"But, I would think that if the motor is stalled it would draw "locked rotor amps" and this ought to trip a properly selected overload or fuse pretty much immediately.? Not so?"
Not so. A motor draws locked rotor current at start and long enough?to accelerate to near synchronous speed. There is a bit more to it than that but it's close enough. There must be a time delay in the overload to allow the motor to start at the locked rotor current; if there wasn't, you could never get the motor started without tripping the overload. Overloads are what we call an inverse time device. That means that the higher the current the faster it trip and the lower the current the slower it trips. Overloads do not trip instantaneously, they always take some time. In the USA, overloads are typically designed for 10, 20 or 30 seconds around 600% of motor current which is a typical locked?rotor current - at least the 3-phase units I am familiar with. Again, it's not quite that simple but close enough. Small single phase motors generally have a lower locked rotor current. The time to trip an overload is going to be longer. In many cases it is longer than the thermal capability of the winding insulation and will cause failure before the overload can react.? On Mon, Feb 1, 2021 at 12:10 PM Alan Muller < alan@...> wrote:
This is interesting information.?? I am NOT an
electrical engineer and claim no expertise in motor protection.?
Certain things jump out:
Many cheap Asian motors don't have enough information on the data plate
to select protection.? Or the claimed horsepower doesn't match the
current rating, or.....
The internal "klixon" type protectors are somewhat responsive
to both motor temperature and current draw.? A simple external?
"starter"--be it melting alloy or bimetal-- doesn't know how
hot the motor is, but only how much current it is drawing.? So
current draw could be within ratings but if the fan is loose or the air
passages clogged with debris, the motor could be cooking.
But, I would think that if the motor is stalled it would draw
"locked rotor amps" and this ought to trip a properly selected
overload or fuse pretty much immediately.? Not so?
My 4x6 gets only light use and I don't let it run unattended.? If I
were to use it more heavily I think I would install an IEC type bimetal
starter and back off the current adjustment until it tripped in normal
use, then turn it up a little.....? Is this sound thinking?
I also have a 14" wood cutting band saw.? The base (factory)
has no provision for ventilation of the motor.? This clearly would
not do for heavy use.
am
At 11:38 AM 2/1/2021 -0800, you wrote:
My stock Horror Freight 4x6 is
TEFC. I just went out and confirmed. The motor is finned and there is a
fan shroud over the rear. When running, the fan blows air over the fins
for cooling. It does not have any overload protection.
Now for my diatribe.
The best solution to prevent damaging a motor due to stalling isto be
present when operating. Leaving the machine unattended is why the motor
will burn up when stalled. I've said this before, overloads do not
adequately protect motors from a stalled position. They definitely don't
hurt but you cannot rely upon them to protect an unattended machine.?
I'm a retired registered electrical engineer with over 45 years of
experience who taught electrical system protection and have been an
expert witness in protection matters. There will always be anecdotal
evidence that suggests an overload will protect against a stalled
condition but I can present you with lots of technical data to show that
is not the case. The simplest explanation is that overloads are designed
for when the motor is running which means they are designed to trip while
the motor is still getting fan cooling. A stalled condition has no
cooling and must trip much faster because of it. There is thermal lag
between the motor winding and any thermal sensing device which may be in
the motor. This lag can be long enough to either damage or fail the
motor's insulation.?
There are electronic overload relays with stall protection that will
protect a small motor like on a 4X6 but the cost of those relays approach
the cost of a replacement motor. If you are really worried about it and
are electronically inclined, you could make your? own stall protection
using something like an Arduino and mechanically sense a stalled
condition and will disconnect the motor. There is more to it since you
actually have to get the motor to start since it is stalled at start
which requires some type of controller beyond a toggle switch.
Personally, I will attend the operation of the machine since that is
easier and more likely foolproof.
On Mon, Feb 1, 2021 at 11:03 AM John Vreede
<vreededesign@...
> wrote:
- Good point Alan, the TE motors at least restrict the access to oxygen
to start a fire and the?? '....molten metal, burning insulation etc'
bit Jim quoted would be covered.
- However I don't know of any OEM TEFC motors on 4x6's, and do know
that at least one major manfr. is still using open motors.?? Has
someone got a new HF saw (HF is probably the biggest seller??), that can
say whether they use TEFC motors?
- This would be an additional thing to look for when buying - jv?
- On Tue, Feb 2, 2021 at 7:40 AM Alan Muller
<alan@...>
wrote:
- Do you consider that totally enclosed motors (TEFC) pose less of a
safety hazard than open (actually shielded) motors??? It seems
likely that an enclosed motor would be less likely to spew sparks and hot
metal than a motor with ventilation openings.
- I think I have noticed that equipment from Asia, even low priced
stuff, is likely to have a TEFC motor where conventional domestic
production (if there still were any) would not.
- am
- At 05:40 PM 2/1/2021 +0000, you wrote:
- John Wrote
- ??€?Don't think you should be concerned with UL certitification and
such.?? Induction motors have been around for 100yrs or so and the
things that make them fail aren't tested for in UL anyway ??????
- I would not go that far? ?? Safety certifications UL and other
wise (UL isn??€?t the only game in town)?? isn?sn??€?t so much about
t testing for things that make things fail, as testing to ensure that
WHEN they do fail, the fail ??€?relatively??€??????? safely. This
relatively safety includes not starting fires {??€??? ¡ molten ten
metal, burning insulation, fflaming particles, or other ignited material
could fall onto flammable material, or through which a flame could be
projected¡.??€???}
- > and not creating a shock hazard.
- ?
- A ??€?Listed??€??? or ??€ ??????Recognized??€??? motor (as compared
to an unlisted/recognized one)?? are far less likely to start a fire
or catch fire, when given the same amount of abuse.
- They are also less like to fail to live up to expectations as a
consequence of having to meet listing requirements.
- ? In particular a motor needs to fall within ~10% of the NEC values
for current for that size motor, at rated nominal voltage.
- There are also temperature rise tests, sheet metal thickness, and
grounding resistance tests.
- There is also a locked rotor test, For motors without a thermal
cutout this can run for 18 days, or until the motor fails. When it fails
(or at the end of the test if it doesn??€?t) there are temperperature
limits, and it still has to pass insulation resistance tests to
demonstrate that it has not created a shock hazard. For motors with a
thermal cutout, the test runs until the cutout operates. If the motor has
an auto-reset cutoff, then the test runs for 18 days.
- ?
- I have replaced the motor on my saw with a UL listed one. BUT I did
not do so until it failed.
- A saw that comes with a UL listed motor, is likely to be
significantly more expensive. If you are not using a flammable cutting
fluid, and make sure that both the motor and saw frame are grounded (and
that your plug has all 3 prongs.) I would not be worried. Just recognize
that the motor likely will die on you the moment you turn your back on it
- ?
- Also recognize that a ??€?CE??€??? markmark is in NO WAY a safety
certification mark like UL, CSA, ETL, etc
- ?
- R James (Jim) Klessig P.E. | Senior Power Systems Engineer |
- Electrical Reliability Services, VERTIV
- jim.klessig@...,
jim_klessig@...
- 1876 Gwin Rd, Mckinleyville | CA | 95519 | USA
- | Cell (707) 497-9611 | eFax 614-410-0653
- ?
- CONFIDENTIALITY NOTICE: This e-mail and any files transmitted with it
are intended solely for the use of the individual or entity to whom they
are addressed and may contain confidential and privileged information
protected by law. If you received this e-mail in error, any review, use,
dissemination, distribution, or copying of the e-mail is strictly
prohibited. Please notify the sender immediately by return e-mail and
delete all copies from your system.
--
John A. Schirra?
Sent from GMail
|
NEC permits breakers controlling motor loads to be sized up to
250% of the locked rotor amperes. Motor could sit their all day
long and cook, and the breaker wouldn't trip.
Motor overload protection is a separate deal, and can be
accomplished with a 'heater' as its called or even a lower rated
time-delay fuse. Cooper/Bussman actually sells a handybox plate
with disconnect switch and fuse holder for this very thing.
On 2/1/2021 3:10 PM, Alan Muller wrote:
toggle quoted message
Show quoted text
But, I would think that if the motor is stalled it would draw
"locked rotor amps" and this ought to trip a properly selected
overload or fuse pretty much immediately.? Not so?
|
Alans comments get to the heart of my uncertainty with overload protection and why I thought the Arduino solution would be preferable.?? I'm very much interested in John and Jim's responses to Alan's questions - jv
On Tue, Feb 2, 2021 at 9:10 AM Alan Muller < alan@...> wrote:
This is interesting information.?? I am NOT an
electrical engineer and claim no expertise in motor protection.?
Certain things jump out:
Many cheap Asian motors don't have enough information on the data plate
to select protection.? Or the claimed horsepower doesn't match the
current rating, or.....
The internal "klixon" type protectors are somewhat responsive
to both motor temperature and current draw.? A simple external?
"starter"--be it melting alloy or bimetal-- doesn't know how
hot the motor is, but only how much current it is drawing.? So
current draw could be within ratings but if the fan is loose or the air
passages clogged with debris, the motor could be cooking.
But, I would think that if the motor is stalled it would draw
"locked rotor amps" and this ought to trip a properly selected
overload or fuse pretty much immediately.? Not so?
My 4x6 gets only light use and I don't let it run unattended.? If I
were to use it more heavily I think I would install an IEC type bimetal
starter and back off the current adjustment until it tripped in normal
use, then turn it up a little.....? Is this sound thinking?
I also have a 14" wood cutting band saw.? The base (factory)
has no provision for ventilation of the motor.? This clearly would
not do for heavy use.
am
At 11:38 AM 2/1/2021 -0800, you wrote:
My stock Horror Freight 4x6 is
TEFC. I just went out and confirmed. The motor is finned and there is a
fan shroud over the rear. When running, the fan blows air over the fins
for cooling. It does not have any overload protection.
Now for my diatribe.
The best solution to prevent damaging a motor due to stalling isto be
present when operating. Leaving the machine unattended is why the motor
will burn up when stalled. I've said this before, overloads do not
adequately protect motors from a stalled position. They definitely don't
hurt but you cannot rely upon them to protect an unattended machine.?
I'm a retired registered electrical engineer with over 45 years of
experience who taught electrical system protection and have been an
expert witness in protection matters. There will always be anecdotal
evidence that suggests an overload will protect against a stalled
condition but I can present you with lots of technical data to show that
is not the case. The simplest explanation is that overloads are designed
for when the motor is running which means they are designed to trip while
the motor is still getting fan cooling. A stalled condition has no
cooling and must trip much faster because of it. There is thermal lag
between the motor winding and any thermal sensing device which may be in
the motor. This lag can be long enough to either damage or fail the
motor's insulation.?
There are electronic overload relays with stall protection that will
protect a small motor like on a 4X6 but the cost of those relays approach
the cost of a replacement motor. If you are really worried about it and
are electronically inclined, you could make your? own stall protection
using something like an Arduino and mechanically sense a stalled
condition and will disconnect the motor. There is more to it since you
actually have to get the motor to start since it is stalled at start
which requires some type of controller beyond a toggle switch.
Personally, I will attend the operation of the machine since that is
easier and more likely foolproof.
On Mon, Feb 1, 2021 at 11:03 AM John Vreede
<vreededesign@...
> wrote:
- Good point Alan, the TE motors at least restrict the access to oxygen
to start a fire and the?? '....molten metal, burning insulation etc'
bit Jim quoted would be covered.
- However I don't know of any OEM TEFC motors on 4x6's, and do know
that at least one major manfr. is still using open motors.?? Has
someone got a new HF saw (HF is probably the biggest seller??), that can
say whether they use TEFC motors?
- This would be an additional thing to look for when buying - jv?
- On Tue, Feb 2, 2021 at 7:40 AM Alan Muller
<alan@...>
wrote:
- Do you consider that totally enclosed motors (TEFC) pose less of a
safety hazard than open (actually shielded) motors??? It seems
likely that an enclosed motor would be less likely to spew sparks and hot
metal than a motor with ventilation openings.
- I think I have noticed that equipment from Asia, even low priced
stuff, is likely to have a TEFC motor where conventional domestic
production (if there still were any) would not.
- am
- At 05:40 PM 2/1/2021 +0000, you wrote:
- John Wrote
- ??€?Don't think you should be concerned with UL certitification and
such.?? Induction motors have been around for 100yrs or so and the
things that make them fail aren't tested for in UL anyway ??????
- I would not go that far? ?? Safety certifications UL and other
wise (UL isn??€?t the only game in town)?? isn?sn??€?t so much about
t testing for things that make things fail, as testing to ensure that
WHEN they do fail, the fail ??€?relatively??€??????? safely. This
relatively safety includes not starting fires {??€??? ¡ molten ten
metal, burning insulation, fflaming particles, or other ignited material
could fall onto flammable material, or through which a flame could be
projected¡.??€???}
- > and not creating a shock hazard.
- ?
- A ??€?Listed??€??? or ??€ ??????Recognized??€??? motor (as compared
to an unlisted/recognized one)?? are far less likely to start a fire
or catch fire, when given the same amount of abuse.
- They are also less like to fail to live up to expectations as a
consequence of having to meet listing requirements.
- ? In particular a motor needs to fall within ~10% of the NEC values
for current for that size motor, at rated nominal voltage.
- There are also temperature rise tests, sheet metal thickness, and
grounding resistance tests.
- There is also a locked rotor test, For motors without a thermal
cutout this can run for 18 days, or until the motor fails. When it fails
(or at the end of the test if it doesn??€?t) there are temperperature
limits, and it still has to pass insulation resistance tests to
demonstrate that it has not created a shock hazard. For motors with a
thermal cutout, the test runs until the cutout operates. If the motor has
an auto-reset cutoff, then the test runs for 18 days.
- ?
- I have replaced the motor on my saw with a UL listed one. BUT I did
not do so until it failed.
- A saw that comes with a UL listed motor, is likely to be
significantly more expensive. If you are not using a flammable cutting
fluid, and make sure that both the motor and saw frame are grounded (and
that your plug has all 3 prongs.) I would not be worried. Just recognize
that the motor likely will die on you the moment you turn your back on it
- ?
- Also recognize that a ??€?CE??€??? markmark is in NO WAY a safety
certification mark like UL, CSA, ETL, etc
- ?
- R James (Jim) Klessig P.E. | Senior Power Systems Engineer |
- Electrical Reliability Services, VERTIV
- jim.klessig@...,
jim_klessig@...
- 1876 Gwin Rd, Mckinleyville | CA | 95519 | USA
- | Cell (707) 497-9611 | eFax 614-410-0653
- ?
- CONFIDENTIALITY NOTICE: This e-mail and any files transmitted with it
are intended solely for the use of the individual or entity to whom they
are addressed and may contain confidential and privileged information
protected by law. If you received this e-mail in error, any review, use,
dissemination, distribution, or copying of the e-mail is strictly
prohibited. Please notify the sender immediately by return e-mail and
delete all copies from your system.
--
John A. Schirra?
Sent from GMail
|
This is interesting information.?? I am NOT an
electrical engineer and claim no expertise in motor protection.?
Certain things jump out:
Many cheap Asian motors don't have enough information on the data plate
to select protection.? Or the claimed horsepower doesn't match the
current rating, or.....
The internal "klixon" type protectors are somewhat responsive
to both motor temperature and current draw.? A simple external?
"starter"--be it melting alloy or bimetal-- doesn't know how
hot the motor is, but only how much current it is drawing.? So
current draw could be within ratings but if the fan is loose or the air
passages clogged with debris, the motor could be cooking.
But, I would think that if the motor is stalled it would draw
"locked rotor amps" and this ought to trip a properly selected
overload or fuse pretty much immediately.? Not so?
My 4x6 gets only light use and I don't let it run unattended.? If I
were to use it more heavily I think I would install an IEC type bimetal
starter and back off the current adjustment until it tripped in normal
use, then turn it up a little.....? Is this sound thinking?
I also have a 14" wood cutting band saw.? The base (factory)
has no provision for ventilation of the motor.? This clearly would
not do for heavy use.
am
At 11:38 AM 2/1/2021 -0800, you wrote:
toggle quoted message
Show quoted text
My stock Horror Freight 4x6 is
TEFC. I just went out and confirmed. The motor is finned and there is a
fan shroud over the rear. When running, the fan blows air over the fins
for cooling. It does not have any overload protection.
Now for my diatribe.
The best solution to prevent damaging a motor due to stalling isto be
present when operating. Leaving the machine unattended is why the motor
will burn up when stalled. I've said this before, overloads do not
adequately protect motors from a stalled position. They definitely don't
hurt but you cannot rely upon them to protect an unattended machine.?
I'm a retired registered electrical engineer with over 45 years of
experience who taught electrical system protection and have been an
expert witness in protection matters. There will always be anecdotal
evidence that suggests an overload will protect against a stalled
condition but I can present you with lots of technical data to show that
is not the case. The simplest explanation is that overloads are designed
for when the motor is running which means they are designed to trip while
the motor is still getting fan cooling. A stalled condition has no
cooling and must trip much faster because of it. There is thermal lag
between the motor winding and any thermal sensing device which may be in
the motor. This lag can be long enough to either damage or fail the
motor's insulation.?
There are electronic overload relays with stall protection that will
protect a small motor like on a 4X6 but the cost of those relays approach
the cost of a replacement motor. If you are really worried about it and
are electronically inclined, you could make your? own stall protection
using something like an Arduino and mechanically sense a stalled
condition and will disconnect the motor. There is more to it since you
actually have to get the motor to start since it is stalled at start
which requires some type of controller beyond a toggle switch.
Personally, I will attend the operation of the machine since that is
easier and more likely foolproof.
On Mon, Feb 1, 2021 at 11:03 AM John Vreede
<vreededesign@...
> wrote:
- Good point Alan, the TE motors at least restrict the access to oxygen
to start a fire and the?? '....molten metal, burning insulation etc'
bit Jim quoted would be covered.
- However I don't know of any OEM TEFC motors on 4x6's, and do know
that at least one major manfr. is still using open motors.?? Has
someone got a new HF saw (HF is probably the biggest seller??), that can
say whether they use TEFC motors?
- This would be an additional thing to look for when buying - jv?
- On Tue, Feb 2, 2021 at 7:40 AM Alan Muller
<alan@...>
wrote:
- Do you consider that totally enclosed motors (TEFC) pose less of a
safety hazard than open (actually shielded) motors??? It seems
likely that an enclosed motor would be less likely to spew sparks and hot
metal than a motor with ventilation openings.
- I think I have noticed that equipment from Asia, even low priced
stuff, is likely to have a TEFC motor where conventional domestic
production (if there still were any) would not.
- am
- At 05:40 PM 2/1/2021 +0000, you wrote:
- John Wrote
- ??€?Don't think you should be concerned with UL certitification and
such.?? Induction motors have been around for 100yrs or so and the
things that make them fail aren't tested for in UL anyway ??????
- I would not go that far? ?? Safety certifications UL and other
wise (UL isn??€?t the only game in town)?? isn?sn??€?t so much about
t testing for things that make things fail, as testing to ensure that
WHEN they do fail, the fail ??€?relatively??€??????? safely. This
relatively safety includes not starting fires {??€??? ¡ molten ten
metal, burning insulation, fflaming particles, or other ignited material
could fall onto flammable material, or through which a flame could be
projected¡.??€???}
- > and not creating a shock hazard.
- ?
- A ??€?Listed??€??? or ??€ ??????Recognized??€??? motor (as compared
to an unlisted/recognized one)?? are far less likely to start a fire
or catch fire, when given the same amount of abuse.
- They are also less like to fail to live up to expectations as a
consequence of having to meet listing requirements.
- ? In particular a motor needs to fall within ~10% of the NEC values
for current for that size motor, at rated nominal voltage.
- There are also temperature rise tests, sheet metal thickness, and
grounding resistance tests.
- There is also a locked rotor test, For motors without a thermal
cutout this can run for 18 days, or until the motor fails. When it fails
(or at the end of the test if it doesn??€?t) there are temperperature
limits, and it still has to pass insulation resistance tests to
demonstrate that it has not created a shock hazard. For motors with a
thermal cutout, the test runs until the cutout operates. If the motor has
an auto-reset cutoff, then the test runs for 18 days.
- ?
- I have replaced the motor on my saw with a UL listed one. BUT I did
not do so until it failed.
- A saw that comes with a UL listed motor, is likely to be
significantly more expensive. If you are not using a flammable cutting
fluid, and make sure that both the motor and saw frame are grounded (and
that your plug has all 3 prongs.) I would not be worried. Just recognize
that the motor likely will die on you the moment you turn your back on it
- ?
- Also recognize that a ??€?CE??€??? markmark is in NO WAY a safety
certification mark like UL, CSA, ETL, etc
- ?
- R James (Jim) Klessig P.E. | Senior Power Systems Engineer |
- Electrical Reliability Services, VERTIV
- jim.klessig@...,
jim_klessig@...
- 1876 Gwin Rd, Mckinleyville | CA | 95519 | USA
- | Cell (707) 497-9611 | eFax 614-410-0653
- ?
- CONFIDENTIALITY NOTICE: This e-mail and any files transmitted with it
are intended solely for the use of the individual or entity to whom they
are addressed and may contain confidential and privileged information
protected by law. If you received this e-mail in error, any review, use,
dissemination, distribution, or copying of the e-mail is strictly
prohibited. Please notify the sender immediately by return e-mail and
delete all copies from your system.
--
John A. Schirra?
Sent from GMail
|
My stock Horror Freight 4x6 is TEFC. I just went out and confirmed. The motor is finned and there is a fan shroud over the rear. When running, the fan blows air over the fins for cooling. It does not have any overload protection.
Now for my diatribe.
The best solution to prevent damaging a motor due to stalling isto be present when operating. Leaving the machine unattended is why the motor will burn up when stalled. I've said this before, overloads do not adequately protect motors from a stalled position. They definitely don't hurt but you cannot rely upon them to protect an unattended machine.?
I'm a retired registered electrical engineer with over 45 years of experience who taught electrical system protection and have been an expert witness in protection matters. There will always be anecdotal evidence that suggests an overload will protect against a stalled condition but I can present you with lots of technical data to show that is not the case. The simplest explanation is that overloads are designed for when the motor is running which means they are designed to trip while the motor is still getting fan cooling. A stalled condition has no cooling and must trip much faster because of it. There is thermal lag between the motor winding and any thermal sensing device which may be in the motor. This lag can be long enough to either damage or fail the motor's insulation.?
There are electronic overload relays with stall protection that will protect a small motor like on a 4X6 but the cost of those relays approach the cost of a replacement motor. If you are really worried about it and are electronically inclined, you could make your?own stall protection using something like an Arduino and mechanically sense a stalled condition and will disconnect the motor. There is more to it since you actually have to get the motor to start since it is stalled at start which requires some type of controller beyond a toggle switch. Personally, I will attend the operation of the machine since that is easier and more likely foolproof.
Good point Alan, the TE motors at least restrict the access to oxygen to start a fire and the? '....molten metal, burning insulation etc' bit Jim quoted would be covered. However I don't know of any OEM TEFC motors on 4x6's, and do know that at least one major manfr. is still using open motors.? Has someone got a new HF
saw
(HF is probably the biggest seller??), that can say whether they use TEFC motors? This would be an additional thing to look for when buying - jv?
On Tue, Feb 2, 2021 at 7:40 AM Alan Muller < alan@...> wrote:
Do you consider that totally enclosed motors (TEFC) pose
less of a safety hazard than open (actually shielded) motors?? It
seems likely that an enclosed motor would be less likely to spew sparks
and hot metal than a motor with ventilation openings.
I think I have noticed that equipment from Asia, even low priced stuff,
is likely to have a TEFC motor where conventional domestic production (if
there still were any) would not.
am
At 05:40 PM 2/1/2021 +0000, you wrote:
John Wrote
?€?Don't think you should be concerned with UL certification and
such.? Induction motors have been around for 100yrs or so and the
things that make them fail aren't tested for in UL anyway ?€?
I would not go that far?? Safety certifications UL and other
wise (UL isn?€?t the only game in town)? isn?€?t so much about
testing for things that make things fail, as testing to ensure that WHEN
they do fail, the fail ?€?relatively?€? safely. This relatively safety
includes not starting fires {?€?? ¡ molten metal, burning
insulation, fflaming particles, or other ignited material could fall onto
flammable material, or through which a flame could be
projected¡.?€?}
and not creating a shock hazard.
?
A ?€?Listed?€? or ?€?Recognized?€? motor (as compared to an
unlisted/recognized one)? are far less likely to start a fire or
catch fire, when given the same amount of abuse.
They are also less like to fail to live up to expectations as a
consequence of having to meet listing requirements.
?In particular a motor needs to fall within ~10% of the NEC values
for current for that size motor, at rated nominal voltage.
There are also temperature rise tests, sheet metal thickness, and
grounding resistance tests.
There is also a locked rotor test, For motors without a thermal cutout
this can run for 18 days, or until the motor fails. When it fails (or at
the end of the test if it doesn?€?t) there are temperature limits, and it
still has to pass insulation resistance tests to demonstrate that it has
not created a shock hazard. For motors with a thermal cutout, the test
runs until the cutout operates. If the motor has an auto-reset cutoff,
then the test runs for 18 days.
?
I have replaced the motor on my saw with a UL listed one. BUT I did not
do so until it failed.
A saw that comes with a UL listed motor, is likely to be significantly
more expensive. If you are not using a flammable cutting fluid, and make
sure that both the motor and saw frame are grounded (and that your plug
has all 3 prongs.) I would not be worried. Just recognize that the motor
likely will die on you the moment you turn your back on it
?
Also recognize that a ?€?CE?€? mark is in NO WAY a safety certification
mark like UL, CSA, ETL, etc
?
R James (Jim) Klessig P.E. | Senior Power Systems Engineer |
Electrical Reliability Services, VERTIV
jim.klessig@...,
jim_klessig@...
1876 Gwin Rd, Mckinleyville | CA | 95519 | USA
| Cell (707) 497-9611 | eFax 614-410-0653
?
CONFIDENTIALITY NOTICE: This e-mail and any files transmitted with it are
intended solely for the use of the individual or entity to whom they are
addressed and may contain confidential and privileged information
protected by law. If you received this e-mail in error, any review, use,
dissemination, distribution, or copying of the e-mail is strictly
prohibited. Please notify the sender immediately by return e-mail and
delete all copies from your system.
-- John A. Schirra?
Sent from GMail
|
Re: [ExternalEmail] Re: [4x6bandsaw] which version to get
Those overload relays are intended to be used with an external contactor that actually controls the motor I would not really want to use that overload contact to control any motor drawing over ~1.5A @ full load.
Even then for proper sensing you ought to run your current through all three legs.
In particular I would not use this one, since the design is intended to have the realy mount directly into the contactor. The three ¡°legs¡± coming out the top are not terminals and there is no way for you to connect to them.
They are intended to slide into the contact terminals of a matching contactor.
Also this rather suspiciously does not show you the FRONT of the relay, where the real manufacturer of those images is, and I suspect you would actually get something rather lower in quality.
?
Here is an image that shows that style of relay as it is intended to be used.
?
Here are a couple more suitable type solutions
?
?
?
no endorsement intended. These are probably not UL or anyone else listed, but is a reputable manufacturer. {If that is actually what you get}
Notice its price tag, and you would still need an enclosure.
?
?
?
R James (Jim) Klessig P.E. | Senior Power Systems Engineer |
Electrical Reliability Services, VERTIV
jim.klessig@...,
jim_klessig@...
1876 Gwin Rd, Mckinleyville | CA | 95519 | USA
|
Cell (707) 497-9611 |
eFax
614-410-0653
?
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From: [email protected] < [email protected]>
On Behalf Of John Vreede
Sent: Monday, February 1, 2021 10:22 AM
To: [email protected] Group Moderators < [email protected]>
Subject: [ExternalEmail] Re: [4x6bandsaw] which version to get
?
Good info, thanks Alan, I'll follow that up. Arduino is cheap enough if from China, but not $12-cheap.?
Arron, if your blade comes off easily, although it's a 'safety feature' it must be very frustrating.? It's probably in need of some tracking adjustment.? The blade should just skim
both rear guide rollers and I suspect the lower and maybe even the upper is pushed hard into the blade.? Back both away until both are visibly clear of the blade and then bring them forward. Unfortunately that will upset your squareness so that will
have to be done afterwards. Maybe the safety feature is worth putting up with....
You've revised my opinion of UL Jim, thankyou for that - jv? ?
?
?
On Tue, 2 Feb 2021, 3:31 am Alan Muller, <alan@...> wrote:
I don'r know of any power tool that needs overload protection more than these saws.? They are often run unattended and can easily jam.? But overload protection can easily enough be added to a motor.
This is one approach:?
But note that these things, which used to cost $25 or so, have gotten absurdly expensive.? But they can be scrounged.? The "heater" needs to be matched to the motor/how hard you want to work the motor.
IEC overloads are cheaper and adjustable:?
A key thing to note is to NOT use a motor with auto-reset protection (no red button).? These reset when they cool off and might start when you are messing with the blade.
am
At 07:24 AM 2/1/2021 -0600, you wrote:
On 2/1/2021 3:24 AM, John Vreede wrote:
I don't know of any OEM motors that have thermal overload re-sets, but Grizzly sell replacement motors for machine tools, that I believe, have them. - jv
? You are correct , the motor on mine is s Griz and it does have TO protection . I too burned my original up while cutting unattended .
--
Snag
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Good point Alan, the TE motors at least restrict the access to oxygen to start a fire and the? '....molten metal, burning insulation etc' bit Jim quoted would be covered. However I don't know of any OEM TEFC motors on 4x6's, and do know that at least one major manfr. is still using open motors.? Has someone got a new HF
saw
(HF is probably the biggest seller??), that can say whether they use TEFC motors? This would be an additional thing to look for when buying - jv?
On Tue, Feb 2, 2021 at 7:40 AM Alan Muller < alan@...> wrote:
Do you consider that totally enclosed motors (TEFC) pose
less of a safety hazard than open (actually shielded) motors?? It
seems likely that an enclosed motor would be less likely to spew sparks
and hot metal than a motor with ventilation openings.
I think I have noticed that equipment from Asia, even low priced stuff,
is likely to have a TEFC motor where conventional domestic production (if
there still were any) would not.
am
At 05:40 PM 2/1/2021 +0000, you wrote:
John Wrote
?€?Don't think you should be concerned with UL certification and
such.? Induction motors have been around for 100yrs or so and the
things that make them fail aren't tested for in UL anyway ?€?
I would not go that far?? Safety certifications UL and other
wise (UL isn?€?t the only game in town)? isn?€?t so much about
testing for things that make things fail, as testing to ensure that WHEN
they do fail, the fail ?€?relatively?€? safely. This relatively safety
includes not starting fires {?€?? ¡ molten metal, burning
insulation, fflaming particles, or other ignited material could fall onto
flammable material, or through which a flame could be
projected¡.?€?}
and not creating a shock hazard.
?
A ?€?Listed?€? or ?€?Recognized?€? motor (as compared to an
unlisted/recognized one)? are far less likely to start a fire or
catch fire, when given the same amount of abuse.
They are also less like to fail to live up to expectations as a
consequence of having to meet listing requirements.
?In particular a motor needs to fall within ~10% of the NEC values
for current for that size motor, at rated nominal voltage.
There are also temperature rise tests, sheet metal thickness, and
grounding resistance tests.
There is also a locked rotor test, For motors without a thermal cutout
this can run for 18 days, or until the motor fails. When it fails (or at
the end of the test if it doesn?€?t) there are temperature limits, and it
still has to pass insulation resistance tests to demonstrate that it has
not created a shock hazard. For motors with a thermal cutout, the test
runs until the cutout operates. If the motor has an auto-reset cutoff,
then the test runs for 18 days.
?
I have replaced the motor on my saw with a UL listed one. BUT I did not
do so until it failed.
A saw that comes with a UL listed motor, is likely to be significantly
more expensive. If you are not using a flammable cutting fluid, and make
sure that both the motor and saw frame are grounded (and that your plug
has all 3 prongs.) I would not be worried. Just recognize that the motor
likely will die on you the moment you turn your back on it
?
Also recognize that a ?€?CE?€? mark is in NO WAY a safety certification
mark like UL, CSA, ETL, etc
?
R James (Jim) Klessig P.E. | Senior Power Systems Engineer |
Electrical Reliability Services, VERTIV
jim.klessig@...,
jim_klessig@...
1876 Gwin Rd, Mckinleyville | CA | 95519 | USA
| Cell (707) 497-9611 | eFax 614-410-0653
?
CONFIDENTIALITY NOTICE: This e-mail and any files transmitted with it are
intended solely for the use of the individual or entity to whom they are
addressed and may contain confidential and privileged information
protected by law. If you received this e-mail in error, any review, use,
dissemination, distribution, or copying of the e-mail is strictly
prohibited. Please notify the sender immediately by return e-mail and
delete all copies from your system.
|
Do you consider that totally enclosed motors (TEFC) pose
less of a safety hazard than open (actually shielded) motors?? It
seems likely that an enclosed motor would be less likely to spew sparks
and hot metal than a motor with ventilation openings.
I think I have noticed that equipment from Asia, even low priced stuff,
is likely to have a TEFC motor where conventional domestic production (if
there still were any) would not.
am
At 05:40 PM 2/1/2021 +0000, you wrote:
toggle quoted message
Show quoted text
John Wrote
?€?Don't think you should be concerned with UL certification and
such.? Induction motors have been around for 100yrs or so and the
things that make them fail aren't tested for in UL anyway ?€?
I would not go that far?? Safety certifications UL and other
wise (UL isn?€?t the only game in town)? isn?€?t so much about
testing for things that make things fail, as testing to ensure that WHEN
they do fail, the fail ?€?relatively?€? safely. This relatively safety
includes not starting fires {?€?? ¡ molten metal, burning
insulation, fflaming particles, or other ignited material could fall onto
flammable material, or through which a flame could be
projected¡.?€?}
and not creating a shock hazard.
?
A ?€?Listed?€? or ?€?Recognized?€? motor (as compared to an
unlisted/recognized one)? are far less likely to start a fire or
catch fire, when given the same amount of abuse.
They are also less like to fail to live up to expectations as a
consequence of having to meet listing requirements.
?In particular a motor needs to fall within ~10% of the NEC values
for current for that size motor, at rated nominal voltage.
There are also temperature rise tests, sheet metal thickness, and
grounding resistance tests.
There is also a locked rotor test, For motors without a thermal cutout
this can run for 18 days, or until the motor fails. When it fails (or at
the end of the test if it doesn?€?t) there are temperature limits, and it
still has to pass insulation resistance tests to demonstrate that it has
not created a shock hazard. For motors with a thermal cutout, the test
runs until the cutout operates. If the motor has an auto-reset cutoff,
then the test runs for 18 days.
?
I have replaced the motor on my saw with a UL listed one. BUT I did not
do so until it failed.
A saw that comes with a UL listed motor, is likely to be significantly
more expensive. If you are not using a flammable cutting fluid, and make
sure that both the motor and saw frame are grounded (and that your plug
has all 3 prongs.) I would not be worried. Just recognize that the motor
likely will die on you the moment you turn your back on it
?
Also recognize that a ?€?CE?€? mark is in NO WAY a safety certification
mark like UL, CSA, ETL, etc
?
R James (Jim) Klessig P.E. | Senior Power Systems Engineer |
Electrical Reliability Services, VERTIV
jim.klessig@...,
jim_klessig@...
1876 Gwin Rd, Mckinleyville | CA | 95519 | USA
| Cell (707) 497-9611 | eFax 614-410-0653
?
CONFIDENTIALITY NOTICE: This e-mail and any files transmitted with it are
intended solely for the use of the individual or entity to whom they are
addressed and may contain confidential and privileged information
protected by law. If you received this e-mail in error, any review, use,
dissemination, distribution, or copying of the e-mail is strictly
prohibited. Please notify the sender immediately by return e-mail and
delete all copies from your system.
|
Good info, thanks Alan, I'll follow that up. Arduino is cheap enough if from China, but not $12-cheap.? Arron, if your blade comes off easily, although it's a 'safety feature' it must be very frustrating.? It's probably in need of some tracking adjustment.? The blade should just skim both rear guide rollers and I suspect the lower and maybe even the upper is pushed hard into the blade.? Back both away until both are visibly clear of the blade and then bring them forward. Unfortunately that will upset your squareness so that will have to be done afterwards. Maybe the safety feature is worth putting up with.... You've revised my opinion of UL Jim, thankyou for that - jv? ?
On Tue, 2 Feb 2021, 3:31 am Alan Muller, < alan@...> wrote:
I don'r know of any power tool that needs overload
protection more than these saws.? They are often run unattended and
can easily jam.? But overload protection can easily enough be added
to a motor.
This is one approach:?
But note that these things, which used to cost $25 or so, have gotten
absurdly expensive.? But they can be scrounged.? The
"heater" needs to be matched to the motor/how hard you want to
work the motor.
IEC overloads are cheaper and adjustable:?
A key thing to note is to NOT use a motor with auto-reset protection (no
red button).? These reset when they cool off and might start when
you are messing with the blade.
am
At 07:24 AM 2/1/2021 -0600, you wrote:
On 2/1/2021 3:24 AM, John Vreede
wrote:
I don't know of any OEM motors
that have thermal overload re-sets, but Grizzly sell replacement motors
for machine tools, that I believe, have them. - jv
? You are correct , the motor on mine is s Griz and it does have TO
protection . I too burned my original up while cutting unattended
.
--
Snag
|
I've had a Horror Freight 4x6 for several years. I leave it plugged in all the time. I've had no trouble with the electrical.?
I've seen evidence that some motor manufacturers in China strip out wire from old motors, splice it together, and use it in their new motors. Having a splice within a motor's winding is hazardous. I doubt that this practice?is widespread and I seriously doubt that any major distributor would continue to sell equipment that caught on fire.
I haven't forgotten about this, and have gotten sidetracked a bit as I spent most of my budget on other items I needed (clearance tool cabinet and shop lights) I've seen some comments about motors burning up, smoking, and overall being a potential fire hazard. I've looked at all the bandsaws I've been able to find and it seems most do not list any certification or UL listing at all with a couple exceptions.? Shop Fox at least comes right out and says their saw is not certified at all.?
?
Jet HVBS-56 is UL listed
General International BS5205 says ETL certification on their website and CSA listing in the manual.? Unclear which it is.?
?
wisdom indicates it would be best to get a unit that has undergone testing to make sure it's safeish.? I'm sure I could unplug the saw after each use, but history tells me I'm not always good with this.? How big a deal is this really???
-- John A. Schirra?
Sent from GMail
|
John Wrote
¡°Don't think you should be concerned with UL certification and such.? Induction motors have been around for 100yrs or so and the things that make them fail aren't tested for in UL anyway?¡°
I would not go that far?? Safety certifications UL and other wise (UL isn¡¯t the only game in town)? isn¡¯t so much about testing for things that make things fail, as testing to ensure that WHEN they do fail, the fail ¡°relatively¡± safely.
This relatively safety includes not starting fires {¡° ?¡ molten metal, burning insulation, flaming particles, or other ignited material could fall onto flammable material,
or through which a flame could be projected¡.¡±}
and not creating a shock hazard.
?
A ¡°Listed¡± or ¡°Recognized¡± motor (as compared to an unlisted/recognized one) ?are far less likely to start a fire or catch fire, when given the
same amount of abuse.
They are also less like to fail to live up to expectations as a consequence of having to meet listing requirements.
?In particular a motor needs to fall within ~10% of the NEC values for current for that size motor, at rated nominal voltage.
There are also temperature rise tests, sheet metal thickness, and grounding resistance tests.
There is also a locked rotor test, For motors without a thermal cutout this can run for 18 days, or until the motor fails. When it fails (or at
the end of the test if it doesn¡¯t) there are temperature limits, and it still has to pass insulation resistance tests to demonstrate that it has not created a shock hazard. For motors with a thermal cutout, the test runs until the cutout operates. If the motor
has an auto-reset cutoff, then the test runs for 18 days.
?
I have replaced the motor on my saw with a UL listed one. BUT I did not do so until it failed.
A saw that comes with a UL listed motor, is likely to be significantly more expensive. If you are not using a flammable cutting fluid, and make
sure that both the motor and saw frame are grounded (and that your plug has all 3 prongs.) I would not be worried. Just recognize that the motor likely will die on you the moment you turn your back on it
?
?
Also recognize that a ¡°CE¡± mark is in NO WAY a safety certification mark like UL, CSA, ETL, etc
?
R James (Jim) Klessig P.E. | Senior Power Systems Engineer |
Electrical Reliability Services, VERTIV
jim.klessig@...,
jim_klessig@...
1876 Gwin Rd, Mckinleyville | CA | 95519 | USA
|
Cell (707) 497-9611 |
eFax
614-410-0653
?
CONFIDENTIALITY NOTICE: This e-mail and any files transmitted with it are intended solely for the use of the individual or entity to whom they are addressed and may contain confidential and privileged information protected by law. If you received this e-mail
in error, any review, use, dissemination, distribution, or copying of the e-mail is strictly prohibited. Please notify the sender immediately by return e-mail and delete all copies from your system.
|
I don'r know of any power tool that needs overload
protection more than these saws.? They are often run unattended and
can easily jam.? But overload protection can easily enough be added
to a motor.
This is one approach:?
But note that these things, which used to cost $25 or so, have gotten
absurdly expensive.? But they can be scrounged.? The
"heater" needs to be matched to the motor/how hard you want to
work the motor.
IEC overloads are cheaper and adjustable:?
A key thing to note is to NOT use a motor with auto-reset protection (no
red button).? These reset when they cool off and might start when
you are messing with the blade.
am
At 07:24 AM 2/1/2021 -0600, you wrote:
toggle quoted message
Show quoted text
On 2/1/2021 3:24 AM, John Vreede
wrote:
I don't know of any OEM motors
that have thermal overload re-sets, but Grizzly sell replacement motors
for machine tools, that I believe, have them. - jv
? You are correct , the motor on mine is s Griz and it does have TO
protection . I too burned my original up while cutting unattended
.
--
Snag
|
On 2/1/2021 3:24 AM, John Vreede wrote: I don't know of any OEM motors that have thermal overload re-sets, but Grizzly sell replacement motors for machine tools, that I believe, have them. - jv You are correct , the motor on mine is s Griz and it does have TO protection . I too burned my original up while cutting unattended . -- Snag
|
I never have to worry about that. My blade gets much resistance and it comes loose at the drop of a hat.
toggle quoted message
Show quoted text
On 2/1/2021 12:15 AM, Terry Coombs wrote: On 1/31/2021 8:15 PM, soloz210@... wrote:
I haven't forgotten about this, and have gotten sidetracked a bit as I spent most of my budget on other items I needed (clearance tool cabinet and shop lights) I've seen some comments about motors burning up, smoking, and overall being a potential fire hazard. I've looked at all the bandsaws I've been able to find and it seems most do not list any certification or UL listing at all with a couple exceptions. Shop Fox at least comes right out and says their saw is not certified at all.
Jet HVBS-56 is UL listed
General International BS5205 says ETL certification on their website and CSA listing in the manual.? Unclear which it is.
wisdom indicates it would be best to get a unit that has undergone testing to make sure it's safeish.? I'm sure I could unplug the saw after each use, but history tells me I'm not always good with this.? How big a deal is this really?
? I believe the main concern is that the saw will stall the motor in a cut . A stalled motor without a thermal overload protection device will overheat and possibly start a fire . Check for a small reset button on the motor near where the wires go in , that will be the overload shutoff reset .
|
Don't think you should be concerned with UL certification and such.? Induction motors have been around for 100yrs or so and the things that make them fail aren't tested for in UL anyway?
You are only really at risk of burning up your motor cutting sticky materials like aluminium or copper where the swarf sticks in the gullet between the teeth,? Then the gullet can be more than half full, the next time that tooth is asked to cut.?
The new swarf has to go somewhere and aluminium, or copper,? is soft enough to squish out of the gullet into the space in between the blade body and the wall of the kerf, where it welds to the kerf wall and is strong enough to jam the blade. Wood and plastic swarf also squish out, but they're too weak to jam the blade, so just push it off course and you get a crooked cut.?
If the blade doesn't come off the wheels, it will stall the motor.? If you don't cut the power within ~20 sec it will start to smoke, irreparably damaging the motor. When it stalls, the start winding cut in again and the current goes up to something like 7x the running current, the insulation overheats and the windings short out = burnt-out motor.
Because the current is still flowing, if you're out of the shop, like off making a cup of coffee, the motor can catch fire.? Never leave a saw cutting aluminium un-attended.?
Generally this doesn't happen cutting steel as the swarf falls away from the teeth at the exit from the cut, and it's too hard to squish into the space between blade and kerf anyway.? ?The only time I've stalled the motor on steel is when I was testing how much bow weight I could load up.? It would stall quite easily above 12lb bow weight in high speed, but that's way too much weight anyway as it damages the blade.? In this instance stalling is horsepower dependent, so too much bow weight and/or too much blade speed will tip it over the edge.
I burnt out my first motor (cutting aluminium) and the replacement is a 1/2HP 'Capacitor-start/Cap-run' motor,? It has a no-load speed of 1375rpm and is quite stable down to 1300rpm (I'm in 50Hz territory), but the motor stalls the instant it hits 1250rpm.? I don't know whether a thermal overload can be retrofitted to a motor that wasn't built with one, so I'm investigating building an Arduino device to count the motor rpm and cut the power when it hits 1260rpm. Theoretically it's do-able and would give very good control and could be programmed for any rpm.? Cap-start 1425rpm motors will stall at a different speed, as would 60Hz motors of different configurations, but the figure is easy to ascertain with a rev counter.
I don't know of any OEM motors that have thermal overload re-sets, but Grizzly sell replacement motors for machine tools, that I believe, have them. - jv
|
On 1/31/2021 8:15 PM, soloz210@... wrote: I haven't forgotten about this, and have gotten sidetracked a bit as I spent most of my budget on other items I needed (clearance tool cabinet and shop lights) I've seen some comments about motors burning up, smoking, and overall being a potential fire hazard. I've looked at all the bandsaws I've been able to find and it seems most do not list any certification or UL listing at all with a couple exceptions.? Shop Fox at least comes right out and says their saw is not certified at all.
Jet HVBS-56 is UL listed
General International BS5205 says ETL certification on their website and CSA listing in the manual.? Unclear which it is.
wisdom indicates it would be best to get a unit that has undergone testing to make sure it's safeish.? I'm sure I could unplug the saw after each use, but history tells me I'm not always good with this.? How big a deal is this really? I believe the main concern is that the saw will stall the motor in a cut . A stalled motor without a thermal overload protection device will overheat and possibly start a fire . Check for a small reset button on the motor near where the wires go in , that will be the overload shutoff reset . -- Snag
|
I haven't forgotten about this, and have gotten sidetracked a bit as I spent most of my budget on other items I needed (clearance tool cabinet and shop lights) I've seen some comments about motors burning up, smoking, and overall being a potential fire hazard. I've looked at all the bandsaws I've been able to find and it seems most do not list any certification or UL listing at all with a couple exceptions.? Shop Fox at least comes right out and says their saw is not certified at all.?
?
Jet HVBS-56 is UL listed
General International BS5205 says ETL certification on their website and CSA listing in the manual.? Unclear which it is.?
?
wisdom indicates it would be best to get a unit that has undergone testing to make sure it's safeish.? I'm sure I could unplug the saw after each use, but history tells me I'm not always good with this.? How big a deal is this really???
|
Updated versions of documents added to the files section
Hi Guys
I've revised the documents on 'Fixing vertical squareness...' and "Buying a used 4x6...' and they ARE added to the Files section. If you're in the habit of copying docs to your home drive then pls download the new versions as they're quite different.
|
Re: Hydraulic Downfeed Cylinder
I purchased the SawCyl with the pressure gauge to go on a 2004 vintage Taiwanese mfg. Harbor Freight saw. This version has the tension spring hooked to an 8mm bolt on the pivot arm so I drilled out the hole in the pivot arm 3/8" for the bolt on the rod end of the SawCyl and found that there is insufficient clearance for the nut to clear the flange on the bottom of the frame casting. I had to grind away some of the casting to allow the saw to drop all the way down. For anyone with this model saw a better way would be to drill out and tap the pivot arm hole to 3/8 x 24 and use the nut on the outside as a jam nut.
|
Cleaning Up Saw Frame Draft
As an alternative to making or buying new parts to go under the tension knob, you can also use a die grinder and files to spotface the area around the hole to make it perpendicular to the hole axis.
Kurt Laughlin
|
John Vreede