3 phase wiring

[CornishPete]

I have a rudimentary understanding of 3ph and star/delta wiring, gleaned from a few YouTube videos, but I have a few questions relating to an Ajax power hacksaw I've just bought and would be grateful for some answers!
Why does the motor plate list 240/415 volts? And why are there two junction boxes when it appears the one feeding the motor is permanently 'star' wired? What's the first one for? And finally I only have single phase 240 supply so would I be best getting a vfd or swapping the motor?
Cheers!

 

[Smouser]

The motor is a dual voltage 3 phase motor. It can either be run by a 240v 3 phase supply or 415v 3 phase supply.

Personally I would get a VFD and run the motor from that. That way, it will also give you speed control.

The switchgear will not work with the VFD, so that can be removed.

 

[Robert Weaver]

Looks like the plate gives the options for star and delta; in delta, the voltage is 240 and in star, the voltage is 415 (2 windings in series).

Two switch boxes helps assembly/installation and makes the motor more generic to the wider application.

Edit: wrong way round

 

[daleyd]

The box on the motor is the final termination point, the other box contains a contactor and buttons to stop/start the motor. As it’s a fairly small motor there is no star/delta starting - it’s direct on line meaning there is no automatic changeover from star to delta which is used on bigger motors to reduce the starting current. The contactor simply passes 3 phase directly to the motor. In star:delta starting there are several contactors and timers which automate the switchover when you push the start button.

As has been said your motor can be connected to either 230v or 440v 3 phase - depending on how it’s connected which can be star or delta (don’t confuse this motor connection with star/delta starting arrangement - that’s a different, albeit related, thing)

 

[Agroshield]

The switchgear will not work with the VFD, so that can be removed.

Agree on the VFD. I am not sure why you would want speed control on a power hacksaw.

It would be better to say that the switchgear is not needed to make it work from the VFD as stopping and starting can be done by pressing buttons on the VFD itself.

The trouble with this approach is that the VFD needs to be exposed (to dust, swarf, etc.) so you can press the switches, and they normally come with a membrane keypad which has a short life when prodded repeatedly with an oily digit. So remote switching of the VFD by some means is highly desirable.

With some thought, you can repurpose the original switch to achieve this*. It has the advantage of preserving the authentic look of the machine if that is important to you.

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To the OP: the photo on the right, bottom is the motor junction box. At the moment, this is in star mode - the three incoming brown phase wires connect to one end of each of the motor coil wires (they are the light brown ones under the phase wire on the top row of terminals. The bottom row of terminals uses the horizontal bus bars (there should be three of them - one side will a double stack) to common the other end of the three motor coils, to form the star point.

If it has been wired correctly from the factory, changing it to delta is as simple as making the three bus bars vertical, one between each pair of terminals. In principle, you should not have to touch any wires. But it is best to remove the incoming phase wires and the bus bars and map out the motor connections with a multimeter (set to continuity) just to confirm**.

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* It may work directly out of the box - at the least it will have a momentary contact for switching the machine on. The difficulty is switching it off - easy if the original switch is a maintained contact, slightly more tricky otherwise. Show us a picture of the front of the switchgear and we can see.

** With the incoming wires and the bus bars removed, top left terminal should show continuity with bottom middle; top middle with bottom right; top right with bottom left. The only other way is a mirror of this.

 

[CornishPete]

Here's the other pictures I have. Looks like there's a switch box that turns the power off once the workpiece is cut through and the blade drops.
Also it will be used at home relatively infrequently so definitely not a workshop environment.
Ideally I was hoping I could leave the saw as is, install a vfd and retain the original features/functionality.

 

[Robert Weaver]

Do you need variable speed and reverse on a hacksaw? With the cost of a vfd, plus remote and box, and if you don't need speed control, a single phase motor would be cheaper.

 

[Agroshield]

...Looks like there's a switch box that turns the power off once the workpiece is cut through and the blade drops.

That is just a rod that presses on the red button, which you would press with your finger as a manual stop, so it adds nothing to the circuit.

The bit you need to open and work out how it works is the box with the red and green buttons on it. In principle, this should be able to connect directly to the VFD control circuitry. The VFD uses low voltage control circuits and minimal current, so wire size and switch capacity is not an issue.

VFDs are cheaper than a motor e.g. https://inverterdrive.com/group/AC-Inverter-Drives-230V/WEG-CFW100C04P2S220G2/ and that is from a bona fide UK-seller who will give you some guarantee*. You do not need to mess about finding a replacement motor with the same frame size and shaft diameter as existing.

Measure the internal dimensions of the box with the contactor in it - the VFD above might even fit into the same box (you would need to provide some ventilation in the bottom of it).

* Inverter drive do not stock it, but have a look to see if there is a 0.55kW version available in the same WEG CFW100 series. Maybe it will save a few pennies.

 

[hotponyshoes]

These saws have 2 speeds as standard which you change by moving the belt position on the pulleys.

I don't think I have ever changed the speed on mine but you could still move the belt around even if you were running it from a vfd.

The original stop switch is also used for the auto cut of. You want that adjusted and working correctly or bits of offcut can snap the blade off.

 

[CornishPete]

Cheers for the replies. More pics attached!
I thought that a vfd would install inline and the rest of the saw would stay in place!
So If the vfd replaces the contactor can the original switch be used to retain the (albeit crude) automatic switching off function?

 

[hotponyshoes]

I *think* that to use a vfd then you would need to run some wires from the original stop switch to a stop input on the vfd but wait for somebody else to confirm that?

It's crude but it works just fine on mine.

One other thing, if you use the vfd for speed control, the coolant pump is driven from the main motor and is adequate but not amazing. If you slow the motor down much you might find coolant flow a bit lacking.

If you want a plug and play solution maybe have a look at the transwave type converters. More expensive than a vfd but there is no setup required. Would probably only be worthwhile if you would be likely to get any similar power 3ph kit in the future but if you eventually want a couple of piller drills, Chop Saw etc it might be cheaper to just spend out of one of those now..

 

[daleyd]

I’d say hotponyshoes is about right - you can use a vfd but there will be a bit of wiring to be done to use the original switches if you wanted, but it’s certainly easy enough to do.

The problem with using the original contactor etc is that once you have a vfd it’s no longer really needed, and because the vfd gives a variable voltage output it wouldn’t work anyway.

Rotary converter would work “as is” but more expensive and you don’t get speed control. Vfd - you get speed control, smoother starting/stopping and other functions but a bit more work to implement (but not really that difficult)

 

[Agroshield]

So If the vfd replaces the contactor can the original switch be used to retain the (albeit crude) automatic switching off function?View attachment 340833

Yes.

Download the programming manual for the one suggested above from here:

https://inverterdrive.com/file/WEG-CFW100-programming-manual

Download the user manual here:

https://inverterdrive.com/file/WEG-CFW100-Manual-Gen-2

Look on page 97/158 at section (e) Figure 9.10. That is exactly what your switch does - momentary NO start and momentary NC stop. It is called 'three wire control'. Every modern VFD can operate in three wire mode.

The common wire (blue on your switch) goes to the GND terminal (page 18 of user manual) of the VFD. The other two wires (black and brown) go to two different digital inputs of the VFD (i.e. DI1 and DI2 on the same page/diagram).

If the VFD does fit in the enclosure, you might not even need to cut any wires - you will just have to change the existing four core 'source' cable for a three core one.

Edit:

 

[CornishPete]

Thanks so much for the replies! I'm away for Easter so will be another few weeks before I tackle this but I'll get a vfd ordered for when I return! Will probably be more questions!!
Thanks again!