Re: VFD and inverter duty 3phase motors

--- In CAD_CAM_EDM_DRO@yahoogroups.com, cnc002@a... wrote:

>
>
> In a message dated 7/29/2004 10:35:03 PM Eastern Daylight Time,
> JanRwl@A... writes:
>
> Should I just get a regular ~3450RPM @60Hz motor, and limit my

VFD to

> 60Hz, or should I go for an inverter duty motor where I can run

much higher

> frequencies/speeds. Any comments would be appreciated.<<
> NO! You should get a motor DESIGNED for 400 Hz operation, with

fresh

> bearings, properly lubricated for that speed. If you go [deleted]

ing with a

> 60 Hz
> motor on 400 Hz, even if you DO manage to get the voltage right

for that f,

> you
> will PROBABLY injure yourself! When five pounds of steel

(armature)

> designed
> for spinning at 3600 RPM is spun at 24,000 RPM and the bearings

seize-up,

> you
> are talking major discobobulation! DON'T DO IT! See Perske,

etc. BUY one

> made for the purpose!
>
>
>
> I couldn't agree MORE, regular 60Hz motors are NOT designed to run

at high

> speed. Not only the bearings but the way the armatures are

designed and

> manufactured are very different. I would think the first thing to

go would

> probably be the armature and I personally have seen a motor

actually explode when

> run around 18,000 rpm and that is 6,000 less than what you could

get with

> certain inverters.
>
> DO NOT USE A 60 HZ MOTOR EVEN IF IT IS INVERTER RATED. The

purpose for

> inverter rating a 60Hz motor isn't so it can run at a very high

speed, but

> actually so it can run at a much lower speed. When you run a

regular asynchronous

> AC motor at low speeds it will get hot because there isn't enough

cooling air

> going over it due to the slow speed of the cooling fan attached

to the

> shaft. In an inverter rated motor the windings, insulation and

sometimes the fan

> are different and designed for this situation. In some cases

they may even

> attach a single phase electric fan to the end of the motor for

cooling at

> lower speeds.
>
> Hope this helps.
>
> Randy Abernathy
> 4626 Old Stilesboro Road NW
> Acworth, GA 30101-4066
> Phone / Fax: 770-974-5295
> Cell: 678-772-4113
> E-mail: Cnc002@a...
>

Hmmmm......what you guys are saying is contrary to the info Baldor
is giving me. They tell me it's ok to run their newer non-inverter
duty 60 hz rated motors up to 5000 rpm.

With an 1800 rpm 60hz motor that would involve programming the max
hertz output of the VFD to 166 hz.