NO, it's strictly single voltage. See here for details;

Whilst everybody thinks of VFDs for 3phase don't forget the 3Ph converters, the likes of TRANSWAVE Etc Noel

Buying a RPC is cost-neutral with a 240-to-415 VFD for the first machine…

But for machines 2 to n+1 the phase converter costs nothing, I am very happy with my Transwave (recently purchased second-hand to replace my home made Converter) and am confident that it made more financial sense.

A static converter has some drawbacks by comparison to a rotary one, but could work out cheaper than a VFD altogether second-hand due to being unfashionable.

.

If John is intending to buy or open to buying additional 3-phase equipment I would recommend a phase converter over spending hundreds on a VFD conversion on each successive machine.

You can connect it for lower voltage by wiring it as double delta. I.e. each pair of windings in parallel and keeping the delta connecton HOWEVER, the voltage will not be the same as changing star / delta in a single speed motor. The single speed star/delta ratio is Sqt3:1 = 1.73:1 ie 415V / 240V.
For double delta the ratio will be 2:1 so if it is a 415V motor it will need 207V to run properly. Many VFDs will allow you to adjust the voltage e.g. by adjusting the V/F ratio away from normal.

Robert G8RPI.

Note that "rotary" converters are inefficent, noisey and not as "smooth" (unless a genuine motor-generator) as a VFD. And you can't change the speed.

Then there is the cost. A 3kW Transwave RT is about £1000 and has a MINIMUM single motor load of 2.2kW. So you can't use it to run a single machine less than that. It's a 2.2kW alone or 2.2kW and up to 800W. That is not "run anyting in the shop". I'm sure lots of people will say " I run a single x.x kW motor as a single load without problems". That may be but it's outside the specification. You can buy at least 5 1.5kW VFDs for £1000.

You can set and forget a VFD for single speed and just have start / stop buttons.

Robert G8RPI.

I have a couple of points:

1. If the Transwave product you were looking at had a minimum motor size, then it's a static converter, not a rotary. Those can actually run smaller motors, but only if a large one is running on the same circuit, so for coolant pumps etc, it's not the end of the world.
2. I specifically compared payback to purchasing on the used market because converters are durable and long lasting machines with a service life of 30+ years, if you're concerned about cost it would never make sense to purchase new, but buying used is rarely any different due to the nature of the machine.
3. In the context of a workshop I have never found rotary converters to be noisy, yes they do create a bit of a hum, but compared to taking a serious cut on any machine tool, drilling, welding, grinding, rivetting or hammer forming, the sound doesn't touch the sides.

When I looked at replacing the system in my workshop recently, I found myself needing 5 VFD's between 0.35kW and 4kW. To do that would have  seen me spending significantly more than £1k on the VFD's, and having to do a major rewire of the control circuitry on my lathe, then having buy several other new components for the privilege of installing my VFD's…

Vs paying £380 for a 7.5kW Rotary Converter which was about 5 years old with low hours and documentation showing it hand been serviced by the manufacturer before it went into storage, which has been plug and play.

VFD's are fine and all, and have their advantages, but my experience is that they're not the only viable solution, and may not be the best solution for all use cases.

Edited By Jelly on 28/10/2022 10:57:19

Jelly,

you are correct I misread. There is no minum load on the rotary. Sorry about that.

Robert G8RPI.

John

Basically you can't simply convert to low voltage delta to use a VFD.

As drawn the plate shows a two speed 440 volt motor. Changing between delta and star merely alters the speed.

To connect in double delta to run off a normal 220 volt VFD, as described earlier by Robert, you need access to all the 12 ends of the 6 windings. Realistically that is a job for a professional who knows how to make sure the windings are correctly orientated. If all the wires do come out to the terminal box its pretty simple for a pro who has experience in such things. 15 minutes perhaps so if there is decent rewinder locally it might be worth asking.

Clive

Running a motor on a VFD at less than the nominal voltage required simply reduces the speed at which things go into constant power mode iwth a pro rata reduction in power at the rated speed. I suspect that for most of us with industrial workshop sized machinery the loss of power will not be noticed. We generally just don't drive large cutters or large work at high speeds. If we do go fast its usually a small cutter or small job so inherently needing less power.

As usual Inverter Drive Supermarket explain running at less than norminal voltage is a way that normal folk can understand.:-

**LINK**

https://inverterdrive.com/HowTo/240V-Supply-to-a-400V-AC-Motor/

Clive

Congratulations! Is it a 380V VFD?

Important not to switch speed whilst the power is on because that's the greatest weakness of a VFD. As it's the sort of thing I do in moments of carelessness, might be worth fitting some form of physical measure to stop it, such as taking the handle off the switch! Or tying a huge red ribbon round it!

Dave

Don't forget that the restriction on load switching applies to the traverse as well. If it is electrically controlled you will have to connected the mortor directly to the VFC and then connect the control switches to the control inputs of the VFD and set it up accordingly.

Robert G8RPI.