Re: AC welder question
- From: RoyJ <spamless@xxxxxxxxxxxxx>
- Date: Sat, 15 Oct 2005 02:42:23 GMT
DC will give you a smoother arc, less spatter. Some rods will only run on DC, but there are a good selection of rods that do run on AC. About the only time you WANT to run AC is when you are running into arc blow (magnetic fields building up that distort the arc)
It's common to build the bridge diode circuit using 4 (or more) diodes. Plain diodes need to have some hefty ratings. The open circuit voltage on the Lincoln runs in the 70 volts or so, there tends to be some serious voltage spikes on top of that. Amperage can be a little closer to the ratings on the welder since the current overloads are not as great.
Amperage in the welder is limited by coil and core design. Commonly the core is fully saturated, no more current can be pulled in the secondary. But when you stick the rod to the work, you WILL pull the full secondary current.
The more diodes comes into play by putting them in parallel. You need to add a tiny bit of resistance to each one to load balance. A piece of 18ga or 16ga copper a few inches long will do.
You do not need to put a reactor in the circuit since you have a pretty massive one in front of the diodes. Plus the DC for welding is much more about electrons flowing the same direction than about about a stead flow of them. If you must have a reactor, it will need to be wound with wire suitable for fairly high duty cycles at the max amperage you plan to run. Using the Lincoln as a base, figure 225 amps at 30% to 40% duty cycle. Duty cycle is figured on a 10 minute basis so this would mean running 4 minutes at full output. Most folks do NOT run their welders anywhere near full output so downrating is quite feasible. No clue on what the reactance would be, just wind a couple dozen turns on a suitable core and call it good.
I'd suggest that you just learn to weld using AC before getting all fussed about going to DC. Pick up 10 pounds of 1/8" 6013 rod plus 5 pounds of 1/8" 6011, burn the whole works on practice pieces. If you still need DC at that point, go get 4 big diodes.
captainvideo462002@xxxxxxxxx wrote:
Someone recently gave me a 225 amp AC welder which was made by Lincoln about 25 years ago. It has been sitting for about 20 years and was previously hardly ever used. It has a switch on the front with positions ranging from 40 - 225 amps. I am an electronics technician by trade but admittedly I don't know much about welding however I have heard that DC welders are much more desirable. So I have some questions: 1. Where or when would it be more desirable to use an AC over a DC welder? 2. (well this ones not a question). I would like to construct on a suitable heatsink, say a 400 amp bridge rectifier circuit and install it between the switch and before the ground and electrode cables? 4. Are the outputs of welders normally protected in some fashion against current overload. Would I need to do this? 5. I understand that I will need a very large choke on the output side. The factory rep tells me that I can use almost any choke from a similar size DC welder of any make. He says these a quite large. Does anyone know what the typical inductance of this choke might be? Thanks very much for any information on this. Lenny Stein, Barlen Electronics
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