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charlie_r
07-09-2012, 08:49 PM
Being the way I am and not being satisfied with my welder's performance as an AC machine using DC wire, I've started the conversion to a full mig unit.

The only wire that seems to be available to me for gasless wire feed happens to be a DCEN (DC straight or DC Electrode Negative). This doesn't work very well when fed AC. At times, especially in close quarters, it becomes almost impossible to control the arc. Not to mention the horrendous amount of spatter, and rather high use of wire!

I went on eBay and found several bridge rectifiers, most of which aren't rated at enough current for this machine. What I did find that would work is this (http://www.ebay.com/itm/MDS150A-3-Phase-Diode-Bridge-Rectifier-150A-Amp-1600V-/260945366640?pt=LH_DefaultDomain_0&hash=item3cc18e4e70). A 150A 1600V 3 phase rectifier. While it is true that my welder only puts out at most 90A @ 36V OCV (open circuit voltage), the extra room on the amps will help. The voltage rating doesn't matter, as long as it is at least twice the volts that it will be asked to pass, in case there are any spikes. Without the proper suppression circuit, there probably are. That will come later.

First pic, the unit sitting in my welder, all hooked up.

http://i1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/th_P1010852.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/?action=view&current=P1010852.jpg)

I have it screwed to an old heat sink from I can't remember what I took apart, just to make sure I can keep it cool enough. Screwing it to the base of the welder would probably have been good enough, though.

Second pic, a close view of it pulled out of the box.

http://i1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/th_P1010851.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/?action=view&current=P1010851.jpg)

You can barely see the ~ marks to the left of each of the AC terminals. I split the heat shrink tubing when I originally put it in, and was too lazy to pull it all back out to fix it. Doesn't seem to matter, though. These wires that are connected to the AC side are directly from the welder transformer.

Third pic, A top view showing how close the input and output terminals actually are.

http://i1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/th_P1010846.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/?action=view&current=P1010846.jpg)

I figure that if it is good enough separation for 150A at 1600V, it should work for this. I do suspect that if this were actually used at it's rated power, there would be an additional shield between the AC and DC, supplied by the installer in whatever enclosure it would be in. Note also, what I made the AC lugs out of: A piece of copper pipe, split, flattened, and cleaned, then drilled and shaped for this purpose. Had to use a 140W soldering gun to get it warm enough for the solder to flow properly.

Fourth pic, The wiring diagram. As you can see, there are 3 pairs of diodes internally, but we only need two. The remaining pair can just sit there and do nothing. Won't bother a thing like that.

http://i1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/th_P1010848.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/?action=view&current=P1010848.jpg)

Note that the ground lead is hooked to the + (positive) terminal on the block, and the torch head is on the - (negative). This is what the welding wire calls for. DCEN.

When I get the rest of the parts needed for a full conversion, I will have to switch them around, because gas shielded requires DCEP, or DC reversed to work properly.

In short, I paid a little over $100 for a transformer, and the rest was thrown in for good looks......But seriously, what more could I expect? It is small, portable, and now works better at what it was halfway designed for, that being hobby welding.

The biggest upside to adding this rectifier is that spatter is reduced to almost nothing, and wire use per inch of weld is less than half what it was without it, along with MUCH smoother welds, with better penetration.

When I continue the upgrade, I will add to this thread with what, why, and how I'm doing it.

When the conversion is complete, I will have paid approximately what a new (actual) mig would have cost me, but this way I can do it on the "installment plan".

Old Peddler
07-09-2012, 09:16 PM
Very good write up Charlie. Thanks, that should help some one out there.

OP


Being the way I am and not being satisfied with my welder's performance as an AC machine using DC wire, I've started the conversion to a full mig unit.

The only wire that seems to be available to me for gasless wire feed happens to be a DCEN (DC straight or DC Electrode Negative). This doesn't work very well when fed AC. At times, especially in close quarters, it becomes almost impossible to control the arc. Not to mention the horrendous amount of spatter, and rather high use of wire!

I went on eBay and found several bridge rectifiers, most of which aren't rated at enough current for this machine. What I did find that would work is this (http://www.ebay.com/itm/MDS150A-3-Phase-Diode-Bridge-Rectifier-150A-Amp-1600V-/260945366640?pt=LH_DefaultDomain_0&hash=item3cc18e4e70). A 150A 1600V 3 phase rectifier. While it is true that my welder only puts out at most 90A @ 36V OCV (open circuit voltage), the extra room on the amps will help. The voltage rating doesn't matter, as long as it is at least twice the volts that it will be asked to pass, in case there are any spikes. Without the proper suppression circuit, there probably are. That will come later.

First pic, the unit sitting in my welder, all hooked up.

http://i1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/th_P1010852.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/?action=view&current=P1010852.jpg)

I have it screwed to an old heat sink from I can't remember what I took apart, just to make sure I can keep it cool enough. Screwing it to the base of the welder would probably have been good enough, though.

Second pic, a close view of it pulled out of the box.

http://i1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/th_P1010851.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/?action=view&current=P1010851.jpg)

You can barely see the ~ marks to the left of each of the AC terminals. I split the heat shrink tubing when I originally put it in, and was too lazy to pull it all back out to fix it. Doesn't seem to matter, though. These wires that are connected to the AC side are directly from the welder transformer.

Third pic, A top view showing how close the input and output terminals actually are.

http://i1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/th_P1010846.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/?action=view&current=P1010846.jpg)

I figure that if it is good enough separation for 150A at 1600V, it should work for this. I do suspect that if this were actually used at it's rated power, there would be an additional shield between the AC and DC, supplied by the installer in whatever enclosure it would be in. Note also, what I made the AC lugs out of: A piece of copper pipe, split, flattened, and cleaned, then drilled and shaped for this purpose. Had to use a 140W soldering gun to get it warm enough for the solder to flow properly.

Fourth pic, The wiring diagram. As you can see, there are 3 pairs of diodes internally, but we only need two. The remaining pair can just sit there and do nothing. Won't bother a thing like that.

http://i1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/th_P1010848.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/welder%20pics/?action=view&current=P1010848.jpg)

Note that the ground lead is hooked to the + (positive) terminal on the block, and the torch head is on the - (negative). This is what the welding wire calls for. DCEN.

When I get the rest of the parts needed for a full conversion, I will have to switch them around, because gas shielded requires DCEP, or DC reversed to work properly.

In short, I paid a little over $100 for a transformer, and the rest was thrown in for good looks......But seriously, what more could I expect? It is small, portable, and now works better at what it was halfway designed for, that being hobby welding.

The biggest upside to adding this rectifier is that spatter is reduced to almost nothing, and wire use per inch of weld is less than half what it was without it, along with MUCH smoother welds, with better penetration.

When I continue the upgrade, I will add to this thread with what, why, and how I'm doing it.

When the conversion is complete, I will have paid approximately what a new (actual) mig would have cost me, but this way I can do it on the "installment plan".

charlie_r
07-09-2012, 10:17 PM
Thank you, OP.

socialtalker
07-10-2012, 02:58 AM
thanks! i paid 13.50 for the bridge rectifier, turns out i had ebay bucks for a discount. woo hoo! i will take a look at this post when it comes in the mail.

charlie_r
07-10-2012, 08:30 AM
ST, let me know if you have any questions when you start to do this. Remember, you will need to use at least an AWG 6 stranded wire between the transformer and rectifier.

socialtalker
07-11-2012, 12:36 PM
thank you! say, how much of the AWG 6 wire will i need? i did a little google search and what i could find is in big rolls that looks like way more than i need. if you can past along a source not obvious i would appreciate it.


ST, let me know if you have any questions when you start to do this. Remember, you will need to use at least an AWG 6 stranded wire between the transformer and rectifier.

charlie_r
07-11-2012, 05:58 PM
For mine, I just used short pieces, about 3" long, from a dead set of jumper cables that were in the shop. HD or Lowes, and most hardware stores would have this, and would be happy to sell you a foot or so of it.

Be aware that the winding tails that come out of the transformer are likely made out of aluminum, so are not solderable. You would have to coat them with a dab of dielectric grease to prevent corrosion at the aluminum/copper junction. If your tails are actual copper, just solder away! Harbor freight sells heat shrink tubing for a reasonable price, and it is advisable to use this over all your connections, as you saw in my pics.

socialtalker
07-18-2012, 03:40 PM
my bridge rect came. one week from overseas! cool!
just have to order the heat shrink tubing first. is 2.5mm the right size?

RunnerPack
07-18-2012, 04:43 PM
Charlie, thanks for starting this thread! I'll be following this one closely. I do have some suggestions for stuff to add, though:

1. I had to do a search to find out what welder you're using. Is this still the HF, 90A, flux-wire welder you mentioned in another thread? You should mention this in the first post. I hope it is, since I have the same one.

2. Some before/after shots (or maybe videos?) of the welds you've made would be nice. I'd like to see if the improvement is worth the trouble/expense.

Also, I had a question: What do you think about using a few smaller rectifiers in parallel? I have a bunch of old PC power-supplies and stuff that have some large (but not large enough) ones. If I could use a few in parallel, I could do this for the cost of a bit of wire (and I may be able to scrounge that...).

Can't wait 'till you start posting about the full MIG conversion stuff...

charlie_r
07-18-2012, 05:53 PM
Socialtalker -- whatever size that will fit loosely over your wire. You use a lighter or heat gun (hair dryer) to shrink it to wrap tightly around your connection.


Runnerpack --


I had to do a search to find out what welder you're using. Is this still the HF, 90A, flux-wire welder you mentioned in another thread? You should mention this in the first post. I hope it is, since I have the same one.

Sorry about that, yes it is the HF 90A flux core welder.


Some before/after shots (or maybe videos?) of the welds you've made would be nice. I'd like to see if the improvement is worth the trouble/expense.

I'll see if I still have a few scraps around with the "before" look. I'll get you some pics of the "after". I can tell you this for sure, it is definitely worth it!


What do you think about using a few smaller rectifiers in parallel? I have a bunch of old PC power-supplies and stuff that have some large (but not large enough) ones. If I could use a few in parallel, I could do this for the cost of a bit of wire (and I may be able to scrounge that...)

Not a good idea to parallel diodes in that manner. very minor differences in each diode will cause one or two of them to try to pass the entire current, with any others in parallel with them handling very little current. Those taking the lion's share of the load will quickly overheat and fail. Best bet is to go ahead and buy a bridge rectifier that can handle the current, plus about 10% or more for the inevitable current spikes. There are 100A versions of them, which will give you the 10%, but they appear to be selling for the same price as the 150A. By going with the higher of the two, you have that much more "wiggle room".

The next step in my conversion will be adding a few capacitors, and probably a choke for current/voltage smoothing. Maybe sometime this autumn, with more of the conversion next year.

Modern man
07-22-2012, 10:27 AM
charlie_r, thanks for the info, I've been considering this conversion for a while, so I'd also be interested in seeing some pics of the results. For those who haven't seen it here is a link to another conversion of the same welder;

http://www.blinkenbyte.org/welder_conversion/welder_conversion.html

and another on building an inductor/choke for the conversion;

http://aaawelder.com/inductor.html

Cheers

charlie_r
07-22-2012, 10:37 PM
Been a bit busy here last few days. Was able to get more materials for the (required) fence, so had to deal with that, among other things.

Maybe in the AM I'll be able to get those pics for you guys.

MM -- thanks for those links! I was going to try to do the calculations (calculus?? me? ......maybe just algebra....lol) myself, but with that aaawelder one I see I don't have to do too much with that.

The blinkenbyte link is where I got the idea from, and had forgotten about it.

socialtalker
07-23-2012, 11:20 AM
i have seen this instruction/diagrams before, i think on weldingweb. i was intrigued, but decided against it because it looked too complex.(dangerous) and expensive.
i liked charlie's mod because it was much simpler. just a bridge rect.
should i be doing something different now? am i supposed to get a heatsink for the rectifier?


charlie_r, thanks for the info, I've been considering this conversion for a while, so I'd also be interested in seeing some pics of the results. For those who haven't seen it here is a link to another conversion of the same welder;

http://www.blinkenbyte.org/welder_conversion/welder_conversion.html

and another on building an inductor/choke for the conversion;

http://aaawelder.com/inductor.html

Cheers

charlie_r
07-23-2012, 04:36 PM
Do you have any old computer power supplies? You can rob one from them, of you could just bolt the rectifier to the bottom of your welder, inside it of course. You might be OK without it, if you keep your welding time short.


Did manage to find a weld that I hadn't cleaned up:

http://i1094.photobucket.com/albums/i459/bcgeorge/th_P1010860.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/?action=view&current=P1010860.jpg)

and here's one that I just did, and blew threw on...then repaired the hole. Wire brushed only, after welding.

http://i1094.photobucket.com/albums/i459/bcgeorge/th_P1010861.jpg (http://s1094.photobucket.com/albums/i459/bcgeorge/?action=view&current=P1010861.jpg)

As I said previously, DC welding seems to be hotter, with better penetration. This same weld prior to adding the rectifier would not have blown through.

You can also see the lack of huge amounts of spatter on the converted weld.

Modern man
07-26-2012, 10:36 AM
Thanks charlier.

Socialtalker, (let me preface my remarks by saying I am not an engineer, electrician or welder, so I know enough to get myself in trouble)
As long as you use the same style rectifier as charlier you could bolt it to the inside of the welders sheet metal housing or fab a metal bracket and put it near the output of the internal fan. I suspect that you won't need a heat sink because you are welding at currents well below the max of the rectifier, plus the limited duty cycle of that little machine should also help keep it cool.
You wouldn't really need any capacitors (my Miller Thunderbolt AC/DC unit has none), but with respect to the choke or inductor, it helps to smooth out the arc by stabilizing the current giving less spatter. This is the best explanation of why you should have one (taken from http://www.mig-welding.co.uk/forum/showthread.php?t=1281&page=2"
"How is a choke of use in a welder? If you have a ripple on the output of a power supply it will be trying to resist the change in level. As the current drops it will 'top it up' and as it rises it will resist the rise. It will flow a heavy current unlike a capacitor which flows none. Capacitors stabilize voltage, chokes stabilize currents."

Cheers

Modern man
08-02-2012, 08:17 AM
charlie_r, just found this other conversion of the HF 90 amp unit. What's really interesting is how he made his own choke from a microwave transformer!

http://weldingweb.com/showthread.php?t=61856

Cheers

socialtalker
08-11-2012, 06:51 AM
i think i have have everything now. not sure i might have to go out and get a couple more copper lugs from the auto parts store for connections. taking a look again at the pictures/diagram, i admit i usually need instructions, not too confident with justs pics. rignt now they appear to be 2 or 3 versions of this conversion that that gets confusing what to follow.

bill82
10-19-2012, 08:08 PM
You can find these things in an old television or an old computer just pull it out and you can use it as you want. Just be sure that the television or computer are not functioning anymore.

pedals
10-20-2012, 03:31 AM
dc is certainly the way to go I just sold my ac mig and bought a dc model and there is no comparison, but it amazes me the way you can modify power tools or work with electricity I take it without a licence in the states. Here in Australia you must hold an electrical licence.