Harbor Freight 90a Flux-core Ac To Dc Conversion

[AFTRD3TH]

Thank you for the responses where exactly does the capacitor connect I know it's on the DC side but is it after the rectifier leading into the ground and torch. The video kind of confused me????

 

[homebrewed]

Thank you for the responses where exactly does the capacitor connect I know it's on the DC side but is it after the rectifier leading into the ground and torch. The video kind of confused me????

It attaches to the "+" and "-" terminals of the rectifier. Same side as the ground and torch. Putting it on the wrong side of the rectifier could be very dangerous so make sure to get it right. That also means connecting the plus side of the rectifier to the plus side of the capacitor and similarly for the negative side of each.

By "dangerous", I mean that the capacitor could possibly explode. They're designed to fail gracefully but putting high-current AC into a big electrolytic capacitor is a pretty extreme overload condition. It might pop a fuse before going bang, but maybe not....

 

[AFTRD3TH]

Thank you, Ill make sure that I make sure I do it right, I made a water block and water loop for my rectifier, as i have read that it produces high amount of head when converting AC to DC. Would a water block be beneficial

 

[homebrewed]

Thank you, Ill make sure that I make sure I do it right, I made a water block and water loop for my rectifier, as i have read that it produces high amount of head when converting AC to DC. Would a water block be beneficial

Not in my experience. I was concerned about power dissipation in my diode bridge as well so I attached a large convection-type heat sink to mine, but it has never gotten very hot in use.

 

[woodchucker]

I have a buddy who impulse bought a Harbor Freight 90A flux-core wire feed welder. I have to admit to looking at them too, especially when they go on sale for under $90. They’re probably not a bad deal for the occasional weekend welding project, plus the 110V portability is nice. But as my dad constantly told me as a kid “you get what you pay for”.

Bottom line is the welds look terrible. Penetration is poor and there is a lot of spatter. Problem with the stock welder is it’s AC output, not DC. Current flows back & forth from the puddle to the wire which causes the flux-core wire to spatter even more than DC flux-core wire welding. All other HF wire feed welders are DC if that tells you anything. I did a little web research, watched a few YouTube videos and found that it’s fairly easy to convert these units from AC to DC. The two pieces of hardware needed are a full-wave rectifier and an electrolytic filter capacitor.

The rectifier takes the sine wave AC and flips the negative wave to the positive side so the output looks like “hills” running from 0V to peak voltage and back down, then back up again. The capacitor smooths out the “hills” to a relatively straight line or DC output. The videos I watched recommended a minimum 47,000 uF electrolytic capacitor with 30V minimum rating (welder outputs 28V). I found a number of eBay sources for the rectifier rated at 1000V and 100A for $10. Found a Siemens electrolytic cap rated at 40V and 47,000 uF for $25 delivered.

Another important component is a shunt resistor across the two leads of the capacitor. The resistor drains the capacitor after welding, otherwise the wire is still grounded and your ground clamp is still hot! Some guys on their conversion discharged the capacitor by touching the wire to the ground clamp; expect a nice spark. The capacitor I found had a shunt resistor already there, drains the cap in about 3 seconds.

The conversion is pretty simple; cut the output leads from the welder’s transformer and jump them to the AC side of the rectifier. The transformer output leads each have a small lead that runs to the welder’s circuit board, so the splicing takes place downstream from that point.

The rectifier has two output leads; + positive and – negative. Those leads run to the appropriate terminals on the capacitor. For flux-core wire, the welder ground clamp should be DC positive. So, the welder’s ground clamp lead is tied to the capacitor’s + Positive lead. The weld gun is tied to the capacitor’s – Negative lead.

One thing I didn’t care for on the on-line conversions is how they mounted the rectifier and capacitor. All of the examples had the rectifier mounted on the side of the case. They mounted the capacitor by drilling a couple of holes in the case and tie strapped in down. I guess that’s probably how Harbor Freight would do it . . .

I chose to mount the rectifier on the back of the case, just looks cleaner to me. Also made a sheet metal bracket to mount the capacitor next to the transformer. The cooling fan had to be moved down to make room for the rectifier. New fan holes were made in the case, in retrospect I should have removed the back panel and punched them on my Roper Whitney #218 press, but went the quicker route of drilling the holes. Then spent 15 minutes cleaning up burrs . . .

You can see from the example welds that the DC conversion makes a world of difference on the quality of the welds. I ran a bead using flux-core wire from my Hobart Handler 190, the HF stock AC and HF after the DC conversion. Much, much reduced spatter and much better penetration. The welder sounds better too, just a sizzle while welding instead of lots of spattering.

So what did I learn? Since everything in my shop will end up being my son’s someday, I went out and bought another Hobart, now have a Handler 140 (110V) to compliment my 190 (220V only). Sure, the Handler 140 110V welder is $500 compared to the bottom line about $150 for the HF 90A converted to DC. But I don’t want my son to inherit my shop and say, “Wow, dad bought a lot of cheap junk!” On the other hand, money doesn’t grow on trees so if you do have one of these HF 90A welders, consider spending around $50 and make some better welds.

Bruce

View attachment 138636 View attachment 138637 View attachment 138638 View attachment 138639 View attachment 138640 View attachment 138641 View attachment 138642 View attachment 138643 View attachment 138644 View attachment 138645 View attachment 138646 View attachment 138647 View attachment 138648

I did this long ago to the blue one.. the one that has no ability to turn off the torch .. it's always hot.
I did mine with a 200 amp bridge rectifier. I sanded a spot on the bottom of the case and used a thermal paste and attached it. I was never able to find a reasonable capacitor, they were freaking expensive. I added a A/C pancake fan, and I am able to run 100% duty cycle, it never bails on me. the weld difference and sound were night and day different. my crappy welds became really decent welds for flux core. Now if I can steady my hand, and follow straight... I lose track of the joint sometimes.

 

[homebrewed]

I believe the torch on my HF version is hot all the time, too. The only thing the trigger controls is the motor that runs the wire feeder. That can get "interesting" if you put the torch down on your welding table.

I'm not sure I would do the conversion now. The cost of the parts is _almost_ as much as what I recently paid for an inverter-style stick welder; and you get to enjoy DC welding right away. Plus it weighs so much less than the HF welder and it has a lot more flexibility, since I can adjust the current (along with a couple of other welding parameters). I'm not going to get rid of my wire welder but I suspect it won't be my go-to welder any more.

 

[woodchucker]

I believe the torch on my HF version is hot all the time, too. The only thing the trigger controls is the motor that runs the wire feeder. That can get "interesting" if you put the torch down on your welding table.

I'm not sure I would do the conversion now. The cost of the parts is _almost_ as much as what I recently paid for an inverter-style stick welder; and you get to enjoy DC welding right away. Plus it weighs so much less than the HF welder and it has a lot more flexibility, since I can adjust the current (along with a couple of other welding parameters). I'm not going to get rid of my wire welder but I suspect it won't be my go-to welder any more.

at the time the BR was only $16-$20 , I bought new connectors to attach the wires, clamp down style... maybe $10.. so not that expensive.

 

[homebrewed]

at the time the BR was only $16-$20 , I bought new connectors to attach the wires, clamp down style... maybe $10.. so not that expensive.

The capacitor was the expensive part, as you commented earlier. Folks that want to include the inductor may need to buy the core, too (I didn't go that far with my mod).

 

[AFTRD3TH]

Hello everyone.
I have upgraded my 125 AMP Harbor Freight (Chicago Electric) welder from AC to DCEN.
A little background: I'm originally from Australia, and I grew up on a Huge farm, often known as a ranch In the US.

With the need to repair farm equipment on a regular basis, welding and fabrication come naturally.

I used a stick and mostly MIG/TIG 240 Volt when I was growing up.
I moved to PA in 2017 I left all of my tools in Australia as shipping was expensive,
I purchased the Harbour Light 125 Amp Welder in 2018 and used it once and I thought it was TRASH I made a home made Stick welder instead.
I was recommended a YouTube video about the conversion, so I decided to do some research on it. That's how I discovered this community.

Parts used
Bridge rectifier, 1600V, 300A
4 Gauge Gun and Ground leads
5 X 63V 22000 uF Capacitors
A dead microwave's 110v fan
2 X 4" heat sinks.
Copper piping from a broken portable air conditioner.
HART battery drill motor as a new feeder motor.
NEMA Power cord.
New heavy duty ground clamp

My welder is double the breadth of a typical welder since I mounted it to the base of a broken portable air conditioner base plate.
I mounted the bridge rectifier vertically on an alloy plate with two thermal paste-coated heat sinks and a microwave cooling fan.

Bridge rectifier temperature does not exceed 70F.

At a later time, I will upload images. The welder performed like a 220v DCEN MIG without spatter.