Turning an AC stick welder into DC

[gemini5362]

I could get more power to my shed from my existing panel if I really wanted to, but the problem is you cant buy single phase welders that draw more than 15A @ 240V.

In order to go bigger, I need to go 3 phase, if for no other reason than, I can't get the equipment.

Although, I have heard stories about running 3 phase welders on a single phase, because in reality they are actually a single phase unit, but are wired to a 3 phase plug because they need the current supply available from a 3 phase outlet.

Cheers

Rohan

My miller mig welder basically welds off of whatever voltage you apply to it. It is a single phase unit and uses 30 amps input if you are hooked up to a 240 volt circuit. Do you not have access to miller corporation products in australia ?

 

[gemini5362]

I believe I understand what rhamer means about a single phase welder wired to a 3ph circuit. During my time in the Army I worked on equipment that needed 3 phase power and at times had to wire in some 110 and 220 volt equipment. First a little primer. Single phase i.e. would be 1 hot and 1 neutral. This could be 110 or 220. 3 phase consists of 4 wires, 3 hot and 1 neutral. Now you might say wait a minute my 220 has 2 hot wires and a neutral. Sort of. If you look at your main panel you see that the neutral "and" the ground are one and the same. It's still considered single phase. Here's where the fun begins as you "can" get just about any voltage from a 3 phase line. Here's how. If you take "any" hot line to neutral you get "approximately" 110 volts. If you take any 2 hot wires on a 3 phase circuit you will get "approximately" 208 volts which is within most specs. for a 220 volt appliance. And of course your 3 phase 240 curcuit. What I believe rhamer is saying is that their standard is to run a 3 phase line into a building and just use 2 phases (208) for the welder etc. Yes they are 120 degrees out of phase and that's why you will only see 208 rms volts. It does work but "can" cause problems with certain types of equipment. In the US if you need three phase power I believe they use a special type of transformer with a special type of capacitor to create 3 phases of power but I'm not sure.

You are so wrong. Basically what you say about 3 phase power is just enough right to be dangerous. Depending on how the power is brought into the building by the type of transformer you use. If you have a delta wired transformer you will get one type of voltage from one leg to ground a y (or star) will give something different. the only consistent voltage is phase to phase and that is provided that you have all three phases available. Anyone that is a beginner at hooking up three phase needs to do some serious research on it before you try to use it. At the least you can destroy some equipment at the worst you can get seriously hurt or expire. A little bit of knowledge about three phase is not a good idea.

 

[rhamer]

Ok, I'm not sure if everybody realises it, but I'm in Australia.

Here we have 3 phase 240v running down most streets and every three houses are on a different phase (generally).

If you want you can have all three phases going to your house if you need it (it just costs more).

So a single phase is 240V and the voltage between any phase of a 3 phase supply and Neutral is 240V. The voltage between any 2 phases is 415V because, like you, the phases are only 120deg not 180deg apart.

As far as I'm aware, there is no equivilent to your 2 phase 180deg 220V arangement.

So as far as equipment goes it is made to either work on a single phase circuit up to 15A or a 3 phase circuit up to large amps.

Remember we have roughly twice the voltage of you guys on our single phase, so that gives us twice the power at the same amperage. So a 15A circuit can actually deliver 3600W compared to a 15A 110V circuit that can only deliver 1650W.

So think of our single phase circut as being equivalent to a 32A 110V circuit.

Cheers

Rohan

 

[RWolf]

Well Gemini5362 I may be wrong but seeing as I'm still around and have worked with single phase and 3 phase for most of my adult life and am now consider a senior by what you've said I should have died a long time ago.

From wikipedia;
Three-phase electric power is a common method of alternating-current electric power transmission.[1] It is a type of polyphase system, and is the most common method used by electric power distribution grids worldwide to distribute power. It is also used to power large motors and other large loads. A three-phase system is generally more economical than others because it uses less conductor material to transmit electric power than equivalent single-phase or two-phase systems at the same voltage.[2]

In a three-phase system, three circuit conductors carry three alternating currents (of the same frequency) which reach their instantaneous peak values at different times. Taking one conductor as the reference, the other two currents are delayed in time by one-third and two-thirds of one cycle of the electrical current. This delay between "phases" has the effect of giving constant power transfer over each cycle of the current, and also makes it possible to produce a rotating magnetic field in an electric motor.

Three phase systems may or may not have a neutral wire. A neutral wire allows the three phase system to use a higher voltage while still supporting lower voltage single phase appliances. In high voltage distribution situations it is common not to have a neutral wire as the loads can simply be connected between phases (phase-phase connection).

Three phase has properties that make it very desirable in electric power systems:

The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load. This makes it possible to eliminate or reduce the size of the neutral conductor; all the phase conductors carry the same current and so can be the same size, for a balanced load.
Power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations.
Three-phase systems can produce a magnetic field that rotates in a specified direction, which simplifies the design of electric motors.
Three is the lowest phase order to exhibit all of these properties.

Most household loads are single phase. In North America and some other countries, three phase power generally does not enter homes. Even in areas where it does, it is typically split out at the main distribution board.
The three phases are typically indicated by colors which vary by country.

Also;

Conversion to other phase systems
Provided two voltage waveforms have at least some relative displacement on the time axis, other than a multiple of a half-cycle, any other polyphase set of voltages can be obtained by an array of passive transformers. Such arrays will evenly balance the polyphase load between the phases of the source system. For example, balanced two-phase power can be obtained from a three-phase network by using two specially constructed transformers, with taps at 50% and 86.6% of the primary voltage. This Scott T connection produces a true two-phase system with 90ï½° time difference between the phases. Another example is the generation of higher-phase-order systems for large rectifier systems, to produce a smoother DC output and to reduce the harmonic currents in the supply.

When three-phase is needed but only single-phase is readily available from the utility company a phase converter can be used to generate three-phase power from the single phase supply.


[edit] References
Stevenson, William D., Jr. (1975). Elements of Power Systems Analysis, 3rd ed., McGraw-Hill electrical and electronic engineering series, New York: McGraw Hill. ISBN 0-07-061285-4.

Also incase it was missed, US wiring Hot to Neutral = ~120VAC, Hot to Hot = ~208VAC, Sound familiar. Now before I get flame that is with an RMS voltmeter not a peak voltmeter there is a difference.

So maybe I'm not so wrong. But hey I've only been involved with electricity for about 40+ years.

 

[RWolf]

BTW; rhamer I did notice where your from and one day would love to visit Australia. I was trying to point out that I understood what you were referring to. Probably didn't make myself very clear but I've never been good at expressing myself in type.

 

[SPIKER]

Ok, I'm not sure if everybody realises it, but I'm in Australia.

Here we have 3 phase 240v running down most streets and every three houses are on a different phase (generally).

If you want you can have all three phases going to your house if you need it (it just costs more).

So a single phase is 240V and the voltage between any phase of a 3 phase supply and Neutral is 240V. The voltage between any 2 phases is 415V because, like you, the phases are only 120deg not 180deg apart.

As far as I'm aware, there is no equivilent to your 2 phase 180deg 220V arangement.

So as far as equipment goes it is made to either work on a single phase circuit up to 15A or a 3 phase circuit up to large amps.

Remember we have roughly twice the voltage of you guys on our single phase, so that gives us twice the power at the same amperage. So a 15A circuit can actually deliver 3600W compared to a 15A 110V circuit that can only deliver 1650W.

So think of our single phase circut as being equivalent to a 32A 110V circuit.

Cheers

Rohan

Rohan:
it is similar in USA as well, (despite what others are saying) most of the USA works similar as it dose down under. We have 3 phase lines running down the street usually at a much higher voltage, say 1450V for ave street voltage, up to 4160 higher power lines and minor distribution lines, then major trunk lines are upwards of 50K +volts. All of these are transformed "stepped down" to more usable voltages such as the common household line voltages of 120/240VAC single phase, and 240/480VAC 3phase. Most single phase systems only use two (2) lines of the 3 lines that is out at the street, just like it is down under. though in USA we include a 4th line at the street which is a ground. The 2 LINES are attached to a pole transformer to step it down to correct voltage. there is then 2 LINES at correct voltage sent out of the transformer low side to you're home, we include the ground wire as a 3rd WIRE which provides a center ground (neutral.) There is often 3 transformers on a single pole the 3 are across the 3 legs and can output 3 phase 240/120. It is wired a s a "Y" WYE where either of the LINES to ground is 120 vac. The common house hold system uses 1 transformer across 2 LEGS of the 3 LEGS/PHASES and a Ground/Neutral. The wave form is USUALLY 120 degrees out, not 180 degrees due to the fact it is derived from the 3 phase power line system.. Down under I think you use "Delta" wiring where the ground is not part of the system only 2 of the legs correct & the ground is used to derive the single line low voltage? and if you measure one leg to ground it is 208vac. and Leg to Leg is 415V correct?

In USA some 3 phase 240vac systems you will have a HIGH leg which is actually 208 vac to ground, this is most common in factory's which have 240VAC 3 phase in coming power and is most often know as a HIGH leg or Wild Leg.. LEG to LEG is still 240 vac, but the 3 legs to ground is 120, 120 and 208. In these systems the 208 leg to ground is marked as a high leg and can only be used as part of a 3 phase or 240 phase breaker in the C.B. panels.

I do admit that I don't know much about DOWN UNDERS codes and or their standard wiring practice, I am getting more experience on 50HZ systems though 380 volts just seems wrong to me after so many years working on only 60 hz stuff

Mark

 

[Bill_C]

No, that is incorrect. The US "split phase" system IS 180 degrees apart. It does NOT merely tap off the two legs of a 3 phase supply--that's connected to thee primary. The transformer SECONDARY is center-tapped, and thus the 2 waveforms are out-of-phase exactly 180 degrees.


split phase power - All About Circuits explains it with references.

 

[gemini5362]

What the heck would I know I have only worked as a plant electrician a couple of times and one of those times myself and another electriciain completely rewired a three phase plant that is still running today and has not blown up yet. I also worked several years as a senior electrician in a steel mill which had its own substation and used electric arc furnaces to melt scrap steel down then added whatever metalurgy was required to meet the customers needs. The steel mill was three phase and we could power a couple of citys off of our substation. When the arc furnaces are running you could watch power meters which measured megawatts bounce off of the stops and that was just one fraction of the plant. We had 125 ton over head cranes that worked off of 250 volts dc and that was powered through a 2000 amp breaker.

Now my objections to the previous posts. Telling someone that you can just go from one leg of the three phase to ground is not telling enough of the story. As a previous poster pointed out depending on how the transformer feeding the power is wired you can get a wild leg and be burning things up in a hurry. I have had to fix several things that were wired by novice electricians that did not know what a wild leg is. So a blanket statement that you can go from one leg to neutral is wrong. You might be able to but not always.


I dont know about other places but the wiring to my house is 180 degrees out of phase.
I could get three phase if i wanted because they have it running about 1/4 mile from my house for some reason. But I have no need for it.



The Basic problem I have with a lot of the advice on electricity is that there are people on here with a lot of experience that makes it sound easy. They also have a tendency to make general statements. Such as you can run from one leg of three phase to ground and get 120volts. I am sure the people making these statements know better but they have forgotten that the system they are use to is not the only one out there. Electricity is very dangerous and very non forgiving. A mistake can cost you or someone else there life. A mistake wiring a house can possibly be a fire later on down the line that burns the house and everything in it to the ground. I make a heck of a lot of mistakes wiring and hooking things up. Most of them dumb mistakes that are pretty small and a result of not thinking things through. I have been working with Electricity in one form or another for 40 years next june. Please try and remember that there are going to be people reading this thread that are not going to have a clue and say well I read on TBN that all I had to do was hook this here and that there and I did not need to hook this up and be sitting with everything all hooked up waiting for disaster to strike.

 

[redneckexplorer]

To Bill C. ..... A split phase system is not a two phase system. You are confusing polarity with phase, yes the waveform is inversed, but it is still in time. If you looked at the typical home service from neutral to each hot leg it will still be in time or phased regardless of the polarity. The typical home system is derived from one phase of a three phase distribution line. When it gets to your home via a middle tapped transformer it is still single phase just like the one phase is was derived from. The U.S. three phase system is three sine waves 120 degrees apart. If what you said is true we could have a very interesting induction motor in our homes, but we don't. We have split phase motors depending upon a start winding and a run winding. As far as the topic at hand, you can build a bridge rectifier (four diodes) for the DC welder but another component that most DC transformer welders have is a reactor for ARC stability.

 

[Tig]

you could series the proper number of 12v batteries to smooth it out.....

Using batteries in a high current application like this sounds VERY dangerous. I would advise against it.