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Welding
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Catweazle



Joined: 17 Feb 2008
Posts: 2602
Location: Little England, over the hills

PostPosted: Fri Oct 19, 2012 6:25 pm    Post subject: Reply with quote

stevecook172001 wrote:
Catweazle wrote:
stevecook172001 wrote:
Would simultaneously winding three, identical, single-core, 30-amp wires exactly the same number of turns on the secondary side and then connecting their respective ends as they came out of the secondary, thus presumably combining their output, produce the same voltage/amperage output (combined) as using one single core 90 amp wire? .


That would be fine, there is no need to use single cored wire in the transformer, you could use heavy stranded wire if you like.
Ah yes, I know about using stranded wire as opposed to using solid core Cat. What I am referring to is taking 3 independent, insulated, 30-amp wires of identical resistance and winding them simultaneously and then joining their respective ends (positive to positive and negative to negative) when they came out of the secondary. Assuming that they were wound to produce 40 volts and (given the total wattage) the total amperage available was, say, 90 then I am assuming that each of the 3 individual wires would pick up 30 amps each on the winding, which would then be recombined when they came out of the secondary to produce a combined amperage reading of 90 amps.


That would be fine, electrically no different to using stranded wire.
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Little John



Joined: 08 Mar 2008
Posts: 8500
Location: UK

PostPosted: Fri Oct 19, 2012 6:52 pm    Post subject: Reply with quote

Catweazle wrote:
stevecook172001 wrote:
Catweazle wrote:
stevecook172001 wrote:
Would simultaneously winding three, identical, single-core, 30-amp wires exactly the same number of turns on the secondary side and then connecting their respective ends as they came out of the secondary, thus presumably combining their output, produce the same voltage/amperage output (combined) as using one single core 90 amp wire? .


That would be fine, there is no need to use single cored wire in the transformer, you could use heavy stranded wire if you like.
Ah yes, I know about using stranded wire as opposed to using solid core Cat. What I am referring to is taking 3 independent, insulated, 30-amp wires of identical resistance and winding them simultaneously and then joining their respective ends (positive to positive and negative to negative) when they came out of the secondary. Assuming that they were wound to produce 40 volts and (given the total wattage) the total amperage available was, say, 90 then I am assuming that each of the 3 individual wires would pick up 30 amps each on the winding, which would then be recombined when they came out of the secondary to produce a combined amperage reading of 90 amps.


That would be fine, electrically no different to using stranded wire.
Excellent, that's what I thought. It would save the significant expense of a single, heavy-gauge wire for the transformer secondaries.

I should reiterate, this is just as mental exercise really. I already have a 180 amp ac oil welder and Aldi and the like sell 160 amp ac welders brand new for about 40 quid!

Just one final thought though. A single one of those site-transformers would make a cracking spot welder!


Last edited by Little John on Fri Oct 19, 2012 9:04 pm; edited 2 times in total
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JavaScriptDonkey



Joined: 02 Jun 2011
Posts: 1683
Location: SE England

PostPosted: Fri Oct 19, 2012 7:49 pm    Post subject: Reply with quote

stevecook172001 wrote:
Ah yes, I know about using stranded wire as opposed to using solid core Cat. What I am referring to is taking 3 independent, insulated, 30-amp wires of identical resistance and winding them simultaneously and then joining their respective ends (positive to positive and negative to negative) when they came out of the secondary. Assuming that they were wound to produce 40 volts and (given the total wattage) the total amperage available was, say, 90 then I am assuming that each of the 3 individual wires would pick up 30 amps each on the winding, which would then be recombined when they came out of the secondary to produce a combined amperage reading of 90 amps.


I'm not sure I followed you there.

If you take 3 independent transformers and try to combine the outputs things will probably end badly. You'd need to also join all 3 return paths otherwise there'd be no circuit but that might allow 90A to flow through your entire circuit, overheating the coils and melting the insulation between windings and core.

As we're talking AC then there's also the question of phasing to consider - will the sine wave outputs of the coils match?
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adam2
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PostPosted: Fri Oct 19, 2012 8:26 pm    Post subject: Reply with quote

3 wires each designed for 30 amps cant carry a total of 90 amps if twisted together or otherwise in close proximity.
They will overheat since the heat can not escape as readily as from a single wire.

High current transformer windings sometimes consist of more than one wire, but that is because it is easier to handle say 3 wires each of 25mm rather than one of 75mm.
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Little John



Joined: 08 Mar 2008
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PostPosted: Fri Oct 19, 2012 8:57 pm    Post subject: Reply with quote

adam2 wrote:
3 wires each designed for 30 amps cant carry a total of 90 amps if twisted together or otherwise in close proximity.
They will overheat since the heat can not escape as readily as from a single wire.

High current transformer windings sometimes consist of more than one wire, but that is because it is easier to handle say 3 wires each of 25mm rather than one of 75mm.
OK that makes some sense to me. I guess the only way to test that out is on a single transformer with a variety of thicknesses of wire. In other words, if all of the 3 wires were individually well in excess of the rating needed for a third of the total amperage (but each still significantly short of the total rating of 90 amps) , then that might sufficiently mitigate the effect you are talking about. Then, again, maybe it wouldn't.
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Little John



Joined: 08 Mar 2008
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Location: UK

PostPosted: Fri Oct 19, 2012 9:01 pm    Post subject: Reply with quote

JavaScriptDonkey wrote:
stevecook172001 wrote:
Ah yes, I know about using stranded wire as opposed to using solid core Cat. What I am referring to is taking 3 independent, insulated, 30-amp wires of identical resistance and winding them simultaneously and then joining their respective ends (positive to positive and negative to negative) when they came out of the secondary. Assuming that they were wound to produce 40 volts and (given the total wattage) the total amperage available was, say, 90 then I am assuming that each of the 3 individual wires would pick up 30 amps each on the winding, which would then be recombined when they came out of the secondary to produce a combined amperage reading of 90 amps.


I'm not sure I followed you there.

If you take 3 independent transformers and try to combine the outputs things will probably end badly. You'd need to also join all 3 return paths otherwise there'd be no circuit but that might allow 90A to flow through your entire circuit, overheating the coils and melting the insulation between windings and core.

As we're talking AC then there's also the question of phasing to consider - will the sine wave outputs of the coils match?
Youíve misunderstood what I was saying JSD
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Catweazle



Joined: 17 Feb 2008
Posts: 2602
Location: Little England, over the hills

PostPosted: Sat Oct 20, 2012 9:28 am    Post subject: Reply with quote

The three wires will have a greater surface area than one wire, so should run cooler. Also, the greater surface area of the conductors will increase the skin effect, enabling the same sized copper to carry more current.
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adam2
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PostPosted: Thu Oct 15, 2020 5:35 pm    Post subject: Reply with quote

My basic welding skills have been called on today. To repair the frame of a mobile home that came apart whilst it was being moved.

Used a piece of angle iron from an old metal bed frame, welded in place across the broken part.

I would not trust such a basic repair for future road movement, but the intention is to scrap the mobile home after short term static use. It only cost £800.
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