Re: Anyone knowledgeable about BTH motors?

pentagrid@xxxxxxxxx wrote:
On Tue, 29 Aug 2006 13:49:26 +0200, muellernick@xxxxxx (Nick
M?ller) wrote:

<pentagrid@xxxxxxxxx> wrote:

snip
Over the commonly used frequency range 0 to 100Hz
pretty well any motor is OK. However some VFD drives can operate
at frequencies as high as 400Hz and this certainly needs motors
designed for operation at this frequency.
Thanks. Having a better picture now.
The VFD on my lathe (a retrofit by me) can drive up to maybe 400Hz, but
the motor simply starts to skip pulses at about 120Hz (and rapidly
getting slower*)). At 120 Hz, I have nearly no power. Useful range is up
to 90 Hz. I assume a special motor would fix that. Do you know at about
what prize factor?

*)
"rapidly getting slower" :-)))


TIA,
Nick

In the ideal case, correct motor voltage should be
directly proportional to frequency. Standard VFDs can only do
this up 50Hz. Beyond this it's constant voltage so that at at
100Hz the motor is getting less than half its proper drive
voltage. This coupled with rapidly increasing frequency sensitive
iron losses severely degrades the motor performance.

Operation at frequencies above 100Hz needs motors with
thinner laminations to reduce iron losses and wound for correct
drive at this higher frequency. 115/200V 3 phase 400Hz motors are
common items in aviation elctronics.

Jim


That's interesting Jim. So if I find that I need to replace my 2 HP 3 speed 2875/1450/950 motor it looks like I need to either find a 2 pole (2875) motor that will be happy running at 950 or less, or a 2 speed 2/4 pole motor. Presumably to get a 2 pole running happily at 950 or less I'll need to use a significantly beefier motor than 2HP and add a blower, so maybe a 3 HP 2 speed 2875/1450 would be a better answer.
What does the team think?

Dave
.

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