Highbeam
Super Member
Make sure you have it dead right before you end up dead wrong. It only takes one amp to get killed and you're messing with 250 amps.
AC Welder to DC conversion.
- Thread starter BloomingtonMike
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PBinWA
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</font><font color="blue" class="small">( Lot's of stuff I don't ever want to know about here. I am also interested in the simple and safe way to turn an AC welder into a DC welder. Has anyone actually done it? My welder is an old but good Lincoln AC225.
Walmart now sells them for 250$. )</font>
Sell it on Craigslist and then buy a DC Welder (might also look on Craigslist for it)!
You can get a Lincoln/Hobart/Miller AC/DC welders for a good price these days.
This has to be the easiest way to turn an AC welder into a DC welder.
Sorry - I couldn't resist. /forums/images/graemlins/grin.gif
Walmart now sells them for 250$. )</font>
Sell it on Craigslist and then buy a DC Welder (might also look on Craigslist for it)!
You can get a Lincoln/Hobart/Miller AC/DC welders for a good price these days.
This has to be the easiest way to turn an AC welder into a DC welder.
Sorry - I couldn't resist. /forums/images/graemlins/grin.gif
Highbeam
Super Member
Allright, you got me. That is the easiest. I should add cheapest to that list. The buzzbox has become my friend.
MMM
Platinum Member
I had the DC side go out on one of my machines and they replaced the "rectifier bridge" for $50. Whether it needs something else to turn it on, etc, I don't know. On the Dc side, I do know there are seperate amperage controls and +/- sockets for DCEP and DCEN. I'm not sure you can get around or modify that without spending a lot of research and $.
Good luck.
Good luck.
PILOON
Super Star Member
Hi all.
First off I have done this once back a few years ago using SCR's that came from a 72 volt fork lift truck.
A welder is merely a transformer. Heavy duty, no less.
The unit I made 'back when' was a step up transformer that had 88 turns on the primary for 110 volt winding of #8 wire so I duplicated that winding to use on 220.
For the secondary winding I used about 60 turns of 1/4" copper tubing for somewhere around 50-60 volt output.
I then soaked the whole mess in varathane varnish to insulate.
I then taught myself to weld at first using 2 vice grips for grounding aand rod holding(+gloves) and eventually got a rod holder.
Now I had only one power setting so I used different rods and sizes to accomplish whatever I wanted to do.
It was powerfull enough that I could use 1/8" cutting rods as well.
Sure learned some oddball techniques, but I never had a weld fail. (burned through a lot, however).
Sure had good penetrations!
Then I converted it to DC with the lift truck SCR's and it worked kinda not bad.
Now I have a real welder!
As far as diodes go, welding is at generally 70 volts so you need voltage ratings a bit higher, probably like 100-150 and they rate PIV (peak reverse voltage) so I'd guess maybe 200-250 PIV then the amps which need to be no less than your welder rating and probably a bit higher for a margin of protection.
The wireing is kinda simple and I believe another poster has already shown it. Main problem is that you have to mount the diodes on two bases(heat sinks) and they need to be insulated from each other otherwise you'll get some nice big sparks.
Otherwise it is 2 wires in (AC) and 2 out (DC)
Spiker:
What you suggest is what I hoped I could do.
As to the SCR's I bought, the huge size suggests that they could handle just about anything. The studs are 5/8" and the leads 3/8" and they were mounted 3 to a heatsink.
My guess is they are 3phase controls for big motors suggesting ample amperage and proper voltage range.
I had nothing to loose since they cost only $5.00/3 (I bought 2 sets)
If I wire respecting the 'bridge' setup the worst that will happen is; wont work if not 'triggered' or when loaded (welding) or shorted I'll pop the breaker.
The buss box being only a transformer is tough and virtually indestructable.
Remember every time you weld you essentially short out the secondary, specially if you stick a rod!
First off I have done this once back a few years ago using SCR's that came from a 72 volt fork lift truck.
A welder is merely a transformer. Heavy duty, no less.
The unit I made 'back when' was a step up transformer that had 88 turns on the primary for 110 volt winding of #8 wire so I duplicated that winding to use on 220.
For the secondary winding I used about 60 turns of 1/4" copper tubing for somewhere around 50-60 volt output.
I then soaked the whole mess in varathane varnish to insulate.
I then taught myself to weld at first using 2 vice grips for grounding aand rod holding(+gloves) and eventually got a rod holder.
Now I had only one power setting so I used different rods and sizes to accomplish whatever I wanted to do.
It was powerfull enough that I could use 1/8" cutting rods as well.
Sure learned some oddball techniques, but I never had a weld fail. (burned through a lot, however).
Sure had good penetrations!
Then I converted it to DC with the lift truck SCR's and it worked kinda not bad.
Now I have a real welder!
As far as diodes go, welding is at generally 70 volts so you need voltage ratings a bit higher, probably like 100-150 and they rate PIV (peak reverse voltage) so I'd guess maybe 200-250 PIV then the amps which need to be no less than your welder rating and probably a bit higher for a margin of protection.
The wireing is kinda simple and I believe another poster has already shown it. Main problem is that you have to mount the diodes on two bases(heat sinks) and they need to be insulated from each other otherwise you'll get some nice big sparks.
Otherwise it is 2 wires in (AC) and 2 out (DC)
Spiker:
What you suggest is what I hoped I could do.
As to the SCR's I bought, the huge size suggests that they could handle just about anything. The studs are 5/8" and the leads 3/8" and they were mounted 3 to a heatsink.
My guess is they are 3phase controls for big motors suggesting ample amperage and proper voltage range.
I had nothing to loose since they cost only $5.00/3 (I bought 2 sets)
If I wire respecting the 'bridge' setup the worst that will happen is; wont work if not 'triggered' or when loaded (welding) or shorted I'll pop the breaker.
The buss box being only a transformer is tough and virtually indestructable.
Remember every time you weld you essentially short out the secondary, specially if you stick a rod!
pat32rf
Veteran Member
I would take a trip over to your local high school and talk to the physics teacher or a grade 12 student. Our buzz boxes work on about 80volts output and I find that most of my welding is multiple passes of small rod, 80-100amp works for me.(my cooling fan burnt out years ago, so I stay away from the high settings). You should be able to mount the diodes on a suitable base and just conect to them for those jobs where you need DC. You will be creating a "full wave rectifier" that needs the ground lead to one side and the stinger lead to the other.You will need four diodes to do this. From the bridge you will then run a new ground and stinger lead. Any science/physics teacher should be able to put it on paper for you.(or any TV repairman)Good luck, want to do the same thing myself when my son comes up with the rest of the diodes. Pat
VinnieNC
New member
Mike,
I plan on converting a Lincoln 225 buzzbox to DC one day also. I have been collecting the parts for years. I think the easiest way is to build a heavy duty diode bridge, with heat sinks and a fan as others have mentioned. I have 4 FAT diodes that I salvaged from a powered fork lift truck. The theaded studs are in the 3/4 to 7/8 inch range, so they are rated for a lot of amps. I also have some large heat sinks that I have scrounged from various sources such as flea markets, ebay.
I plan to build my bridge in a box and mount it externally on the welder with its own fan. I saw one on the net a few years ago that someone invented and marketed. I think it was called something like "Easywelder". In their design, they connected the ground and hot leads from the welder to terminals on the sides of the bridge box, then connected the "POS" and "NEG" welding leads to two other terminals on the box using wing nuts. The wing nutted connections provided a quick and easy way to reverse the polarity if needed. I will try to attach a pic of a diode bridge that I copied from a website. The "Load" will be your work clamp and electrode clamp connections.
I have called Lincoln tech support in the past and was told that the only differences electrically between the AC only and the AC/DC is the addition of the bridge and a coil. I am not sure how much impact the coil has on the performance, but it would be easy enough to make one out of some heavy copper ground conductor or tubing.
HTH
I plan on converting a Lincoln 225 buzzbox to DC one day also. I have been collecting the parts for years. I think the easiest way is to build a heavy duty diode bridge, with heat sinks and a fan as others have mentioned. I have 4 FAT diodes that I salvaged from a powered fork lift truck. The theaded studs are in the 3/4 to 7/8 inch range, so they are rated for a lot of amps. I also have some large heat sinks that I have scrounged from various sources such as flea markets, ebay.
I plan to build my bridge in a box and mount it externally on the welder with its own fan. I saw one on the net a few years ago that someone invented and marketed. I think it was called something like "Easywelder". In their design, they connected the ground and hot leads from the welder to terminals on the sides of the bridge box, then connected the "POS" and "NEG" welding leads to two other terminals on the box using wing nuts. The wing nutted connections provided a quick and easy way to reverse the polarity if needed. I will try to attach a pic of a diode bridge that I copied from a website. The "Load" will be your work clamp and electrode clamp connections.
I have called Lincoln tech support in the past and was told that the only differences electrically between the AC only and the AC/DC is the addition of the bridge and a coil. I am not sure how much impact the coil has on the performance, but it would be easy enough to make one out of some heavy copper ground conductor or tubing.
HTH
Paddy
Veteran Member
BloomingtonMike,
why convert to DC? I have an AC 225 Lincoln welder, they work great.
Patrick
why convert to DC? I have an AC 225 Lincoln welder, they work great.
Patrick
slowzuki
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If you have ever used a good DC welder you'll find they work "greater" /forums/images/graemlins/cool.gif
I learned on DC stick and boy what a surprise moving to AC stick, much harder to achieve good welds and many rods aren't able to be used.
I learned on DC stick and boy what a surprise moving to AC stick, much harder to achieve good welds and many rods aren't able to be used.
SPIKER
Elite Member
the COIL they are refering to is to adjust the welding voltages, basically I belive that they use the coil to provide the TRIGGER for the SCRs as you adjust the COIL it cuts IN the SCR at a different time in the wave form, the current keeps it firing as soundguy mentioned, the SCR will shut off as the AC waveform passes 0 volts and will not turn ON untill it reaches it's GATES's on threshold, adjust the coil higher resistance the gate gets less voltage and the signwave form moves higher up, the DC does not et turned ON untill later and the DC voltage over the full ac's waveform is lowered then. I BELIVE, (it has been a LONG while since I even looked at a scr setup. I do know that some of them can shut off the DC at different points too, these are called something different maybe? I have seen SCRs that have 2 gate wires, perhaps these are the type that are used to adjust voltage in & out. if you do use a SCR bridge and tie the gate to the cathode? end of the SCR it will trigger as soon as the AC waveform goes positive, the gate will stay ON all the way untill the ac reaches back down to "0" the current stops and the gate shuts off and then the ac goes - and will not activate that scr anylonger, in this manner it basically acts as a simple DIODE not an SCR.
Mark M
Mark M