[aarggh]

Hi all,

Hoping someone can clear this up for me, I have a dual voltage (230/415) 3 phase single speed motor powering a saw. It's for aluminium so it will be fairly high rpm, probably at least 1800-3000 at a guess. The motor is rated at 2.2kw, and the 3 phase input is currently wired in star fashion. I have spare 2.2kw Huanyang VFD's I could try, but have held off for now as i'm finding a lot of conflicting posts about the need to derate by 50% when you have single phase in, 3 phase out, although a lot of posts indicate that you only need to derate when it is over 3HP? Some people have also mentioned to not connect the earth from the VFD to a star wired 3 phase motor? Is this not required for the 240v phase reference?

So,

1 - if the dual voltage 3 phase motor is rated 2.2kw, will a 2.2kw VFD suffice, or do I need a 5kw rated one?
2 - with 1 phase in, 3 phase out VFD, the motor wired for star, the ground from the VFD is connected to the ground tabs on the motor?

cheers,
Ian

[neilw20]

Wire the motor as star and connect to single phase powered 240v input VFD.
If the VFD is a lower rating than than the motor it will limit it's own current.
If the motor is rated less than the VFD power, then the VFD can be programmed for a lower maximum current.
It is all in the VFD manual.

[Al_The_Man]

Hi all,

Some people have also mentioned to not connect the earth from the VFD to a star wired 3 phase motor? Is this not required for the 240v phase reference?

Any de-rating requirement is usually stated in the manual, if it is needed.
The Earth ground should be taken to both the VFD and motor frame, the opposite end connected to the star point ground in the enclosure, together with the service ground.
There is no neutral reference required with a 3 phase motor.
Both a 2 pole or 4 pole motor can be taken to ~3500rpm.
Al.

[neilw20]

By the way, Al mentions the star point ground, and doesn't mean the star point of the windings if Y connected.
I am running a 2 pole motor to 4800 RPM, and I have a VFD designed 2HP motor that runs to 6000RPM, all from a 240vAC supply.

[Al_The_Man]

Hoping someone can clear this up for me, I have a dual voltage (230/415) 3 phase single speed motor powering a saw. The motor is rated at 2.2kw, and the 3 phase input is currently wired in star fashion.

Ian

If it is currently wired in star fashion that is for 415v, you need to connect delta for 230v.
Al.