Switching Single phase To 3 Phase

[Delaney]

Looking to move workshops.
I currently run 3 phase motors (not sure as of writing if VFD compatible).

I’ve got a couple Felder machines. All 2022 models.

FB710 bandsaw
AD410 planer
k700 panel saw
SCM DMC 90 wide belt sander
Extractor

The workshop I’m visiting today does not have 3 phase, so am exploring possibilities to be able to use single phase.

My motors are rated 3 phase 400v. The machine that takes the most power is the sander. I think around 7kw when operating, as it has two motors.

I would be interested in hearing peoples experience and tips to do so. I assume VFD’s are the most common way to convert?

Many Thanks.

 

[ChaiLatte]

The VF in VFD is 'variable frequency'. Its main claim to fame is that is gives variable speed. The VFD device is a sophisticated control computer for the motor; it has all sorts of protective (overload) capability and can do things like soft start and braked stop.

If you have been using the machines plugged directly into a 415v three phase outlet, most of these capabilities are not required.

In your case, a traditional rotary converter (Transwave are about the best-known manufacturer) might be a better fit. MT7 or MT11 here: https://transwave.co.uk/Rotary-Converters

You would need to ensure the incoming supply and distribution board can accommodate the rotary converter, which might need some rewiring (MT7 needs 40A breaker and MT11 needs 60A breaker).

It is not clear if your extractor is single or three phase. If it runs when the sander is running and is three phase, you have to add its demand to that of the sander. If it is single phase, the single phase supply needs enough capacity for rotary converter plus extractor.

Edit: if you read this before your visit, take a good look at the incoming supply (and fuse rating) to the premises. Perhaps take a photo and post it here. If the wire coming in looks like a drinking straw, there may be challenges; if it looks as thick as your arm, it will be OK.

 

[Fitzroy]

The main 'problem' with VFDs is that you need to wire them direct to the motor, on older simple machines with a switch and a motor this is no big issue on more modern machines with micro safety switches etc it can all become a real faff to keep it working the same. Also your machines are probably still going to be valuable on the second hand market in 20years, messing about with the electrics and a VFD will likely impact any future resale value. A solution that serves all the machines a three phase supply so that you just plug and play would be an awful lot simpler. at MrLatte has said a rotary converter would suit this.

 

[Katomi woodsmith]

Stupid question
Why change from 3phase

 

[jetsetwilly]

Firstly I would always ask about cost to bring 3 phase to the workshop - it can vary hugely but sometimes it's worth it.

Agree with others - for your modern machines it'll be better to get 3 phase to them than to wire in VFDs to all of them. Are rotary converters still state of the art?

 

[ChaiLatte]

Are rotary converters still state of the art?

They are proven, simple, robust technology.

For a plug and play situation, where you are plugging into 230v single phase and playing with 415v three phase on multiple machines, there are very limited other options (Drives Direct, JFK Electrical, various Chinese offerings). It is a bit of a niche market.

Things are different if it were a single machine - that is where an individual 220v three phase output VFD would be more economic. With 4-5 machines as the OP, the rotary converter machine and wiring cost (amounting to a 40A or 60A breaker, cable and isolator, by any standard electrician) can effectively be divided up between them and there is zero labour/reconfiguration on the machine (the reconfiguration would need an industrial control engineer, less easy to find and a lot more expensive in itself; reconfiguration required on every machine).

 

[guineafowl21]

Like you, I’ve just moved from a 3ph to 1ph workshop with several 3ph machines.

One VFD/machine option was out due to expense and faff.

“Digital phase converters” are often just VFDs, unless you go for a very expensive pure sine type. You need to buy a much bigger one than the largest motor you have.

Picked up a 10hp rotary phase converter secondhand. Other than a bit of noise, the extra few seconds it takes to turn on and off, and slightly slower spin-up times, it’s like having normal three phase.

Hardly any circuitry, and easy to replace components, so it’s got the robustness of electromechanical things. Compare with solid state power devices.

 

[Sideways]

This should do it:

https://www.jfkelectricalni.com/product/digital-phase-converter-11kw-15hp-240v-in-400v-out/

No affiliation but two friends have bought from him and the units, though not more than a couple of years old, are working fine.

Don't cheap out.
Get a size bigger than you think you could get away with and you will run the device comfortably inside it's performance envelope. Components will be less stressed, wil run cooler and this should increase the lifetime and long term reliability of the drive.

On a DPC like this, the largest single motor that it can start is 60% (I forget, you need to check) of the rated power.

 

[Spectric]

In your case, a traditional rotary converter

I cannot remember how many years it has been since seeing a rotary convertor used, the digital phase convertor is the way to go and with that many three phase machines you would not want to start changing each of them to run on their own VFD. The best solution would be to get a three phase supply laid on but otherwise a digital phase convertor as @Sideways has mentioned but maybe spend a bit more and get more power and TP&N .

Your limiting factor will be the existing single phase supply, but if you are a one man band and not using several machines at once then you could use a smaller convertor that would place less demand on the single phase supply and do any of your machines require a neutral ?

 

[ChaiLatte]

...the digital phase convertor is the way to go

Please do a survey of the market and see how many people use this term.

It is a made up term, used as a marketing hook by two sellers: Drives Direct and JFK. It is meaningless. The device at the core of what they sell is a standard VFD that has been rewired to give 415v three phase output from a 230v single phase input.

There is no brand name, major manufacturer supplying these devices. Find a Siemens, Omron or other version of the same thing.

I am not against the device; I have owned a Drives Direct one for many years but I only mess around in my garage and know that one day when it lets the smoke out, I will have to buy a new one. What I worry about is trying to influence people's purchases based on a misunderstanding of how it fits in the power supply landscape.

Transwave are a long established manufacturer whose products are built of industrial lego and are easily repaired if any part does go wrong in 20 years time. As above, 230v in 415v out VFDs are a niche market which means a person should understand and accept the risks that attach to this. Any advice that does not stress this is not well made by the advisor and does not serve the best interests of the advisee.

 

[guineafowl21]

Yes, I nearly bought one of those JFK units, but the chap rang me up to check what I was running (obviously had some problems with returns). He was really helpful.

They’re not pure sine, so are harsh on older motor windings if run without an expensive sine wave filter, and don’t like DC brakes or two-speed motors (his words).

I know of someone who runs one with an idler motor to get round the drawbacks, but then, all he’s essentially got is a rotary with added solid-state unreliability, in my view.

 

[Sideways]

I agree that it is "no name" Chinese beneath, but as @guineafowl21 says, the seller in Norther Ireland is helpful so this a different proposition from buying off aliexpress.
The manual is slightly Chinglish but it is extensive, very different to the minimal instructions that come with many Chinese VFDs.
It is vastly more compact than a rotary converter of the same power.
It is again more compact and in my view superior to a Transwave or other traditional static type converter. Those are primitive by comparison and in their own, different way, don't create an ideal balanced 3 phase supply.

The caveats about DC brake and two speed motors are entirely valid but in a small workshop may not matter. I have industrial machines in my own and they don't have DC brakes or 2 speed motors.
The point about pure sine is also fairly made, and I haven't put the scope on one to see if they are any worse than a typical VFD, but VFDs also requires costly filters in some instances. Generally these aren't needed nor are they fitted.

Final point - sizing is all.
As I pointed out, a device like the JFK has a maximum size motor that it is able to start when it used to power multiple motors at the same time. This is significantly less than the headline power figure. I suspect that inexperienced installers or DIY purchasers have been buying undersized drives and overloading them. Hence my cautionary note and perhaps the explanation why the chap from JFK was trying to head off these errors at time of order.

 

[guineafowl21]

Re: balanced 3ph supply.

I haven’t looked too far into it, but my rotary appears to supply a neutral that is some way away from earth potential, so not ideal.

The skewed neutral, I think, means the star points of my motors are not electrically where they should be, which could stress the old insulation.

On the other hand, VFD/inverter outputs are choppy, so again may stress older windings that are not inverter-rated.

One last thing to note - many (all?) of those JFK units specify a 32A ‘C’ breaker for inrush. An individual VFD per machine may not need this, because of soft start capability.

My rotary also needed a 32 ‘C’, as startup was nuisance-tripping the 32 ‘B’ I had initially. Changing the trip curve of the breaker requires consideration of loop impedance, and possibly a supply upgrade.