Considering a 3 phase CNC small lathe - - - have 240V single phase

[MrMetric]

Rich is right on the target. I've done both. In fact, even though I have a Phase Perfect, I elected to rewire my Hurco CNC because the *only* think on it that was 3 phase was the spindle motor, which was driven by a VFD. Ironically, that particular unit itself was run on single phase. I ended up having to replace that VFD, but I kept the concept and simply reworked the inputs to the mill, thereby ensuring everything was on single phase.

The PP is a nice solution, but *very* expensive. My replacement CNC to the Hurco is a true 3 phase machine, though, so I'm glad I have the PP. The new CNC uses a Mitsubishi control which has amplifiers that require 3 phase. Sure, internally I'm sure it still makes a HV DC bus, but they put phase detection logic in it. And, you have to use their amps because there is a proprietary interface between the control and the amps. Not an easy thing to get around unless you want to do a whole conversion.

I think Rich's comments are accurate though. There is a lot of "well, in this scenario then.... but in that scenario, things are a little different..."

 

[awake]

I really like VFDs. Both of my lathes are fitted with them. They are especially good for powering up to about 4kW machines off single phase domestic supplies (unless you live in the USA with 115VAC).

Just a point of clarification - I do not believe there is anywhere in the USA where 240V (or some variation, perhaps 230V) is not available in a house. It comes from the transformer with a neutral that allows the 240V to be split into two legs, and most interior outlets do indeed make use of the resulting 120VAC (or variations such as 115VAC). But it would be a rare house that does not include some 240VAC circuits - for electric stoves, water heaters, HVAC systems - and it is trivial to add a 240VAC circuit to a circuit box (assuming it is not completely ancient).

Let me hasten to say that I am NOT an electrician. I have run a few circuits in my own garage, carefully observing national and local codes, and those codes always presuppose 240VAC plus neutral coming into the house. But the USA is a big country, and I can't rule out the possibility that there is some odd-ball corner that does things differently than everyone else!

 

[MrMetric]

I could envision where someone might have an ADU (auxiliary dwelling unit) and they split one side for unit A, and the other for unit B.... That would be *really* weird, probably not code, and very limiting, though. In general, I would agree with you. Every pole transformer I've ever seen has a 240 secondary... But, as you said, it is a big country.

 

[ajoeiam]

I could envision where someone might have an ADU (auxiliary dwelling unit) and they split one side for unit A, and the other for unit B.... That would be *really* weird, probably not code, and very limiting, though. In general, I would agree with you. Every pole transformer I've ever seen has a 240 secondary... But, as you said, it is a big country.

(Wacky Beeg Grin!!!!!!!!!!!!!)
Sorry - - - - some poles have a 208 V secondary, some a 230 V secondary, some a 460 V secondary, some have a 575 V secondary, and some may even have an over 1.0k V secondary (not very familiar with those - - - sorry! IIRC maybe the next is 2.4k V but dunno for sure!). So 'every' pole does NOT have a 240 V Secondary.

Some of the distribution voltages are 4k V, 7.2k V (common here on our antiquated system!!!!!!!!!!), 14.4k V common in most of western Canada (maybe even in other areas but dunno), and then there are others all the way up to some 1 M V DC - - - - but that's serious high power long distance transmission line country!

 

[Chiptosser]

So for my set-up.
I have single phase coming into my shop.
I have a rotary a phase convertor set-up that I assembled.
10hp motor, starting contactor Allen bradley, Start caps, run caps, Momentary start switch, stop, switch.
I run two cnc mills. one with a 10hp driven by a Mits, Vfd. As recieved from the factory.
The other is a knee mill 4hp, with a standard manual variable speed spindle.
A Clausing 17 x 80 Colchester lathe 15hp, Yes, it drives it,
Two drill presses, 3/4, 11/4hp
Parker Majestic surface grinder, 11/2hp
Quincy air comp. 24cfm, driven by a large frame general elec. 5Hp.
Yes, I can run everything at the same time!
You have to run the controls off of one of the live power feeds. the controls are single phase.

 

[skyline1]

Assuming 220 Volts is the line - line voltage 40 amps is about 15 KVA which is a pretty big machine for a home shop as others have pointed out and at this sort of power any type of converter be it rotary or solid state is likely to be expensive.

Your single phase supply will need to be pretty hefty too as this will draw nearly 70 Amps, not allowing for converter loss which will push it up even more. you will need a cable of at least 16 sq mm to carry it, that's about 4 AWG.

As it is a CNC and therefore electronically controlled the conversion is more complicated than a simple motor where the idler motor "autoconverter" idea could be used.

If you can obtain a schematic for it this will give you a much better idea of what is involved.

I don't want to sound like a killjoy and this sort of thing is possible (Chiptosser has proved it) if your mains can handle it.

Best Regards Mark

 

[MrMetric]

(Wacky Beeg Grin!!!!!!!!!!!!!)
Sorry - - - - some poles have a 208 V secondary, some a 230 V secondary, some a 460 V secondary, some have a 575 V secondary, and some may even have an over 1.0k V secondary (not very familiar with those - - - sorry! IIRC maybe the next is 2.4k V but dunno for sure!). So 'every' pole does NOT have a 240 V Secondary.

I was referring to pole transformers for residential dwellings. Industrial or multi-unit dwellings are a totally different beast and out of the context of what the OP was driving at. That said, I am not a power engineer nor did I ever claim to be. My exposure is also mostly limited to the West coast. In the middle of the country things may be different. But, ultimately, prior to switched mode power supplies (which generally have a much wider band of acceptable input power) I've only really heard of one voltage being available for products sold in the US/Canada: 120VAC. That was the context for the comment. I suppose there might be some pole that has a single phase transformer that goes to just 120V, but I'd be a little surprised.

Oh, there is another caveat to my comment. Some residential areas still have three phase running along the top if they are close to a commercial building or school. It haven't seen many pole transformers in the residential areas serviced by those setups have three phase, but it *is* possible. I used to know a guy locally that managed to convince our utility to swap out the transformer on the pole in his back yard to a three phase unit (he was lucky because the run was servicing a school). He ended up with zero need for a phase converter. When he got cancer, he sent me a note asking if I wanted to buy his house so I could have a shop with true three phase.... I never broached the subject to my wife though. Moving so you can get nice power for your shop is something that only two types of people can do. The first is a single person. The second is someone who will be single soon.

 

[Chiptosser]

Most three phase services in the us, uses three transformers at the service poles, not just one.

 

[MrMetric]

Fair enough. To be honest, most of the industrial services that I've looked at have had underground vaults. I have no idea what they have in there. And, frankly, I haven't really cared. I'm not a contractor so I don't really have that much interest in commercial installations. What I can or cannot do in my home, which is definitely fed with single phase 240V, is far more important/interesting to me. I do know that the one residential customer that had 3 phase power (last post), however, had a single transformer. But, that was a non-standard installation for the power company. In fact, I vaguely recall that he had two drops, but don't quote me on that.

 

[kvom]

What HP is the lathe motor? VFD is fine up to 2 HP, but they get expensive for larger.

 

[ajoeiam]

I was referring to pole transformers for residential dwellings. Industrial or multi-unit dwellings are a totally different beast and out of the context of what the OP was driving at. That said, I am not a power engineer nor did I ever claim to be. My exposure is also mostly limited to the West coast. In the middle of the country things may be different. But, ultimately, prior to switched mode power supplies (which generally have a much wider band of acceptable input power) I've only really heard of one voltage being available for products sold in the US/Canada: 120VAC. That was the context for the comment. I suppose there might be some pole that has a single phase transformer that goes to just 120V, but I'd be a little surprised.

Oh, there is another caveat to my comment. Some residential areas still have three phase running along the top if they are close to a commercial building or school. It haven't seen many pole transformers in the residential areas serviced by those setups have three phase, but it *is* possible. I used to know a guy locally that managed to convince our utility to swap out the transformer on the pole in his back yard to a three phase unit (he was lucky because the run was servicing a school). He ended up with zero need for a phase converter. When he got cancer, he sent me a note asking if I wanted to buy his house so I could have a shop with true three phase.... I never broached the subject to my wife though. Moving so you can get nice power for your shop is something that only two types of people can do. The first is a single person. The second is someone who will be single soon.

I was likely being overly pedantic and nowhere was it specified 'residential'.
This 'only 240V single phase' is also very common even in rural areas.
Three phase is considered 'weird' (at least by the way power companies act) in North America (dunno about Mexico though!!).
Most of even the homes in at least Germany have 3 phase available - - - that facilitates serious hobby machinery! (grin!)

It may have been possible to get 3 phase if it were running by easily years ago.
Today, on the other hand, you have to show demaind and amount and both have to be over certain minimums and even then I think one would have to argue hard.
If I were building where the power wold need to be brought in I think I would avoid the becoming absolutely stupid costs and just go off grid - - - - its quite simple today compared to 30 or more years ago!

 

[ajoeiam]

Most three phase services in the us, uses three transformers at the service poles, not just one.

That may depend upon the size of the service.
I had a three phase service installed at a former location.
The 150KVA transformer was a single piece.
Was told that I got that size (had asked for a 50 KVA service) because there was another 150KVA service in town (at the hockey/curling arena) at that them using such would mean less spare parts for them - - - I didn't argue.

 

[ajoeiam]

What HP is the lathe motor? VFD is fine up to 2 HP, but they get expensive for larger.

Hmmmmmmmmm - - - - I've seen VFDs even past 2k HP - - - - - but I would bet that they're NOT cheap.
The fact that one needs to oversize the VFD (the rating that I've found was to use 58% when using the vfd to produce the third leg) that gets to be the expensive part!
I'm thinking that when you calculate the costs of up-rating 3 or 4 larger VFDs it might be cheaper to get an electronic inverter and then size the vfds for just rated but I haven't calculated that as of yet!

 

[skyline1]

At one time it was common practice to derate Motors running on VFDs by between 33% and 50% and not run them at less than 50% of their nominal 50/60 Hz speed. this was for cooling reasons. Motors running slower than their nominal speed are less efficient and produce more heat, and at the same time the cooling fan which is usually integral with and connected to the motor shaft is also running slower so produces less cooling effect.

However VFD and motor design has improved over the years and it is now possible to buy VFD rated motors. In the case of the larger sizes often with a separate constant speed cooling fan.

With A good quality VFD it should not be necessary to derate the VFD itself but with many of these cheap Chinese VFDs that are flooding the market it often is mainly because they are not up to their stated ratings in the first place and will either shut down or fail if fully loaded.

It is possible to get VFDs right up into the Megawatt range but their size and cost seems to rise almost exponentially with power.

It is technically possible to produce a solid state single to 3 phase converter in the 15 - 20 Kw Range fixed or variable frequency the technology is essentially the same but there are few about and those that are, are more expensive than they should be.

I think the main reason for this is lack of demand. The manufacturers reason (rightly or wrongly) that individuals or companies using equipment of this sort of power are likely to have 3 Phase available anyway and would have no need for such a unit in the first place.

Best Regards Mark

 

[MrMetric]

skyline... I think the bigger issue with the "technically possible to produce a solid state single to 3 phase converter" comment is that Phase Perfect apparently has a defensible patent on it (or, maybe nobody has tried to infringe upon it to see just how defensible the patent really is?). Frankly, given the fact that VFDs have been widely used as phase converters, albeit not in a distribution mode, has always wondered just how well the patent would really hold up in court. But I have never looked at it, and I am not a lawyer. It is definitely true that the distribution model has different requirements as you have exactly what we have all been saying you do *not* want to do if you use a traditional VFD: put some type of interrupter in the circuit between the VFD and the motor. PP, by the way, also only generates the third leg, the other two are passed through unaltered (except that they obviously go through a relay contactor).

My understanding is that there is an additional consideration to just heat when using a non-VFD rated motor. I was told that older motors don't have as good insulation on the windings. Because of this, the increased dv/dt used in speed control can result in micro-arcs between windings. Over time, these will increase in size and eventually cause a complete short in the windings. Is this true? Honestly, I do not know. It kind of makes sense to me, but I'm not a motor designer so I would be hard pressed to actually weigh in on the whole thing with any type of certainty.

 

[Chiptosser]

My set-up is a residential application. I have a 200 amp service. This is my hobby shop, I have had the good luck of buying some equipment, that not all people have the capacity or equipment to handle. I like good quality heavy duty machines that I can use without question. So, on the electrical end, I have had to figure out how to power it, without killing the bank. I have set-up other peoples rotary convertor system for single use and multiple motor uses. The information is out there, you just have to read it.
I have only one VFD it is built into my largest mill for the spindle. It is powered by the two live power legs from the rfc. You have to learn how to balance the power legs with capacitors.

 

[skyline1]

skyline... I think the bigger issue with the "technically possible to produce a solid state single to 3 phase converter" comment is that Phase Perfect apparently has a defensible patent on it (or, maybe nobody has tried to infringe upon it to see just how defensible the patent really is?). Frankly, given the fact that VFDs have been widely used as phase converters, albeit not in a distribution mode, has always wondered just how well the patent would really hold up in court. But I have never looked at it, and I am not a lawyer.

As is often the case the problem appears to be not technological but legal, I'm not a lawyer either but I agree that it is doubtful if this patent would actually stand up.

My understanding is that there is an additional consideration to just heat when using a non-VFD rated motor. I was told that older motors don't have as good insulation on the windings. Because of this, the increased dv/dt used in speed control can result in micro-arcs between windings. Over time, these will increase in size and eventually cause a complete short in the windings.

This is an additional reason (along with increased bearing wear) for the derating of older motors and leads to an additional recommendation of not running them at more than 200 % of their nominal speed.

My set-up is a residential application. I have a 200 amp service

I don't know about the States but here in the U.K. that's quite a hefty service for single phase residential supply. Ours are generally limited to 100 amps. at 240 volts

I believe the U.S. system is centre tapped to earth 120v each side giving a split 120/240v system whereas ours is unipolar with the neutral tied to earth. so I guess your currents may be higher.

Best Regards Mark

 

[Chiptosser]

I knew someone would bring that up! I can run this system on 100a supply.
Running everything will not max out the supply. I have a air-conditioning or heating system and lights that uses most of my usage, and capacity, like 75 %.
My idler motor is very low draw, What you have to allow for is the start up surges, very important! There are soft start controls out there for that, if that worries you with your supply capacity. Do the research for where you are.

 

[roncohudd]

I was likely being overly pedantic and nowhere was it specified 'residential'.
This 'only 240V single phase' is also very common even in rural areas.
Three phase is considered 'weird' (at least by the way power companies act) in North America (dunno about Mexico though!!).
Most of even the homes in at least Germany have 3 phase available - - - that facilitates serious hobby machinery! (grin!)

It may have been possible to get 3 phase if it were running by easily years ago.
Today, on the other hand, you have to show demaind and amount and both have to be over certain minimums and even then I think one would have to argue hard.
If I were building where the power wold need to be brought in I think I would avoid the becoming absolutely stupid costs and just go off grid - - - - its quite simple today compared to 30 or more years ago!

All you really need is how much input it needs then double it for a three phase motor. You can rope star it or put a pony motor to start it. I ran both my mills that way for years.

 

[skyline1]

If you are considering an "autoconverter" type rotary converter this series might be interesting It is based on the U.K. electrical system but the principles apply to all supplies and it goes into the design of them in detail.

Best Regards Mark