Re: 3 phase motor math

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "AbbyKatt" <cnc@a...> wrote:

> Hi guys,
>
> I have a nice old 3 phase motor I want to hook up to my VFD. I've

gone

> through all the motions of opening it up and cleaning it a bit, and
> checking the resistace between windings and ground, and it seems

okay.

> What I don't know however is whether it's wired right..
>
> My VFD outputs 220V, so I'd need the motor to be in the Delta
> configuration.
> The motor has the following written on it:
>
> Volts: 220/380-415
> Amps: 3.45 / 2.0
>
> I measured 25ohms between each connection point...
> But the usual V=IR formulas totally don't yield me any answer.. it

must

> be because it's 3 phase and AC.
>
> I Googled for 3 phase motor/resistance/amps formulas but only came

up

> with a lot of junk people were trying to sell me, and some other

stuff.

> How do I work out what voltage this motor is currently configured

for?

>
> Thanks!
> -Abby
>
>
> [Non-text portions of this message have been removed]

Abby,

If you hook it up to the VFD with the motor under no load, it will
almost certainly spin up if it is in either Y or Delta. Then all
you need to do is use the current monitor on the VFD to see if it's
pulling enough current. Obviously if it is currently wired Y it will
pull less current and be weaker than it should be.

It just happens I have a motor on my bench at the moment where I've
had to do exactly this, as like yours the terminals are buried deep
in the motor (mine was Y and weak and needs butchering to get at the
terminals!)

Andrew Mawson
Bromley, Kent, UK