Two Idlers, Star/Delta

Hopefuldave · May 16, 2017

I saw an interesting transformerless 240 - 415v convertor diagram at http://www.mig-welding.co.uk/forum/threads/rotary-phase-converter-plans.32135/#post-350783, and I'm thinking I may try this for my shop, but 240-Delta/415-star motors over 4HP/3KW are rare as rocking-horse droppings in the UK: I've also seen RPCs with two or more motors (where the first acts as RPC to get the second rotating) - presuming I can put enough interlocks in to prevent the motors running at different voltages (one star, the other delta) and tune each with its own balancing capacitors, am I going to run into Big Problems? My assumption is that the motors won't need to be mechanically linked, although that could make the second draw a lot less current when first powered up?

An example of this convertor's shown at 23 Volts 1 phase to 4 Volts 3 phase rotary converter - YouTube - it seems to work, at least a single-motor version...

Any thoughts?

Dave H. (the other one)

9100 · May 16, 2017

Unless you have a passion for close up views of terminal strips and mumbled narrative, what's the point? He shows diagrams of two motor connections but nothing about how to convert one voltage to another. You can make a nine wire motor output double the input voltage but a motor cannot be simultaneously connected in star and delta.

Bill

Hopefuldave · May 16, 2017

Firstly, 9-wire motors don't exist anywhere but north America, the civilised world uses 6-wire star-delta (my location's a Clue);
Second if you'd read the guy's post and can read a schematic he's not running a motor in both at once, but switching between once up to speed - as shown also in the other guy's video if one pays attention. I'll allow the "mumbled narrative", but English may be his second (or third, fourth) language, far better than my (guessing) Dutch or Swedish...

Anyway, it's an interesting and inventive circuit, constructive comments would be nice, like what are the pitfalls of running paired motors in an RPC?

Dave H. (the other one)

9100 · May 16, 2017

Hopefuldave said:
Firstly, 9-wire motors don't exist anywhere but north America, the civilised world uses 6-wire star-delta (my location's a Clue);
Second if you'd read the guy's post and can read a schematic he's not running a motor in both at once, but switching between once up to speed - as shown also in the other guy's video if one pays attention. I'll allow the "mumbled narrative", but English may be his second (or third, fourth) language, far better than my (guessing) Dutch or Swedish...

Anyway, it's an interesting and inventive circuit, constructive comments would be nice, like what are the pitfalls of running paired motors in an RPC?

Dave H. (the other one)

As far as running multiple motors in an RPC, that is what you are doing when you run shop equipment. Whether the motor is in a box or running a spindle, it still contributes to generating the third phase. I used to run on a Rotophase converter that was rated at 12 hp but starting only 4 hp at a time. I had a 7 1/2 hp drive that I started on it by having everything else in the shop running with no loads so their motors contributed to balancing the phases.

Once again, how is that setup boosting 230 V to 400? All I see is long rambling explanations of how to configure a motor for one voltage or another. If you have 230 V single phase, you can generate 230 V three phase. If you have 400 V single phase, you can make 400 V three phase. If you have 230 V single phase, how do you generate 400 V three phase?

Bill

Hopefuldave · May 16, 2017

If you look at the schematics, it switches between delta with 240 across one side of the triangle and star with 240 between star centre point and one arm - both config's apply 240 across one winding, but in star the induced (generated) voltages in the other two windings (if at 120* and an equal 240v, subject to balance caps etc.) give 415 across the "points" of the star winding pairs - as the guy's meters show pretty clearly. If it were possible to get to a neutral on a delta winding, the phases would measure about 138v to neutral with 240 across each side of the triangle.

It's pretty much how a star-delta motor winding works, not at all like USAnian 9-wire which effectively puts two 220v star windings either in parallel (220v) or series (440v)- this is why rest-of-world motor voltages are root3:1 not 2:1. I could do the Jommetry if you like, it was part of my tech' education quite a few years ago, but it stuck with me...

Re multiple motors, that's what I though - they'll "synchronise" (almost, ignoring slip) and act as a single motor as far as phase conversion goes.

Do I have a passion for terminal strips? well... My lathe's main electrical panel:

Thanks,
Dave H. (the other one)

Monarchist · May 16, 2017

9100 said:
Once again, how is that setup boosting 230 V to 400? All I see is long rambling explanations of how to configure a motor for one voltage or another. If you have 230 V single phase, you can generate 230 V three phase. If you have 400 V single phase, you can make 400 V three phase. If you have 230 V single phase, how do you generate 400 V three phase?

Bill

Substitute our more-common US-turf, 230/240 and 460/480 windings, and ISTR that sometime in the past four or five years - if, in fact, memory does serve - you actually dallied with a similar concept yourself, did you not?

Can it work? Seems so .... after one fashion or another.

Is it good choice? Personally, I'd have to pass.

With a 240 VAC 10 HP Phase-Craft + Weg RPC and a 15 kVA R.E. Uptegraff Delta-Delta 230-480 multi-tap transformer?

I just haven't had to concern meself with that.

I would observe that if this were as easy, efficient, reliable, and trouble-free as either RPC ==> 3-P transformer, or 1-P transformer ==> RPC, there would have been diagrams and examples all over three, if not more, continents, and for a Very Long Time Already.

The need was not uncommon.

The 'technology' of it didn't need to await even the invention of the Vacuum tube, let alone transistors, IC's, the internet, nor You Tube videos.

Not much there but ignorant Iron-alloy and Copper wire. 1800's technology, not rocket insemination.

'Common use over long years' seems very much not the case, so I cannot get all that excited about it, now, as what may be nought but the classical 'parlour trick'.

Clever enough. Even 'interesting'.

Also borderline useless, 'real world' application.

JM2CW

Hopefuldave · May 16, 2017

Unlikely you'd find a 240v motor over 3KW/4HP in Europe, anything above will be 415v (delta) or higher (star), this is NOT America!

I have a couple of small (1/2 - 1 HP) star/delta motors kicking about, no harm in a bit of experimentation before I empty my wallet for a couple or more *available in the UK, Europe and the rest of the world* 3KW motors to build around...

Dave H. (the other one)

Monarchist · May 16, 2017

Hopefuldave said:
Unlikely you'd find a 240v motor over 3KW/4HP in Europe, anything above will be 415v (delta) or higher (star), this is NOT America!

I have a couple of small (1/2 - 1 HP) star/delta motors kicking about, no harm in a bit of experimentation before I empty my wallet for a couple or more *available in the UK, Europe and the rest of the world* 3KW motors to build around...

Dave H. (the other one)

Doesn't matter a wit what a hobbyist/experimenter can 'find'.

The Physics are the same everywhere on THIS planet, and seem to even be holding at least to well beyond the orbit of Pluto.

The major and minor makers of motors, transformers, and 'cousins' have known enough about wires and core material for close-on 200 years to craft any sort of specialized gadgetry they could find a commercial market for.

Three-phase became an early "winner" over 1, 2, 4, 5, 6..12 phase partly because it delivered the greatest actually USEFUL gain for the fewest transmission conductors and least practical device complexity - source-end, consumption-end, transmission and switchgear in between.

Crafting 'custom', optimized, idlers for shifting voltage has few barriers to those who could make motors by the brazillians as early as the end of the 1800's.

How many such low-voltage in, high-voltage out - or the reverse - devices even exist as RPC's in the market - or ever have?

This isn't even electricity 101. It is grocery store 'rithmetic 101.

JST · May 16, 2017

Yes, a star mootor, powered by a single voltage between one line and neutral, CAN work.

It does not work particularly well, if my testing of the system is anything to go on.

The "idler" has to supply 2/3 of the load motor power, instead of 1/3, so for equal load motors, you need roughly double the idler size that is needed for the "standard" setup. All that 2/3 power must come in through a winding sized for 1/3 of the idler power. So right away you can guess the idler needs to be roughly double the load motor, in order that 1/3 of idler power is 2/3 of load power.

Then you consider that the idler consumes some current as well (usually about 40% of FLA just at idle), and you can estimate that you want an idler about 3x the load motor, instead of the usual 1 1/2 x.

Monarchist · May 16, 2017

JST said:
Yes, a star mootor, powered by a single voltage between one line and neutral, CAN work.

It does not work particularly well, if my testing of the system is anything to go on.

The "idler" has to supply 2/3 of the load motor power, instead of 1/3, so for equal load motors, you need roughly double the idler size that is needed for the "standard" setup. All that 2/3 power must come in through a winding sized for 1/3 of the idler power. So right away you can guess the idler needs to be roughly double the load motor, in order that 1/3 of idler power is 2/3 of load power.

Then you consider that the idler consumes some current as well (usually about 40% of FLA just at idle), and you can estimate that you want an idler about 3x the load motor, instead of the usual 1 1/2 x.

There ya go. That damned 'rithmetic!

Even so.. it 'just might' end up with lower mass than RPC idler + transformer..

But mass vs efficiency is not likely to be a design choice, as need of RPC in hang gliders or light aircraft seems to be essentially 'invisible'.

FWIW-not-much department:

Overall losses probably put the end-to-end efficiency at or even BELOW that of a 1-P motor driving a 3-P alternator 'head' that HAS NO dodgy, weak-kneed 'generated leg', and at least can deliver 100% 'nameplate' worth of 'true' 3-P, properly sized.

Those are not common, either, so vanilla RPC works pretty well, even if one is but a statistician, not ingineer.

JST · May 16, 2017

Saw one of those 1P-3P generator setups at a motor shop that was closing up. If I had had any sense, I'd have bought it, but at that time I didn't need to make any 3 phase, so I didn't.

It looked really heavy too, and it was in the cellar.

Monarchist · May 16, 2017

JST said:
Saw one of those 1P-3P generator setups at a motor shop that was closing up. If I had had any sense, I'd have bought it, but at that time I didn't need to make any 3 phase, so I didn't.

It looked really heavy too, and it was in the cellar.

Far better way to test their work to its nameplated limits than an RPC.

Otherwise hardly worth the extra losses and space needed, but yeah. You do bit of R&D as well, IIRC.

beckerkumm · May 16, 2017

Phase Perfect makes an all in one unit to go from 240 single phase to 480 three phase. I don't remember the cost other than too high to interest me. Dave

Monarchist · May 16, 2017

beckerkumm said:
Phase Perfect makes an all in one unit to go from 240 single phase to 480 three phase. I don't remember the cost other than too high to interest me. Dave

All 'niche market' stuff, recycled salvage Franken-wired or even that particular Phase-Perfect.

Utility guru's, larger facility experience, just look at Joe Smallholder as if he were somehow reading-challenged, even retarded.

You want 480 3-P, you order 480 3-P. Need higher voltages? Got those, too.

Where's the problem?

johansen · May 16, 2017

JST said:
Yes, a star mootor, powered by a single voltage between one line and neutral, CAN work.

It does not work particularly well, if my testing of the system is anything to go on.

The "idler" has to supply 2/3 of the load motor power, instead of 1/3, so for equal load motors, you need roughly double the idler size that is needed for the "standard" setup. All that 2/3 power must come in through a winding sized for 1/3 of the idler power. So right away you can guess the idler needs to be roughly double the load motor, in order that 1/3 of idler power is 2/3 of load power.

Then you consider that the idler consumes some current as well (usually about 40% of FLA just at idle), and you can estimate that you want an idler about 3x the load motor, instead of the usual 1 1/2 x.

It could work if you use a synchronous motor or build a synchronous motor from an induction motor.

Connecting a motor in Y and supplying nameplate volts to just one leg of it, will either consume the entire thermal budget of that one winding, or it will burn out, in both cases you're left with no excess. the 33% nameplate amps at no load is for all three phases connected. with one phase connected only, your current will be 57%, with half of a phase connected (Y connected motor, your 57% nameplate is now double that, so you've got one coil with no thermal margin left. reducing the nameplate volts will significantly reduce the no load current, but that makes the motor even less efficient.

with a synchronous motor you need not supply any reactive current to the motor, so that winding needs only to supply the loses of the motor. this would leave you with some thermal budget left to draw an additional load from the other two phases.

Maybe you could use capacitors on the other two phases to supply reactive current to the induction motor, you would need them anyway to get the voltage up to usable levels?

I made a post about using an induction motor as a voltage doubler about a year ago(in this case it was cutting the voltage in half.) the efficiency was poor.

http://www.practicalmachinist.com/v...-motor-please-320479-post2786980/#post2786980

9100 · May 16, 2017

I just sat through that pointless video again to make sure I hadn't missed anything. All he describes are standard components that any half baked electrician should already know about. He doesn't show any kind of schematic for the system, nor does he say he is applying 230 V between neutral and one of the points of the star. Everyone is assuming he is and it seems to be the only way to make it work, but he doesn't say so or give any other explanation.

Personally I agree that a transformer would work better.

I sold my hanger, which I was using to store junk against the airport rules after I sold the Cessna 195, and we stacked the junk in the shop anyway it would fit, so I haven't been able to play with my broken star transformer setup. If it works out, changing voltage along with generating another phase would be a matter of adding windings. It might be possible to improve balance at the same time. The transformer would replace the balancing function of the motor in an RPC so there would be nothing running.

Bill

SAF · May 17, 2017

230V to 415V RPC Example

Here is a sample drawing for the 230V input, 415V output, design in question. Appears that the assumption of one phase powered in the star mode is correct. I'm with JST on needing 3X load HP for the idler. The benefit I see is the Y output at 415, at the cost of 1.5X bigger than a 230V YY RPC of the same output capacity.

Taken from this post, the builder used a 15HP 230/415V, 6wire, idler motor. That would yield 5HP usable output capacity.

SAF Ω

9100 · May 17, 2017

That works, but I agree that it is expecting a lot from one winding. Assembling one from all new components would be expensive, so it depends on the builder's scrounging skills. Personally, I would look at a standard RPC and a transformer first.

Bill

WHHJR · May 17, 2017

Beating head against wall vs VFD (and transformer) is not a choice I would like to make again. ie VFD shop here with simple control schemes for each machine as needed.

3¢

Monarchist · May 17, 2017

WHHJR said:
Beating head against wall vs VFD (and transformer) is not a choice I would like to make again. ie VFD shop here with simple control schemes for each machine as needed.

3¢

Swapping-out 3-P for DC motors because they are easier-yet to power from 1-P may be 'slight' beating of head against wall.. but WTH - the big-bronze pull-handles are already bolted to a stout wall, it is almost like an orgasm when you take a break from it, and I don't much watch Tee Vee, anyway...so..

4¢

Two Idlers, Star/Delta

Cast Iron

Diamond

Cast Iron

Diamond

Cast Iron

Diamond

Cast Iron

Diamond

Diamond

Diamond

Diamond

Diamond

Hot Rolled

Diamond

Stainless

Diamond

Stainless

Diamond

Stainless

Diamond

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