The secondary sees DC which saturates the transformer.Except that you'd normally transform first then rectify so the transformer sees the full mains cycle.
Jack
The secondary sees DC which saturates the transformer.Except that you'd normally transform first then rectify so the transformer sees the full mains cycle.
Hmmm, okay. Big gap in my transformer knowledge, hence the query on your answer. So what would it take to reverse the magnetic flux in the secondary - a suitable resistor (and diode so it only works in one direction)?Which part?
A half wave rectifier results in current flowing only in one direction in the transformer secondary. This produces a unidirectional magnetic flux in the transformer which will saturate it. Transformers are normally designed to have a net flux of zero.
If the transformer saturates, the coupling between the primary and the secondary drops. This results in, inter alia:
1 The input impedance of the transformer drops (so more mains current) and
2. Less output current.
Both are a direct result of the loss of coupling between the primary and the secondary windings.
There will be less output because of the half wave rectifier (wasted half cycle) but the reduction I am talking about is in addition to that.
If that doesn't answer your question, please be more specific.
Jack
Half wave supply comes from allowing only half the AC cycle to pass through.Electrical stuff is beyond me.. but..
Looking at what modern inverters can already do with the input like adjust automatically between 110v-440v, single or 3phase,
And at what they can do with the output,
Square wave, sine wave, tri wave,
Output frequency from 20-400hz,
ac balance adjustment and so on...
I would think that using only half wave rectification and generating an output that you could weld (fairly well with) would certainly be possible.
I can't see any reason why you would do this though?
My understanding of the electrical supply to my shed is that I wold either have the full waveform available or I'd have a power cut and nothing at all available?
Where do you get a half wave supply from?
One leg of 3ph to neutral?
A partially broken generator?
Half wave rectification outputs a pulsing DC current at the supply frequency (50 Hz) whereas full wave rectification outputs at double the supply frequency (100 Hz). I make no claim regarding the relative merits of either method for welding (I'm still using an AC buzz box) but if you need a smoothed DC output, full wave rectification is preferred. From what @Jack Ryan has suggested, there may also be some benefits regarding the effect on the transformer.Are there any situations when you may only have a half wave supply available and might need to run a welder from it?
Or is this just a theoretical discussion?
There needs to be a full wave rectifier so that each half cycle's magnetic flux averages to zero.Hmmm, okay. Big gap in my transformer knowledge, hence the query on your answer. So what would it take to reverse the magnetic flux in the secondary - a suitable resistor (and diode so it only works in one direction)?
Bigger transformers generally require more DC current to saturate them but the transformer in use is designed for the welding current of the machine it is used in. Unless an oversized transformer is used, it will saturate and transformer size is the biggest issue/cost/weight with (transformer) welding machines.And, does the size of the transformer have an influence - like, bigger transformer, less saturation?
If this is correct you could easily then see a low amps pulsed positive (or negative) half cycle welder suitable for welding thin metal.
My one off attempt at tig weling a thin coffee mug failed miserably until I tried pulsed dc - wow, what a difference!
Generally a half wave rectifier in a welding machine is the result of a broken full wave rectifier.Are there any situations when you may only have a half wave supply available and might need to run a welder from it?
Or is this just a theoretical discussion?
There needs to be a full wave rectifier so that each half cycle's magnetic flux averages to zero.Hmmm, okay. Big gap in my transformer knowledge, hence the query on your answer. So what would it take to reverse the magnetic flux in the secondary - a suitable resistor (and diode so it only works in one direction)?
The rectifier diode prevents DC from feeding directly back to the transformer directly, so the secondary doesn't "see" any DC as such. It just has to grunt every other half cycle. This results in an asymmetric load presented by the primary, because the secondary only has to do work during one half cycle, and this makes the incoming mains slightly asymmetric, making it behave as if there is a slight DC bias.The secondary sees DC which saturates the transformer.
Jack
Just for completeness, it is possible to build a full wave rectifier using just 2 diodes if the transformer is centre tapped. However, I doubt that will apply in this situation.You didn't answer the question
There needs to be a full wave rectifier so that each half cycle's magnetic flux averages to zero.
So could this be done with a diode resistor? Yes wasteful, as would be having an oversized transformer, but that's a secondary issue, especially if it's an experimental lashup, or even poor man's tig.
Yes.Just for completeness, it is possible to build a full wave rectifier using just 2 diodes if the transformer is centre tapped. However, I doubt that will apply in this situation.
Two Diode Full Wave Rectifier Circuit » Electronics Notes
A two diode version of a full wave rectifier circuit can be usefully used on a number of occasions to make use of both halves of an alternating waveform.www.electronics-notes.com
Still never answered the questionJust for completeness, it is possible to build a full wave rectifier using just 2 diodes if the transformer is centre tapped. However, I doubt that will apply in this situation.
Two Diode Full Wave Rectifier Circuit » Electronics Notes
A two diode version of a full wave rectifier circuit can be usefully used on a number of occasions to make use of both halves of an alternating waveform.www.electronics-notes.com
That is the question.Errm, que? Who didn't answer the question?
A single diode causes current to flow in one direction, this results in an average DC current which may saturate the transformer.The rectifier diode prevents DC from feeding directly back to the transformer directly, so the secondary doesn't "see" any DC as such. It just has to grunt every other half cycle. This results in an asymmetric load presented by the primary, because the secondary only has to do work during one half cycle, and this makes the incoming mains slightly asymmetric, making it behave as if there is a slight DC bias.
You didn't answer the question
There needs to be a full wave rectifier so that each half cycle's magnetic flux averages to zero.
So could this be done with a diode resistor? Yes wasteful, as would be having an oversized transformer, but that's a secondary issue, especially if it's an experimental lashup, or even poor man's tig.