Re: [Emc-users] Spindle Voltage?

[John Kasunich]

On Tue, Nov 3, 2015, at 09:41 AM, Todd  Zuercher wrote:
> I recently purchased an inexpensive router spindle off of ebay. It is rated 
> at 6kw and 380v 3ph. The old spindle I'm replacing was dual voltage and could 
> be wired Y or delta, for 200-240 or 380-460 (7HP). Stupid me I didn't think 
> to check the old VFD and it is only capible of low voltage (running 208 3ph). 
> 
> So my question, what are the repercussions of feeding this motor with only 
> 208 3ph? 
> 
> If the only problem is a loss of a percentage of power, but not more than 
> half, I can live with that. (It cost less than 1/3 the price of the 
> original.) 
> 

If you keep the same voltage-to-frequency ratio and maximum current the motor 
will be happy.
But of course the speed will be lower.  For example, if it is designed for 
380V, 240Hz, 14,400RPM,
the volts-per-hertz ratio is 380/244 = 1.5833.  If the VFD can only deliver 
208V, then you will be
limited to 208/1.5833 = 131Hz, and the top speed will be 7860 RPM.  It will 
still deliver rated torque
at rated current, but since the speed is lower the kW will be lower - only 
about 3.8kW.

You can run it at a lower voltage-to-frequency ratio, but you won't get the 
same torque.  For example
you could run it at 208V and 240Hz.  You would get a no-load speed of 
14,400RPM, but the torque-
per-amp will be lower - you'll still only get 3.8kW.


-- 
  John Kasunich
  jmkasun...@fastmail.fm

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Re: [Emc-users] Spindle Voltage?

[Karlsson & Wang]

It depends. For an asynchronous motor lower voltage will mean lower available 
torque although it is technically possible to get full torque up to there 208 
volt is needed for full power but only if the inverter deliver 208 volt at this 
point. For a synchronous permanent magnet motor voltage is needed to get the 
rpm up although it may be possible to weaken the magnetic field to get rpm up.

Nicklas Karlsson



On Tue, 3 Nov 2015 09:41:37 -0500 (EST)
"Todd  Zuercher"  wrote:

> I recently purchased an inexpensive router spindle off of ebay. It is rated 
> at 6kw and 380v 3ph. The old spindle I'm replacing was dual voltage and could 
> be wired Y or delta, for 200-240 or 380-460 (7HP). Stupid me I didn't think 
> to check the old VFD and it is only capible of low voltage (running 208 3ph). 
> 
> So my question, what are the repercussions of feeding this motor with only 
> 208 3ph? 
> 
> If the only problem is a loss of a percentage of power, but not more than 
> half, I can live with that. (It cost less than 1/3 the price of the 
> original.) 
> 
> -- 
> 
>  
> 
> Todd Zuercher 
> mailto:zuerc...@embarqmail.com 
> 
>  
> --
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Re: [Emc-users] Spindle Voltage?

[Przemek Klosowski]

On Tue, Nov 3, 2015 at 10:02 AM, John Kasunich 
wrote:

> But of course the speed will be lower.  For example, if it is designed for
> 380V, 240Hz, 14,400RPM,
> the volts-per-hertz ratio is 380/244 = 1.5833.  If the VFD can only
> deliver 208V, then you will be
> limited to 208/1.5833 = 131Hz, and the top speed will be 7860 RPM.  It
> will still deliver rated torque
> at rated current, but since the speed is lower the kW will be lower - only
> about 3.8kW.
>

It's not my specialty so I am trying to go over the numbers
methodically---please check if I am getting it right.
At nominal 380V the thing runs at 6kW6kW * 208/380 and 60*240 Hz, i.e.
14400 rpm. At 208V it should do 208/380*14400, or 7880 rpm, close enough.
But for power, P=omega*T, 6kW * 208/380, or 3.28 kW. amirite?
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Re: [Emc-users] Spindle Voltage?

[Todd Zuercher]

The VFD is an old EMS G3+ (Yaskawa) drive.  The old motors were 200-240v(or 
380-460v), 18,000rpm, 7hp.  When running the old motors they were drawing about 
5-7amps when running at 300Hz.  The new motor's tag says 380v, 18,000rpm, 6kw 
and when running with the VFD set to 300Hz shows about 2 amps current draw.  
The first test cut with a 1/4" down spiral through two layers of 1/4" MDF 
(200ipm feed) has no audible drop in rpm, and the VFD shows about 2.5 amps.  I 
think it looks good enough for me.


- Original Message -
From: "Karlsson & Wang" <nicklas.karls...@karlssonwang.se>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Sent: Tuesday, November 3, 2015 11:15:33 AM
Subject: Re: [Emc-users] Spindle Voltage?

> On Tue, Nov 3, 2015, at 09:41 AM, Todd  Zuercher wrote:
> > I recently purchased an inexpensive router spindle off of ebay. It is rated 
> > at 6kw and 380v 3ph. The old spindle I'm replacing was dual voltage and 
> > could be wired Y or delta, for 200-240 or 380-460 (7HP). Stupid me I didn't 
> > think to check the old VFD and it is only capible of low voltage (running 
> > 208 3ph). 
> > 
> > So my question, what are the repercussions of feeding this motor with only 
> > 208 3ph? 
> > 
> > If the only problem is a loss of a percentage of power, but not more than 
> > half, I can live with that. (It cost less than 1/3 the price of the 
> > original.) 
> > 
> 
> If you keep the same voltage-to-frequency ratio and maximum current the motor 
> will be happy.
> But of course the speed will be lower.  For example, if it is designed for 
> 380V, 240Hz, 14,400RPM,
> the volts-per-hertz ratio is 380/244 = 1.5833.  If the VFD can only deliver 
> 208V, then you will be
> limited to 208/1.5833 = 131Hz, and the top speed will be 7860 RPM.  It will 
> still deliver rated torque
> at rated current, but since the speed is lower the kW will be lower - only 
> about 3.8kW.
> 
> You can run it at a lower voltage-to-frequency ratio, but you won't get the 
> same torque.  For example
> you could run it at 208V and 240Hz.  You would get a no-load speed of 
> 14,400RPM, but the torque-
> per-amp will be lower - you'll still only get 3.8kW.
> 
> 
> -- 
>   John Kasunich
>   jmkasun...@fastmail.fm

I agree. To keep voltage-to-frequency ratio up to the maximum voltage and then 
just increase frequency is probably the best.

The VFD may use space vector control instead of voltage-to-frequency ratio.

Did you double check if your motor is Delta connected and may be Y connected 
instead?


Nicklas Karlsson

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Re: [Emc-users] Spindle Voltage?

[Ed]

On 11/03/2015 10:16 AM, Karlsson & Wang wrote:
>>
>> I have been running a 480 V motor at 240 V for a while now on a manual
>> mill. At half the voltage you get  one fourth the power.
>>
>> Ed.
> A half voltage and same speed you get half power. At half speed and half 
> voltage you however get one fourth the power.
>
>
I went right over the VFD part, was thinking line volts and line Hz.

Ed.


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Re: [Emc-users] Spindle Voltage?

[Stephen Dubovsky]

Trickier than that.  Depending on the corner point it may be able to
develop the same hp at half speed w/ twice the torque.  One would think
that an induction motor that needed variable speed would be designed to top
out somewhere on the const hp part of the curve than right on the corner
point.  Induction motors can naturally field weaken so that can have a 2+:1
const hp regions.

FWIW, permanent magnet machines can do the same but there are two 'gotchas'
to be careful with.  1) Too much field weakening can demagnetize the
magnets limiting the useful range and 2) if there is a fault and you have
to turn the drive off while in this mode, the field weakening will also
disappear and the back EMF will jump suddenly, rectify back through the
bridge, and make the bus voltage jump (possibly by a factor of 2+!).  You
may need a way to mechanically disconnect the motor from the bridge in a
fault to protect the vfd from overvoltage.  Been there, done that, have the
t-shirt!

Another thing to note.  Space Vector Modulation (SVM) is a bridge
modulation scheme - a type of PWM.  Can be used in V/Hz drives or flux
vector drives which are both control methods.  They are not directly
related.  You can have a V/Hz control using SVM or a flux vector control
using something like hysteresis modulation.  SVM is typically the superior
modulation (most efficient). (neglecting state space control)

SMD

On Tue, Nov 3, 2015 at 2:12 PM, Przemek Klosowski <
przemek.klosow...@gmail.com> wrote:

> On Tue, Nov 3, 2015 at 10:02 AM, John Kasunich 
> wrote:
>
> > But of course the speed will be lower.  For example, if it is designed
> for
> > 380V, 240Hz, 14,400RPM,
> > the volts-per-hertz ratio is 380/244 = 1.5833.  If the VFD can only
> > deliver 208V, then you will be
> > limited to 208/1.5833 = 131Hz, and the top speed will be 7860 RPM.  It
> > will still deliver rated torque
> > at rated current, but since the speed is lower the kW will be lower -
> only
> > about 3.8kW.
> >
>
> It's not my specialty so I am trying to go over the numbers
> methodically---please check if I am getting it right.
> At nominal 380V the thing runs at 6kW6kW * 208/380 and 60*240 Hz, i.e.
> 14400 rpm. At 208V it should do 208/380*14400, or 7880 rpm, close enough.
> But for power, P=omega*T, 6kW * 208/380, or 3.28 kW. amirite?
>
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[Emc-users] Spindle Voltage?

[Todd Zuercher]

I recently purchased an inexpensive router spindle off of ebay. It is rated at 
6kw and 380v 3ph. The old spindle I'm replacing was dual voltage and could be 
wired Y or delta, for 200-240 or 380-460 (7HP). Stupid me I didn't think to 
check the old VFD and it is only capible of low voltage (running 208 3ph). 

So my question, what are the repercussions of feeding this motor with only 208 
3ph? 

If the only problem is a loss of a percentage of power, but not more than half, 
I can live with that. (It cost less than 1/3 the price of the original.) 

-- 

 

Todd Zuercher 
mailto:zuerc...@embarqmail.com 

 
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Re: [Emc-users] Spindle Voltage?

[Ed]

On 11/03/2015 08:41 AM, Todd Zuercher wrote:
> I recently purchased an inexpensive router spindle off of ebay. It is rated 
> at 6kw and 380v 3ph. The old spindle I'm replacing was dual voltage and could 
> be wired Y or delta, for 200-240 or 380-460 (7HP). Stupid me I didn't think 
> to check the old VFD and it is only capible of low voltage (running 208 3ph).
>
> So my question, what are the repercussions of feeding this motor with only 
> 208 3ph?
>
> If the only problem is a loss of a percentage of power, but not more than 
> half, I can live with that. (It cost less than 1/3 the price of the original.)
>
I have been running a 480 V motor at 240 V for a while now on a manual 
mill. At half the voltage you get  one fourth the power.

Ed.


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Re: [Emc-users] Spindle Voltage?

[Karlsson & Wang]

> On Tue, Nov 3, 2015, at 09:41 AM, Todd  Zuercher wrote:
> > I recently purchased an inexpensive router spindle off of ebay. It is rated 
> > at 6kw and 380v 3ph. The old spindle I'm replacing was dual voltage and 
> > could be wired Y or delta, for 200-240 or 380-460 (7HP). Stupid me I didn't 
> > think to check the old VFD and it is only capible of low voltage (running 
> > 208 3ph). 
> > 
> > So my question, what are the repercussions of feeding this motor with only 
> > 208 3ph? 
> > 
> > If the only problem is a loss of a percentage of power, but not more than 
> > half, I can live with that. (It cost less than 1/3 the price of the 
> > original.) 
> > 
> 
> If you keep the same voltage-to-frequency ratio and maximum current the motor 
> will be happy.
> But of course the speed will be lower.  For example, if it is designed for 
> 380V, 240Hz, 14,400RPM,
> the volts-per-hertz ratio is 380/244 = 1.5833.  If the VFD can only deliver 
> 208V, then you will be
> limited to 208/1.5833 = 131Hz, and the top speed will be 7860 RPM.  It will 
> still deliver rated torque
> at rated current, but since the speed is lower the kW will be lower - only 
> about 3.8kW.
> 
> You can run it at a lower voltage-to-frequency ratio, but you won't get the 
> same torque.  For example
> you could run it at 208V and 240Hz.  You would get a no-load speed of 
> 14,400RPM, but the torque-
> per-amp will be lower - you'll still only get 3.8kW.
> 
> 
> -- 
>   John Kasunich
>   jmkasun...@fastmail.fm

I agree. To keep voltage-to-frequency ratio up to the maximum voltage and then 
just increase frequency is probably the best.

The VFD may use space vector control instead of voltage-to-frequency ratio.

Did you double check if your motor is Delta connected and may be Y connected 
instead?


Nicklas Karlsson

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Re: [Emc-users] Spindle Voltage?

[Karlsson & Wang]

On Tue, 03 Nov 2015 08:54:32 -0600
Ed  wrote:

> On 11/03/2015 08:41 AM, Todd Zuercher wrote:
> > I recently purchased an inexpensive router spindle off of ebay. It is rated 
> > at 6kw and 380v 3ph. The old spindle I'm replacing was dual voltage and 
> > could be wired Y or delta, for 200-240 or 380-460 (7HP). Stupid me I didn't 
> > think to check the old VFD and it is only capible of low voltage (running 
> > 208 3ph).
> >
> > So my question, what are the repercussions of feeding this motor with only 
> > 208 3ph?
> >
> > If the only problem is a loss of a percentage of power, but not more than 
> > half, I can live with that. (It cost less than 1/3 the price of the 
> > original.)
> >
> I have been running a 480 V motor at 240 V for a while now on a manual 
> mill. At half the voltage you get  one fourth the power.
> 
> Ed.

A half voltage and same speed you get half power. At half speed and half 
voltage you however get one fourth the power.

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