Thread: best way to run 3 phase stuff on 240v ?

Originally Posted by thorens

hi every one.
I looking to update my lathe to a bigger lathe and found most of good lathe is run 3 phase and i don't have 3 phase main installed so what would i do to get around using 3 phase lathe ?
Cheers
Peter

Try doing a search for 'phase converter' or 'VFD'

hi mate how big of a lathe. i think its a common problem. you can easily run say up to a 3 hp single phase motor may be more. so slip a single phase motor in to it

Read through some of these threads.

https://www.woodworkforums.com/f65/24...se-vfd-128758/

https://www.woodworkforums.com/f155/3...verter-131395/

https://www.woodworkforums.com/f189/3...nverter-96179/

https://www.woodworkforums.com/f78/3-...4-5-pin-32872/

https://www.woodworkforums.com/f65/2h...running-52259/

https://www.woodworkforums.com/f78/3phase-motor-61964/

https://www.woodworkforums.com/f189/2...roject-125170/

There are heaps more there but these will give you an idea of how it works.

[QUOTE=Cliff Rogers;1372931]Read through some of these threads.

https://www.woodworkforums.com/f65/24...se-vfd-128758/

https://www.woodworkforums.com/f155/3...verter-131395/

https://www.woodworkforums.com/f189/3...nverter-96179/

https://www.woodworkforums.com/f78/3-...4-5-pin-32872/

https://www.woodworkforums.com/f65/2h...running-52259/

https://www.woodworkforums.com/f78/3phase-motor-61964/

https://www.woodworkforums.com/f189/2...roject-125170/


Thanks all.
I have decide to not go 3 phase stuff. will stick with the 240v .
any one have a good medium size lathe that want to let go? prefer spidle bore at around 30mm or more.
Cheers
Peter

define medium size....

To me medium size would be a 20 inch swing +

I have made a Static Phase Converter with automatic start. The circuit consists of a few mains rated capacitors and a timer circuit, mains relay and momentary switch. Input is single phase 240V. You basically take a 3ph motor and run it as a 2phase unit with the 3rd phase unconnected. Caps are used to provide phase shift for the 2nd phase and extra caps are used in parallel momentarily to increase power to provide starting torque. The timer circuit is tuned to cut out the start caps when motor is at full revs. Theoretically this method gives max 2/3rd rated motor power, there's slightly more vibration. You can also use this method to drive a pilot motor which will produce 3phase power to drive a second motor. simply connect the two motors in parallel with a switch to activate the second motor once the pilot is up and running (rotary phase converter).

The timer circuit isn't strictly necessary as you can use personal judgment when to release the momentary switch, almost press and release. I used this on my Bridgeport 2J2 mill before I got 3phase to the workshop. The mill has a 2hp motor and with this circuit it would start in under 1.5seconds connected in delta wound mode

Most three phase motors will run on single phase (delta 240) if you provide external starting torque (i.e. rope around the pulley). The danger is in stalling the motor so you need to be quick with the power switch otherwise you can burn out the winding

The 3ph motors supplied with the 9" Hercus lathes (1/2hp Cadet) are difficult to convert to delta winding as the "star point" is buried deep under the stator windings and fixed in with laquer, at least the two I looked at had this problem. I had no success with them.

I know I have two phases running to the house. Can a 3 phase motor be wired up to two 240V outlets on the different phases to run a 3ph motor as swarfmaker suggests above on 2 phases?

I imagine the earth leakage breakers would trip without doing something funky to the neutral lines?

Be careful... it depends on the phase angle.

If you have 2 phases of a 3 phase main supply the phase angle is 120°

If you are on the end of a SWER line in the bush & you have 2 phases off the pole transformer, the phase angle is 180°

If you get it wrong, it could end in tears.... & maybe smoke.

Just an academic question on my behalf Cliff. I actually think there is a 3 phase cable attached to our property pole here, but only 2 of the 3 wires run into the house. The 3rd looks to be cut off at the top of the pole.

What Cliff is saying is correct (regarding phase angles), but it is still quite possible to run a (decent) 415V 3 phase motor off 480V split phase or SWER.

I run static phase converter that sounds very similar to Swarfmaker's except I run it off 480V split phase and my start caps get switched out when a certain voltage is reached (rather than after a certain time) .

So far I have run a dust extractor, panel saw (these run together), spindle moulder and metalworking lathe off this converter without issue. There is no step-down transformer used, so the motors all run off 480V.

Fuzzie, how many power meters do you have in the box? If two then you have two phases coming in. You may only have a single phase plus neutral. My old mains supply had two phases plus neutral on a 3 core supply cable. There were two separate meters in the box too. I guess if you have a CRO and you can identify the two separate circuits you could use a couple of wallwart plugpacks to isolate the supply and use the CRO to measure the phase angle to see if you have the 120deg separation. You may need to use caps to boost starting torque as the 2phase config may not automatically rotate. You could get 3phases by shifting the second phase using the capacitors and then you would only need run capacitors permanently switched in and that should give a rotating magnetic field with near full starting torque. Using capacitors doesn't necessarily give a true 120deg phase shift but near enough. of coarse this is nowhere near as good as a VFD. My Bridgeport has the varispeed head so I have infinite speed control between 50 and 1400 (or so ) RPM.

Originally Posted by Fuzzie

Just an academic question on my behalf Cliff. I actually think there is a 3 phase cable attached to our property pole here, but only 2 of the 3 wires run into the house. The 3rd looks to be cut off at the top of the pole.

I'm not sure if the number of meters is all that definitive eg. we have 3 meters (2 phases and off peak).

Also an easy was to tell if it's 2 phases of 3, or split phase/SWER is to measure the voltage across the phases :

0V - same phase
415V - 2 of 3 phases
480V - split phase/SWER

Originally Posted by Swarfmaker1

Fuzzie, how many power meters do you have in the box? If two then you have two phases coming in.

Not quite true... We have two meters, one is for off-peak power (hot water system) the other for everything else... Every state is probably different..

I would be surprised if he has 2 phases coming in.... That would mean you have 480V phase to phase... Not very common...

Originally Posted by .RC.

I would be surprised if he has 2 phases coming in.... That would mean you have 480V phase to phase... Not very common...

It seems to be fairly common in this area for 2 phases to be connected. The pool pump and the aircon are on circuits connected to one phase and the rest of the house on the other phase. I don't actually understand why that is, it seems to me the supply load would be evened out down the street by connecting houses sequentially across the three phases. But who am I to question how SEQB did things back in 1970?

A couple of years ago we had the original fuse board upgraded to circuit breakers and ELCBs when we had the pool pump connected to regulated supply. I think the question was raised at the time about the number of meters/phases and the answer was that there were more than (I think) 5 power circuits on the board and 2 phases were required by Energex regulations.

BTW I'm on city supply and virtually in line of site to the local substation.