Single Phase To Three Phase Rewind - Lathe Uprate

All the 3 phase motors I've seen here in the UK are 440/220 depending on whether they are wired in Star or Delta. You just remove a cover and shift 3 links to changeover. I've done it on 2 motors which I now run on a vfd which is single phase 220 volt. I also ran my lathe motor and a 3 hp milling machine motor on single phase for 20 years before vfd converters became cheap and commonplace. I set the links to delta and put single phase across 2 of the delta points and a capacitor bank to the 3 point giving me the phase shift. The only drawback is you lose starting torque but that does not matter in most cases. The method is well known and described in the book Electric Motors by Cox [used to be by MAP but not sure who prints it now].

Ken I said:

Richard, you often see motors rated for 440V @ 60Hz and 380V @ 50Hz - because they will pull the same current because of the impedance change matching the voltage. The 440V run will output 20% more power - same torque, more revs.
380 x 60 ÷ 50 =456 (allowing for resistance they are typically made as equivalents).
Other than that you see the ratio 1.732 (Square Root of 3) pop up a lot in three phase equations such as 380 ÷ 1.732 = 219 ie 220V so a 380V motor connected in Star is only 220V when connected in Delta.
As regards 440 it could only have a 220 option with a double set of windings - doable but unlikely.
The number of "possibilities" is large but generally not done for reasons of cost.
You can always run a motor under-volt - with concomitant loss of torque/power - but overvolt can generate massive current and burnout in short order.

Example: Let's imagine a 220V motor that pulls 1A therefore the impedance is 220 Ohm - but that 220 is made up of 210 Ohms of inductive impedance and 10 Ohms of resistance.
If saturation occurs at 220V (the limit of the induction portion of the impedance) then every 10V over will apply only to the 10 Ohm resistive part and add another 1A to the load - ie 5% overvolt gives 100% overcurrent. Whereas 5% undervolt would result in 5% undercurrent.

Since the resistive component of AC devices is generally very small, once you exceed the saturation voltage the current rise is very steep indeed.

All hell lets loose if you venture past saturation.

Regards, Ken

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Ken, could you not set the VFD to run at a higher frequency if you are running “Over voltage”
The impedance would then be higher and as the V/F can be reduced in a linear fashion it will reduce the output voltage at the plated frequency ?

rutzen said:

All the 3 phase motors I've seen here in the UK are 440/220 depending on whether they are wired in Star or Delta. You just remove a cover and shift 3 links to changeover. I've done it on 2 motors which I now run on a vfd which is single phase 220 volt. I also ran my lathe motor and a 3 hp milling machine motor on single phase for 20 years before vfd converters became cheap and commonplace. I set the links to delta and put single phase across 2 of the delta points and a capacitor bank to the 3 point giving me the phase shift. The only drawback is you lose starting torque but that does not matter in most cases. The method is well known and described in the book Electric Motors by Cox [used to be by MAP but not sure who prints it now].

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I've done this too. It is perhaps worth noting that older Brookes motors (UK) don't have links to shift - you have to go in there and (gingerly, without damaging the insulation and shorting a turn) find the star point where 3 windings come together. On mine this was wrapped in cloth tape, and wasn't too hard to find, though the lead-out junctions to the enamelled windings were also wrapped up and it took a bit of digging about. Then you unsolder the star point and bring each wire out separately on insulated cable, connecting them in delta as shown in the diagram upthread in the terminal box.

I was much relieved that I managed to do this without messing it up! Motors like this tends to be cheap as it is perhaps not widely known that you can jig them for a VFD. The only mistake you can make when re-connecting is to connect two ends of the same winding together - but you can beep this out before you start. If it goes the wrong way, swap two connections.

Thanks for that info. I suspected that the motor would not give its full potential on a 220 line voltage and I understand that the mining industry uses a different (higher) line voltage to the domestic one presumably to obtain more power from the same frame size. I believe that Canada uses a line voltage of around 560 volts and the marine industry uses a greater than 230 line voltage for presumably similar reasons i.e. more power per frame size. Comments?

John, You could run a 440V 60Hz. motor off 220V @ 30 Hz and still develop its full torque - but at half revs thus still only half power - which then flatlines as you go on up to 220V @ 60Hz at which point you are at full revs but half torque - so still only half power.

The point I made at the beginning of this post (and the attachment on getting more power out of a three phase motor) is take whatever you have to hand - or want to start with - figure out what you want out of it - and rewind to suit.

Rutzen most UK motors are 440V 60Hz / 380V 50Hz (UK Frequency) Star - therefore 260V 60Hz /220V 50Hz in Delta

MRA - that's a cool trick with the Brookes motor - but who knew ? I haven't seen an internal Star point in any recently manufactured motor.

Regards, Ken

John Antliff said:

I believe that Canada uses a line voltage of around 560 volts

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Standard nominal system voltages in Canada:
120/240V 1~. mostly residential. This is what I have so I need a transformer to bring the voltage back down to 220 for the phase convertor and the 220V 3~ machines then back up for the CNCs using 575V
120/208V 3~ Y. Residential, apartment complexes, small commercial, industrial.
240/416V 3~ Y. uncommon but mostly industrial
277/480V 3~ Y. Common in southern Ontario factories
347/600V 3~ Y. Standard industrial supply, commercial offices, and other applications.
When I lived in western Canada voltage for small industrial/commercial buildings was 220V 3~

Double post deleted

Ken I said:

Richard, you often see motors rated for 440V @ 60Hz and 380V @ 50Hz - because they will pull the same current because of the impedance change matching the voltage. The 440V run will output 20% more power - same torque, more revs.
380 x 60 ÷ 50 =456 (allowing for resistance they are typically made as equivalents).
Other than that you see the ratio 1.732 (Square Root of 3) pop up a lot in three phase equations such as 380 ÷ 1.732 = 219 ie 220V so a 380V motor connected in Star is only 220V when connected in Delta.
As regards 440 it could only have a 220 option with a double set of windings - doable but unlikely.
The number of "possibilities" is large but generally not done for reasons of cost.
You can always run a motor under-volt - with concomitant loss of torque/power - but overvolt can generate massive current and burnout in short order.

Example: Let's imagine a 220V motor that pulls 1A therefore the impedance is 220 Ohm - but that 220 is made up of 210 Ohms of inductive impedance and 10 Ohms of resistance.
If saturation occurs at 220V (the limit of the induction portion of the impedance) then every 10V over will apply only to the 10 Ohm resistive part and add another 1A to the load - ie 5% overvolt gives 100% overcurrent. Whereas 5% undervolt would result in 5% undercurrent.

Since the resistive component of AC devices is generally very small, once you exceed the saturation voltage the current rise is very steep indeed.

All hell lets loose if you venture past saturation.

Regards, Ken

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Brilliant! I knew there was something simple in the balance of Impedance v voltage and frequency that did this ... because I was taught as a boy that motors go BANG very quickly with over-voltage. But this explanation is the best I have heard in 5 decades or more. - Thanks Teacher!
K2

Ken I said:

John, You could run a 440V 60Hz. motor off 220V @ 30 Hz and still develop its full torque - but at half revs thus still only half power - which then flatlines as you go on up to 220V @ 60Hz at which point you are at full revs but half torque - so still only half power.

The point I made at the beginning of this post (and the attachment on getting more power out of a three phase motor) is take whatever you have to hand - or want to start with - figure out what you want out of it - and rewind to suit.

Rutzen most UK motors are 440V 60Hz / 380V 50Hz (UK Frequency) Star - therefore 260V 60Hz /220V 50Hz in Delta

MRA - that's a cool trick with the Brookes motor - but who knew ? I haven't seen an internal Star point in any recently manufactured motor.

Regards, Ken

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After looking at your photos, I have several questions: How old is this lathe? Does it have a brand name? I could see it on one phot but not well. It's awful about the low quality work done by the Chinese, as I said elsewhere, their purpose isn't to build something well, it is to SELL you anything and claim it is just exactly what you asked for. How long have you had it? Did you manage to take care of all those problems you pointed out?

Richard, in my first post I wrote :-
"A BV20BL Ø220mm (over bed) x 520mm Chinese Lathe supplied under a local brand name. I have no idea who the Chinese manufacturer is or what other brand names it goes under – if you recognize it under other brand names or suppliers please let me know. "
It is dated 2016-1 Serial No 160103 - I bought it in new August 2016 from a local machine tool dealer "Adendorff" under their brand name "Mac-Africa" but their stock-in-trade is typically from the East - no other clues whatsoever - If anyone recognizes this as some other brand - let me know please.

The machine is a mixture of well made to downright awful - most of the latent problems I have fixed or improved - these are the list of changes made to date :-

Some Other Problems / Changes / Improvements.

In all I made the following changes to the lathe :-



1) Rewind motor to three phase.
2) Add VFD drive.
3) Add tachometer display.
4) Change ratios and “V” belt to Synchroflex T5 belt.
5) Speed change potentiometer for VFD.
6) Kipp – quick release handle for tailstock.
7) Kipp – quick release handle for carriage lock.
8) Tailstock quill – overtravel warning line.
9) Cross axis grubscrews as anti-twist for MT2 tang.
10) Spare axles for mounting changegears.
11) Knob for opening door (and hanging dustcoat).
12) Door securing bolt replaced with NiB magnet to keep door closed.
13) Oil change / Sight Glass improvement.
14) The chuck was held on with cap screws in counter-bores – nearly impossible to get out with a “short” Allen Key and immensely time consuming – so I replaced them with Hex shoulder screws.

Just a threaded bush on a hex bolt – you can imagine how horrid it was with cap screws. Much easier with a 13mm AF spanner than a sawed off 6mm Allen key.

All my chucks have had their adaptor flanges turned whilst reverse mounted – in-situ on to another bar turned in another mounted chuck to ensure closest possible concentricity and trueness. Thereafter they were clocked for the best repeatable concentricity (one of three possible positions) and stamped with the alignment dots indicated.

Even the 4-jaws are marked because I might remove the chuck to my mill or rotary table and then return to the lathe – always a good idea to put it back the same way it came off.

Hope this thread has been of some help or inspiration to improving your equipment.

Regards, Ken

Richard Hed said:

After looking at your photos, I have several questions: How old is this lathe? Does it have a brand name? I could see it on one phot but not well. It's awful about the low quality work done by the Chinese, as I said elsewhere, their purpose isn't to build something well, it is to SELL you anything and claim it is just exactly what you asked for. How long have you had it? Did you manage to take care of all those problems you pointed out?

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40 years ago China was exporting poorly made equipment. Today, you can buy any quality you desire, as even the major manufactures around the world have their equipment built by them. Our hobby would not have so many members if only high quality machine tools were available.
So far every lathe I've seen from China, no matter how cheap, the spindle comes adjusted (or can be adjusted) true to the lathe bed. My first lathe came from Taiwan built in 1976, and it was a "pre-assembled" kit. I still use that lathe, and have done lots of fixes to make it better and more accurate.
China sells the quality people can afford. I have seen my share of tools that were junk, but I'm not seeing that these days.

ignator said:

40 years ago China was exporting poorly made equipment. Today, you can buy any quality you desire, as even the major manufactures around the world have their equipment built by them. Our hobby would not have so many members if only high quality machine tools were available.
So far every lathe I've seen from China, no matter how cheap, the spindle comes adjusted (or can be adjusted) true to the lathe bed. My first lathe came from Taiwan built in 1976, and it was a "pre-assembled" kit. I still use that lathe, and have done lots of fixes to make it better and more accurate.
China sells the quality people can afford. I have seen my share of tools that were junk, but I'm not seeing that these days.

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Absolutely. Remember when "made in Japan" was an insult? remember the poor quality of Taiwan's Jet lathes when they came out? Now the same for Chinese stuff. the only place that I know of that came out with relatively high quality stuff from the beginning was Korea, and I don't really know much about that except for computers and cars. The next place will be India--Their problem is lack of capital in small cottage industries, I believe and so their problems might take a lot longer to iron out. The place I bought a tool from had sharp edges and was made from literally junk but lookt good on the outside and did the jobs properly, however the handle was busted (didn't really matter) when it arrived--I communicated this to him and he was all crying that to send the part would absorb all his increase. I told him that is not my problem, that he made it incorrectly thus it broke. He said he wojuld have his people fix the sharp edges. I tried to explain how to fix the prob which caused the handle to break but I don't know if he understood. Since the tool didn't really need the hand, i let it go on his promise to try to fix the problems. These people are trying really hard--I would like to know if he is really fixing the probs. The handle broke because he didn't use a counter drill--I could tell he used a regular drill bit which was too large and it weakened the screw which the handle was attached to. A very simple fix--IF one has a counter drill! I understand the simple tools we take for granted in the west are very difficult to get in India. Go figure--if theat is true, they are doing great cottage industries.

Better get your tools now while they are still cheap--even Jet tools are expensive nowadays.

In my 30 plus years as a Machine Maintenance Manager responsible for the maintenance & repair of millions of dollars worth of machine tools, I found that the "Go To" lubricant for most gear boxes was EP68 (Extreme Pressure 68 weight oil). This grade lubricant was recommended by so machine tool manufacturers for small medium gearboxes we adopted it as our standard and it never let us down. For large gearboxes (50-200 HP) we would use something heavier and for really light application a lighter grade but for most applications you could not go wrong with good old EP68.

Colin

a hint on the Tach for those following along - I personally don't like a magnet sticking out like that for several reasons, but there are alternatives - On my Logan lathe, I used an inductive pickup reading the teeth on the bull-gear, and then a RedLion counter/tachometer to display the result - that RedLion product can be programmed to divide or multiply so you can convert the pulses per revolution from the sensor to RPM. I was able to get the sensor and the readout surplus pretty inexpensively. the actual sensor is about 1 inch long and 1/4 inch in diameter as I recall - it's been a while since I looked at it -

Hi Ken, Really good useful stuff here, Thanks!
I am just unsure who should not operate the lathe, according to your "Danger" notice. - In my experience (As I am an Engineer, not Machinist or Toolmaker), it should be "Engineers and Managers"!
I always wanted a sign (tongue in cheek) "Everyone thinks they know best, but Engineers KNOW we know best" - Then I was told (by a Woman) that women wrote that motto about Women, before Engineers invented the planet! (Change "Men" for "Everyone" and "Women" for "Engineers"). No intent to be sexist or anything...

K2

Ah K2, you've zoomed into my danger label - I censored it for the photo - given to me by an Australian friend "Not To Be Operated By F***wits."
Hope no one is too offended by this.
Here's another favorite


Regards, Ken