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Thread: 3 phase & neutral
11-13-2010, 11:39 AM #1
3 phase & neutral
Hi guys, 1st post so be gentle with me.
I have a hardinge lathe that needs 440v 3 phase & neutral.
I am picking up a site transformer tomorrow 230v to 110v 5kva that i am hoping to run backwards either before or after the motor to get about 480v
if the above is ok how do i know the 3 phase motor i am buying will do the job, there seems to be a few differant connection set ups with 3 6 9 and 12 connections i have seen so far & 240v/440v or 400v 0r 415v.
I have done a search or 2 but there is so much info i'm having trouble getting at the data i need.
11-13-2010, 04:21 PM #2
I am going to respond to your comments in order...
ur going to pick up a site xfmr - not sure what that is - rated 230->110 and want to use it to get 440v. dont waste your fire extinguisher on this! it wont work. You did not say if it is 3ph or not, but I suspect what your idea was, was to put 220 that you have available into the 110 side and take 440 out the 230 side, right? dont do it - it will self destruct and maybe catch fire along the way! you can run a transformer 'backwards' yes, but you cannot put more voltage in a winding that it is designed for. to put 220 or 240 into the 110 side of that transformer will blow it up.
next u say u r buying a 3ph motor? didnt the machine come with one? why buy one?
tell us more details!
11-14-2010, 12:26 AM #3
sorry should have made it clear, the lathe is 3 phase 440v i only have single phase 230v available and need to make a rotory inverter and increase voltage to 440v. I do not want to put a single phase motor in the lathe.
11-14-2010, 12:59 AM #4
Hifly, are you sure the motor wiring can't be reconfigured to accept 220, or is it only 440?
11-14-2010, 08:23 AM #5
Okay, first of all... if the Hardinge is a good deal, go ahead and buy it, and don't worry about power conversions- it can be made to work well, for next-to-nothing, regardless of what you have for power.
HOW that is done, depends on many factors, and we can help you do it, but before making big investments in time and effort here...
Important question: are you SURE that the Hardinge needs NEUTRAL? If so... what for? Some machines will have coolant pumps, lighting, crossfeed motors, and controls that use lower voltage than the drive motor. If this machine has those, then we solve that problem with smaller transformers that convert our primary power source to what those devices need.
IF the power supply is ONLY for the spindle motor, then we solve the spindle motor supply needs using whatever solution makes most sense for you and your shop... and we do it in a way that gives you the performance you need, under the prevailing technical, space and budget constraints.
You WILL need expertise and experience. Fortunately, the guys in these threads can provide you with enlightenment, along with expertise and experience, and when you're done, you'll have become educated to a much higher level of value, than simply having a machine that works.
Tell us more about the situation!
11-14-2010, 03:55 PM #6
u r getting lots of good advice here! plse dont jump off and buy a rotary inverter to change 220 to 415 until the wizards here give u maybe much better choices to consider! perhaps a small low cost 230->440 transformer and a low cost vfd so u get even more benefits like variable speed, soft start, quicker stops....
11-15-2010, 07:26 AM #7
Thanks for all the input, I will not be changing the motor in the lathe, I also do not need a variable speed facility as the lathe already has that. All i need to supply is 440v & neutral. Its the supplying the neutral bit that i am having problems sorting out. The transformer is not an issue as long as i derate its current rating by a factor of 4 in this case.
Can anyone advise if a 3 phase motor wired in a star config will provide me with the neutral i need and if not how do i produce it with a rotory phase converter, if the star config is good to go, what do i need to look for connection wise on a motor or will any 3 phase 415/440v motor do?
11-15-2010, 08:42 AM #8
Three phase motors do not require a neutral. I would say that the neutral and one phase is used as a conventional 230V supply for stuff like control and lighting circuits. This wiring could be separated out and powered from an ordinary single phase circuit.
11-15-2010, 08:46 AM #9
my lathe requires a neutral to run the feed motor, i do not want to hack the lathe wiring around i want to leave it in original condition. so what i need to do it make a rotory phase converter that will supply 440v 3 phase & neutral
11-15-2010, 09:40 AM #10
Check your lathe's wiring diagram.
Most Hardinges I have seen have had single-voltage "consequent pole" two-speed motors. Six wires.
Yet, these same lathes had dual-voltage speed changing motors which are also three-phase.
11-15-2010, 12:53 PM #11
There is no wiring diag, the main motor is 440v only.
I was hoping that as this is the section on phase converters and transformers i may get some advice on phase converters and transformers and not suggestions that i change the motor or wiring on my lathe, which i will not be doing. Thank you all for your input but none of it is relevant to this post.
11-15-2010, 02:37 PM #12
"... but none of it is relevant to this post."
There IS a wiring diagram, but you don't have it.
EVERY Hardinge lathe which I have seen has required only L1, L2 and L3, and NEVER N.
Typically, if Hardinges need, say, 120 single-phase, then they ALWAYS have an integral control transformer with a 230/460 primary and a 115/230 secondary.
Take ANY of the two phases and you can generate 115 or 230, as is needed, and required, for the control system.
11-15-2010, 03:02 PM #13
11-15-2010, 03:12 PM #14
I do electrical work...
And I might have the answer you need...
But with your attitude I'll take my answers elsewhere...
People are just trying to help you....
Some people just dont see that...
11-15-2010, 04:02 PM #15
You are going to build a pretty specialized converter here.
Because your incoming line is only 240 volt you will have what
is essentially corner-grounded three phase when you are done.
I do not think that a star connected converter will provide the
correct neutral for you.
Probably the only person here who could determine this
definitively is peter, the moderator, and you two don't seem to
Other posters here have done this (taken single-voltage 440 volt
hardinge lathes and used either one transformer feeding a 440
volt rotary converter, or used a 240 volt rotary converter and
a three phase transformer) however this has been done for US
market HLVHs which do not require the neutral.
So in this sense you are blazing new territory. You might possibly
be able to find some other source of information on the internet
where there are more knowledgeable people. Doubt it but I've
been wrong before. If you go on rcm you might ask don foreman
but fitch williams is out of the usenet game I think.
11-15-2010, 06:08 PM #16
It IS relevent
It is ALL relevant.
Here's what your problem REALLY IS:
You have a machine that does NOT directly interface your mains. You need to make it interface your mains.
We ASSUME that you want to do it in a safe, sensible, and economic way.
There are several ways to do so, ALL of them involve somehow learning about, and correcting whatever improper modification was done that made the machine REQUIRE a neutral.
If you'd like to keep it as it is, you can do it:
1) Give up safe.
2) Give up sensible.
3) Give up economic.
These guys, myself included, know exactly the kind of situation with which you're faced. We've faced them, not just in the US, but in the UK, and South Africa, and Asia, and Central America. Electricity flows, and 3-phase works in all places equally. Local methods of mains and configuration vary, as well as how machines are manufactured to suit both general and specific markets.
You want it done well, right, and safe? Split out the spindle motor, and either build an RPC, add a three-phase step-up transformer, and power THAT motor... then add a SECOND transformer to step mains down to run the feed motor. You'll have all the performance with which the Hardinge was originally built. Silly, but if that's the way you want it, that's what you'll have to do.
Want it done better? Again, segregate it out. Install a single-phase transformer to step up for a 400+v VFD, tolerate the setup experience, and then enjoy what modern technology can do for an already incredible machine. Finally, make a dedicated power system for the feed motor. It ain't that complicated.
Don't get upset at these guys- they're giving you the best advice you can get... you can't PAY to get better. If you don't have a diagram, instead of being upset, JUST ASK. Since it's a US-made machine, there's a very good chance that the fine folks at Hardinge STILL HAVE the original sales documentation. ( Hardinge Inc. )
IF they don't have a diagram, I'd bet that someone around here DOES, and most of us are computer-savvy enough to scan and email it to you.
11-15-2010, 06:15 PM #17
Because I've never been into a UK hardinge lathe, I can't say for
certain they don't require a neutral. A photo of the electrical
cabinet might help here to enlighten us colonial heathens...
11-15-2010, 06:18 PM #18
And your question re. star connection neutrals
Yes, if you use a star-connected motor diagram, and apply mains power across the three phases, the center will be at a synthesized theoretical neutral.
IF it's balanced.
If you build an RPC, and connect it to the motor, and test this theory, you'll either fry the motor, or yourself in the process, because the nature of most rotary converters, is a phase relationship which does not yield 'symmetrical neutral'. You will, effectively, make anything connected to Neutral (and grounded) hot.
It is for this reason, that most of us respond to you as if this isn't wise. Matter of fact, in all the machines I've worked on, converted, or troubleshot, I have found NO true industrial machine (and Hardinge is never anything less) that ever required or used a neutral. True industrial measure is to install a step-down transformer across one of the primary input legs to provide lower control voltages accordingly. I highly doubt that, regardless of what it was built for, that your Hardinge was originally built that way, it sounds like it was 'hacked' when you got it... and I certainly wouldn't leave it that way unless I wanted my shop floor to be the falling point of a friend's corpse.
11-16-2010, 03:03 AM #19
I agree with Dave Kamp and here is my additional 2 cents.
I have converted Hardinge 2 speed 440v 3ph machines to use 230v single phase power. As I remember none required a neutral, in fact I've converted numerous 3 phase machines in my shop to use 230v single phase and none of them required a neutral. I used a standard dry power transformer and wired it as an autotransformer to get 440v single phase power. I then used a VFD that would accept 440v single phase and convert it to 440v 3 phase to feed the machine. I’m not sure this type of VFD is still available,it was a Fincor, but you could use a 3ph input VFD and derate it. If it has phase protection be sure you can override it. Here in the US the machine has control transformers to transform the 440v to the lower control voltage. Be sure not to use the wild leg to power the internal transformers. It can be set up to use all the original machine control functions.
A 440v rotary has specific issues you must be aware of. If you transform the single phase voltage to 440v, the idler is 440v then any capacitors must be capable of handling over 600v. If you use a 230v idler you will need a 3 phase transformer to step up to 440v.
Although you don’t need the variable speed I found the VFD an excellent way to go on the Hardinge 440v only machines.
I'm curious about your single phase power. Here in the US 230v one line is -110v and the other is +110 volts, basically 180 deg out of phase to get 220v between the lines. To get 110v house current a neutral is used. Voltage between the neutral and either 220v hot line is 110 v. The neutral is used to run a 110 v single phase motor from the line. Industrial machines get 110v, if needed, from a step down control transformer (no neutral).
Is your 230v system similar or is it 230v to ground?