Running several 3 phase machines

What is the best and cheapest way to run a few different 3 phase machines off 240volts?Can a single VFD be used and plugged in separately to each machine when needed?

I don't see why not, in principle, as long as the motors are about the same sort of spec. But you would need to be very careful not to have more than one on at once, I suggest (although a free-wheeling motor might not be a problem). The same speed control would operate each individual motor at the same revs (or a multiple if the motor windings were doubled or halved).

But I am no expert at such things - perhaps my amateur comments will prompt an expert to offer advice?

Cheers, Tim

Hi Andy,

I agree with Tim, and you will of course turn the VFD off before disconnecting one motor and connecting the other.

Thor

Just wire up a 3 phase circuit with a rotary converter. As long the converter is sized for the largest motor that you wish to run, there is no minimum, unlike a static converter.

Pete

Edited By Spurry on 08/09/2016 10:02:59

Andy,

I plan to do the same with the two motors of my "TN" machine.

So far as I am aware; the only significant problem might be electromagnetic interference, leaking from the plug & socket assembly ...

Unless you can find some exotic connectors, it would be wise to put the plug & socket inside a screened box.

MichaelG.

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http://www.model-engineer.co.uk/forums/postings.asp?th=109971

Edited By Michael Gilligan on 08/09/2016 10:08:15

The milling machine is 2 hp and the lathe is 1.5hp.Rotary converters are a lot more expensive, from what I have read I will need a 3hp which is over £700.Is anyone running a few machines on a single VFD and have found that it works ok?

I have 18 motors in my workshop all running off individual VFD's

For the cost of inverters/vfd's secondhand on ebay they about the cost of a decent plug and socket

out of perhaps 30 bought i've not had a dead one

mostly i have paid 20-30 £ each

and you can then tune each vfd to each motors charecteristics

I'm sure if you are carefull then using one will work but beware powering up an unconnected vfd they apparently dont like it though i have never tried it

Edited By daveb on 08/09/2016 15:06:10

Ideally the motors would be of similar rating if you are going to swap them over. Some VFDs can accept config data for 2 motors and be switched over, allowing different ratings to be driven (eg a big motor and a small one). Obviously if you have a VFD set up for a big motor and you drive a small motor, you aren't going to have protection against overload etc without this kind of feature and it may overdrive the smaller machine.

As Ian says, you get get them for peanuts. Even if you buy new you are talking £100 for a 1.5HP or so, decent brand.

Rotary converters and converters in general tend to overwork the motor by only delivering 60% of the rated power and over heat due to slow fan speed, i'd steer clear of them and go for VFD's, it's more expense but you'll get a healthier and more diverse speed controll at the end of it.

Michael W

I know very little about VFDs so any help choosing and setting up would be great.Here are the three motor plates Mill,lathe and bandsaw.The mill and lathe are thr most important I was hoping I could slow the bandsaw down with the VFD but I could change it to single phase.So is it possible to run these three machines with the one VFD without any problems,only one at a time of course.Sorry the pics arn't great.

Andy,

I'd always go for an inverter thats rated over the maximum power for the motor, so if you've got 1.5hp motor, go for a 2hp inverter to be on the safe side,

Also i've had a good experience buying from transwave converters, or failing that Newton and tesla.

I dont think i've ever heard of someone running multiple motors from one VFD, sorry. 

Michael W

Edited By Michael Walters on 08/09/2016 20:25:36

Andy, The only time you need to overrate a VFD is in an application where there is a high starting torque. Not a requirement in my workshop. Regards, Michael.

Two of the motors are twin speed how does this work with the VFD?

I use one VFD for three machines, as I'm not very good at multitasking, and can only use one machine at a time, so there are no problems at all.

Even setup a distribution board for the lathe and miller, to incorporate a changeover switch using the same breakout box, as they are close together.

The drill has its own breakout box and is routed via an extension lead, also fitted a 7 pin socket to the VFD, for the breakout box changeover.

Not sure about what the interference is though...

Bernard

Hi Michael,

I agree that it's not always necessary, sometimes you can "get away with it". I usually use the leadscrew or gear train with lathe, and found that the extra strain on the motor, overheated it on heavy interference cuts.

To be fair, this incident wasn't with a fan cooled inverter, and could account for that. There is a 10% margin on the power anyway. 

I would only try running 1 VFD off several motors if you're confident you can handle the wiring situation. 

Michael W

Edited By Michael Walters on 09/09/2016 09:32:13

Some of the older properties in my village are supplied by power cables on poles that look similar to telegraph poles. They can get 3 phase power to their houses for quite a low cost compared to properties with underground services. The poles carry 3 phases plus neutral so it is a relatively easy process to connect the other two phases and a suitable meter (unlike digging holes in the ground). If I had this as an option I would give it serious consideration.

Martin

One of your motor plates only shows 400v, one shows 400 for both star and delta which is unusual and may be a misstamp, and the other is unreadable. There could be problems here. as you need a 220v delta configuration for a low cost VFD.

However the less exotic old blue Transwave boxes do produce 40ov.

I contacted a VFD supplier who says I would have to change the two dual speed motors to run off the VFD yet reading on the net there are loads of guys running dual speed motors but they set them to the one speed and use the VFD for speed control.