Used Lathe Pinnacle PL1340C Gap Bed

What you will have is as you say, a transformer fed from a single phase (2 wire) HV overhead line.

A common neutral but with 2 single phase 230v ( but could be up to 253v ) live supplies 180 degrees apart. You would expect somewhere in the range 440 to 500 volts between them.

Hello Robert,

I'm sure others on the forum know more about wiring to such a supply than I do.

But for what it is worth, since you do not have the third phase available with the supply arranged as it is, I suggest you run the lathe motor from the Transwave converter you have been offered, with that coupled to one of these two phases. In time, you may well want to run a second 3 phase machine, say a milling machine. You could then supply that from the same source. As a one man operation [I assume] you are very unlikely to be using power on both lathe and milling machine simultaneously.

The other phase can be used to supply a distributed load for lighting, heating and other power outlets within your workshop

Kind regards Brian

Edited By Brian Wood on 15/05/2020 09:15:55

My 3 HP Excel lathe runs from a Transwave static inverter and has done for 8 years. On odd occasions it sounds "Wrong" turning the inverter of for a while and restarting cures it. Talk to Transwave to see if it would run a two speed motor, I have my doubts.

Just spoken with transwave, they have said the static converter will run it, but it may not be all the speeds, or it may just run the motor on one speed and not the other, he also said if that doesnt work then put an idler motor between the static converter and the lathe, (which i can probably get used) and this would make the Lathe motor work as normal. so i think i will probably go for the static and try it out and see if it works.

Robert have you ascertained yet if the lathe is 2 speed?

Hi Ian,

Yes it is, there is a speed selector switch on the front down at the bottom, can see it on one of the Ebay photos.

So I have just looked at your pictures again. The motor is 3hp on high speed & 2hp on low speed. As long as the transwave is rated at 3hp you should be able to run both speeds. The motor will be probably dual wound. If so it only uses one set of windings at a time. So total input would never be more than 3hp. Hope that makes sense.

Steve.

Where does this supply come from ?

how do you get 2 phases 180 degrees apart?

Hello Ian,

It will be much the same as the supply we had by overhead cable in the Yorkshire Dales when we lived there. The cottage lower down had two phases installed to even the load at the local transformer. One of these was used to power storage heaters, the other was used for standard domestic supply.. Our supply was an extension of one of these phases..

The neutral was of course common to both our properties

There were bullocks in the field over which the supply was carried on the usual poles and with the usual behaviour exhibited by a bunch of young bullocks, they managed to fell one of the power poles. The neutral broke and was left thrashing about on the ground like a snake, shedding sparks as it did.

In the meantime, below us someone was using their oven to cook breakfast and we got the full interphase voltage of 440v through our supply, there being no neutral left coupled. I recall it did a lot of superficial damage to radios, lights and other appliances that could not handle the sudden voltage surge.

These would of course have been phases 120 degrees apart, not 180.

Regards Brian

Edited By Brian Wood on 16/05/2020 09:44:44

So was Stuarts post a typo about 180 degrees and 500v between phases rather than 415v ?

'Two-phase' confuses the wotsits out of me, maybe because it's become a terminological inexactitude!

The original 2-phase system was 90° out of phase, but it's almost completely obsolete. As far as I know, doesn't exist in the UK.

A second possibility is 'split phase', ie single phase on the transformer input, and a 'neutral' centre-tapped winding on the output creating two live wires 180° apart. This is like the US system delivering 110V and 220V to the same house. (I think.)

The third possibility is as Brian describes, two phases and neutral run from a distant three-phase system. The two phases would be 120° apart.

Most of UK distribution is straightforward 3-phase and single phase. Two phase seems reserved for remote premises. Most of the farms round here get true 3-phase, but the smaller ones and isolated groups of a few houses in the boondocks often have some sort of 2-phase arrangement. I've not found anything that explains how '2-phase' works, either 120° or 180°. Does anyone know which system, or it both, is used in the UK?

Dave

Ian and S.O.D,

I can only describe what happened in our case and I imagine the simplest way of setting up overhead supply as it was in our case would be a tapping off two phases in the village transformer. along with a neutral and run that on poles across the fields.

The sparking from the neutral where the broken cable was thrashing about in the field was quite impressive, it also attracted the attention of the stupid bullocks as you might imagine. It took a lot of arm waving to keep them off it.

Regards Brian

Hi, my younger brother (who lives in a town house) had two phases in his house when he bought it, the previous owners had panel heaters fitted and as Brian Wood has said, these were on one phase and all the rest of the house was on the other, he eventually had the second phase removed, as it was a higher standing charge and had proper C/H installed.

Most transformer type welders in industrial workshops are only wired across two phases out of three and where you get shops with two or more, they are usually balanced out over all three phases.

Regards Nick.

Edited By Nicholas Farr on 16/05/2020 11:40:49

I've been running my workshop off one of the converted 10 hp Plug & Play 440 volt output single to 3 phase VFD units from Drives Direct for the last decade or more.

Expensive but it does what it says on the tin. For all practical purposes its the same as having proper 3 phase from the electric company. Albeit with rather low maximum power rating.

Drives Direct say it can start motors up to 5 hp and run up to 10 hp in total. I've had 9 hp running off mine. Start rating is probably true off load but I'd consider 3 hp a more appropriate maximum if things have to run up on load like my Smart & Brown 1024 lathe does due to not having a clutch. I'd definitely want to run a reciprocating compressor up unloaded. My compressor is a Hydrovane and the box it doesn't even blink when that cuts in. Does just fine on the old 3 hp two speed motor fitted to my wartime P&W model B despite(?) the wonderfully steam punk, true to period, oil immersed contactor system.

I splashed out on the smoothing inductor set supplied for CNC use. Drives Direct said that was unnecessary if just running motors but I'm happier without sharp transients floating around the shop.

Despite having built several I don't care much for static converters. OK when they work but if they lay back their ears and decide not to co-operate they can be major league frustrating. Best thing to do with one is to make it a pseudo rotary by hanging a big pilot motor on it. Transwave rotary converters work well but they do like a nice stiff mains input supply. Especially if running close to nominal capacity.

If installing a Transwave I'd use 1/2 nominal capacity as the maximum single motor load rather than the book 2/3 rds. 90% of the time book will do just fine but if it doesn't sorting the issue can be major league frustrating for folk without the rather special equipment needed. Basically you need to monitor phase current and relative shift as well as voltage and understand exactly how things interact. Easier to just over-rate a bit.

The last Transwave I had issues with would start, not start or run at half speed the motor on a hydrovane pretty much at random. Everything else in the workshop had run just fine right from first installation ten years back. Wired in, hit the switch and everything worked just like that. Couldn't have been easier. Re-wiring the supply back to the incomer with heavier cables almost sorted it but it still occasionally glitched and decided to run the compressor at half speed. Sorted with an inverter in the end. Totally idiot thing was that that particular compressor had been run just fine for several years via an identical Transwave rotary converter box in another workshop.

Bottom line with converters or plug'n play VFD boxes is don't shave the margins. Choose a decent brand, like Transwave,or known to be reliable supplier and buy a bit of extra margin so its certain to work even if your supply and set-up is less than ideal. I'd be chary of lower end offerings from folk like Machine Mart. Ordinary VFD boxes of decent brand seem to be bulletproof if rated power is the same as the motor tho' but they can't cope with two speed motors.

Clive

No, it wasn’t a typo. The split phase arrangement is used in some rural areas in the U.K. where there is only a single phase (2 wire) HV 11kV or 6.6kV overhead network available. It is now considered to be non-standard and only used when there is no alternative. For normal single phase supplies, a standard single phase transformer is used with a phase and either separate neutral and earth conductors or a combined neutral/earth conductor.

With a split phase network, a transformer with a single HV winding and either a centre tapped secondary winding or two separate windings connected as below:-

The neutral is common, but the two phases are 180 degrees apart. So between each phase and neutral you get a nominal 230v (actually up to 253 v depending on transformer tapping and voltage drops etc). Between the two phases you will get double this. In a single property, you could have say storage heaters on one and the rest of the house on the other ( with 2 consumer units).

In this case, running the workshop (with a single phase to 3 phase converter for the lathe) from one supply and rest of the property from the other.

Obviously in all cases needs there to be separation and labelling so that anyone doing work understands that there could be up to 500 volts between items on the 2 supplies.

Stuart

What Stuart says make sense. But the OP thinks he has something different, as he talks about the transformer taking two phases from the overhead? The voltage readings he gives for phase to neutral and phase to phase on the outpur don't seem to make sense for 2 phases of a 3-phase system or for the configuration elucidated by Stuart. May be it's a one off special?

Andrew

Quotes from the OP:-

‘The 2 phases are coming in from a "split phase" transformer, taking the two phases from overhead, putting a meter across the two reads 445v, and each phase to neutral is 239. that is what i have, so any suggestions would be greatly appreciated.’ and ‘Just to say, the DNO people said when they were installing the power cable that it was a 2 phase supply, split 180 degrees apart on a center tapped transformer. hope thats of some help?’

Andrew

This is what I would expect with a split phase supply. Depending on the network voltage drops and loads, you could get anything from about 220v to 250v on each and 440v to 500v between the two. The discrepancy in each phase to neutral and between the two could be because the load and therefore voltage drops changed between readings or one of the phases has a higher load than the other because of other properties connected to the same transformer.

Stuart

Edited By Stuart Smith 5 on 16/05/2020 16:31:24

Robert lives in the Shetlands so guess that transformer type would be possible. Not the sort of thing you would find on a housing estate.

Steve.

I do not think i have anything different, i have a 2 phase (Split Phase) supply from a center tapped transformer, the workshop is out in the rural part of shetland and no 3 phase overhead.

Just tested the voltages again, not sure if i got a duff reading the other day or was there a voltage drop at the time, but what i have now is 241 phase to neutral and 480v phase to phase.

A question for all of you, have any of you ever heard of the Unique 3 Phase system, an american guy with another take on the 3 phase conversion using a transformer and capacitors, (dont really know fully how it works but looks interesting)

Thanks
Robert

Stuart

so both phases are 180 degrees apart?

or in phase?

I can understand that both are at 240v relative to neutral

and 2x 240 =480 live to live but surely they will still be in phase