How can I convert a 3-phase lathe to single-phase

[arch1]

Hi to all. This is my first post. I'm an ex-Woodwork teacher and I've been an occasional visitor as guest over the years, but have never got down and dirty as I'm no longer
consistently involved in a specific craft. I still love the smell of wood, get and split mountains of firewood (mixed feelings there!) and design and construct stuff in wood or metal for myself and the kids as needed.
Recently an old colleague asked me if he could use a 3-phase-powered wood lathe I've been meaning to commission for the last ten years, but sadly never started on the journey.
I was wondering where to start in order to convert it to single phase power. Is the best/cheapest option to simply replace the motor, or can they be easily re-wired? Who might do such work? If you assume I'm totally ignorant of all things to do with AC you wouldn't be far off the mark. Feel free to be patronising.

[PJM16]

There's really only 2 options for such a task. The best is to get the motor swapped out for a single phase motor or you can purchase a phase inverter which aren't cheap. Either way speak to a motor rewinder about costs but last I heard an inverter is approx $1,000 per kW, depends on the kW of the motor as to price for swapping out with a single phase motor.

Good luck with it all.

[rob streeper]

Swap the motor or fit a variable frequency drive. Personally I'd install a VFD. Very easy to do - just follow the directions included with your drive. VFD's run from about $100 up to about $300 (USD) for motors under 3 h.p., usually less than an equivalent motor swap. Bonus is that you get variable motor speed.

[Fuzzie]

Some motors can be wired for either 1 or 3 phase. I think it's called a Delta connection and I think BobL has a thread somewhere on here about how the different wiring for the phases work.

[NCArcher]

As Rob and Fuzzie have mentioned. The best (IMO) way is to install a Variable Frequency Drive (VFD) It allows you to run the origainal 3 phase motor from a standard single phase outlet and not only gives you variable speed but comprehensive motor protection as well. To run the motor from a VFD you have to be able to connect the motor in Delta. Some motors it is straight forward and just involves swapping the motor connections around. Some need to be modified to allow you to swap the connections. I had a local motor winder modify three lathe motors for around $80 each. A good VFD can be had for under $300. Do a search on here for VFD or variable speed and you should find a wealth of information.

[Fuzzie]

I'm not suggesting a VFD. I know some motors can be wired for single or 3 phase because my chinese thicknesser has instructions for wiring the motor either way. I use it 240V single phase. I think people use a VFD on lathes for speed control more than emulating 3 phase power??

Unfortunately my motor knowledge pretty much ends there. Not all motors can do this.

[Woodturnerjosh]

I'm not suggesting a VFD. I know some motors can be wired for single or 3 phase because my chinese thicknesser has instructions for wiring the motor either way. I use it 240V single phase. I think people use a VFD on lathes for speed control more than emulating 3 phase power??

Unfortunately my motor knowledge pretty much ends there. Not all motors can do this.


I know this is off topic (a little) but can you show the wiring diagram? I haven't heard of this being done without needing to add capacitors to a phase and I've never seen a motor that came with all that...very interesting!

Josh

[Big Shed]

I'm not suggesting a VFD. I know some motors can be wired for single or 3 phase because my chinese thicknesser has instructions for wiring the motor either way. I use it 240V single phase. I think people use a VFD on lathes for speed control more than emulating 3 phase power??

Unfortunately my motor knowledge pretty much ends there. Not all motors can do this.


I would venture to suggest that those Chinese instructions are referring to US 3 phase (220V).

[BobL]

Here is close to complete summary of 3P 415V to 3P 240 V conversion Via a VFD for WW machines

Upgrading can vary from easy to a PITA depending on the machine and the motor.

Firstly if you want to use the variable speed capability of the VFD you should replace the existing motor with a more powerful (Typically double the power) 3 phase motor.
The reason for this is because (unless you purchase a more expensive Vector Drive VFD) at half speed all motors have half power.
The motor also has to be 240V 3 Phase compatible, if not the motor has to be reconfigured internally - this is not a job for the fainthearted and should be done by qualified motor rewinder.

Doesn't sound too bad so far but unfortunately it RARELY stops there

a) Enough space to mount the replacement motor.
Not all motors are the same size and may not physically fit in the space provided.
The easiest arrangement is where the motor is on the outside of the machine so space is not as critical.
If the motor location position has to be moved longer (or shorter) belt(s) may be needed and belt tensioning arrangements allowed for.

b) The motor mounting holes to match
If not, new holes may need to be drilled in the machined motor mounting plate or an adapter plate to be constructed .
Motors that use "feet" are much easier to swap out than motors (such as on bandsaws) that are flange mounted although it's possible to make adapters.

c) The old pulley needs to match the new motor shaft.
1HP motors tend to use 16/19 mm shafts, 2HP motors tend to use 19/24 mm shafts and 3HP tend to use 24/28 mm shafts.
It's not always possible to bore out the holes in pulleys as it may leave too little material especially if new keyways need to be cut (i.e. not easy)
A simpler alternative is to purchase a new pulley but this may not always be possible e.g. pulley is specialised such as on a DP or BS.

d) The switches on a machine usually need to be changed especially if they cannot handle higher currents. Besides VFD use different switching arrangements anyway.

My experiences on converting some 3phase to VFD machines are as follows
************************************************************************
MW Hercus lathe: motor changed from 1/2 to 1HP, straight swap in terms of motor mounts but had to purchase a $20 pulley with a larger (19 mm) bore to suit the larger motor. Motor cost $50 and VFD was $285, This is a special vector controlled VFD so it provide usable more power at low revs and even usable torque at 1/10 the speed. I still need to change gears for some work.

Woodfast Mini WW lathe: motor changed from 1/2 to near new 1HP 240V 3P , the bigger motor would not physically fit in space so had to mount it underneath the bench and use a longer belt. a completely new motor mount and tensioning mechanism was needed. This lathe used a special 6 position V-groove pulley and I could not bore out old 16 mm diameter pulley to fit new 19 mm motor shaft - in the end I turned a completely new Al pulley (cost was $30 for Al block for pulley). Lathe was in very good condition. Motor was $30, VFD was $120 - definitely worth doing - hardly ever change the physical gears

Sherwood Drill press: motor changed from 1 to 1.5HP, straight swap, motor mount holes in slightly different positions but new motor had a 16mm shaft and had to make a shaft adapter to fit the 19mm bore DP pulley. See here VSDing a DP (http://www.woodworkforums.com/f155/vsding-dp-167663) This motor cost me $30 and the VFD $140. The DP was in average condition probably only just worth doing. Still have to change the gears for >12mm holes in metal and >25 mm in wood.

Clisby Compressor: 4HP motor changed to 5HP. Motor mounts were different and new motor shaft was shorter so made an adapter plate to short motor so the pulleys lined up better. 28 mm Pulley was easily swapped. Motor cost $30 and VFD was $225? I bought the compressor for a good price so I was prepared to spend the money. Compressor located in enclosure, exhaust fan failsd motor overheated and died. Replace motor with 4HP SP as variable speed unnecessary.

3HP 1m long x 6" wide belt sander.
Complex 2 speed 3P Motor deeply integrated into machine. Had to be rewired internally to run under 240V retaining full power at 5Hz but losing two speed capability but not needed because VFD gives variable speed.
Machine was free - only cost was $150 for the VFD plus switch gear. This works a treat

Carbatec Bandsaw; Original 2HP SP flange mount replaced with 3HP 3P foot mount - details here.19" BS upgrade (http://www.woodworkforums.com/f27/19-bs-upgrade-195900)
This motor cost me $70 and the VFD was $180. The bandsaw is in very good condition and I deemed it worth doing and it works very well

Nova WW lathe done for another member. 1HP flange mounted motor replaced with a 2HP foot mounted motor via a home made adapter.
See here http://www.woodworkforums.com/f8/converting-nova-lathe-vfd-206530?highlight=Nova+VFD
Issues with pulley required it to be bored out to 24mm to suit new motor - seems to be hanging in there, client very pleased with the job

Have also converted 3 grinders and a fan. 2 of the grinders run alternately off one VFD.

Switch gear was replaced on all of these as I completely rewired them to run through VFDs.
All my machines have safety EM or mechanical latching switch inputs to the VFD which still the motor

[Fuzzie]

It seems from Bob's answer I have the wrong end of the stick again. I can't say I understand all the Chinglish in my manual but I assumed the attached wiring diagram didn't also require a change of motor, perhaps it does.
392099

[NCArcher]

It seems from Bob's answer I have the wrong end of the stick again. I can't say I understand all the Chinglish in my manual but I assumed the attached wiring diagram didn't also require a change of motor, perhaps it does.

The diagram shows the control connections for two different motors. If it's out of a manual you would follow the diagram that matches the motor you were supplied.

[BobL]

Yeah they show wiring for two different motors , a 1P and a 3P.

There is a way that a 3P can run on 1P using a capacitor on one of the phases but its not an optimum arrangement.

[Bohdan]

Some motors can be wired for either 1 or 3 phase. I think it's called a Delta connection and I think BobL has a thread somewhere on here about how the different wiring for the phases work.

A 3ph motor can be wired for single phase with capacitors but the power output is significantly reduced. A 3ph motor wired "delta" will run on 230v 3ph and the same motor wired "star" will run on 415v 3ph with the same power. Star/delta starters are used to bring a motor up to speed in "star", limiting the starting current, and then switch to "delta" for full power.

Your best bet is a VFD with the original motor and if the motor power is not enough at slow speed change pulleys to run at a higher motor speed.

[John.G]

Contrary to everyone else's opinion your best bet if you own the place and don't expect to leave for a few years is install 3 phase power.
You only pay for it once... The other choices you'll pay for every time you turn it on, or look at other equipment, etc etc etc.
Price it up... It just might surprise you

[BobL]

A 3ph motor wired "delta" will run on 230v 3ph and the same motor wired "star" will run on 415v 3ph with the same power.

Thats correct but not all 3P motors are like that.
Some 3P motors are sold wired as delta to develop full power on 415V which means they run at half power on 240V 3P.
If these are rewired as star they need 680V to run at full power.

[rob streeper]

I did a motor swap VFD upgrade to my bandsaw a couple of years ago. True, 120v single phase to 240v three phase but the setup was easy. http://www.woodworkforums.com/f27/refit-delta-14-single-speed-woodworking-bandsaw-phase-metal-cuttin-181012

[arch1]

Fellas, I'm overwhelmed with the interest in and contributed wealth of knowledge on my question. Some of the detail is over my head but the range of suggested approaches has opened my eyes to the issues involved and given me some direction for further thought. I will check on available resources locally, look more carefully at my existing set-up, and come back to the forum to fill in gaps in info as needed. Many thanks to all.

[ian]

how big -- in amps or horsepower -- is the existing 3-phase motor?

before going too far, you want to be sure you have the power supply (in amps) to power the VFD you'd need to in turn power the motor on the lathe.

most sheds only have a single 10 amp circuit which could easily be overloaded.

[BobL]

how big -- in amps or horsepower -- is the existing 3-phase motor?

before going too far, you want to be sure you have the power supply (in amps) to power the VFD you'd need to in turn power the motor on the lathe.

most sheds only have a single 10 amp circuit which could easily be overloaded.

A 10A supply can deal with up to a 3HP motor on a VFD because it can be used with a soft start to reduce start up currents.
Don't know of too many wood lathes that need more than this

[John.G]

A 10A supply can deal with up to a 3HP motor on a VFD because it can be used with a soft start to reduce start up currents.
Don't know of too many wood lathes that need more than this

Soft starts are the most common "electrical fault" item in a sawmill: seems every time you turn around you're replacing one. On a bigger motor with high starting load like a saw there ain't much by way of options. But at that size I'd be really trying to stay DOL, or going for a VFD. ( I don't have any experience with VFD's, but they can't be worse )

[BobL]

Soft starts are the most common "electrical fault" item in a sawmill: seems every time you turn around you're replacing one. On a bigger motor with high starting load like a saw there ain't much by way of options. But at that size I'd be really trying to stay DOL, or going for a VFD. ( I don't have any experience with VFD's, but they can't be worse )

I didn't mean using a VFD AND a separate soft starting device, but using a VFD AS THE soft starting device.

[John.G]

I didn't mean using a VFD AND a separate soft starting device, but using a VFD AS THE soft starting device.

Im with you now - I thought you meant using soft start instead of VFD. My apologies.