Re: [Emc-users] [OT] power factor and VFDs (was "Single Phase Lathe spindle motor question")

[RogerN <re...@wi...>]

----- Original Message ----- 
From: "Kent A. Reed" <kn...@er...>
To: "Enhanced Machine Controller (EMC)" <emc...@li...>
Sent: Wednesday, March 09, 2011 7:31 AM
Subject: [Emc-users] [OT] power factor and VFDs (was "Single Phase Lathe 
spindle motor question")


> On 3/9/2011 7:23 AM, RogerN wrote:
>> For what it's worth, I have a lathe with a 7.5HP motor and used a 10HP
>> Hitachi VFD like this:
>>
>> <...>
>>
>> One time I let the lathe just idle, not cutting anything, the VFD showed 
>> 13A
>> 3 phase to the motor, the input to the drive was ~5A single phase, the 
>> VFD
>> handles the power factor problems and draws closer to true power from the
>> line.
>>
>> Roger Neal
> Gentle persons:
>
> I don't have a dog in this fight since I don't envision ever advancing
> beyond fractional-horsepower motors at home.
>
> Still, Roger's comment intrigues me. A home-based shop could cause
> mystifying problems in the household if the power factor gets out of
> hand. Do VFDs really make this a non-issue?
>
> Regards,
> Kent

I didn't realize this until someone explained it replying to posts about 
VFD's on a metalworking newsgroup, that's why I measured it.  On the line 
side you have rectifiers and capacitors for your DC Bus voltage.  On the 
motor side you have the inductive load powered by the DC bus through 
switching semiconductors.  I don't think power factor is a huge issue for a 
home shop but it was nice to find out my drive was only using 5A single 
phase at idle when the motor was using 13A three phase.  This was good for 
me to know since I share the 240V 30A circuit with the dryer, welders, and 
air compressor, just have to make sure I don't run too much at once, so far 
I've never tripped the breaker!

Roger Neal