A while back I bought a Rockwell 11 inch lathe with a mechancial variable
speed drive. This drive works well but seems to have a lot of friction.
The lathe came with the original 1HP 3PH motor. I installed a 1HP VFD
and I managed to make the lathe run. The VFD could not start the lathe
unless the Mechancial VS was set to less than 1/2. I Adjust some parameters
in the VFD to increased the starting torque which pretty much solved the
problem. However the VFD indicates the motor is drawing nearly full
current just turning the spindle at max RPM. And yes the spindle bearings
are fine!

The original motor starter was set up for a 2HP motor even though the
lathe only has a 1HP motor. Its very difficult to read the motor tag
inside the lathe cabinet and the front swithc say 2HP, so the electrician
probably put on a 2HP contactor with 2HP heaters.

So anyway I am considering installing a larger motor. I found some 1.5
HP 1140RPM motors fairly cheap. I think the lower RPM motor will develop
more torque and the VFD will still allow me to achieve full spindle speed
by increasing the freq to 90.

I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is
that the lower speed motor will develop more starting torque and I can
still get the same spindle speed by increasing the freq on the VFD.
For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5)
where the existing motor will only develop 1/2 HP(900/1800) at the same
RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will
develop more low end torque that a 2HP 1740 RPM motor that I was
originally considering.

what do you think?

chuck

In article , cas@w-
sherwood.ih.lucent.com says...


I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is
that the lower speed motor will develop more starting torque and I can
still get the same spindle speed by increasing the freq on the VFD.
For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5)
where the existing motor will only develop 1/2 HP(900/1800) at the same
RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will
develop more low end torque that a 2HP 1740 RPM motor that I was
originally considering.

what do you think?


Unless you're actually experiencing problems operating the
lathe--not enough power on heavy cuts, for example--I
wouldn't bother. It's not unusual for the VFD to indicate
that the motor current is near nameplate current even when
lightly loaded. It's not necessarily an indication that the
motor is producing rated power, but rather is operating at
low power factor, which is typical of lightly loaded
motors.

I've tried without success to use a VFDs current sense as
an indication of overload on a conveyor. The difference
between normal load and gross overload, short of stalling
the motor, was not large enough to sense reliably.

Ned Simmons

I've tried without success to use a VFDs current sense as
an indication of overload on a conveyor. The difference
between normal load and gross overload, short of stalling
the motor, was not large enough to sense reliably.

I have experienced the same. I look at the motor current
and then load the machine and I only see very small changes.
Therefore I question the VFD current display.

I have had my mill kick out on overload when drilling (high load)
at very low freq(10Hz). I think it has seriouly derated the motor
at that speed though.

chuck

In article ,
Charles A. Sherwood wrote:

A while back I bought a Rockwell 11 inch lathe with a mechancial variable
speed drive. This drive works well but seems to have a lot of friction.
The lathe came with the original 1HP 3PH motor. I installed a 1HP VFD
and I managed to make the lathe run. The VFD could not start the lathe
unless the Mechancial VS was set to less than 1/2. I Adjust some parameters
in the VFD to increased the starting torque which pretty much solved the
problem. However the VFD indicates the motor is drawing nearly full
current just turning the spindle at max RPM. And yes the spindle bearings
are fine!

Hmm ... mechanical variable speed mechanisms are not very
efficient -- lots of friction losses in that variable-speed belt.

The original motor starter was set up for a 2HP motor even though the
lathe only has a 1HP motor. Its very difficult to read the motor tag
inside the lathe cabinet and the front swithc say 2HP, so the electrician
probably put on a 2HP contactor with 2HP heaters.

So anyway I am considering installing a larger motor. I found some 1.5
HP 1140RPM motors fairly cheap. I think the lower RPM motor will develop
more torque and the VFD will still allow me to achieve full spindle speed
by increasing the freq to 90.

I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is
that the lower speed motor will develop more starting torque and I can
still get the same spindle speed by increasing the freq on the VFD.
For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5)
where the existing motor will only develop 1/2 HP(900/1800) at the same
RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will
develop more low end torque that a 2HP 1740 RPM motor that I was
originally considering.

what do you think?

Well ... my 12" Clausing step pulley lathe has a 1-1/2 HP motor,
and I think that is a good fit for it. Your 11" would not need quite as
much horsepower, but the variable-speed pulley will require more to
drive it properly, so I think that I would consider the 1-1/2 HP at a
minimum, with perhaps the 2 HP which your switch and contactor suggest
being the better choice.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Charles A. Sherwood wrote:
A while back I bought a Rockwell 11 inch lathe with a mechancial
variable speed drive. This drive works well but seems to have a lot
of friction. The lathe came with the original 1HP 3PH motor. I
installed a 1HP VFD and I managed to make the lathe run. The VFD
could not start the lathe unless the Mechancial VS was set to less
than 1/2. I Adjust some parameters in the VFD to increased the
starting torque which pretty much solved the problem. However the
VFD indicates the motor is drawing nearly full current just turning
the spindle at max RPM. And yes the spindle bearings are fine!

The original motor starter was set up for a 2HP motor even though the
lathe only has a 1HP motor. Its very difficult to read the motor tag
inside the lathe cabinet and the front swithc say 2HP, so the
electrician probably put on a 2HP contactor with 2HP heaters.

So anyway I am considering installing a larger motor. I found some 1.5
HP 1140RPM motors fairly cheap. I think the lower RPM motor will
develop more torque and the VFD will still allow me to achieve full
spindle speed by increasing the freq to 90.

I am considering a 1.5HP to replace the exisiting 1HP motor. My logic
is that the lower speed motor will develop more starting torque and I
can still get the same spindle speed by increasing the freq on the
VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM
(900/1140x1.5) where the existing motor will only develop 1/2
HP(900/1800) at the same RPM (assuming constant torque). I think a
1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740
RPM motor that I was originally considering.

what do you think?

chuck

You're aware that most VFDs when fed from single phase power must be derated
to 75%?

I'm not particularly knowledgeably about electrics, but couldn't you just
tong one of the motor leads to see what the ACTUAL current is?

"Charles A. Sherwood" wrote in message
...

A while back I bought a Rockwell 11 inch lathe with a mechancial variable
speed drive. This drive works well but seems to have a lot of friction.
The lathe came with the original 1HP 3PH motor. I installed a 1HP VFD
and I managed to make the lathe run. The VFD could not start the lathe
unless the Mechancial VS was set to less than 1/2. I Adjust some
parameters
in the VFD to increased the starting torque which pretty much solved the
problem. However the VFD indicates the motor is drawing nearly full
current just turning the spindle at max RPM. And yes the spindle bearings
are fine!

The original motor starter was set up for a 2HP motor even though the
lathe only has a 1HP motor. Its very difficult to read the motor tag
inside the lathe cabinet and the front swithc say 2HP, so the electrician
probably put on a 2HP contactor with 2HP heaters.

So anyway I am considering installing a larger motor. I found some 1.5
HP 1140RPM motors fairly cheap. I think the lower RPM motor will develop
more torque and the VFD will still allow me to achieve full spindle speed
by increasing the freq to 90.

I am considering a 1.5HP to replace the exisiting 1HP motor. My logic is
that the lower speed motor will develop more starting torque and I can
still get the same spindle speed by increasing the freq on the VFD.
For example the 1140 RPM motor will develop 1HP at 900 RPM (900/1140x1.5)
where the existing motor will only develop 1/2 HP(900/1800) at the same
RPM (assuming constant torque). I think a 1.5HP 1140 RPM motor will
develop more low end torque that a 2HP 1740 RPM motor that I was
originally considering.

what do you think?

chuck

On 30 Sep 2003 18:05:11 -0400, (DoN. Nichols)
wrote:

in the VFD to increased the starting torque which pretty much solved the
problem. However the VFD indicates the motor is drawing nearly full
current just turning the spindle at max RPM. And yes the spindle bearings
are fine!

Hmm ... mechanical variable speed mechanisms are not very
efficient -- lots of friction losses in that variable-speed belt.

Pull the variable speed crap out, and run it direct drive. It will be
smoother, quieter and easier on your VFD. Stick the stuff in a box so
you can include it with the lathe when you upgrade to a different lathe.

Gunner



"If I'm going to reach out to the the Democrats then I need a third
hand.There's no way I'm letting go of my wallet or my gun while they're
around."

"Democrat. In the dictionary it's right after demobilize and right
before demode` (out of fashion).
-Buddy Jordan 2001

On Wed, 01 Oct 2003 00:54:28 GMT, "ATP"
wrote:

Charles A. Sherwood wrote:
A while back I bought a Rockwell 11 inch lathe with a mechancial
variable speed drive. This drive works well but seems to have a lot
of friction. The lathe came with the original 1HP 3PH motor. I
installed a 1HP VFD and I managed to make the lathe run. The VFD
could not start the lathe unless the Mechancial VS was set to less
than 1/2. I Adjust some parameters in the VFD to increased the
starting torque which pretty much solved the problem. However the
VFD indicates the motor is drawing nearly full current just turning
the spindle at max RPM. And yes the spindle bearings are fine!

The original motor starter was set up for a 2HP motor even though the
lathe only has a 1HP motor. Its very difficult to read the motor tag
inside the lathe cabinet and the front swithc say 2HP, so the
electrician probably put on a 2HP contactor with 2HP heaters.

So anyway I am considering installing a larger motor. I found some 1.5
HP 1140RPM motors fairly cheap. I think the lower RPM motor will
develop more torque and the VFD will still allow me to achieve full
spindle speed by increasing the freq to 90.

I am considering a 1.5HP to replace the exisiting 1HP motor. My logic
is that the lower speed motor will develop more starting torque and I
can still get the same spindle speed by increasing the freq on the
VFD. For example the 1140 RPM motor will develop 1HP at 900 RPM
(900/1140x1.5) where the existing motor will only develop 1/2
HP(900/1800) at the same RPM (assuming constant torque). I think a
1.5HP 1140 RPM motor will develop more low end torque that a 2HP 1740
RPM motor that I was originally considering.

what do you think?

chuck

You're aware that most VFDs when fed from single phase power must be derated
to 75%?

Pretty much true. Or even lower, depending on manufacture and age of the
unit (Ie the older ones are not as efficent as the newer bleeding edge
ones)

Gunner



"If I'm going to reach out to the the Democrats then I need a third
hand.There's no way I'm letting go of my wallet or my gun while they're
around."

"Democrat. In the dictionary it's right after demobilize and right
before demode` (out of fashion).
-Buddy Jordan 2001

In article ,
Jon Grimm wrote:
I'm not particularly knowledgeably about electrics, but couldn't you just
tong one of the motor leads to see what the ACTUAL current is?

A clamp-on ammeter will probably show the same thing that the
VFD's readout shows. The problem is that the current is out of phase
with the voltage, so only a percentage of it is actually doing work.
This is called the "power-factor", and an accurate power measurement
requires measuring the voltage and the current and the phase shift
between them. The clamp-on ammeter will measure *only* the current.

As the motor gets closer to full nameplate power being
delivered, the phase shift will reduce so the current will bear a closer
relationship to the power being delivered.

The VFD *could* calculate the power, as it has both the voltage
and the current data -- but nobody seems to bother to program them to do
so -- and in terms of heating the motor windings and fuse blowing or
circuit breaker tripping, as well as power lost heating the external
wiring, the current alone is what really matters.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

In article , Gunner says...

Pull the variable speed crap out, and run it direct drive. It will be
smoother, quieter and easier on your VFD. Stick the stuff in a box so
you can include it with the lathe when you upgrade to a different lathe.

Rule one. Never throw anything out.

Rule two. Have lots of room, for rule one.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

You're aware that most VFDs when fed from single phase power must be
derated
to 75%?


On older VFD's this is generally true, but almost all of the new VFD's rated
for 3 HP or less are designed to run full output power with only single
phase input power.

Also, I agree with Gunner, yank out the mechanical vari-speed drive and run
the motor direct using the VFD for speed control. I did this on my Clausing
5914 and it works great. You need to pick your motor pulley size carefully-
I picked mine so that when the motor is double speed the lathe is at its top
rated spindle speed.
By the way, this is a real easy conversion to do on a 5914 since the spindle
already has a toothed belt pulley on it- make a new motor plate, use the
existing motor plate brackets moved up to the upper slots, buy a new motor
pulley and belt and you're done.

You don't get full HP at lower spindle speeds, but you don't have the losses
(and noise) from the mechanical vari-speed anymore (which aren't small) so
power generally won't be an issue.

Good luck-

Paul T.

You're aware that most VFDs when fed from single phase power must be derated
to 75%?

I disagree. This is a new Teco VFD sold by dealers electric and is rated
for 2HP with single phase input.

Also, I agree with Gunner, yank out the mechanical vari-speed drive and run

Its seems aweful silly to remove a prefectly good working Mechanical VS
drive. Yes, it makes a little noise and it wastes a little power but it
works just find and give more flexability than using the VFD alone.
I have a VFD on my mill and DC motors with speed controllers on my
lathes but I don't think they give quite enough adjustment range to be
used with only one belt speed.
chuck

No no no no. Think about it. The VOLTAGE is essentially constant at
all loads (120 V, 240 V or whatever the wall socket is giving). If
the power varies, the only way it can vary is by varying the current.
I think there's something wrong with your lathe, motor, or VFD current
meter to give flat current response regardless of load. Big lathes
often have ammeters to indicate load. These would be ineffective if
the meter always read the same value. The VFD on my 11" 3 HP lathe
shows 2.8 A at no load and climbs to 13 A at full load (then trips on
overload :-( ).

This is NORMAL, believe it or not! The problem is the current sensors
in the
VFD only read current, not power. The inductance of the motor is such
that it
draws nearly constant current at all loads, but the phase angle changes
dramatically.
So, the motor draws roughly 3 A at idle, to 3.5 A at full load, but the
power draw
goes from, perhaps, 1/4 Hp at idle to 1+ Hp at full load. My mill with
a 1 Hp motor
works exactly the same way. It also has nothing to do with the VFD.

In article 9866af06.0310011228.3f2aa297
@posting.google.com, says...
No no no no. Think about it. The VOLTAGE is essentially constant at
all loads (120 V, 240 V or whatever the wall socket is giving). If
the power varies, the only way it can vary is by varying the current.

You're not only ignoring the issue of power factor
mentioned in several other posts, but also the fact that
the voltage output by the VFD varies with frequency. The
simple VFDs we're talking about here are often referred to
as volts/Hz drives beacause the voltage output when running
below base speed is proportional to frequency. For example,
the drive will deliver 24V @ 6Hz, when set up for a 240V
60Hz motor.

Ned Simmons

Ned Simmons wrote:
In article 9866af06.0310011228.3f2aa297
@posting.google.com, says...
No no no no. Think about it. The VOLTAGE is essentially constant at
all loads (120 V, 240 V or whatever the wall socket is giving). If
the power varies, the only way it can vary is by varying the current.

You're not only ignoring the issue of power factor
mentioned in several other posts, but also the fact that
the voltage output by the VFD varies with frequency. The
simple VFDs we're talking about here are often referred to
as volts/Hz drives beacause the voltage output when running
below base speed is proportional to frequency. For example,
the drive will deliver 24V @ 6Hz, when set up for a 240V
60Hz motor.

Ned Simmons

The Allen Bradley 1305 seems to have some sort of feedback loop running, it
makes adjustments based on what it thinks is the actual motor speed.

On Wed, 01 Oct 2003 23:36:31 GMT, "ATP"
wrote:

Ned Simmons wrote:
In article 9866af06.0310011228.3f2aa297
@posting.google.com, says...
No no no no. Think about it. The VOLTAGE is essentially constant at
all loads (120 V, 240 V or whatever the wall socket is giving). If
the power varies, the only way it can vary is by varying the current.

You're not only ignoring the issue of power factor
mentioned in several other posts, but also the fact that
the voltage output by the VFD varies with frequency. The
simple VFDs we're talking about here are often referred to
as volts/Hz drives beacause the voltage output when running
below base speed is proportional to frequency. For example,
the drive will deliver 24V @ 6Hz, when set up for a 240V
60Hz motor.

Ned Simmons

The Allen Bradley 1305 seems to have some sort of feedback loop running, it
makes adjustments based on what it thinks is the actual motor speed.

In the A-B's I'm using, you can select closed or open loop. For my
applications, I run open loop. I provide my own control loops
external to the drive. I don't know if the 1305 has the same feature
or not.

Pete Keillor

In article 3yJeb.2364$oX5.1292572
@news4.srv.hcvlny.cv.net,
says...
Ned Simmons wrote:
In article 9866af06.0310011228.3f2aa297
@posting.google.com, says...
No no no no. Think about it. The VOLTAGE is essentially constant at
all loads (120 V, 240 V or whatever the wall socket is giving). If
the power varies, the only way it can vary is by varying the current.

You're not only ignoring the issue of power factor
mentioned in several other posts, but also the fact that
the voltage output by the VFD varies with frequency. The
simple VFDs we're talking about here are often referred to
as volts/Hz drives beacause the voltage output when running
below base speed is proportional to frequency. For example,
the drive will deliver 24V @ 6Hz, when set up for a 240V
60Hz motor.

Ned Simmons

The Allen Bradley 1305 seems to have some sort of feedback loop running, it
makes adjustments based on what it thinks is the actual motor speed.


Sounds like what is often referred to as a "sensorless
vector" drive. True vector drives use an encoder or other
feedback device to sense rotor velocity and sometimes
position.

Ned Simmons

I have a VFD on my mill and DC motors with speed controllers on my
lathes but I don't think they give quite enough adjustment range to be
used with only one belt speed.
chuck

I find for general prototyping and small production run work, the "constant
torque" provided by the VFD is fine at the lower spindle speeds (versus the
"constant horsepower" that a mechanical vari-speed tries to provide which
gives you even higher torque at low spindle speeds). If I was pushing my
lathe and mill to the max cutting capabilities at the lower spindle speeds
perhaps the VFD would be limiting.

But with a 2HP motor on both my lathe and mill, I've never had any need for
more power at the lower speeds using the VFD's. I set up both VFD's to run
from 20% underspeed to 200% overspeed, giving me a 10 to 1 speed range. Add
in the back gears and that a very wide speed range on both machines.

But if you're happy with your mechanical vari-speed drives, stick with them.
In my case on the Clausing, I didn't like the extra noise and maintanence
hassles. On the Bridgeport I was tired of changing belt pulley settings, but
I didn't realize how much I would like the automatic spindle braking and
quick reversing until I had it.

Paul T.

I think you will end up needing a new VFD, too!

For testing, I borrowed a 1HP Teco VFD from my surface grinder.
I decided to buy a 2HP Teco VFD dedicated to this machine so
that I can use a bigger motor if I need it. For now, I suspect
the existing motor will work ok. I still think that an 1200
RPM motor would give me a big increase in low speed torque
and if I find a cheap one I will try it out.

What does it do when it fails to start?

It hums. I started using a custom VF curve and started the motor
out with a higher percentage and I made it start reliabily.
I think the default it 5% and I pushed it to 20% to make it start
well. However I think this means I should not operate the motor
at too low a freq or it will burn out the motor.


If the VFD can be set for higher than nominal amps, try setting it as
high as it will go.

The VF curve change solved the problem. I also enabled a torque boost
but that didn't seem to make much difference. The VFD will also tolerate
an overload for 1 minute.

thanks for the advice!
chuck