90A Flux-Core Welder conversion to DCEN - Redux

[xaust]

I am a beginner/hobbyist welder. I bought the Harbor Freight 90A Flux Core welder (SKU 94056) because I am cheap.
I like to tinker with stuff. I was inspired by several posts related to upgrading this welder, most notably this must read post by dugndeep.

These are the mods I have made to this welder:

- 0.030" tip
- Lincoln NR-211-Mp 0.030" flux wire (Lowes)
- Lincoln Electric Flux Cored Wired Welding Nozzle (Lowes Item #178849)
- knurled drive wheel (HF replacement part - $5)
- parts holder
- improved work lead clamp
- fan
- DCEN

I will give more details on the last two in this post.

First off I decided to not add a capacitor. I felt that a bridge rectifier and choke would get me close enough to a usable welder without breaking the bank.

These are the parts that I used:
- MDS150A 3-Phase Diode Bridge Rectifier 150A Amp 1600V
- aluminum heatsink for rectifier 3.75" x 2.5" x 0.75"
- homemade choke (see below)
- 35' 8AWG stranded THHN wire (choke and misc wiring)
- 6 copper plumbing coupling 1/4" (for crimps)
- 5 8AWG slot head screw terminal lugs (Home Depot L35-B2)
- 115VAC muffin fan
- 68VDC 15 Joules varistor (Mouser 576-V82ZA12P)
- heatshrink
- misc bolts, nuts, washers

I purchased the rectifier directly from China via ebay. This cost $24.50, free shipping. It was shipped via USPS. I ordered it on 10/11 and it arrived on 10/17. I was able to track it all the way online. Sweet. 150A and 1600V gives enough headroom that you don't have to worry about frying this bad boy. The bridge I used is a three-phase bridge. You simply use two of the three legs. One spare! I mounted the bridge and the heatsink on the back of the welder with the welder case sandwiched between the two. Make sure you sand the case paint off both sides of the case. The paint will impede the conduction of heat. I also used PC heatsink grease on all mating surfaces.

I knew that a choke was going to be important and buying one would be problematic. I opted to wind my own. I used the main transformer core from a defunct 1200W microwave. I used a sawzall to slice the existing windings off. I then was able to get 23 turns of the 8AWG stranded wire onto the core. I measured the resulting inductance as 1.4mH (millihenries). I was shooting for 2+ but this was all I was going to get. The choke is placed in series with the work lead. I tested it prior to final assembly by clamping it between the work lead clamp and the work piece. Tip: When installing the choke in the case I loosened the work lead grommet and pulled the work lead into the case for a little bit of slack to work with.

The varistor is there just to provide some protection for the wire speed control/drive circuit. The wire speed circuit uses the raw AC right out of the transformer. The varistor is placed across these leads. It protects from any "fly back" that might make its way back from the choke. Probably overkill but easy and cheap.

The fan was mounted on the inside of the right hand case cover. I oriented the fan so that it exhausts the hot air from the welder.

The 1/4" copper couplers (Home Depot plumbing) worked GREAT for all wiring connections. I was planning on also soldering all connections but realized right away that that would be entirely superfluous.

I used slot head screw terminal lugs for connections to the bridge. FYI - the bridge has 5mm hex bolt connections. The slot head screw terminal lugs worked well and were fast and easy to use.

Results
-------
I did some test welds prior to the mod. I already said I am a complete newbie welder, right? When the mod was complete the difference was very dramatic. Prior to the mod I would characterize the arc as chaotic. Lots of spatter. After the mod the spatter was nearly all gone! Obviously DCEN vs. AC makes a big improvement on spatter. A real welder on this forum can no doubt give the technical reason why that is. Also, most of my simple projects prior to the mod involved fillet welds (inside tee). For the life of me I could not get a fillet weld that didn't look like dragon snot. After the mod the arc was much better behaved. My very first try at a fillet weld was WAY better than anything I had been able to do previously. Everything runs pretty cool. The heatsink on the back gets warm to the touch but not so hot that I cannot put my hand on it. I am very pleased with the mod and now really look forward to continuing to use the welder for projects.

Open Circuit Voltages:
@MIN 24.5VDC
@MAX 28.8VDC

Pics to follow.

[xaust]

This is the bridge rectifier and heatsink I used. Bridge was purchased from ebay China.

[xaust]

This is my DIY choke. 23 turns of 8AWG stranded wire THHN on a transformer core from a 1200W microwave. Measured out as 1.4mH.

[xaust]

These are some more of the parts that I used in this mod.
First the varistor, 68VDC 15 Joules varistor (Mouser 576-V82ZA12P).
Then the 1/4" coupler that worked perfectly as a crimp for all the wire-to-wire connections, no soldering. This is a simple cheap part from the plumbing department of your local big-box hardware store.
Then the 8AWG slot head screw terminal lugs that I used to connect to the bridge rectifier. This is a Home Depot L35-B2.

[xaust]

Here is the before and after pics of welds. Note the dramatic reduction in spatter after the mod. This was 1/8" mild steel.

[xaust]

As I mentioned above, as a newbie welder using a bottom-of-the-line welder, I was finding it virtually impossible to do a fillet weld. After the mod my very first try at a fillet weld using 1/8" mild steel was 10X better than anything I had done before (not saying much, I know). Note that this first fillet weld passed the "sledge hammer weld test" with flying colors.

[xaust]

Here are the pics of the internals and externals of the mod.

[xaust]

Finally some quick pics of some of the other simple mods I have made to this box.
The first is the knick-knack box that I attached under the cover of the welder. This is for spare tips, etc.
The second shows the improved work lead clamp (HF) and the Lincoln Electric Flux Cored Wired Welding Nozzle (Lowes Item #178849) that protects the nozzle from all the funk.

That is it for modding this box. On to other projects!

[Gamble]

On 1/8th you probably want to be on max volts for that. I had the same one with no mods, but it looks like you are off to a good start.
I had good luck with this keeping the wire speed low or like 1/4 way up and just moving slow.

[xaust]

Agreed on the MAX setting for 1/8" and above. As far as wire speed is concerned, as I use this box more and more, I am figuring out that I had the wire speed too low for much of what I was doing. I now am running somewhere between 4 and 6 depending on what I am working on.

[DSW]

When you bend test a filet weld, you weld only one side, then bend the piece TOWARDS the weld, not away as you did.

I honestly doubt that machine even with the mods will do aceptable welds on 1/8".

[xaust]

When you bend test a filet weld, you weld only one side, then bend the piece TOWARDS the weld, not away as you did.

Cool - did not know that! I will give that a try over the weekend. Thanks for the info.

[dugndeep]

I like it,great job there Xaust.There's no comparison when you convert these little welders over to DC.
Where the 94056 90 amp didn't come with a fan,the transformer sets a little farther back to the rear of the case so you have a little more room up front for the choke.
I'm still planning on getting some 8 awg magnet wire and rewinding my choke one of these days,just had other projects and haven't had time,into winterizing the home at the moment getting ready for winter,had some snowflakes and sleet here today.But anyway,nice job on your modding.

[xaust]

Thanks for the support dugndeep.
Here is my re-test of a fillet weld on 1/8" mild steel. This is with a single weld on one side and then a bend down on the weld side. Before and after pics explain it better. The welder was set at MAX, wire speed 5, 0.030" wire. Looks OK to me. Weld itself is still ugly. Practice, practice, practice.

[valley]

xaust, I don't think we'll call you a newbe. I've welded for pay years ago, I'm impressed, I have one of the HP Flux core welders[mine came with a fan]. I have done some not bad welds with it, I think yours are very very nice and your mod is even better. I'm not confident I can do that mod, if I can figure it out I'll do it.

Just came back to this site. Forgot my password and have changed my IP so I reregestered. This was worth seeing. Thankyou Richard

[bigbeachdog]

xaust, thanks for the nice write up. I want to do this same mod to my HF 90 amp wire welder but I have a couple of questions. Where did you install the varistor? I like your choke but did you try to weld with/without it? Do you feel that the inductance value of your choke is about right or should it be higher or lower?
Thanks

[xaust]

bigbeachdog,
The varistor is there to protect the wire speed control circuitry. Electrically speaking the varistor is wired in across the AC input to the wire speed control board. Mechanically speaking it was easiest to for me to get this connection by wiring the varistor across the main transformer output leads. If you look above at the picture that has the timestamp, "10/24/2011 11:55", you will see the varistor. It is the red disc component that is near the bottom right corner of the picture. It may be difficult to see but the two big red leads that it is attached to are the transformer output leads. Even more difficult to see is that there are wires going from these junctions up to the speed control board.
I did try the welder with and without the choke. Before I wired the choke in permanently I tried welding with it in series with the ground lead. It definitely made a difference. It reduced spatter and made for a less chaotic weld. By that I mean that things ran "smoother". I am able to create and maintain a puddle easier than without the choke.
I think more inductance would be good but I was constrained by size. Could only fit so many wraps on the core. Nevertheless having what I got in there is a big improvement to not having it at all.

[xaust]

My choke ended up at 1.4mH. Based on some research that I did I was shooting for several mH. But like I said above I was constrained by the core I was using and the size and type of wire I was using.

[bigbeachdog]

Thanks xaust. It also looks like you took out the stock fan and replaced it with a computer type fan on the side facing the main transformer. Was that to give room for your choke?

Cheers

[bigbeachdog]

Never mind, I re-read your posts & got the answer.

[bigbeachdog]

So, if I used magnet wire (insulated with a fine coat of varnish?) instead of regular insulated wire, I could add quite a few more turns and increase the inductance? I know I would probably have to file smooth the corners of the transformer and maybe add some paper or plastic to cover the corners and protect the wire insulation from scratches.

[xaust]

Magnet wire should work OK - you just need to be careful related to the amps it can handle and how well the varnish will hold up to heat. What you have going for you is that the duty cycle is so low. I used 8AWG wire which, I think, is only rated to 60A but that is 100% duty cycle. Handling 90A is no prob for something that is only on for 10% of the time with long rests between and a cooling fan.

[Fat Bastard]

So by this post your interest lay more in the electronics and modification tinkering than in welding?

If not I would think even when finished you will have spent many times more on a still under-powered machine and not so much time welding.

Cool enjoy.

[bigbeachdog]

FB, No, the main interest is in modifying a machine to work better (ie. on thinner material). Most of the supplies I would use come from my "scrap" bin or the local salvage yard, so cost is minimal. I am semi retired (plenty of time) & not a pro welder, so anything I can do to improve the functionality of my equipment, at what I consider to be a reasonable cost, I'll do.
I bought the HF machine on fleabay for about $50 and might add another $20 to do this mod so I consider it a good investment. I can always resell for that price. I try to weigh the cost vs benefits but you also need to consider the fun factor.

Cheers

[xaust]

I bought a tool. Had the wherewithall to improve it. Did so. Been using the tool for it's intended purpose ever since. I don't see the problem.