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Old 10-10-2015, 12:49 PM
Built Not Bought
Join Date: Oct 2014
Posts: 150
Default Harbor Freight Welder Mod.

This is a little write up on my welder, Converting it From AC to DC.

Hi Guys and gals, I have a harbor freight welder i been using for about 2 years for all my projects, and it has not failed me on any projects, Al though i have replaced it twice since then, either from accidentally running it over or leaving it outside in the rain.. Oops, But good thing harbor freight has a No questions asked warranty..

So here is a Little info about this welder,
This is a 90 Amp-AC, 120 Volt, Flux Cored Welder, Duty cycle is 20% @ 90 AC amps, High setting 90amps, Low setting 60amps. It can weld 18 gauge to 3/16 in. thick steel, With variable wire speed, Not capable of using gas.

So if u know a little bit about these u can say its a low end welder, And before i go on let me tell u i am no expert at all, on welders or welding.
But what i can tell u is, i have used this welder to do many amazing things for what its worth. For example using it to weld 1/4 thick steel to my frame for mounding my 9000lb wench to my ranger, it has held up recovering myself and trucks as large as F250 duallys, also welding my friends rear end of his 240sx, Being a horrible idea and expecting to rear end to blow up on the track and someone possibly getting hurt, it has surprisingly held up through drifting events in the last 2 years. But i am in no way telling anyone to do something so dumb, And we will continue on.

AC - Alternating current (means electrons are flowing back and forth 60 times a sec or 60 Hertz.)

DC- Direct Current ( Meaning the electrons are flowing in one direction, From Negative to Positive.)

The advantage on DC over AC is instead of the welds flowing back and forth like AC, while in DC you are throwing the welds in one direction, Hopefully what you are trying to weld. This may not apply to all welding, but my conclusion of this will be at the end of all this nonsense typing.

Here is what the welder looks like.

Here is a list of items i used.
90amp Harbor Freight welder ( Harbor Freight on sale $99 )
100A Amp 1000V Bridge Rectifier (Ebay $18.50)
39,000uf 75v DC Capacitor (Ebay $14.99)
Some Heat shrink
4 gauge wire
and a few connectors.
For the capacitor u may not be able to find the exact same capacitor, but as long as it is not anything smaller than 25,000uf 50v, u should be fine.

The two main pieces u need is the Bridge rectifier and the capacitor

A bridge rectifier is an arrangement of four or more diodes in a bridge circuit configuration which provides the same output polarity for either input polarity. It is used for converting an alternating current (AC) input into a direct current (DC) output.
The purpose of the capacitor is to provide a steady DC output. The raw rectified DC requires a smoothing capacitor circuit to enable the rectified DC to be smoothed so that it can be used to power electronics circuits without large levels of voltage variation. Basically it will regulate the voltage and keep it smooth instead of "choppy"

First off i do not take credit for this mod, i am merely sharing with my fellow ranger enthusiasts of the information i learned from youtube and googled info.

Opening up the side pannels and separating the wires from the transformer inside.

Then adding connectors as sutch to the wires leading to the welding handle and ground clamp.

My capacitor being so large thankfully it fit inside the small case. This is important, if u notice in the picture the Ground wire is leading to the Positive side of the capacitor, and the welding handle is Negative, That is important.

Next thing was to make placement for the Bridge rectifier, I wanted mine outside the case because it has its own heatsink so it should be cooler than being side with other hot components.

The rectifier will be marked with what it Positive and what is negative try not to mix those up or the capacitor can potentially explode

Here is a Crude drawing of how things should be wired up inside.

And final assembly, It is Important to not let any bare wires or metal parts touch, and try not to let wires cross or touch each other.

How it looks Now.

Here is The difference in welding , On the Left is After it was Modded, On the Right is Before the Mod.


Ive noticed a huge difference in the welds, IT seems to be welding deeper hotter and also the welds even look cleaner shiny! Even alot less splatter.

Q: So is it worth getting a harbor frieght welder and doing this mod??
A: Definitely NO!, if u can pick up a better welder for a little bit more price, and maybe with gas capabilities.

Q: Is it worth doing the mod if i already have this welder sitting around??
A: Definitely YES.

Simple cheap mods:
Trim Gun Nozzle For less Stick out
Change 120v power chord to thicker longer Chord
Mod the Feed wheel spacing
Change Crappy Ground clamp to something better (I will be using Vice Grips)


Simple Mods

AC to DC conversion
2000 Ford Ranger XLT 4.0 OHV 4x4,33 Kenda MT Stock Rims,Grille Guard,IPF Lights,Electric Fan,rear class 3 receiver, Custom Front 2" receiver, 9000lbs wireless Winch on 2" receiver tray, Custom 3" Body Lift,Torsion Bar Crank,Rear Shackles 3",Modded Front Shocks(longer),Limit Straps,Custom Rear Bumper,Custom Headers-back Dual Exhaust, Glasspacks,Tool Box, Uniden CB Radio, Air Tank /w compressor, Train Horns, Custom Hidden Snorkel, Panasonic Double-Din Deck, 10" Rockford Fosgate P2 Punch Subwoofer

Last edited by AMMOBUILT; 10-11-2015 at 05:45 PM.
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Old 10-10-2015, 08:36 PM
stateranger stateranger is offline
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Posts: 2,908
Default Re: Harbor Freight Welder Mod.

Thanks for sharing this, I've been thinking about getting this welder as well.
2014 F150 xl 3.7 6 speed auto.

Originally Posted by pk9298 View Post
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Old 10-11-2015, 07:08 AM
cvar cvar is offline
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Join Date: Jun 2012
Posts: 1,310
Default Re: Harbor Freight Welder Mod.

Hey, thanks for the tips! I have that welder. Eventually, I'm gonna mod it the same way, and hope it improves the welds. Seems an easy fix. :-)
1997 4x4 Mazda B4000 SE, Ext.Cab
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Old 10-11-2015, 07:30 AM
02BLUEdge 02BLUEdge is offline
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Default Re: Harbor Freight Welder Mod.

Nice write up! Welds look much better than before the mod.
2002 Blue Edge <-- Retired off road toy
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Old 12-29-2016, 01:10 PM
Justaquestion Justaquestion is offline
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Default Re: Harbor Freight Welder Mod.

Just a quick question if anyone is still following g this thread and could answer a question for me. I have a 39,000 uf 50 vdc capacitor, is that an appropriate sized capacitor for this modification? I found the bridge rectifier no problem, but was unable to fine a 75 vdc capacitor for s reasonable cost.
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Old 12-29-2016, 08:10 PM
cvar cvar is offline
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Join Date: Jun 2012
Posts: 1,310
Default Re: Harbor Freight Welder Mod.

At 12min 40sec in this video, he says the welder's secondary voltage is 24-28V (no load), and it drops from there to a low of about 16V. That's the actual voltage fed to your caps. So 50V capacitors will be fine. No need for 75V caps.
1997 4x4 Mazda B4000 SE, Ext.Cab

Last edited by cvar; 12-29-2016 at 08:14 PM.
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