Why are 3 phase motors with VFD so popular in the UK?

And it would have been full of glass tubes or "valves" and taken up a room of your house.

This is one of the reasons that I have chosen to avoid doing any unnecessary VFD conversions to machines and to stick with a convertor running the whole workshop.

The effort required to power the ancillaries on, and replicate the relay logic of a well appointed manual machine tool can be substantial, and I have seen more than one mechanically sound machine end up inoperable and being sold as a project/for parts after someone got in over their head trying to convert it.

It's not usually hard to do, so much as it is awkward, time consuming and head scratching.

There's a reason that you rarely if ever see manual machine tools in industry retro-fitted with a VFD for speed control of the motor, even if they have had to have upgraded control circuits for PUWER98 or just because the old circuits failed after 50+ years service.

Not always.🙂 I simply bypassed any control circuitry (the starter) and connected my lathe motor to the VFD.

The most likely alteration is that of converting to delta (simple, or motor disassembly required). Or purchase a more expensive VFD.

Still rather better than an expensive converter, IMO.

Edited By not done it yet on 24/01/2023 11:16:34

IMO there's no "better" or "worse", just appropriate for the use case...

People should select the approach which suits their budget, aspirations and equipment best, which will be different for each user.

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For you, the VFD's are the best option.

For my investment in a single converter I can run the Lathe, Mill, Drill and Grinders which would all have required one or more VFD's, and I didn't have to re-wire the Lathe to get it to work properly (because the electrical and mechanical controls are closely intermeshed, and some functions would be lost if the switches buried in the mechanism weren't connected to the VFD)...

I can also run my Migatronic 500 Mig Welder, Oxford Welder (doesn't need 3-phase but the arc is smoother when running on it) and the recently acquired Plasma Cutter;

Running welders is something which can only be done on a Rotary Phase Convertor (and then only with a specific option fitted).

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So for about £400 outlay, I'm running 7 machines or about £57 per machine, before you consider that 3 of those machines can't be VFD converted at all so I just wouldn't be able to have them at home.

Had I bought the RPC brand new, the price would be closer to £200 per machine, which given that for two of the machines I wouldn't have seen much change from £300 per machine buying VFD's for them still makes it look economic in the long run.

If I was running smaller machines, or machines which had motors which were more easily adapted to running on 240V 3-phase, then the economics would stack up for VFD's instead, but I wouldn't be able to run such nice welding gear then.

If a machine, with a single phase motor, works to your satisfaction, then leave well alone, If it does not meet your requirements and a VFD and 3 phase motor will, Then do the conversion. It is as simple as that

Buying a new 3 phase motor and a good brand of VFD is not cheap. Some of the cheap Chinese VFDs are not user friendly and have a dubious reputation, although many on this forum are very satisfied with them. New 3 phase motors are cheaper than equivalent single phase ones, but prices are not bargain basement. Only other alternative is a second hand item, but then you need to have some experience in bearing replacement and rewiring the input to match the VFD

I have both 3 phase VFD powered machines and single phase powered ones. Horses for courses.

Andrew

I have an old (about 80 years) lathe and a Chinese mill that I've converted from single phase to VFD/3 phase, a smaller mill with brushless DC motor and a bench drill with single phase motor. I certainly don't regret doing the conversions, the biggest improvement being the in finish I can achieve with the mill. The only reason I haven't converted the bench drill is that if I need high speed low vibration for small drills I can use the small mill.

Russell

“Why are 3 phase motors with VFD so popular in the UK?”

I’m not sure they are, I have five or six machines in my shed and only one is 3 phase with an inverter.

The main reason is the machines tend to be dedicated to a particular type of work and or material. They are chosen for that work so the original speed(s) are appropriate to the task so there is no need or advantage to having variable speed. Unlike hobbists they are not trying to do everthing with one or two machines, often on the edge of their capabilities. The single phase supply issue is moot.
One thing you DO see in industrial settings is replacement of mechanical variable speed drives on older specialist machines with VFD set ups.

Not related to machining is the widespread retrofitting of VFDs on pumps, fans, conveyors and the like. There are big energy savings in running these at just the right speed. The savings will soon pay for a VFD. There can also be government incentives for improved efficency. Running at optimum speed can bring process performance improvements too.

Robert G8RPI.

Edited By Robert Atkinson 2 on 24/01/2023 19:49:34

Thanks~ an analogy i can relate to.

If anyone in Australia is looking for a VFD, I have just got my hands on 3, 2nd hand Bosch Rexroth 1.5kw 3610 EFC units. On will be used to convert my S7 to vfd and 2nd will replace a cheap Chinese one currently on the drill press.

If anyone is interested on the 3rd unit PM me.

Peter

Regarding VFD in here in UK , if and when industry upgrades, if ever, at all, out goes the original drive motor and all, lots find there way to ebay and other auction site, auto jumble sale, etc. Some folk buy a VFD kit and take the easy, but costly way out, other do a DIY job. I've found it easy and cheap to buy a second hand motor and a VFD via ebay. I have read on 'here' about those VFD from PRC and which are not user friendly and have a dubious reputation, but I've not actually met a person who has had any problems whatso ever. I'm no expert on computing and I have managed to program for my mates. Simply have a look on youtube plenty of instruction there, maybe I'm lucky. John

The overwhelming reason why 3 phase is preferred overall is, as has been understood since the late 19th century when Tesla amongst others invented much of the underlying technology, the substantial saving in iron and copper in generators, transformers, and distribution for a given amount of power. Added to that, given a 3-phase alternator, the 3-phase motor is a "natural" complement to re-generate mechanical motion. In many countries 3-phase is connected domestically as well but in the UK and others money was saved in the distribution network by only connecting most houses to one phase. As electric heating and vehicles become more important in this respect as in so many others this short-sightedness is catching up with us.

My take is rather the other way round! Recent inexpensive VFDs tend to be rather simpler than older models, and come with sensible defaults. The Manuals may be a little Chinglish but I find them comprehensible, and the VFD has a good chance of powering a motor out of the box.

In contrast, the manual of an ancient VFD is likely to be aimed at a professional installer who has done a course! Full featured VFDs of the older type often require the owner to configure many details. Multiple configuration options allow the installer to match the VFD to a particular motor in sophisticated ways, but the level of complexity they provide is over the top for driving a home workshop machine.

Buying second-hand or new, I'd make sure a manual was available and that I understood it. If not, better to go with a new unit of basic type, PRC or not, because lots of the people on the forum can advise. If baffled by manuals of any sort, buying from one of the firms who sell bundles is a good option. They make sure the VFD and motor are compatible, and provide wiring, controls, instructions and a help line!

Dave