Powr-Kraft 230ac to AC/DC Modification

[MatLioLec]

Hello, my name is Mathieu LeClair. I'm a tradesmen welder from NB, Canada. I'm a bit new to the industry but I do have a college degree and several certifications. I'm also new to this forum, but I have been here quite a few times when I would be looking up information on welding related subjects.

With that said, I'm pretty sure the subject of AC to DC modification has been somewhat exhausted, but I'd like to possibly have a few questions answered so I hopefully don't waste my money on components that shouldn't be in a welder.

First off, here is a schematic I found and modified to fit my applications. If anyone has any suggestions, feel free. By the way, both the secondary and the primary are connected, so if anyone is wondering why it's shown on the schematic, it's because it's shown on the transformer. Generally, it would be considered a Autotransformer, but since it's a welder with a magnetic shunt, it would be better to call it a leakage transformer.




So yeah, keep in mind, I don't claim to be a pro at drawing schematics, so things like "the tap on the secondary shouldn't be right there" or "if you intend to use schottky Diode, thats not the right symbol for it" or whatever is overall useless information.

Anyways, so yeah schottky diodes! I have some picked out, I think they might work.. this is actually what I'm here for.. I'm not a 100% it would be good for this application. Anyone here know why it would or wouldn't be? They're actually pretty inexpensive, 13 bucks on ebay, S&H included and they give you two connected to a plate for a common Cathode! Also, since theirs a nice separation between the two, I could just cut the cathode plate to split them up if I wanted. (in which case I'll have too for that design)

http://www.fulisemi.com/admin/PDf/im...00100CT-BS.PDF


As far as the Filter Capacitor goes, I'm pretty confident that I found the right one. It's a 63v 18mF electrolytic cap. I spoke with a local here that used to work in a shop that rewinds electric motors and what not, and he was the guy there that was a pro with welders I guess (now retired). he suggested at least 15mF and said that he tried adding a lot more, but after a while, it just makes it worse. So 18 should do for starters.

Also going to get nice Dinse connect panel connectors for it. Should turn out pretty good and I could finally start working on some more welding certificates. The tests are done with a 3-phase Miller XMT 450 CC/CV WCC.. so in my opinion, I should at LEAST be practicing with a decent DC welder for 7018s

[Rick V]

Hey don't read me wrong, I love tinkering too... BUT...

I think you would be a lot further ahead to sell your AC-only welder and pick up a used AC/DC welder. I've seen them on Kijiji in the last few weeks for as low as $100 for a 225/140 amp Century; a typical Lincoln 225/125 AC/DC goes for $350 but I picked one up for $200. I picked up three Linde 250 AC/DC for $100, $75 (no leads) and $300 with 50ft leads and 25ft #8 extension cord.

As far as that schematic goes, I don't understand the purpose of that single diode sitting all by it's lonesome; all that will give is low voltage 1/2 wave output - duh?? Further, you are missing a key component - the large inductor needed for arc stabilization. What about a switch for changing the amperage settings? That's why I suggest simplying buying a used working AC/DC welder; it has all those components and also has resale value. Unfortunately, you would never recover the $$ you would put into changing an AC machine to AC/DC.
IMO

[MatLioLec]

yeah the kijiji in this area isn`t as good as in other places. first off, it`s slim pickings and second, the closes location in the actually listing is a small city an hours drive and it represents the north eastern to central northern area of the province.. so theirs a chance i could be looking at stuff that in my town and 5 minutes drive.. or something that could be about 2h30 hours drive on the highway.

don`t get me wrong, kijiji`s awesome, but the population is too low to have some good kijiji listings. and also, since the diodes are 13 dollars for 2, i have the cap and i could fabricate the panel sockets if i wanted too to save on money.. since that is where the biggest expense is. i think making the necessary modifications is more cost effective. also, a 4-way switch (or two 2-way switches) is (are) hard to come by it seams. i contemplated making my own.. but rejected the idea since installing 4 outputs would be simpler if not just very, very inexpensive. as easy as a couple of lugs died from some brass round bars and some rubber washers to insulate them from the panel.

i gotta sort of agree with that diode at the bottom.. i first made it without that diode, but after showing it to a tech around here, he suggested putting it there. but it just seems like diode 6 and diode 2 serve the same purpose.

and for those DC Link Chokes.. it would be in there if i didn`t get the idea that putting a capacitor would have a more dramatic effect. tho they work best in conjunction to each other. and if i was to put one in. i`d make it from scratch, and after working out the details, i was thinking of avoid that.. especially since i`m short on details when it comes to making it. like the size of the core and the gauge of wire and the windings needed. doesn`t need to be too fancy. some say a laminated core isn`t as necessary as a regular transformer. i figure 2 or 4 AWG magnet wire would be fine.. but what i`m vexed about would still be the size of the core and the windings. i have a rough, really rough idea of how big and how much.. but if i can`t fine tune it, it`s not enough for me.

[MatLioLec]

btw, i live in Ottawa for about 2 years. nice place. i bet the classifies there are great!

[Rick V]

For stick welding the capacitor across the output is not what you want. That just blows the end off the rod with an inrush of current. You want the opposite, an inductor in series with the positive output - after the diode bridge. The inductor opposes any change in current - exactly what you want to keep the current constant. It prevents blowing the end of the rod when starting the arc and smooths the arc when welding. I posted my experience with making an arc stabilizer... suggest you search for that on this site. I can't recall the details now but I recall I needed about 1 millihenry to smooth the arc. The wire has to be sized for the welding current; I started with #4 AWG then moved to #1 AWG gauge equivalent wound around a ferrite core.

As for living in Ottawa - cool! Where in NB you living now? I lived in Fredericton for 11 years.

[Rick V]

Another thing to consider...
You might want to house the rectifier bridge in a separate box with a fan. The inductor could be a separate build too. That way, if you sell your present welder, you haven't made any price reducing modifications to it. You save you bridge rectifers and you can always add the inductor into a new welder output to smooth out the DC even more.

[MatLioLec]

yeah now that i`m looking more into it since you brought it up.. now i`m thinking of putting one in there for sure. been looking at other DIY designs and hearing results. i wonder if making a basic shunt would help to make it adjustable? sort of like an Arc Control knob on a miller? tho i`m sure that knob does more then adjust the frequency.

I live in the northern end. it`s actually as north as you can get in NB. Dalhousie. nice place if you got money and/or a good job. but sucks if you don`t. the economy around here is horrible.

[MatLioLec]

i just realized that my schematic is totally retard.. i think?? i'm gonna have to revise it and try to wrap my brain around it. i don't claim to be a pro at making those hahaha.

[MatLioLec]

new and improved and simplified!

[MatLioLec]

Further, you are missing a key component - the large inductor needed for arc stabilization. What about a switch for changing the amperage settings?

IMO

[ccawgc]

Your last diagram looked better, until my virus scan program kicked me off your picture site.
See the diagram I am posting here. It is a simple AC/DC arc welder made by century.
Some arc welders put some inductance in both the AC and DC circuts, and some use a low tape for AC and a High tap from the transformer for DC. This keeps the scale on the welder the same for both. Allows for the voltage drop of the diodes and the inductor.
For safety do not tie the primary winding to the secondary winding.
You want a step down transformer to drop voltage and increase amps.
An auto transformer while having many voltage steps, has limited current.
It is limited by the wire size used to wind it. These welders either have switched primary and fixed secondary or fixed primary and switched secondary to control the welder output.
Switching done with either an electronic switch or a manual tap switch.