Personally I'm very happy with Weg VFDs. I've got 6 of them running various machines and have proved very reliable.

The instructions are comprehensive and they're in English, not Chinglish. The price is reasonable, not rock bottom or sky high.

Rob

I have a Toshiba & a Omron. I used to install Jaguar imo. They are great but i would suspect a bit expensive when new.

Not heard any horror stories of the far eastern ones. They all seem reasonably priced.

Steve.

Major brands may cost more, but manuals in something closer to English, plus there is a support system where if necessary you can speak to real people.

From previous reports here, some vendors also give very good support – so that's another good option.

If you are totally confused, I'd suggest stick with a major brand or a recommended vendor.

Please what ever you don’t purchase one off eBay. I have know connection with this company bar for purchasing three inverters from over the years with very good backup. The company is. Inverter drive supermarket. U.K. company and good prices and very good customer care

I recently bought an Invertek inverter from inverter drive supermarket, 1/2hp drive, £96 plus tax so very reasonable for a UK manufactured unit, IDS also do an easy start guide for this range of inverter, which is an excellent illustrated guide that goes through all the settings needed in a genuinely easy to understand manner.

I also like to buy local for environmental reasons, this may not bother you but if a product doesn't have to be shipped across the globe and the manufacturer is in a country that handles industrial waste in a responsible manner I'll always put their goods further up my might buy list.

A feature that is worth having on a VFD is sensorless flux vector control, this has the ability to calculate the rotor position and can maintain good torque down to low frequencies. Different manufacturers call this feature by different names but they usually include one of the words or more. It is not necessary to understand how it works, just that it does improve performance at low speed, it may need to be selected when setting the parameters. It is worth remembering that to take a decent cut on large diameter work it will help if the belts and back gear are used to slow the lathe and thus keep the motor speed up, when you slow the motor the power is also decreased so at low motor rpm you will also lose power. Mechanical speed reduction will multiply the torque and thus maintain the power. VFD control is wonderful but is not magical. It transforms the lathe and I fully recommend one but although it will help a lot to minimise belt changes do not expect to never have to change the mechanical ratios.

Mike

Chipping in again. It is a bit of a can of worms. As i previously stated i have 2 branded versions. The Omron has a 160 page manual. Enough to scare most unelectrical minded person away. It has so many parameters that the eastern models do not have. But you will pay a premium in the price. Have a look at my video where i talk about the inverter & the controls + what you can program into it. Many of the forum members may find this video of some aide if thinking of going down the inverter /VFD route. The nearest new Omron i can find is circa £390. Yes very expensive for a hobby machine. Which probably gives the imports eastern made ones a bonus on price. Beware if buying from another country as there could be various duties to be paid. Take care & a nearly Happy new year to all.

Steve.

The myford lathe with a 3 phase motor

Edited By Steviegtr on 30/12/2021 23:02:33

Emgee is correct. To add to that it is important to make sure the earth is connected to the frame of the vfd from the 240v input & on the motor earth connection. The only thing to note is the screen from the SY cable should only be connected at the VFD & then isolated at the Motor. Giving full screening against spurious emissions from the inverter.

Steve.

VFD boxes are consumable devices. In particular the capacitors lead a very hard life. Real VFD rated capacitors are not cheap. Lesser types may last for a while but they will fail. The power electronics work hard too.

Inexpensive import boxes are built down to a price so capacitors will be skimped on and power electronics devices specified with little margin for overload. The drive programs will be generic and, probably, not exceptionally efficient which doesn't help component life.

For folk like us putting the box to relatively intermittent use and, generally, running well within its capabilities the $64,000 question will we put enough hours on it for it to go pop! Industrial rated boxes built to run 24/7 for 5 or 10 years will be overkill. But 10 hours a week, which is a lot of spindle time for most of us, is only 500 hours a year so getting 5,000 hour life from a cheap box would do fine for most of us.

Certainly don't cheap out on a compressor drive tho'. Even a Hydrovane has hefty start up loads.

I can afford the name brand premium so buy from IDS. Folk with shallower pockets have less choice. The worst thing about low end unbranded via E-Bay et al is that the actual source is unknown. Suppliers just buy boxes and may have lucked into some better end ones several years back but this years ones may not be so good. No way to know. Most of the really cheap boxes are built via production line rejects from Chinese brand makes. Rejects from a 24/7 long life line will still be more than up for our use. Further down the scale? Who knows?

Clive

Unless you know what you're doing:

• Don't buy cheap direct from the far-east. There's no support in the event of a fault or you don't understand the instructions! (Which may be poorly translated as well as aimed at experts.)
• Don't buy a top-end sooper-duper Industrial brand. These are usually bought by customers needing high-end features that they configure themselves. Not unusual for dozens of industrial VFDs to be networked together and programmed from a back-office PC. The manual is a few hundred pages of terse configuration information aimed at a specialist. Older units are particularly likely to be amateur unfriendly. Newer ones may come with defaults suited to 'man-in-shed', but don't bet on it!.

Inexpensive units bought from UK suppliers are a better bet. Support varies, but consumer protection applies. These tend to be relatively straightforward and usually come with default settings suitable for a simple installation – almost plug and play, but don't bet on it. A certain level of comprehension is needed. Best avoided if you have a hazy understanding of electric motors, control wiring, earths, EMC, what might upset an RCD, phases, star, delta, watts, and other magic. The forum can be helpful.

At extra cost there are a number of UK firms selling VFDs and VFD/motor packages specifically aimed at the amateur conversion market. These companies do most of the hard work matching motors to electronics, have a good understanding of typical problems, provide decent instructions and a reasonable level of support. Recommended for anyone who doesn't have the time or inclination to plumb the depths of electro-sorcery!

Dave

If I remember correctly most vfds have a low IP rating of 20 and should be mounted in an enclosure to provide additional protection. I have seen others with higher protection ratings but even these ones were enclosed. Personally I would always fit one in an enclosure with external controls. I really wouldnt like trying to hit one of those small buttons in an emergency to stop the drive.

Unfortunately the question in the OP is unanswerable. Unless anyone has done long term reliability tests on a range of VFDs?

There seems to be some confusion regarding filtering and control schemes. Most smaller VFDs do not come with internal mains filters, and do not use power factor correction at the front end. The primary purpose of the mains filter is to reduce the current pulses taken from the mains. This reduces harmonic content and improves power factor. The mains filter is concerned with conducted emissions, not radiated. The problem of radiated emissions is mostly associated with the outputs of the VFD, where the PWM waveforms have fast edges and hence a high harmonic content. These radiated emissions are normally dealt with by shielding the output signals. I'm not going to discuss the ground at one end or ground at both ends controversy!

A simplified model of an induction motor says that torque is proportional to phase current. An induction motor will be designed to produce rated current at a rated voltage and a given frequency, aka base speed. In the UK rated voltage will normally be 415V phase to phase, in star, at 50Hz. As the frequency increases the currents will fall as no more voltage is available to drive extra current through the windings. Although current, and torque, fall the speed rises, so power stays constant above base speed. As the frequency decreases the rated voltage will drive more current through the windings. In the longer term this can lead to increased resistive heating of the windings and ultimate failure. As the frequency decreases it is normal to decrease the voltage to keep the phase currents constant. Torque also stays constant below base speed.

End of Part 1 – in case I hit the wrong key and the whole lot disappears.

Andrew