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I Forge Iron

Worth having 3 phase?

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I am setting up a shop at the moment that only has access to single phase. Is it wort h shelling out £300 for a converter and getting someone to wire it up or choosing kit that will run off the domestic supply? Is there a noticeable power drop when using a converter on things like drills and grinders? 



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First it is always prefered to have your equipment match your power lines.  Any converter will cost you to purchace, and to operate that converter, due to losses to heat in its operation, and the law of conservation of energy, nothing will ever be 100% efficient.  Some style converters can work a range of items up to their rated loads, other styles have to be matched to the load work exactally.


Second remember that Horsepower is a rating of work performed, so Horsepower is Horsepower, ignore the arm chair experts that state one form of electric motor HP is more than another,  it does not matter.  If you get a 50 HP single phase motor it will cost a lot more to purchase than a 3 phase 50 HP motor, but both will do the same amount of work, because work done is how Horsepower is determined, no matter if its electricial, wind or water powered.


Third, larger 3ph motors are less costly to purchase than their single phase counter parts, and electricial costs per Kwh are less for high usage customers on a 3 phase service than on a single,  but not all areas are wired for a full 3 phase connection, because installation costs for 3phase are higher for both the building and the lines in to the area, and most do not need what it offers enough to justify the added expence.



I hope I helped you to understand, rather than to only further confuse you.

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The deciding factor for me was the cost of 3ph equipment.  I now have 3 machines that came to me wired for 3ph.  By having a converter (I bought 30 hp of rotary converter)  I was able to save the cost and labor of converting the machines to 1ph.  Lots of old iron goes for cheap because it's 3ph, and people don't want to bother with it.  One other thing, 3ph motors are often cheap, because people can't run them.


Just my .02



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on a domestic supply you will be limited anyway, there are many converters out there ( I have maybe 50 in my shop, mostly awaiting new homes ), on a domestic socket in the uk you can run about 3hp and as steve says you wont get more out than you put in.

I use inverters for controlling 3 phase motors quite often and have them that take up to 45 amps per phase at 415 volts, I have large welders on 32 amp per phase and several plasma cutters.

you may be better off getting a 3 phase supply put in as then you can get lots of cheap machines though converting most is not hard when all you need to do is change the motor and modify the wiring to suit ( only do this if you know what you are doing or call in a qualified person )

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If you are "only" looking at a £300 phase converter, it's probably not worth doing 3-phase distribution wiring.


For the guys across the pond, I should point out that UK and European mains distribution are rather different to North American ones. Our domestic supplies are 230V single-phase to Neutral and we get one phase of a 400V phase-phase, 230V phase-Neutral distribution system. This means that the first stage in a UK phase converter needs to be a step-up transformer from 230V to 400V. After that, things are the same both sides of the pond (except the Voltage of course). The transformer is a big chunk of cost and £300 represents maybe a 3HP static.


If you've lucked into a 5HP, or larger, Rotary at £300, the wiring makes more sense.


For reasonably modern motors up to about 3HP (say 1970 onwards, maybe even the late '60s), you usually have 6 terminals in the motor and can run in Star (Wye) for 400V and Delta for 230V. These can be run in Delta from a 230V Variable Frequency Drive: single-phase in, 3-phase out and you get variable speed as a bonus.


The price for a new Chinese 2.2 kW VFD, buy-it-now on Ebay, has just dipped to £69.50 delivered (shipped from within the UK, so no import duties). I've played with 3 of them so far (I bought 2 myself and set one up for someone else) and they all worked perfectly.


If you are going to be messing around with your shop wiring, it's never a bad idea to have a nice meaty circuit with a 32A blue CEENORM socket on it and a 32A type "C" MCB feeding it, as it gives you somewhere to plug in welders, phase converters, etc, over 3 kW.

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