core needs to have knurls on the feed rollers to feed well.  Flux core penetrates better with gas (reverse DCEP here).  Either way, that setup is a good starting point for general purpose welding on things that don't need to be pretty to work.  Spend some time practicing, burn together as much scrap as you can find (but clean your joints!) and have fun with it.


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## Be_Zero_Be (Oct 30, 2018)

Thanks for the quick response Neighbor 

I verified the output by putting a 100 Ohm resistor across the electrode and the ground lead.
I checked the output with a voltmeter and an oscilloscope.


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## benmychree (Oct 30, 2018)

Try it one way or the other; you will see what works best.


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## markba633csi (Oct 31, 2018)

Looks like a nicely built unit- two hefty transformers 
I thought most migs were electrode negative but maybe not? 
Mark


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## Gauge12man (Oct 31, 2018)

A lot of these wire-feed welders can be used for either mig or flux-core. For mig, you need electrode positive (reverse polarity) while flux-core requires electrode negative (straight polarity). You can confirm on the Miller website. I don't have the knowledge to comment on the capacitor.

https://www.millerwelds.com/resources/article-library/mig-welding-the-basics-for-mild-steel
https://www.millerwelds.com/resources/article-library/flux-cored-welding-the-basics-for-mild-steel


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## Be_Zero_Be (Nov 1, 2018)

Thanks for the comments and advice.
A better mod might be a polarity reversing switch or contactor.
I am still researching adding capacitors.


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