3 Phase For My Lathe From 240V; What Is The Best Way?

[workwright]

Hi in an earlier post on my Emcomat 17S I got a lot of excellent advice and help, Thanks!  I have now got to the next step - getting it to work.  A summary, the lathe is modern and is all wired internally and I do not wish to alter any of the machines wiring. It has a plug for 415V 3 phase fitted, the machine using L1 L2 L3 and PE.  By moving bridge strips in the lathe's electrical cabinet the machine will run on 230V 3~, 415V 3~, or 460V 3~. It is currently set up for 415V 3~.  I want a plug and play box rated to drive the 4HP main motor with the capacity to drive the integral suds pump ( about 1/2 HP).  It would also be nice to put a 415V main into the workshop since I have a couple of other machines powered from an old static converter. (the other machines are single voltage 415 3~)

It seems in the UK  there are three makers of rotary converters (one SMP seeming to be a bit more modern than the other two in its design) This would be the old fashioned way on doing it.  The other route seems to be a plug and play inverter but they all seem to have features that I do not want (soft start, variable speeds, jog etc) I can see this is useful if it is attached to a single machine but is not needed if one is going to use multiple machines.  The other important fact is the workshop has a 35A supply that would cost quite a lot to uprate since the workshop is a good 50m from the house consumer unit. Any advice is most appreciated, regards, workwright.

 

[workwright]

Hi, thanks for the reply. All the features of the lathe-  control gear,main motor,suds pump, lighting, is already wired to be able to work on any of the three voltages as in my intro post. You just alter the bridge positions in the electical cabinet.  It incorpoates a transformer in the cabinet.  THis is why I do not wish to alter or rewire anything that is already there.  The latest info I have got has raised a different problem.  My workshop is about 35m from the consumer unit in the house,and the supply to it is not thick enough wire to cope with the rotary converter I looked at.  ( it is 2.5mm, they suggested 4mm but safest would be to rewire with 6mm with a 32A breaker)  SO this is another expense not forseen.  A friend with a similar problem purchased a diesel suitcase  3phase generator which is very quiet.  However what capacity of generator would I need to start and run a lathe rated at (in manual) 3kVA total load 4HP motor.  A 5.6kW generator for example is about £200 less than the price of a 5kW rotary converter.  This new lathe is never going to be used much, it is much larger capacity than the bulk of the work I do.  Thanks any more info / advice very welcome.

 

[apprentice87]

Hi workwright,

Can i ask you the price of the rotary converter?? Why do you not do yourself a BIG favour and just ask the DNO what it would cost to fit you out with a proper three phase supply. It WILL be a LOT cheaper than you think...

Static converters are a load of crap by the way... You COULD though, just add an "idler motor" to yours and make it MUCH better. I built a home made rotary converter once from scratch, and it worked amazingly well too. You do realise that a rotary convert is just a static one with a motor connected to it?????? Could save yourself a LOT of money there.....

By the way, Transwave, [you know who they are] are seriously the most honest people you will EVER meet.

Many years ago, i was talking to them about buying one of their converters. I told them the price I had been quoted for the installation of "proper" 3 phase, and their reaction???

"I will stop you right there, if you can have true 3 phase installed for that price, you would be much better off doing that. Converters are just a solution to get you out of a corner NOT a replacement for the genuine thing"

Listen to what Canoeboy and no doubt Sidewinder tell you, as there is NO-ONE that will give you better advice than these two.

IF, you decide to go down the converter route, be guided by the nice [honest] people at transwave......

Myself?? proper three phase thanks... Was only £1200 about 4 years ago... [25meter run of cable, digging up the road, supplying the cable, ducting, meter box etc...] [Thanks WPD!!!]

john...

 

[Sidewinder]

To re-iterate john's advice.

GO 3ph IF YOU CAN!

I know Transwave as well, good bunch, seconded.

You need to be careful with generator sizing.

This isn't a CNC machine? Please remind us.

Your lathe will not perform as well or be as reliable on a generator or a converter as it will on "real" 3ph.

The thing with the voltages you listed is that you have none of them!

230V 3ph is "Japan".

415V 3ph is "Europe"

460V 3ph is "States side"

IIRC, and this is from memory sorry.

IF you swap the 3ph motor for a 1ph it will not give you the same torque output.

You will not get the torque speed curves on the spindle that the manufacturer quotes on their literature with a "common" generator, or a converter of any form, to get these you need "true" 3ph.

If you need a 34A supply over 50m and you need it reliable, a converter will rely on minimal volt drop to be efficient also, so I would be designing for max 3%.

I would not size the cable tight on 32A either as you will have other loads.

I would look at a 40, 50 or 63A supply.

Taking a 40A supply over 50m with 3% volt drop, which in my opinion would be required, not just for the converter, but, you would be running lights etc of this which require a max 3% VD on the circuit.

I am guessing an SWA cable, 70 deg rated, else you will need to ensure that the terminations either end are rated for 90 deg, very few are.

So IMHO to give you a sufficiently stiff supply, you would be looking at a 16mm sq cable to give you 40A @ 50m.

That is without considering the EFLI.

This would give you some margin for volt drop in your final circuits.

So your cable is going to be around £230, plus installation materials, plus installation, so around £1000 (ish) if you can do some of the work and find someone cheap to do the job, and that does not take into account any of the other potential issues that might need to be looked at.

The cable cost could easily jump to around £320, plus the other bits

However, with a 7,5kW main spindle motor IIRC< you would need a larger converter.

Checking, I would go with an 11kW, that's a 60A supply, (63A), working back that would be a 25mm sq cable cable circa £515 (very ish), plus install materials, plus installation. I would go for around £1800 + vat fitted if the install is perfectly straightforward, and there is nothing else needed, and you were within a short radius of my base, and if you did all the donkey work, so say £1500, plus the converter, plus, etc. etc.

Easily £3-4k including the vat.

For goodness sake check out the price of a 3ph supply.

 

[apprentice87]

Absolutely could not agree more....

With a "proper" supply you will be able to run welders, any machine you are able to get into your shed, and be FAR better off. All for a lot less money than you think. The DNO expect YOU to do all the design work, and fill in a form that will be VERY difficult for you to do. I have done TWO new supplies now, and avoided filling in the "not really applicable form" by sending all the info they require in a simple letter. If you want a price off the DNO, send me a message listing what you are installing and i will write the letter for you..

Please do not swap all your motors for single phase ones, as you will ruin your machines. Single phase motors are rough running unreliable crap, the cabling will cost you the earth [more current required] and the DNO hate them anyway.......

Another thing, do not forget, once you have a proper supply, it will increase the value of your property big time...

P.S. Never mind what vendors of inverters try to tell you, people like Canoeboy and Sidewinder, are doing industrial electrics like this every single day, and i mean huge industrial installations and hospitals and the like, they are the absolute TOP people at what they do..

john...

 

[Adrian41uk]

The thing with the voltages you listed is that you have none of them!

230V 3ph is "Japan".

415V 3ph is "Europe"

460V 3ph is "States side"

I agree with your points on not using a genny & the torque curves of a 3ph v 1ph motor ... but

Japan is 200V L-L, Brazil is 220V L-L

An inverter powered from 230V 1ph will produce 230V L-L 3ph (not 400V - they cant step-up the voltage) so the usual 'trick' is to reconfigure the motor from 400V star into 230V delta to use it with an inverter. The inverter controls the motor speed by altering the frequency of the 3 phase output.

 

[Sidewinder]

I agree with your points on not using a genny & the torque curves of a 3ph v 1ph motor ... but

Japan is 200V L-L, Brazil is 220V L-L

An inverter powered from 230V 1ph will produce 230V L-L 3ph (not 400V - they cant step-up the voltage) so the usual 'trick' is to reconfigure the motor from 400V star into 230V delta to use it with an inverter. The inverter controls the motor speed by altering the frequency of the 3 phase output.

Adrian,

I did say it was from memory, and the Japan is in quotes, I meant that to be that sort of Southern Hemisphere region.

The machine builder will have supplied this tapping for that market.

The tappings on machine tools do not always match the actual market voltages.

The changing of the motor is OK if it is a 230/400, but if it is a "400/690" you're goosed.

I am also more than aware of how inverters work!

I have been a field service & applications/design engineer for a manufacturer in the past.

However, others may not be so thanks for your input.

I have the dubious pleasure of working on a lot of "Japanese" machines in the UK with step down transformers, right PITA, IMHO.

 

[Marvo]

If you're looking at rotary converters then rather go with 3 of these configured to give a 3-phase output from a single phase input. They're not cheap but you get what you pay for, they'll also accommodate a large overload or start current for a few seconds. I've installed these in critical back-up and marine applications for several years and we've never had one fail. You'll still probably need to run a bigger single phase supply from your CU as well. 

 

[Sidewinder]

Marvo,

In the UK, I suspect a real 3ph supply would be cheaper!

 

[workwright]

Hi, thanks for all the comment , it is sort of helpful.  My local supplier SSE (Scotttish Hydro) have a ready reckoner for 3 Phase supplies. It prices my job at £1700+..The 3 phase line (post step down transformer) crosses my land and is 35m from the workshop.  So all I need is a pole and a 6m cable to terminate in the workshop.  There are two problems to this, one it is £700 more than I have to spend on what is an indulgence - I just wanted to preserve a beautiful example of precision engineering - a last gasp of a workshop world that is fast disappearing under the march of the machines (CAM) and rather than stuff it I wanted it to function.  It is not part of my business workshop that earns cash in my retirement years.(look up wrightscale on the web) The second problem was that the SSE estimate site defaults to "commercial property" as soon as you enter 3 phase...... We have been very careful to avoid this status by conducting our business within the various regulations to ensure our home is not a business property.  So I do not wish to bring any unnecessary hassle to my front door.

So my need is simple, get a 3kVA total load on 400V (nominal) 3 phase to operate.  It seems that the advice for me has been given. 1) Increase the cross section of the supply cable to at least 4mm, better still 6mm and (2) buy a 4kW (5HP max motor load) rotary converter from Transwave.  Like some of you I have had nothing but help from Transwave in the past. They supplied the static converter that has run (noisily) A Britan repitition lathe( main motor 2.5HP 2 speed instant reverse and a 1/2HP auxillary motor) for the last 25 years in the business workshop. (when it became a bit dodgy 5 years ago they diagnosed the problem over the phone. The replacement parts and instructions arrived the next day FOC. Thanks for advice, more is always helpful.  Regards.

 

[apprentice87]

Hi workwright,

You say about SSE and "commercial" Not sure what difference it would make.. I get the power itself from SWALEC, they are owned by SSE, and they class anything less than 35KVA as domestic anyway.

At £1700 though i would snap their arm off...

Had a look at your site... Wow!!!! brilliant stuff!!!!

john..