I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

Here's one very encouraging piece of news (related to what Karl said):
switching of the speed selector lever while the motor is running does
not destroy the drive. It simply trips on a overvoltage error and lets
the lathe coast to stop.

I am very satisfied with this behavior. It is as perfect as it gets.

The drive can easily accelerate the lathe, even at the highest
speed setting, etc.

Right now it trips when I press OFF, no doubt due to too ambitious
braking that is the default setting right now.

What I need to do is:

1) A lot of settings need to be set such as no braking, fixed
frequency (60 Hz), one-two second acceleration, etc etc.

2) Wire it properly to turn on with the limit switch operated by lathe
ON/OFF/BRAKE lever

3) Place the VFD deep inside the lathe cabinet so that it would not be
a hazard or distraction. There is no need to access the drive once it
is set up. So I will put it away. This will be a single phase lathe
that would be operated with its original control and no weird wiring
outside.

The ONLY thing that I may allow to be visible outside is the FAULT
indicator shown by a LED bulb. Maybe a FAULT with RESET
pushbutton. That's all. I do not want switches, potentiometers, none
of that stuff is necessary.

--
Due to extreme spam originating from Google Groups, and their inattention
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from Google Groups. If you want your postings to be seen by
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Ignoramus30183 wrote:
I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

Here's one very encouraging piece of news (related to what Karl said):
switching of the speed selector lever while the motor is running does
not destroy the drive. It simply trips on a overvoltage error and lets
the lathe coast to stop.

I am very satisfied with this behavior. It is as perfect as it gets.

Sounds good.

Right now it trips when I press OFF, no doubt due to too ambitious
braking that is the default setting right now.


You probably can set a 1 second rampdown and it won't trip, or put the
braking resistor on.

What I need to do is:

3) Place the VFD deep inside the lathe cabinet so that it would not be
a hazard or distraction. There is no need to access the drive once it
is set up. So I will put it away. This will be a single phase lathe
that would be operated with its original control and no weird wiring
outside.

The ONLY thing that I may allow to be visible outside is the FAULT
indicator shown by a LED bulb. Maybe a FAULT with RESET
pushbutton. That's all. I do not want switches, potentiometers, none
of that stuff is necessary.

Be sure to leave good air circulation, it will generate some heat.

I still need to make a shroud so that there is no direct path for chips
to fly into the unit. My VFD is up above the machine on the headstock end.

Good Luck,
Bob

On 2008-07-17, BobH wrote:
Ignoramus30183 wrote:
I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

Here's one very encouraging piece of news (related to what Karl said):
switching of the speed selector lever while the motor is running does
not destroy the drive. It simply trips on a overvoltage error and lets
the lathe coast to stop.

I am very satisfied with this behavior. It is as perfect as it gets.

Sounds good.

Right now it trips when I press OFF, no doubt due to too ambitious
braking that is the default setting right now.


You probably can set a 1 second rampdown and it won't trip, or put the
braking resistor on.

I will experiment. The issue is, obviously, higher spindle speeds,
requiring longer rampdown.

The other thing I can do is this: the limit switch for tutrning the
lathe on and off, has a normally closed and normally open switch. I
obviously use the N.O switch for RUN. But I can use the N.C. switch
for RESET.

What I need to do is:

3) Place the VFD deep inside the lathe cabinet so that it would not be
a hazard or distraction. There is no need to access the drive once it
is set up. So I will put it away. This will be a single phase lathe
that would be operated with its original control and no weird wiring
outside.

The ONLY thing that I may allow to be visible outside is the FAULT
indicator shown by a LED bulb. Maybe a FAULT with RESET
pushbutton. That's all. I do not want switches, potentiometers, none
of that stuff is necessary.

Be sure to leave good air circulation, it will generate some heat.

I still need to make a shroud so that there is no direct path for chips
to fly into the unit. My VFD is up above the machine on the headstock end.


The base is very big, there is plenty of space, and also the motor is
in the providing some extra circulation. Should be fine.

--
Due to extreme spam originating from Google Groups, and their inattention
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from Google Groups. If you want your postings to be seen by
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Ignoramus30183 wrote:

I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

The first of those VFDs is doing nicely on my Bridgeport. The second,
along with the 3HP motor from my former RPC is looking like it will end
up replacing the aged 1/2HP motor with failing starting cap on my lathe.
I really need to find a bigger lathe too...

On 2008-07-17, Pete C. wrote:

Ignoramus30183 wrote:

I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

The first of those VFDs is doing nicely on my Bridgeport.

That's very nice to hear. I am delighted.

The second, along with the 3HP motor from my former RPC is looking
like it will end up replacing the aged 1/2HP motor with failing
starting cap on my lathe. I really need to find a bigger lathe
too...

3 HP motor to replace a 1/2 HP motor???

By the way, starting caps cost relatively little.

--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
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Ignoramus20788 wrote:

On 2008-07-17, Pete C. wrote:

Ignoramus30183 wrote:

I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

The first of those VFDs is doing nicely on my Bridgeport.

That's very nice to hear. I am delighted.

The second, along with the 3HP motor from my former RPC is looking
like it will end up replacing the aged 1/2HP motor with failing
starting cap on my lathe. I really need to find a bigger lathe
too...

3 HP motor to replace a 1/2 HP motor???

Why not? There is room to install it, being a 3ph motor it's pretty
compact, and being on a VFD I can set limits wherever I want.


By the way, starting caps cost relatively little.

Yes, but I'm too lazy to chase after one for a motor I don't care for
anyway.

Ignoramus30183 wrote:
I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

Here's one very encouraging piece of news (related to what Karl said):
switching of the speed selector lever while the motor is running does
not destroy the drive. It simply trips on a overvoltage error and lets
the lathe coast to stop.

I am very satisfied with this behavior. It is as perfect as it gets.

The drive can easily accelerate the lathe, even at the highest
speed setting, etc.

Right now it trips when I press OFF, no doubt due to too ambitious
braking that is the default setting right now.

What I need to do is:

1) A lot of settings need to be set such as no braking, fixed
frequency (60 Hz), one-two second acceleration, etc etc.

Braking is GOOD, a real safety feature. Even if you have to cobble up a
braking resistor, it is well worth it. I get less than one second stops
on my 15" Sheldon, with a pair of 100 W vitreous enamel resistors wired
up to the braking circuit.

2) Wire it properly to turn on with the limit switch operated by lathe
ON/OFF/BRAKE lever
Yes, that would be really nice. I have the original
forward/reverse/stop buttons on my Sheldon hooked to the VFD,
and it is quite nice. I added a jog button, that is nice for when the
gears don't engage.

Jon

On 2008-07-17, Pete C. wrote:

Ignoramus20788 wrote:

On 2008-07-17, Pete C. wrote:

Ignoramus30183 wrote:

I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

The first of those VFDs is doing nicely on my Bridgeport.

That's very nice to hear. I am delighted.

The second, along with the 3HP motor from my former RPC is looking
like it will end up replacing the aged 1/2HP motor with failing
starting cap on my lathe. I really need to find a bigger lathe
too...

3 HP motor to replace a 1/2 HP motor???

Why not? There is room to install it, being a 3ph motor it's pretty
compact, and being on a VFD I can set limits wherever I want.

Sounds like fun. I hope that if something gets stuck, the bigger motor
would not break gears or something.

i

--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/

Ignoramus20788 wrote:

On 2008-07-17, Pete C. wrote:

Ignoramus20788 wrote:

On 2008-07-17, Pete C. wrote:

Ignoramus30183 wrote:

I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

The first of those VFDs is doing nicely on my Bridgeport.

That's very nice to hear. I am delighted.

The second, along with the 3HP motor from my former RPC is looking
like it will end up replacing the aged 1/2HP motor with failing
starting cap on my lathe. I really need to find a bigger lathe
too...

3 HP motor to replace a 1/2 HP motor???

Why not? There is room to install it, being a 3ph motor it's pretty
compact, and being on a VFD I can set limits wherever I want.

Sounds like fun. I hope that if something gets stuck, the bigger motor
would not break gears or something.

Just have to set the current limits appropriately. Also with two stages
of belt drive, a slipping belt is more likely.

On 2008-07-17, Jon Elson wrote:


Ignoramus30183 wrote:
I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

Here's one very encouraging piece of news (related to what Karl said):
switching of the speed selector lever while the motor is running does
not destroy the drive. It simply trips on a overvoltage error and lets
the lathe coast to stop.

I am very satisfied with this behavior. It is as perfect as it gets.

The drive can easily accelerate the lathe, even at the highest
speed setting, etc.

Right now it trips when I press OFF, no doubt due to too ambitious
braking that is the default setting right now.

What I need to do is:

1) A lot of settings need to be set such as no braking, fixed
frequency (60 Hz), one-two second acceleration, etc etc.

Braking is GOOD, a real safety feature. Even if you have to cobble up a
braking resistor, it is well worth it. I get less than one second stops
on my 15" Sheldon, with a pair of 100 W vitreous enamel resistors wired
up to the braking circuit.

Does your sheldon include a mechanical brake?

Are your 1 second stops, actually happening at high spindle speeds?

My drive already has a braking resistor, IIRC. Some of mine do and
some don't. But even if not. I have some resistors.

2) Wire it properly to turn on with the limit switch operated by lathe
ON/OFF/BRAKE lever
Yes, that would be really nice.

I already did so, it is awesome.

I have the original forward/reverse/stop buttons on my Sheldon
hooked to the VFD, and it is quite nice. I added a jog button, that
is nice for when the gears don't engage.

What is your jog frequency?

Myself, when gears don't engage, I just grab the chuck and rock it a
little.

--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/

On 2008-07-17, Pete C. wrote:

Ignoramus20788 wrote:

On 2008-07-17, Pete C. wrote:

Ignoramus20788 wrote:

On 2008-07-17, Pete C. wrote:

Ignoramus30183 wrote:

I wired the VFD to the lathe. Not in the best way yet, but enough to
experiment. Toshiba VF-A3 3.7 kW VFD, similar to what I sold to Pete
C, only bigger and with cracked top cover. (I have more for sale, 2.2
and 3.7 kW)

The first of those VFDs is doing nicely on my Bridgeport.

That's very nice to hear. I am delighted.

The second, along with the 3HP motor from my former RPC is looking
like it will end up replacing the aged 1/2HP motor with failing
starting cap on my lathe. I really need to find a bigger lathe
too...

3 HP motor to replace a 1/2 HP motor???

Why not? There is room to install it, being a 3ph motor it's pretty
compact, and being on a VFD I can set limits wherever I want.

Sounds like fun. I hope that if something gets stuck, the bigger motor
would not break gears or something.

Just have to set the current limits appropriately. Also with two stages
of belt drive, a slipping belt is more likely.

What you may find, and here I am NOT speaking from position of
knowledge, is that your big motor will draw big current even at low
load. What will change with load, is more power factor than current.

But who knows.

--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/

On Thu, 17 Jul 2008 14:57:34 -0500, Ignoramus20788
wrote:

On 2008-07-17, Pete C. wrote:


Just have to set the current limits appropriately. Also with two stages
of belt drive, a slipping belt is more likely.

What you may find, and here I am NOT speaking from position of
knowledge, is that your big motor will draw big current even at low
load. What will change with load, is more power factor than current.


You're absolutely correct. I tried it to detect jams on a conveyor.
The current difference between unloaded and jammed was too small for
the VFD to discriminate. My lathe runs unloaded at about 60% current,
it's grunting at 70%.

--
Ned Simmons

You probably can set a 1 second rampdown and it won't trip, or put the
braking resistor on.

I will experiment. The issue is, obviously, higher spindle speeds,
requiring longer rampdown.


you REALLY DO NOT want a rampdown if you are going to use the mechanical
brake - set it to coast



** Posted from http://www.teranews.com **

On Thu, 17 Jul 2008 18:01:26 -0700, "William Noble"
wrote:


You probably can set a 1 second rampdown and it won't trip, or put the
braking resistor on.

I will experiment. The issue is, obviously, higher spindle speeds,
requiring longer rampdown.


you REALLY DO NOT want a rampdown if you are going to use the mechanical
brake - set it to coast

Correct, else the VFD will be fighting the mechanical brake





** Posted from http://www.teranews.com **

I had some bad news last night.

As the drive was running the motor, the motor leaks a lot of current
through its insulation. (like Joe Gwinn story) Not good. Phase
converter does not create this effect, so it is due to voltage spikes
from the drive that this old insulation cannot handle. I do not want
to ignore this issue by grounding, as I feel that it can ruin the
motor.

I may try to locate a line reactor to dampen this, and shorten some
cables, but for now I will go back to the phase converter.

i

You don't quantify the amount of motor insulation leakage current, or
describe how it is that you became aware of it.

This effect is probably present in many home shop machines that users have
converted to VFD operation, of which many of them are probably unaware.

Proper earth grounding of a machine is mandatory, regardless of what the
power source is.
There are no perfect insulating materials, only good ones and better ones.
Insulation in motors is rated for maximum voltage and temperatures.

Once the insulation materials are compromised, (arc-over or similar path is
established), in any electrical device, the earth ground path is critical
for safety.

The motor insulation current leakage (in power line operated, or VFD-driven
motors) is documented for those interested in looking for the info.

Motors that are rated for VFD operation are typically labeled Inverter Rated
Duty or something similar. The insulation in these motors is specifically
chosen to minimize/reduce leakage currents for the fast rise times of the
VFD output voltages (variable time square waves, in appearance).

A motor that isn't rated for inverter duty could be a dual voltage motor
rated at 240 or 480VAC. If the motor is operated with a VFD output at 240V,
the insulation is generally up to the task of minimizing the current
leakage.
If that motor were operated with a VFD output of 440V or greater, then the
insulation's intended rating will be exceeded.

WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Ignoramus31221" wrote in message
...
I had some bad news last night.

As the drive was running the motor, the motor leaks a lot of current
through its insulation. (like Joe Gwinn story) Not good. Phase
converter does not create this effect, so it is due to voltage spikes
from the drive that this old insulation cannot handle. I do not want
to ignore this issue by grounding, as I feel that it can ruin the
motor.

I may try to locate a line reactor to dampen this, and shorten some
cables, but for now I will go back to the phase converter.

i

On Fri, 18 Jul 2008 07:51:27 -0500, Ignoramus31221
wrote:

I had some bad news last night.

As the drive was running the motor, the motor leaks a lot of current
through its insulation. (like Joe Gwinn story) Not good. Phase
converter does not create this effect, so it is due to voltage spikes
from the drive that this old insulation cannot handle. I do not want
to ignore this issue by grounding, as I feel that it can ruin the
motor.

I may try to locate a line reactor to dampen this, and shorten some
cables, but for now I will go back to the phase converter.

Dropping the drive's carrier frequency should also help, and is free.
You may notice more audible noise. Some drives also have a setting
that softens the corners of the chopped output and that will also
help. I assume this lowers the efficiency of the drive, but that's
presumably of little concern here unless the drive is not well
ventilated.

--
Ned Simmons

On 2008-07-18, Wild_Bill wrote:
You don't quantify the amount of motor insulation leakage current, or
describe how it is that you became aware of it.

I measured it yesterday with an clamp on ammeter, it came out as 9
amps (!). Really a shocking amount.

This effect is probably present in many home shop machines that users have
converted to VFD operation, of which many of them are probably unaware.

Proper earth grounding of a machine is mandatory, regardless of what the
power source is.
There are no perfect insulating materials, only good ones and better ones.
Insulation in motors is rated for maximum voltage and temperatures.

Once the insulation materials are compromised, (arc-over or similar path is
established), in any electrical device, the earth ground path is critical
for safety.

that's why I decided to discontinue.

The motor insulation current leakage (in power line operated, or VFD-driven
motors) is documented for those interested in looking for the info.

Motors that are rated for VFD operation are typically labeled Inverter Rated
Duty or something similar. The insulation in these motors is specifically
chosen to minimize/reduce leakage currents for the fast rise times of the
VFD output voltages (variable time square waves, in appearance).

A motor that isn't rated for inverter duty could be a dual voltage motor
rated at 240 or 480VAC. If the motor is operated with a VFD output at 240V,
the insulation is generally up to the task of minimizing the current
leakage.
If that motor were operated with a VFD output of 440V or greater, then the
insulation's intended rating will be exceeded.

This is a single voltage (two speed) 220v motor. :-(

i

WB
.........
metalworking projects
www.kwagmire.com/metal_proj.html


"Ignoramus31221" wrote in message
...
I had some bad news last night.

As the drive was running the motor, the motor leaks a lot of current
through its insulation. (like Joe Gwinn story) Not good. Phase
converter does not create this effect, so it is due to voltage spikes
from the drive that this old insulation cannot handle. I do not want
to ignore this issue by grounding, as I feel that it can ruin the
motor.

I may try to locate a line reactor to dampen this, and shorten some
cables, but for now I will go back to the phase converter.

i


--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/

In article ,
Ignoramus31221 wrote:

On 2008-07-18, Wild_Bill wrote:
You don't quantify the amount of motor insulation leakage current, or
describe how it is that you became aware of it.

I measured it yesterday with an clamp on ammeter, it came out as 9
amps (!). Really a shocking amount.

Nine amps?...!! If that's true, the motor is toast, and should be
replaced. Immediately. When we talk of leakage, we mean a few
milliamps.

The VFD is not causing this.

Unless the clamp-on is confused by the high-frequency output of the
inverter drive.

One way to tell is to hook all three windings of the motor together and
connect them to 110 volts through a light bulb (not through the VFD),
and measure the current to ground. In a perfect motor, the current will
be zero. (The motor will not even try to run, or be in any danger, and
single-phase is what to use.)

Do not use an ordinary ohmmeter for this. The test must be made with
full power voltage, or more. Or a megger, if you have one:
http://en.wikipedia.org/wiki/Megger.

If the current is in the amps, at least one winding is shorted to the
frame, and the motor must be replaced or rewound.

This is *exactly* why one firmly grounds the frame of a machine tool.

Joe Gwinn


This effect is probably present in many home shop machines that users have
converted to VFD operation, of which many of them are probably unaware.

Proper earth grounding of a machine is mandatory, regardless of what the
power source is.
There are no perfect insulating materials, only good ones and better ones.
Insulation in motors is rated for maximum voltage and temperatures.

Once the insulation materials are compromised, (arc-over or similar path is
established), in any electrical device, the earth ground path is critical
for safety.

that's why I decided to discontinue.

The motor insulation current leakage (in power line operated, or VFD-driven
motors) is documented for those interested in looking for the info.

Motors that are rated for VFD operation are typically labeled Inverter
Rated
Duty or something similar. The insulation in these motors is specifically
chosen to minimize/reduce leakage currents for the fast rise times of the
VFD output voltages (variable time square waves, in appearance).

A motor that isn't rated for inverter duty could be a dual voltage motor
rated at 240 or 480VAC. If the motor is operated with a VFD output at 240V,
the insulation is generally up to the task of minimizing the current
leakage.
If that motor were operated with a VFD output of 440V or greater, then the
insulation's intended rating will be exceeded.

This is a single voltage (two speed) 220v motor. :-(

i

WB
.........
metalworking projects
www.kwagmire.com/metal_proj.html


"Ignoramus31221" wrote in message
...
I had some bad news last night.

As the drive was running the motor, the motor leaks a lot of current
through its insulation. (like Joe Gwinn story) Not good. Phase
converter does not create this effect, so it is due to voltage spikes
from the drive that this old insulation cannot handle. I do not want
to ignore this issue by grounding, as I feel that it can ruin the
motor.

I may try to locate a line reactor to dampen this, and shorten some
cables, but for now I will go back to the phase converter.

i

On 2008-07-18, Joseph Gwinn wrote:
In article ,
Ignoramus31221 wrote:

On 2008-07-18, Wild_Bill wrote:
You don't quantify the amount of motor insulation leakage current, or
describe how it is that you became aware of it.

I measured it yesterday with an clamp on ammeter, it came out as 9
amps (!). Really a shocking amount.

Nine amps?...!! If that's true, the motor is toast, and should be
replaced. Immediately. When we talk of leakage, we mean a few
milliamps.

Probably a measurement error due to spikes.

No leakage without VFD.

The VFD is not causing this.

Unless the clamp-on is confused by the high-frequency output of the
inverter drive.

That's my feeling.

One way to tell is to hook all three windings of the motor together and
connect them to 110 volts through a light bulb (not through the VFD),
and measure the current to ground. In a perfect motor, the current will
be zero. (The motor will not even try to run, or be in any danger, and
single-phase is what to use.)

Do not use an ordinary ohmmeter for this. The test must be made with
full power voltage, or more. Or a megger, if you have one:
http://en.wikipedia.org/wiki/Megger.

I think that I have a megger.

If the current is in the amps, at least one winding is shorted to the
frame, and the motor must be replaced or rewound.

This is *exactly* why one firmly grounds the frame of a machine tool.

I think that the motor is not leaking 9 amps and it was a measurement
issue. I will try using a analog clampon next time. But there is
leakage of some, unspecified amount.

i

In article ,
Ignoramus31221 wrote:

On 2008-07-18, Joseph Gwinn wrote:
In article ,
Ignoramus31221 wrote:

On 2008-07-18, Wild_Bill wrote:
You don't quantify the amount of motor insulation leakage current, or
describe how it is that you became aware of it.

I measured it yesterday with an clamp on ammeter, it came out as 9
amps (!). Really a shocking amount.

Nine amps?...!! If that's true, the motor is toast, and should be
replaced. Immediately. When we talk of leakage, we mean a few
milliamps.

Probably a measurement error due to spikes.

No leakage without VFD.

How did you test this?


The VFD is not causing this.

Unless the clamp-on is confused by the high-frequency output of the
inverter drive.

That's my feeling.

OK. When I say that the VFD is not causing this, I mean that ordinary
high-frequency current coming through the capacitance between windings
and frame are not nearly that large, by orders of magnitude.


One way to tell is to hook all three windings of the motor together and
connect them to 110 volts through a light bulb (not through the VFD),
and measure the current to ground. In a perfect motor, the current will
be zero. (The motor will not even try to run, or be in any danger, and
single-phase is what to use.)

Do not use an ordinary ohmmeter for this. The test must be made with
full power voltage, or more. Or a megger, if you have one:
http://en.wikipedia.org/wiki/Megger.

I think that I have a megger.

I suspected as much. Don't know why.


If the current is in the amps, at least one winding is shorted to the
frame, and the motor must be replaced or rewound.

This is *exactly* why one firmly grounds the frame of a machine tool.

I think that the motor is not leaking 9 amps and it was a measurement
issue. I will try using a analog clampon next time. But there is
leakage of some, unspecified amount.

An analog meter should be less affected by the high-frequency noise, but
analog electronic meters (I have a few) are affected by HF noise.
Passive analog meters should be immune.

Some kinds of high-end DMM are designed to make accurate measurements of
true RMS currents and voltages in inverter-driven motors. I know Fluke
makes such meters, and I imagine that they are not alone. I think the
key is "true RMS" and a RMS bandwidth that exceeds the chop frequency by
a factor. But I have not tried this yet.

You can also open the green wire and put a passive analog AC ammeter in
series. Or a power resistor, and look at the waveform with a scope.

I would be tempted to test a few other motors, for comparison, as well.

Joe Gwinn

Ignoramus20788 wrote:


Does your sheldon include a mechanical brake?
No! Motor - gearbox - spindle, no clutch, no brake, no varispeed drive.


Are your 1 second stops, actually happening at high spindle speeds?
Yes, the highest nominal speed is 1250 RPM, there is a version of the
lathe with a two-speed motor, but I don't have that. I could take the
motor up to 120 Hz and get 2500 RPM, but the idea of an 8.25" chuck at
2500 RPM scares me!


What is your jog frequency?
I think it is 5 Hz, I don't remember exactly. it is a programmable
parameter.


Myself, when gears don't engage, I just grab the chuck and rock it a
little.


Yes, works fine in high speed mode, but with the backgear engaged, it
takes a lot of force to turn the chuck. I could EASILY live without it,
but since the VFD supported the feature, I put it in, just a push button
and one more wire.

Jon