Lathe motor replacement

Edited By Hywel Evans on 15/01/2017 16:36:18

Edited By Hywel Evans on 15/01/2017 16:37:21

Edited By Hywel Evans on 15/01/2017 16:39:12

Edited By Hywel Evans on 15/01/2017 16:40:40

Edited By Hywel Evans on 15/01/2017 16:42:26

Edited By Hywel Evans on 15/01/2017 16:42:54

1. You need to check the inverter installation manual with regard to what the manufacturer wants in the line to the inverter, some of them require a contactor feeding it, some don't.

2. The reversing switch on the single phase motor would probably be reversing the feed to the start winding/capacitor (on the 3 phase version of your machine it would be swapping two of the incoming phases). You can't simply wire the existing electrics into the inverter. Having said that you probably can use the existing switches after rewiring the machine.

Best solution is to ask the supplier and read the installation manual. A good supplier will be able to give you guidance as to how to set up the parameters on the drive and give you guidance on the best way to fit/wire it.

Martin

Best practice is to have a switch or isolator on the incoming supply and use the inverter controls for everything else. Easiest, and probably not that much more expensive than DIY, to buy a pendant or control box made to work with your inverter. Wired my own in the past but these days I'd just get the pre-made box, despite having suitable components to hand, saving all the hassle and futzing about. If you are not set-up and ready its an easy 2 or 3 hours to make a box and not that much less to splice something in based on what's on the machine. Just sorting out the which connection goes where can be a serious puzzle for the uninitiated.  Sometimes life is too short!

Clive.

Edited By Clive Foster on 15/01/2017 17:20:10

You won't need a NV switch or your old reverse switch , the default setting for the inverter should be set to motor off and all you need is a toggle switch wired into the reverse terminal on the inverter to rerse the motor although you could possibly use your old switch for this .

You will need start and stop buttons and you can also have a jog button , an emergency stop button gets wired into the fault terminal once again depending on what type of switches your machine has ( momentary or latching ) you may be able to use them on the inverter

The other option is to mount the inverter directly above the head of the lathe and use the little control panel on it and just wire in your emergency stop using the old switch if it has one.

My inverter manual stated it is not recommended to have any sort of switch between the motor and the inverter as it can damage the power transistors .

All the Dewhurst switches I've seen can be wired to either reverse the phase of the start winding in the case of a single phase motor or transpose two phases in the case of a three phase motor. Beware, this might take a bit of figuring out to a non-electrically savvy person.

Edited By Brian Oldford on 15/01/2017 18:49:06

To summarise most of what has been said in the previous replies.

The VFD already functions as a NVR switch (unless you reconfigure it) as by default it will not let the motor run until it gets a valid start command on one of its digital input terminals.

In theory, for a fractional HP motor you do not need any contactor or isolator on the input of the VFD if its fitted with a 13A.

Whatever the existing switches and controls are its more than likely they will be suitable to act as stop/start and reversing controls. Most VFDs just require a simple contact closures to select the functions. Its unlikely you will find the controls on the front of VFD easy to use, partly because its not easy to put the VFD where they are convenient, but also up/down buttons are not ideal for the speed control. Wiring a potentiometer in a convenient position is much better. (three wires)

Before you start wiring up any switches think how you want to control the lathe. On my lathe and mill I have a three position toggle switch, FWD in the down position, REV in the up position, centre OFF. I imagine any existing switch (Drum type) would be ideal for the same purpose and would only need three low voltage wires to connect it to the VFD.

I'm not a fan of 'stickies' but 'VFD usage' and (dare I say it) 'Lathe levelling' are both crying out for definitive guidance

Ian P

With a 13A plug that is within easy reach, is what I meant to say.

Edited By Ian Phillips on 15/01/2017 19:14:17

My own preference for this type of conversion is to use existing switches, knobs etc, for their original functions. This way there is no need to have to re-label control panels and anyone who has operated a similar machine will have no problems in finding the relevant controls.

The other consideration for inverter installation is the buttons provided on the unit are fine for testing or setting up the unit but are probably not the best in terms of durability for daily operation, nor are they very big. Its much better to have proper industrial type control gear that is designed for the job.

The.other thing to consider is that the inverter is not the best thing to mount on top or adjacent to the machine as (to my mind) they are not the most robust of items and will come off second best in an impact situation. They are often not provided with the best ingress protection when dealing with swarf etc. Installing them in a suitable enclosure is better for them and (in the case of a metal enclosure) can also help with EMC/RF issues.

Anyone who can operate a multimeter and has the competence to install an inverter should be able to re-configure the electrics on a machine to work with an inverter. If you don't feel that your competence extends this far then you should be seeking advice from someone who does!!!!

Martin

PS Ian has just said almost the same things as I was typing this post

Edited By Martin Cargill on 15/01/2017 19:19:36

Edited By Martin Cargill on 15/01/2017 19:21:36

Should the inverter be installed in an enclosure, consideration needs to be given to ensure there is sufficient cooling to prevent any possible overheat scenario.....

Hywel

I've just re read your original post and perhaps realise that you are asking if you can use the old 3 phase reversing switch to switch motor direction by having this wired between the inverter and the motor.

This is not a suitable method.

The drive unit will have low voltage control inputs for start/stop/reverse etc and it is possible (and sensible) to re configure the wiring to use the old switches to feed these inputs.

Martin

PS just read your last post. The existing contactor should be able to power the invertor. The inputs to the inverter controls only require pushbuttons and not contactors.  Can you give us a link to the manual ?

PPS I have two Viceroys so I know the controls fitted  to them. 

Edited By Martin Cargill on 15/01/2017 19:40:59

Edited By Martin Cargill on 15/01/2017 19:42:35

Hywel

I just skimmed through both manuals but did not spot where it recommended using a magnetic contactor. I can see that a contactor might be worthwhile if using a large, high current motor but for a FHP motor any normal switch that can handle the current should be fine.

What do you mean above by using 'contactors for on and off''?

Ian P

The point they are making is that you should use the inverter for turning the motor on and off. Any switch in the incoming supply should only be used when the motor is already off. Or an emergency.

Same for reverse, it is not a good idea to switch the 3 phases to the motor unless you can guarantee the motor is off when doing so. Again better to use the inverter to do reverse.

Toby

The reason they mention a contactor is that some inverters take way more current than switches can easily handle. If you fit one it would usually finish up wired to be used in an NVR fashion. You might just use an NVR switch to do it on something that can run off a 13amp plug. There shouldn't be any need though as the inverter will behave like an NVR switch. Remove the volts say due to a mains failure and when it comes back the inverter wont switch the motor back on. Or shouldn't.

There is a bit of a catch though. When powered up inverters take a big gulp of current which isn't good for contacts in switches. Best to use one that is over rated for the job.

There can be a need to isolate the inverter so some sort of switch should be fitted. An oridnary NVR could be used but isn't ideal for fault conditions that shouldn't happen which could cause the on contacts to weld. You could use a panic stop button - they are used because the button actually forces the contacts apart. A better option which does the same thing is a rotary on of switch. It's obviously on or off. A panic button could also be added after that for panics and nothing else.

One option as they can be bought all in one box might be an nvr switch and a panic button.

It's all an area where people tend to do what they do rather than follow a set of rules. If the machine is owned by a business things get a bit different,

John

=

Edited By Ajohnw on 15/01/2017 23:14:01

It seems that the easiest and safest option is to do away with the existing switch and replace with a pendant remote controller. As Clive says, the time spent faffing around making your own (if like me you have to learn to do it first) means that I might as well buy one. Does anyone have any reccomendations - I've seen some comment about poor ergonomic design on the forum. The outputs are 24 V and 12 V for the potentiometer.

Hywel

Edited By Hywel Evans on 16/01/2017 08:53:29

Horses for courses really. On my lathe I made my own control panel, on my drill I am re-using the drills start/stop switches to control the inverter but not using the existing contactor, E-stop etc.

I don't have any experience of using a ready built control panel/pendant though.

Toby

The block diagram you showed does not have a major omission, but rather too much confusing information!

The last thing that block diagram should show is a reversing switch in that position, in fact in any position!

The text says it is not recommended so why show it in the first place.

All a VFD block diagram need is a box containing the VFD and a box containing the motor. Another box to show the main power switch (NVR/Isolator or whatever) and a box showing the potentiometer and switches.

Ian P

Toby,

Distinct lack of over current protection on the incoming mains side to the inverter......either a fuse or an mcb....

I see a switched fuse spur, but, that also powers other ancilliaries.

As previously stated, no hard and fast rules, use the guidance offered and do what suits you without putting yourself in danger....

Thanks for the feedback Ian.

The reason I put the reversing switch in is that it often comes up when people want to re-use the existing wiring and existing switch and I am sure I have read here people saying they have used it in the location shown. So I didn't want to ignore it.

Same goes for the output filters (reactors). Personally I would not fit one unless there was a proven need, but others have for good reason. Hence the optional bit.

If someone wants just a basic block diagram showing the inverter and motor and controls then they are best looking in the inverter manual. That will also show the control configuration which might be specific to the inverter.

That was my reasoning anyway, what do others think?