3 phase or single (230v) phase

[The Artilleryman]

Which is best & why?

I've got 3 phase and 16A single phase but am unsure which is best - given the same max current output.

I'm erring towards a Murex Tradesmig, but unsure whether to get the 251 or 280-3, if anybody has experience of these machines, I'd be grateful for info.

 

[piman]

Hello The Artillaryman,

a three phase sixteen amp supply has nearly twice the power of a sixteen amp single phase supply..

I can't comment on the machines though.

Alec

 

[frank horton]

using 3phase on welder that can use both voltages, they always a better feel...to me anyway....
where ever poss I always use 3phase....even the bench grinder....

 

[DennisCA]

Hello The Artillaryman,

a three phase sixteen amp supply has nearly twice the power of a sixteen amp single phase supply..

I can't comment on the machines though.

Alec

Wouldn't it have at least three times the power since it's three 16A supplies?

 

[Munkul]

Wouldn't it have at least three times the power since it's three 16A supplies?

Yes, it's nearly 3 times... not quite though.

Working out power from 3 phase current is hard work, I use a calculator like this

https://www.rapidtables.com/calc/electric/Amp_to_kW_Calculator.html

Anyways, MIG welding is DC current, and 3 phase is easier to rectify to smooth DC current, than single phase is. Also, because of the industrial level power input, 3 phase machines are generally built for industrial use, not hobby use. Heavier transformers with better duty cycle, beefier wire feeders, etc.

That's why in general, 3 phase MIGs are regarded as simply "better". Not always, but in general
If I were given the choice, I'd always go 3 phase for a MIG. Always.

 

[eddie49]

I second everything that Munkul has written.
Since a 3-phase supply has three AC waveforms 120 degrees apart, when this is full-wave rectified to DC the output waveform has six peaks in a full 360-degree cycle at 50Hz, rather than two. The unsmoothed DC output has 6 peaks, running at 6 times the frequency of the AC input, rather than 2 peaks at twice the frequency. Thus after simple rectification, the output of a 3-phase welder is a much smoother DC that that of a single-phase welder. So 3-phase welders do not need capacitors to smooth the output.
Since they were built for professional/industrial use, 3-phase welders are going to be of inherently higher quality that typical DIY/hobby single-phase machines. Additionally, due to the limited availability of 3-phase power, on the second-hand market 3-phase welders will be cheaper.

 

[armalites]

If you've got 3ph then a 3ph welder is a no brainer. You open up the upper power levels and can be bought cheaply second hand.

This isn't too far from you and there may be a deal to be done.

https://www.ebay.co.uk/itm/Lincoln-...c4e9:g:ndoAAOSwLApdrYMr&LH_ItemCondition=3000

 

[piman]

Hello Dennis,

no, the phase relationship gives a 1.732 (Square root of three) power .

Three phase power is root three x volts x amps x power factor.

Alec

 

[DennisCA]

It seems to me that for most practical purposes, you get more than 2x the power out of a 3 phase connection though, but I guess the factor I am thinking of is that the 3 phase connection can run at 400 volts instead of 230 V. Or 240/415 in the UK.

 

[Munkul]

It seems to me that for most practical purposes, you get more than 2x the power out of a 3 phase connection though, but I guess the factor I am thinking of is that the 3 phase connection can run at 400 volts instead of 230 V. Or 240/415 in the UK.

Yes, that's my understanding? Please correct me if I'm wrong.
We're comparing one single 240v line-to-neutral supply, to 3 phases of 415v line-to-line.

If it was 1.732 times, then this calculator is wrong

https://www.rapidtables.com/calc/electric/Amp_to_kW_Calculator.html

EDIT: 1.7x applies when you compare alike line voltages. With UK supply, we have 3 lines of 240v-to-neutral, but 415v line-to-line. So 2 phases give 1 / 1.732 of the output of all 3 phases.

 

[DennisCA]

Yes that's how I understand it as well, though there are some 3 phase systems which only put out 230V phase to phase, Norway at least does that, for some reason. And VFDs running on 230V as well.

 

[Bond]

I'm a hobby welder doing rusty cars and light fabrication, doors, gates etc... I've used a 30 year old single phase Cebora and a similar aged Sealey Supermig 180-1 and got reasonable results.

First time using a borrowed similar age Migatronic 3 phase and I was blown away by the improvement in my welds with no change to my technique, using my own gas and wire. I think a combination of the technical reasons of 3 phase eddie says above plus the better build quality of these industrial machines.

Now I have a 3 phase Murex Transmig 253 not sure how old maybe 20ish years old? Superb. Wire feed motor is the size of a coffee jar and has 2x feed rollers, it really is a proper machine.

Only downside is the physical size, my Murex has a wire feed unit mounted on top but even the bottom power unit is twice the size of my little Sealey. Wasn't really apparent until I got the Murex home and had them side by side!

Based on my experience I would without a doubt get a 3 phase machine if you are able to, whatever you are welding I think you will find it much easier.

 

[mtt.tr]

Yes, it's nearly 3 times... not quite though.

Working out power from 3 phase current is hard work, I use a calculator like this

https://www.rapidtables.com/calc/electric/Amp_to_kW_Calculator.html

Anyways, MIG welding is DC current, and 3 phase is easier to rectify to smooth DC current, than single phase is. Also, because of the industrial level power input, 3 phase machines are generally built for industrial use, not hobby use. Heavier transformers with better duty cycle, beefier wire feeders, etc.

That's why in general, 3 phase MIGs are regarded as simply "better". Not always, but in general
If I were given the choice, I'd always go 3 phase for a MIG. Always.

Sqrt of 3

But you can pull 16a per phase

 

[hobby_machinist]

I was wondering something about three phase breakers, the new automatic one that you can reset when they go out. Lets say its 16a, does that mean i can pull 16a from each phase, in total 48a, or 16a from all three phases together so 5.33a per pahase, or if im using only two that means it trips at 8a per phase load?

 

[mtt.tr]

I was wondering something about three phase breakers, the new automatic one that you can reset when they go out. Lets say its 16a, does that mean i can pull 16a from each phase, in total 48a, or 16a from all three phases together so 5.33a per pahase, or if im using only two that means it trips at 8a per phase load?

16 amp per phase but being 120 degrees apart you will only achieve (16*3 )/sqrt3 the same reason 3 phase voltage is not 230*3

 

[matt1978]

Yes that's how I understand it as well, though there are some 3 phase systems which only put out 230V phase to phase, Norway at least does that, for some reason. And VFDs running on 230V as well.

Yes it’s the same in some parts of Belgium where they have conventional 1ph 230v but also 3ph 230v and then conventional 3ph 400v.

 

[The Artilleryman]

UK voltages are :- 400v 3 phase, 230v single phase. Have been for many years - nothing has changed other than the tolerances the generators are allowed -5% to + 10%. Last time I put the MFT on the house feed I got 238V.
The supply cable in the street is 400v 3 phase, each individual property is supplied by 1 phase and neutral - 400v /sqrt 3 = 230v

 

[Barking Mat]

3 phase rocks. If you've got the choice to for it.

 

[The Artilleryman]

If you've got 3ph then a 3ph welder is a no brainer. You open up the upper power levels and can be bought cheaply second hand.

This isn't too far from you and there may be a deal to be done.

https://www.ebay.co.uk/itm/Lincoln-Electric-Powertec-305C-Compact-MIG-Welder-300amp-3-Phase-400v-Machine/233375778025?hash=item365647c4e9:g:ndoAAOSwLApdrYMr&LH_ItemCondition=3000

Not sure it will go low enough for occasional thin work, will be playing around with 1mm tomorrow night at college with a tradesmig 280-3 to see what it will do.

Most of my hobby work will be 3mm to 5mm with some 8mm.

Cannot be bothered with trying to mig with cheap poorly built chinese crap at my age.