Ask Transwave if a step up transformer is available or a 230/240 volt input 400 volt output VFD and what the cost would be. You may have the options of rooting out the star point, adding a transformer, getting a step up VFD or replacing the motor. You can then consider what is the best solution for you. There are probably videos on the internet of people accessing the star point.

Martin C

If all you want to do is run the motor at it's rated speed 1450rpm then a transwave converter will give you 400v but if you really want variable speed ie a VFD then rewiring to delta. I would try to rewire if you must as Brooks motors are amongst the best. Good luck Noel.

Three phase motors contain three windings (coils), that can be connected up in either of two configurations, Star or Delta:

On many motors, the ends of the three coils are brought out to the terminal box, ChooChoo's W2, U2, V2, U1, V1, W1, where W1 and W2 are the start and end of coil 'W'. etc. When this is done, the user can connect the motor in either star or delta. Star connected motors require 400V, delta needs 230V.

Unfortunately, not all motors provide full access to both ends of all the coils. Instead the connections are made inside the motor, not easily available to the user. ChooChoo's motor was sold for 400V service, with no intention it would ever be changed. However, it may be possible. When the motor is opened up to expose the windings, it's likely the star point (marked N above) is accessible. If so, break the connection and extend the 3 wires outside the motor so the coils can be reconnected in Delta in a terminal box.

Alternatively, it's recently become possible to buy affordable 230V input VFDs that produce 400V out to drive a star motor without modification. I'd be inclined to go that way because it's less work! When buying the VFD, it may be specified as 220/380V rather than 230/400V because most of the world is 220V based. Should be 'good enough'.

Usual Health and Safety warning when working with mains power, but be aware a 400V shock is much nastier than ordinary mains. Never work on live wiring and make sure the connections are understood etc.

Dave

Sorry Dave, can't let that one pass.

400 volts (line to line) is the same thing as 230 volts (line to neutral).

Three phase motor suitable for 400 v line to line in star needs 230 volts line to line in delta so only 133 volts line to neutral. It's the line to neutral (earth) voltage that bites you, you'd have to try hard to grab two phases simultaneously.

However VSD outputs aren't necessarily symmetrical about earth.

I doubt that any machine in the home workshop will have a motor large enough to be wound for 415v in Delta but large motors probably in excess of 7.5hp could well be wound for 415v in delta and 690v in star. A motor large enough to to benefit from star-delta starting will be wound for 415v in delta. At work we used some hoist motors that were on the cusp of being wound for being 415v or 230v in delta, as we ran them on a VFD then it was important to check the motor plate and set the VFD to match. These days it is likely that a small motor will be wound for 415v in star but it is not a certainty.
Mike

You may be able to convert to delta, there's nothing to loose if you are careful with insulating and wiring. The alternative is a new motor to go with the VFD, Inverter Drive Supermarket sell both and also have their own "quick start guides" with some VFD'S that they sell. It makes the wiring and programming so easy. The only thing which could be a problem is that you might have problems with the motor shaft diameter and having to make an adaptor plate to mount the motor, I did with the Tom Senior light vertical.

**LINK**

Your motor is only 1hp and running it from a VFD intended for delta would loose too much power. It is not recommended to have any switch between the VFD and the motor, even an emergency stop, as the VFD could be damaged. An emergency stop in the power supply would not stop the motor as quickly as the switching recommended by the VFD manufacturer.

For the price of a Transwave converter, I could buy 2 motors and 2 Schneider VFD's, all the switchgear and wiring, with money left over.

Edited By old mart on 25/03/2022 22:05:02

Driving electric motors made before 1967 with a VFD is a bit risky.

I know the forum likes to believe ancient British electric motors are far better than any modern foreign rubbish. But get real! Although old British motors were well-made they were limited by the technology of the time, and don't forget old age and damp storage does them no favours.

Two reasons a VFD might damage an old motor:

• Inferior Insulation. The enamel used to insulate magnet wire has improved considerably over the years. Old enamels aren't as electrically, physically or thermally robust as the later ones.
  • The first enamels were only good for about 80°C, soon improved to 100°C rising to 120°C around WW2, then 140°C during the 1950's. Modern enamels can take at least 180°C and some motors run at about 220°C.
  • Cracks and bubbles were a serious problem in older enamels. Liquid enamel has to be carefully applied to bare copper wire because the dried layer can be flawed by bubbles, thin areas, and cracks caused by drying and winding the wire. Modern enamels are formulated to reduce the risk. Old magnet wire suffers because age and heat cycles tend to worsen the minor insulation flaws introduced by imperfect manufacturing methods. Damp makes flaws physically worse and much reduces the insulation's effectiveness overall. Much damage is caused when flawed insulation flashes over: magic smoke and the motor has to be rewired.
• Bearings. For many decades, bearing makers received persistent complaints that the bearings used in electric motors often wore out quickly. The cause was eventually traced to leakage currents earthing through the bearings. The current caused tiny sparks that eroded the bearing surface. Once identified, the problem was easily fixed by slightly altering the motor design. Motors made after 1967 are highly unlikely to have this fault. However, if an old motor is discharging through the bearing, the sparks are made much worse by spikey VFD waveforms.

1967 is the year after which the bearing problem was universally fixed and all motors were wound with modern enamel magnet wire.

Does it matter? Maybe not. Weak insulation and tiny sparks inside the bearings are unlikely to cause an instant bleeding obvious failure.

Bearing damage might never show up in a home-workshop and there's a reasonable chance even ancient insulation will be 'good enough' for a VFD. Problems are more likely to show up after many hours of operation than as an instant spectacular fail.

I wouldn't go out of my way to fit an old electric motor, but if I had one to hand I'd dry it out carefully before using it. The worst that can happen is having to replace the old banger with a new one!

Dave

In the past 3 or 4 years some one on this forum published am excellent article, with good clear pictures on how he located the Star point and brought out 3 extra wires into his motor terminal box. I have done the conversion for my friends, all on older motors, and as yet to hear of a failure, they bought their inverters via ebay and again not heard of a failure, could be they are just lucky ! I have an insulation tester up 1000volts which I used to give the motors a test before use. Have a go, you have not much to lose, you need to look out for a lump in the windings area which needs to be carefully opened up, and three wires attached. I used three different coloured wires for identification purposes, fibre glass insulation tube and heat shrink and a small amount of resin is readily available via ebay. Best of luck and let us know how you get on. John