Inverter or converter

Help Required

Looking for advice on the best route to go down to power up my 3ph Lathe and milling machine, i have very limited electrical knowledge on this subject so bare with me.

I have a Lathe (M300) with 3hp motor and suds pump plus a vertical mill with 2hp main motor 1/4hp feed motor and suds pump, it looks like the motors on the miller are dual voltage but i don't think the Lathe is, nothing stated on the data plate.

My dilemma is should i go with a rotary converter (told by Transwave i need the DD MT3 model) to power all these from one source ie just plug the machine i want to use into the converter and off you go, not so cheap.

The issue i have is the size of these double decked units and with the rate electricity prices are going running multiple motors sounds expensive. But the fact i dont need to alter the machines wiring does appeal because i won't be able to do that myself, they tell me i just need to have a 25amp supply fitted from my comsumer board.

The way i understand inverters to work is that i need one for every motor i want to run, this sounds expensive and does require wiring alterations which are probably beyond me so more expence getting a electrician.

I also have heard the inverters can cause the consumer units to trip out when under load and cause noise interference, that would go down like a lead balloon with the wife. I assume you need to have a separate supply fitted to cure these possible problems.

So the inverters appeal but the cost could be more than living with a rotary converter with the slave motor running all the time.

Any advice from someone who has gone down this route before would be appreciated.

Robert

All that I would say is that 5 inverters would/could be cheaper than the rotary converter.

Cheaper to run, too - no auxiliary motor taking power all the time it is switched on.  No need to turn the power off to change direction, either.

There are lots of useful programming options with VFDs. Variable speed, soft start, braking, jogging, easy reversing, and others.

Having said that I’m not sure about the lathe. Most motors can be re-wired to run 240V three phase, but some machines have peculiar interlocks or dual speed motors, multiple contactors, etc. 400V VFDs tend to be expensive items.

The other option is for a vastly over-sized inverter, which could run all of the motors (without any programming options, of course).

I like my 5 VFDs. Virtually no current draw when idle. Suit my machines and all the ones I have bought have given no trouble. Hence I would not entertain a rotary converter for my hobby workshop.

Others will be along shortly, to differ with my opinion, I expect.

Edited By not done it yet on 14/03/2022 15:55:40

Vfd can cause mcb to trip on switch on, easy cured by getting a slow blow mcb. As you possibly don't want to run lathe and mill together you could share an inverter, I wouldn't bother, as others say they are not that expensive. Modern vfd is not noisy. You might get the suds pump and feed motors to run on Steinmetz connection, but you'd need to rewire to delta

Edited By duncan webster on 14/03/2022 16:17:06

Edited By duncan webster on 14/03/2022 16:18:05

Robert

Given the current prices of name brand VFD boxes from the likes of Inverter Drive Supermarket (my go to) and other reputable suppliers the Transwave converter system is not really cost effective for your proposed use. In your situation as a non-electrical person the big win of a converter is that it is simply plug and play with no need for modifications to the machine electrics.

I'd set up permanent lines to the machines with an isolator in the way rather than swopping at the converter. Lets you put the converter out of earshot. The buzz of the internal motor and transformer can be obtrusive.

I suspect that if you have the set-up professionally installed and signed off you will need separate plugs and isolators anyway to meet current regulations. I like the yellow bodied with red lever control ISO isolators made by Lewden for this sort of thing. Not silly expensive and its obvious whether things are on or off, even from right across the workshop. Can be hard to find tho'

20 amp version here **LINK**

https://www.powerdiscount.co.uk/lewden-iso-20-isolator-20a-4-pole-ip56-59886-p.asp

Same thing under ERL brand **LINK**

https://www.electroreplacement.com/erl-4-pole-isolator-switch-20a-35a-45a-63a-max-415v-ip66

I absolutely don't approve of the round knob isolators because its hard to see if they are on or off from any distance.

If your motors are dual voltage and you can find affordable help with the wiring changes you will only need two inverters. The extra load of the suds pump and mill feed motor swill not worry a decent brand inverter. Especially if you don't exploit the speed changing capability of the VFD and simply use it as a 50 hz source.

That said most dual voltage suds pump motors work fine using the "capacitor trick" to run off single phase supply and its arguable that having a three phase feed motor tracking spindle speed makes life a little easier when milling. Most relatively modern feed motor systems use DC motors run off a transformer connected to one phase of the 3 phase supply which can easily be transferred to the normal single phase mains supply so no need to connect to the VFD anyway.

But you will need to find help if you are not confident with electrics.

Clive

When I considered how to power my Harrison M300 and Bridgeport mill I weighed up the options, and in the end decided to go for a proper 3-phase supply, Although not particularly cheap I needed to upgrade the incoming supply anyway, 60A plus a wind yer own fuses box. In retrospect it was a good choice as it makes it simple to run the two speed motors that some of my later machine tools have plus all the ancillary motors. If I ever get an electric vehicle it will make charging quicker.

An inverter inherently generates conducted emissions on the mains and radiated emissions on the motor cables. However, both are simple to deal with, using off the shelf filters for the mains and shielded cable for the motor connections. I have 2 inverters on my CNC mill and have not had any problems with noise or unwanted tripping.

Andrew

There is a 3rd (4th?) option which is a digital phase converter. These have been discussed here so you should be able to find the thread. They work differently from an inverter because the mains itself is used to supply one phase, with some clever electronics to produce the other two. So the frequency is fixed at 50 Hz but I believe that they can be used as a "drop in" replacement for rotary phase converters (which are horrible in this day and age). Drives Direct i believe stock them for one and should be able to advise.

Robert, like you I have a 3HP lathe and 2HP mill. The lathe does not support star/delta so I bought a Transwave static inverter. The lathe runs fine on the static inverter but the mill would only run for a short time before tripping out. A friend fitted the mill with a VFD for me and all has been well for over ten years. I am not confident to attempt the wiring, best left to the experts.

The plug and play digital phase converters sold by Drives Direct are an effective substitute for proper three phase mains supply. Mine is well over a decade old and doing just fine.

In principle nothing particularly clever about them. Just a normal style of single phase inverter with voltage doubling rectifier on the input. In practical the clever bit is making it work properly and seamlessly. Back in the day lots of folk offered voltage doubled inverters that sort of worked up to a point on E-Bay et al.

Not cheap. Price is similar to with Transwave converters of similar rating.

You can also get rather less costly Chinese made 380 volt nominal output inverters which should be able to run the lathe and mill motors without major wiring changes. Basically just bypass the existing controls and use the inverter buttons instead. They are said to work OK but I'm a little unconvinced as the suppliers seem to be E-Bay type "list and send" folks without proper technical back up.

Clive

Running a couple of big 3-phase machines with multiple motors off a single-phase supply isn't for the faint hearted.

A great deal depends on how much you can do yourself because paying someone else is costly, and it might be difficult to find a suitably knowledgable electrician. Anyone on the forum know of one?

The easiest answer is to pay for a true 3-phase supply to be installed because the machines will just plug into it and go. Unfortunately it's liable to be very expensive. However, worth asking for a quote because much depends on how much work is involved. Digging a trench across a main road costs a fortune, slinging wires from an existing pole outside the front door might be painless.

Next easiest is the type of converter that allows machines to be plugged in. They're bulky, inefficient, noisy and expensive but straightforward to use. They still exist because retrofitting a VFD to your complicated machines needs more work, in particular rewiring the control circuitry.

VFDs are small, efficient, quiet, inexpensive and provide speed control. Unfortunately the affordable type are fitted one per motor, and can't be shared. Not too difficult to fit to simple one-motor machines, but problematic when suds pumps, machine lights and other accessories are fitted. It will also be necessary to replace or rewire the contactor, and maybe to rewire the safety interlocks and front-controls, and fix star/delta on the motor, Not a beginner job. The newer "Digital VFD" are a possibility, but I don't think they're cheap or well-understood, at least by me! Popping the MCBs is a minor problem, even if it happens!

With luck someone who has converted the sort of machines you have to VFD will be along to explain there's a set of straightforward instructions suitable for beginners. Several members could do it from first principles, but I doubt you'll get many volunteers because it's an intimidating amount of work and it has to be done safely.

In your position, I'd reluctantly compare the cost of installing real three-phase with the cost of a converter. Unless the forum can identify an electrician who does this type of VFD installation for reasonable money.

Good luck

Dave

In my house built 2 years ago, 3phase to the building was the same price as single phase to the building. With the high density housing going up around us, the electric supplier instructs the electricians which phase the house has if single phase, or if 3 phase, which phase is the kitchen. This is to lower the overall current on any one phase for their peak demands. The advantage for me was 3phase to the garage of course. Recently , older houses with the asbestos main boards, are being upgraded with new meters, and 3phase connections at no additional costs. The new connections put the oven, electric hob if separate, on their own phase, with the rest of the house on the other.

So it may check to see if any such upgrades are happening in your area at all.