Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
I have yet to purchase a 4x6 bandsaw (harbor freight) and all this talk about overheating and burning up motors is making me question if I should buy one.
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On Jan 1, 2020, at 3:01 PM, Jim.Klessig@... <jim.klessig@...> wrote:
?
“This is getting overly complex??? In most cases a NEMA motor starter with properly selected heaters should protect the motor against overloads and blade
jams, no??“
?
To a degree, yes. Protection is however a dance between how often you have to reset it versus how much thermal damage you are willing to accept.
Some overloading is normal and expected for a motor. Normal rule of thumb for electrical equipment, is that each 10 deg C rise you have, shaves 5-10 years off of the expected lifetime of your insulation system. ?
[That is rise over rated temp, and extended running temp, not just occasional excursions]
?
The intent of the protection is really to prevent fire and shock, not preserve the lifetime of the equipment.
In industrial use it might be perfectly acceptable to get a 5 year life, in exchange for not having to reset the protection 5 times a day.
?
?
OUR EMAIL ADDRESSES HAVE CHANGED
We were
xxxxx@vertivCO.com and we are now
xxxxx@...
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?
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
?
?
This is getting overly complex??? In most cases a NEMA motor starter with properly selected heaters should protect the motor against overloads and blade jams, no?? Or an IEC-type starter for that matter.
Well, it's New Years? Eve in this part of? the world.? So Happy.
am
At 03:57 PM 12/31/2019 -0800, you wrote:
Sorry guys been out of the loop a few days ((long hot summer days here in NZ, out on the 'bike, swimming etc while you're all shivering!)
Thanks for the sensor link Jerry.
I didn't think about North America being on 60Hz while rest of us are on 50Hz, Robert.? Normal cap start induction motors here are rated for full load speed of 1425rpm while you're on ~1725rpm.? My motor (TEFC/cap start/cap run) says full load @ ~1360rpm on
the maker plate.? Its happy down to 1300rpm but stalls below 1250rpm (as tested with a tacho).? I suppose 60Hz motors will be ok to something like 1600rpm and stall around 1550rpm.
The reason I think its important to be able to monitor and protect the motor is that to get any reasonable cut time performance out of a 4x6 you need about 20lb of weight on the teeth.? This translates to bow weight (weight in just lifting the sawframe off
its stop) of 8 to 9lb on mild steel, but over 9lb, depending on your blade speed, you can stall the motor.? The tests I've done with increasing bow weight and measuring rpm and cut time all look like the attached pdf - increasing bow weight reduces the cut
time until the motor stalls.
In practice Jim, it seems, for a 4x6 with only 1/2HP, they'll all run below their rated rpm at what would be considered a normal cutting speed Will be worse for those with only 1/3HP.? Of course the motor makes more than its rated HP if you load them up so
they run below their rated rpm.? This only gets to be a problem if you are running continuously and then they'll over-heat, but with stop/start running that most of us do (with possible exception of Jerry!) thats not a problem. See the graph on pg 2 of the
attachment for how torque varies with speed on a CS induction motor.
You can run higher bow weight without stalling, if the blade speed is reduced, but bow weight in excess of 8-9lb damages the blade (causes gullet cracking and swages over the back of the blade) - jv
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
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
??? ??? probably cost to as much as the saw is worth .? ya can
get yerself a power strip & swap the breaker for a lower value
??? animal
On 1/1/2020 12:28 PM, John Vreede
wrote:
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Jim, is there any way that a 'NEMA motor starter with properly
selected heater ' can be retrofitted to our 1/3 or 1/2 HP motors??
I figured that motor protection would be built deep into the motor
at time of manufacture and so not retrofitable (if that's a word),
as motors with an overload reset button seem to be.? Is a NEMA
motor starter built into? the motor or can it be spliced into the
power feed to the motor?
What I'm looking for is something I can fit myself, and reasonably
cheap, which the motion sensor route seems to promise.?
Are there any other devices that would do this??
Thx - jv
|
Re: motor acted funny the other day
Motor overloads usually will not protect for a stall condition. I'm a retired electrical engineer and specialized in power system analysis and protection.?
Most of these small motor only have a thermal switch embedded? in the motor windings. If the windings get too hot?the switch?opens the circuit to the motor.
The problem with the thermal switch is temperature lag - the switch warms at a slower rate than the windings in the hottest spot of the motor.
Larger motors use a thermal replica relay which uses a resistor and thermal switch to approximate the heat in the motor.
Motor thermal overloads have to be able to withstand the starting and acceleration current of the motor. They also have to be able to detect an overload condition within the insulation limits of the motor. These two criteria make it dificult to protect for a stall condition. I have not seen any of the more sophisticated electronic motor protection relays that are suitable for single phase motors. If you really want to apply stall protection, you will need to make your own. The only known alternative would be to adapt a three-phase protection relay to work on single phase at a cost of many humderds of dollars for the relay alone. Not practical for a motor worth around $200 for a 1 HP.
There are two ways of determining a stall. The oldest method is with a speed switch on the motor shaft. The other is with a time delay after motor start and electronics. The first one is difficult to implement since you need slip rings to make the electrical connection to the centrifugal switch and was the only practical method prior to modern electronics. The second method involves sensing application of voltage to the motor and implements a time delay to enable the stall protection which allows the motor to start. The time delay is just longer than the motor start time. The stall protection is either an instantaneous or very short time delay at some current above a nominal load condition. This can be problematic for loads with intermittent overloads such as a saw.
If you want to make your own, you need to? have a contactor that would start and stop the motor plus some means of measuing current. It should be possible using an Arduino. Closing the contactor will indicate that the motor has been energized. Current sensing is more problematic. A current transformer would be the best way to go but would be expensive unless you made it yourself. I'm not certain but it may be possible to use a hall effect transducer but I believe they are normally only applied on DC and not AC. In any case, the Arduino would need to be programmed to energize the contactor from a start pushbutton, a short time delay later the stall protection is enabled. If the motor current goes above a preset level the Arduino would shut off the contactor. The Arduino would also need a stop button to shut off the motor and reset the time delay for the next start. Current level and time delay would be set by trial and error. You could probably build one for around US $50. Personally, I'll just stay next to the saw and shut it off if it stalls.
On Tue, Dec 31, 2019 at 7:34 PM Alan Muller < alan@...> wrote:
This is getting overly complex??? In most cases a
NEMA motor starter with properly selected heaters should protect the
motor against overloads and blade jams, no?? Or an IEC-type starter
for that matter.
Well, it's New Years? Eve in this part of? the world.? So
Happy.
am
At 03:57 PM 12/31/2019 -0800, you wrote:
Sorry guys been out of the loop
a few days ((long hot summer days here in NZ, out on the 'bike, swimming
etc while you're all shivering!)
Thanks for the sensor link Jerry.
I didn't think about North America being on 60Hz while rest of us are on
50Hz, Robert.? Normal cap start induction motors here are rated for
full load speed of 1425rpm while you're on ~1725rpm.? My motor
(TEFC/cap start/cap run) says full load @ ~1360rpm on the maker
plate.? Its happy down to 1300rpm but stalls below 1250rpm (as
tested with a tacho).? I suppose 60Hz motors will be ok to something
like 1600rpm and stall around 1550rpm.
The reason I think its important to be able to monitor and protect the
motor is that to get any reasonable cut time performance out of a 4x6 you
need about 20lb of weight on the teeth.? This translates to bow
weight (weight in just lifting the sawframe off its stop) of 8 to 9lb on
mild steel, but over 9lb, depending on your blade speed, you can stall
the motor.? The tests I've done with increasing bow weight and
measuring rpm and cut time all look like the attached pdf - increasing
bow weight reduces the cut time until the motor stalls.
In practice Jim, it seems, for a 4x6 with only 1/2HP, they'll all run
below their rated rpm at what would be considered a normal cutting speed
Will be worse for those with only 1/3HP.? Of course the motor makes
more than its rated HP if you load them up so they run below their rated
rpm.? This only gets to be a problem if you are running continuously
and then they'll over-heat, but with stop/start running that most of us
do (with possible exception of Jerry!) thats not a problem. See the graph
on pg 2 of the attachment for how torque varies with speed on a CS
induction motor.
You can run higher bow weight without stalling, if the blade speed is
reduced, but bow weight in excess of 8-9lb damages the blade (causes
gullet cracking and swages over the back of the blade) - jv
-- John A. Schirra?
Sent from GMail
|
Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
John,
Cooper bussman makes a fuse cover that fits on a regular handy box.
Catalog is here:
You can pop a TL time delay fuse in this and it makes a great motor
protector. I use them with small 120V motors in applications such as
this. A little cheaper than a full motor controller with heater. Only
drawback is you have to replace the time delay fuses.
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On 1/1/2020 3:28 PM, John Vreede wrote: Jim, is there any way that a 'NEMA motor starter with properly selected
heater ' can be retrofitted to our 1/3 or 1/2 HP motors?
I figured that motor protection would be built deep into the motor at
time of manufacture and so not retrofitable (if that's a word), as
motors with an overload reset button seem to be. Is a NEMA motor
starter built into the motor or can it be spliced into the power feed
to the motor?
What I'm looking for is something I can fit myself, and reasonably
cheap, which the motion sensor route seems to promise.
Are there any other devices that would do this?
Thx - jv
|
Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
The motor starters are external so will work with
our motors if you get the exact right size and service factor
rating.? However, I haven't seen any cheap ones but also haven't
bought one for a long time.
The thing I'm considering is cheap in parts but you have to build
it.? Of course everyone here builds things.? The main thing is it
will even detect a loose belt that's slipping, a motor starter
will never detect that.
I specified the motion sensor on the upper wheel because for that
to turn EVERYTHING else has to be working well.
On 1/1/20 12:28 PM, John Vreede wrote:
Jim, is there any way that a 'NEMA motor starter with properly
selected heater ' can be retrofitted to our 1/3 or 1/2 HP motors??
I figured that motor protection would be built deep into the motor
at time of manufacture and so not retrofitable (if that's a word),
as motors with an overload reset button seem to be.? Is a NEMA
motor starter built into? the motor or can it be spliced into the
power feed to the motor?
What I'm looking for is something I can fit myself, and reasonably
cheap, which the motion sensor route seems to promise.?
Are there any other devices that would do this??
Thx - jv
--
Jerry Durand, Durand Interstellar, Inc.
tel: +1 408 356-3886
|
Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
Jim, is there any way that a 'NEMA motor starter with properly selected heater ' can be retrofitted to our 1/3 or 1/2 HP motors??
I figured that motor protection would be built deep into the motor at time of manufacture and so not retrofitable (if that's a word), as motors with an overload reset button seem to be.? Is a NEMA motor starter built into? the motor or can it be spliced into the power feed to the motor?
What I'm looking for is something I can fit myself, and reasonably cheap, which the motion sensor route seems to promise.?
Are there any other devices that would do this??
Thx - jv
|
Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
“This is getting overly complex??? In most cases a NEMA motor starter with properly selected heaters should protect the motor against overloads and blade
jams, no??“
?
To a degree, yes. Protection is however a dance between how often you have to reset it versus how much thermal damage you are willing to accept.
Some overloading is normal and expected for a motor. Normal rule of thumb for electrical equipment, is that each 10 deg C rise you have, shaves 5-10 years off of the expected lifetime of your insulation system. ?
[That is rise over rated temp, and extended running temp, not just occasional excursions]
?
The intent of the protection is really to prevent fire and shock, not preserve the lifetime of the equipment.
In industrial use it might be perfectly acceptable to get a 5 year life, in exchange for not having to reset the protection 5 times a day.
?
?
OUR EMAIL ADDRESSES HAVE CHANGED
We were
xxxxx@vertivCO.com and we are now
xxxxx@...
?
?
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] [mailto:[email protected]]
On Behalf Of Alan Muller
Sent: Tuesday, December 31, 2019 7:34 PM
To: [email protected]
Subject: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
?
This is getting overly complex??? In most cases a NEMA motor starter with properly selected heaters should protect the motor against overloads and blade jams, no?? Or an IEC-type starter for that matter.
Well, it's New Years? Eve in this part of? the world.? So Happy.
am
At 03:57 PM 12/31/2019 -0800, you wrote:
Sorry guys been out of the loop a few days ((long hot summer days here in NZ, out on the 'bike, swimming etc while you're all shivering!)
Thanks for the sensor link Jerry.
I didn't think about North America being on 60Hz while rest of us are on 50Hz, Robert.? Normal cap start induction motors here are rated for full load speed of 1425rpm while you're on ~1725rpm.? My motor (TEFC/cap start/cap run) says full load @ ~1360rpm on
the maker plate.? Its happy down to 1300rpm but stalls below 1250rpm (as tested with a tacho).? I suppose 60Hz motors will be ok to something like 1600rpm and stall around 1550rpm.
The reason I think its important to be able to monitor and protect the motor is that to get any reasonable cut time performance out of a 4x6 you need about 20lb of weight on the teeth.? This translates to bow weight (weight in just lifting the sawframe off
its stop) of 8 to 9lb on mild steel, but over 9lb, depending on your blade speed, you can stall the motor.? The tests I've done with increasing bow weight and measuring rpm and cut time all look like the attached pdf - increasing bow weight reduces the cut
time until the motor stalls.
In practice Jim, it seems, for a 4x6 with only 1/2HP, they'll all run below their rated rpm at what would be considered a normal cutting speed Will be worse for those with only 1/3HP.? Of course the motor makes more than its rated HP if you load them up so
they run below their rated rpm.? This only gets to be a problem if you are running continuously and then they'll over-heat, but with stop/start running that most of us do (with possible exception of Jerry!) thats not a problem. See the graph on pg 2 of the
attachment for how torque varies with speed on a CS induction motor.
You can run higher bow weight without stalling, if the blade speed is reduced, but bow weight in excess of 8-9lb damages the blade (causes gullet cracking and swages over the back of the blade) - jv
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.
|
Re: Longer explanation of why the speed of the motor isn't 1800 or 1500 rpm.
From: Jim.Klessig@...
Date: Tue, 31 Dec 2019 12:10:55 EST ? “Largely correct, but it isn’t line losses or friction and drag that causes the reduction in speed . . .” ? Thanks for that clear, simple, explanation, Jim! ? KL
|
Re: motor acted funny the other day
This is getting overly complex??? In most cases a
NEMA motor starter with properly selected heaters should protect the
motor against overloads and blade jams, no?? Or an IEC-type starter
for that matter.
Well, it's New Years? Eve in this part of? the world.? So
Happy.
am
At 03:57 PM 12/31/2019 -0800, you wrote:
toggle quoted message
Show quoted text
Sorry guys been out of the loop
a few days ((long hot summer days here in NZ, out on the 'bike, swimming
etc while you're all shivering!)
Thanks for the sensor link Jerry.
I didn't think about North America being on 60Hz while rest of us are on
50Hz, Robert.? Normal cap start induction motors here are rated for
full load speed of 1425rpm while you're on ~1725rpm.? My motor
(TEFC/cap start/cap run) says full load @ ~1360rpm on the maker
plate.? Its happy down to 1300rpm but stalls below 1250rpm (as
tested with a tacho).? I suppose 60Hz motors will be ok to something
like 1600rpm and stall around 1550rpm.
The reason I think its important to be able to monitor and protect the
motor is that to get any reasonable cut time performance out of a 4x6 you
need about 20lb of weight on the teeth.? This translates to bow
weight (weight in just lifting the sawframe off its stop) of 8 to 9lb on
mild steel, but over 9lb, depending on your blade speed, you can stall
the motor.? The tests I've done with increasing bow weight and
measuring rpm and cut time all look like the attached pdf - increasing
bow weight reduces the cut time until the motor stalls.
In practice Jim, it seems, for a 4x6 with only 1/2HP, they'll all run
below their rated rpm at what would be considered a normal cutting speed
Will be worse for those with only 1/3HP.? Of course the motor makes
more than its rated HP if you load them up so they run below their rated
rpm.? This only gets to be a problem if you are running continuously
and then they'll over-heat, but with stop/start running that most of us
do (with possible exception of Jerry!) thats not a problem. See the graph
on pg 2 of the attachment for how torque varies with speed on a CS
induction motor.
You can run higher bow weight without stalling, if the blade speed is
reduced, but bow weight in excess of 8-9lb damages the blade (causes
gullet cracking and swages over the back of the blade) - jv
|
Re: motor acted funny the other day
Sorry guys been out of the loop a few days ((long hot summer days here in NZ, out on the 'bike, swimming etc while you're all shivering!)
Thanks for the sensor link Jerry.
I didn't think about North America being on 60Hz while rest of us are on 50Hz, Robert.? Normal cap start induction motors here are rated for full load speed of 1425rpm while you're on ~1725rpm.? My motor (TEFC/cap start/cap run) says full load @ ~1360rpm on the maker plate.? Its happy down to 1300rpm but stalls below 1250rpm (as tested with a tacho).? I suppose 60Hz motors will be ok to something like 1600rpm and stall around 1550rpm.
The reason I think its important to be able to monitor and protect the motor is that to get any reasonable cut time performance out of a 4x6 you need about 20lb of weight on the teeth.? This translates to bow weight (weight in just lifting the sawframe off its stop) of 8 to 9lb on mild steel, but over 9lb, depending on your blade speed, you can stall the motor.??The tests I've done with?increasing bow weight and measuring rpm and cut time all look like the attached pdf - increasing bow weight reduces the cut time until the motor stalls.
In practice Jim, it seems, for a 4x6 with only 1/2HP, they'll all run below their rated rpm at what would be considered a normal cutting speed Will be worse for those with only 1/3HP.? Of course the motor makes more than its rated HP if you load them up so they run below their rated rpm.? This only gets to be a problem if you are running continuously and then they'll over-heat, but with stop/start running that most of us do (with possible exception of Jerry!) thats not a problem. See the graph on pg 2 of the attachment for how torque varies with speed on a CS induction motor.
You can run higher bow weight without stalling, if the blade speed is reduced, but bow weight in excess of 8-9lb damages the blade (causes gullet cracking and swages over the back of the blade) - jv
|
Longer explanation of why the speed of the motor isn’t 1800 or 1500 rpm.
Walter Wrote
“Motor speed is dependant on the number of poles in the motor and the frequency of the AC voltage being supplied to it.?
North America 60 Hz, therefore a four pole motor will run at 1800 RPM less line losses (friction, drag, etc) ?so usually about 1725 RPM,
Europe and some other countries 50 Hz, so 1500 RPM less loses so about 1425 RPM.”
?
Largely correct, but it isn’t line losses or friction and drag that causes the reduction in speed (and line losses are totally different than drag or friction in any case.)
?
An induction motor operates by creating a rotating magnetic field. The magnetic field induces currents in the rotor’s conductors.
This creates a magnetic field in the rotor.
?
Until the rotor is actually rotating, the induced field is in sync with the stator field, and produces no torque.
Essentially the rotor does not know which way to rotate, both ways “look” equally good,
so it just sits there getting hot, because there is a lot of current flowing.
?
Imagine it as there being a south pole of a magnet on the stator, lined up with a north pole on the rotor. It doesn’t want to move.
?
To get it moving you can spin it by hand, and it will start going whichever way you turn it.
That isn’t really useful, so you add a start circuit.
The capacitor and inductance of the motor in the start winding phase shift a little bit of the current that the rotor sees,
and all of the sudden there is torque, and the motor “knows “ which way to go.
The magnet on the stator has moved “ahead” a little, and rotor turns to line them back up.
This very turning action induces more current into the rotor, but it lags further behind. So the rotor turns more.
More current gets induced in the rotor and the process dogpiles on.
?
The speed rises and eventually the start circuit cuts out. But because the rotor is now producing torque it doesn’t care.
?
Now if you come up to full synchronous speed somehow (The 1800 rpm or 1500 rpm above)
the rotor is no longer cutting through the field created by the stator, and there is no current induced in the rotor.
?
With no field in the rotor, there is nothing for the stator field to “pull” on so the torque drops to 0.
If the torque drops to 0 the rotor slows down, and a little current is induced, creating torque.
This difference in speed is called the “slip”.
At any given speed the slip is what generates the torque required by the load.
As your load increases, the rotor speed drops, so the slip gets bigger, as the slip increases so does the induced current, and hence the torque.
?
This need for slip is why the “no load” speed of the motor is less than the synchronous speed.
The “full load” speed of the motor is even lower.
As the load increases further you reach a point where the stator poles can no longer pull “hard” enough, and you slip poles, and the motor stalls.
The start circuit cuts back in, but can not produce much torque. So the motor soon starts humming the “death song of its people”.
?
Different motor designs will have different speeds where this breakdown occurs,
which is why differing motors of the same nominal “Hp” rating may not work for a particular application.
?
?
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.
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Re: motor acted funny the other day
?
Capacitor start motors have two sets of windings, a
sart winding and a run winding.? The start winding is connected with a
capacitor in it to give a phase shift which causes a shift in the magnetic poles
which pushes the rotor and causes the rotor to rotate.
?
Motor speed is dependant on the number of poles in
the motor and the frequency of the AC voltage being supplied to it.? North
America 60 Hz, therefore a four pole motor will run at 1800 RPM less line losses
(friction, drag, etc) ?so usually about 1725 RPM, Europe and some other
countries 50 Hz, so 1500 RPM less loses so about 1425 RPM
?
?
When a Capacitor Start motor reaches about 80% of
its speed, the centrifugal switch opens up and removes the capacitor from the
circuit and the motor is then running only on it's run windings.?
?
If the motor is dragged down in speed, such that it
slows below the 80% of running speed, the centrfugal switch drops out and
re-energizes the start windings and puts the capacitor back into the
circuit?trying to get the motor back up to speed.
?
The problem is that the start capacitor can only be
energized for a few seconds before it overheats and lets the magic smoke
out.
?
If the motor is being dragged down in RPM it is as
Robert said that there is probably some other problem?that needs to be
solved.
?
That motor should be able to maintain its rated
speed, 1725 RPM all day long regardless of how much it is loaded, providing that
it is not being grossly overloaded.? If it is slowing to 1250 RPM then the
machine needs to be analysed to determine why that is and corrected or motors
will just keep on blowing.
?
Walter Townsend, TTDr
?
?
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----- Original Message -----
Sent: Monday, December 30, 2019 4:01
PM
Subject: Re: [4x6bandsaw] motor acted
funny the other day
I
was told by another member that 1250 RPM was earlier given as the speed at
which the motor would suddenly stall, not the RPM at which it was being
routinely loaded down to.? If that’s the case, I missed it, and everyone
should just disregard my comments.
?
?
?
Normally such motor protection
is done by monitoring current, not speed. Current is relatively easy and cheap
to monitor, speed not so much. The easiest and cheapest way would be to put in
a fuse. If the cost of fuses becomes an issue, the problem is not being
addressed. The protection should not be required regularly, it is just to
prevent burning out the motor in the event that something goes wrong, Such as
stalling the motor or over loading it to the point that it slows
down.?
On
Monday, December 30, 2019, 04:44:24 PM EST, Robert Downs via Groups.Io
<wa5cab@...> wrote:
I’ll
comment that if the motor is a 1750 RPM nominal and ?routinely loads down
to 1250 RPM, either the ?motor id/was too small, the blade pressure is
too high, or something else is wrong.? Because my original motor and the
replacement (after stupidly letting it run unattended) didn’t/don’t slow down
much at all.? So there may be a real problem that you are trying to put a
bandaid on instead of fixing.
?
|
Re: motor acted funny the other day
May I mention:
Problems happening, is why I kinda keep an eye on what my saw is doing.
Any other tool, or piece of equipment in my shop, or out of it, as well.
I may wander a little, and work on my lathe or mill while my saw is cutting away, but if the saw stalls, or breaks a blade, I am quite close enough to know it.
?
Just a thought……
?
J
Bill
?
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Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Jerry Durand
Sent: Monday, December 30, 2019 4:17 PM
To: [email protected]
Subject: Re: [4x6bandsaw] motor acted funny the other day
?
Just a side note, my idea to monitor the upper wheel will detect loose/broken blade, slipping drive belt, AND motor stall.
A fuse monitors stall.
On 12/30/19 4:01 PM, Robert Downs via Groups.Io wrote:
I was told by another member that 1250 RPM was earlier given as the speed at which the motor would suddenly stall, not the RPM at which it was being routinely
loaded down to.? If that’s the case, I missed it, and everyone should just disregard my comments.
?
?
--
Jerry Durand, Durand Interstellar, Inc.
tel: +1 408 356-3886
?
|
Re: motor acted funny the other day
Just a side note, my idea to monitor the upper
wheel will detect loose/broken blade, slipping drive belt, AND
motor stall.
A fuse monitors stall.
On 12/30/19 4:01 PM, Robert Downs via
Groups.Io wrote:
I
was told by another member that 1250 RPM was earlier given
as the speed at which the motor would suddenly stall, not
the RPM at which it was being routinely loaded down to.? If
that’s the case, I missed it, and everyone should just
disregard my comments.
?
--
Jerry Durand, Durand Interstellar, Inc.
tel: +1 408 356-3886
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Re: motor acted funny the other day
I was told by another member that 1250 RPM was earlier given as the speed at which the motor would suddenly stall, not the RPM at which it was being routinely loaded down to.? If that’s the case, I missed it, and everyone should just disregard my comments. ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Jack Delaney via Groups.Io
Sent: Monday, December 30, 2019 17:34
To: [email protected]
Subject: Re: [4x6bandsaw] motor acted funny the other day? Normally such motor protection is done by monitoring current, not speed. Current is relatively easy and cheap to monitor, speed not so much. The easiest and cheapest way would be to put in a fuse. If the cost of fuses becomes an issue, the problem is not being addressed. The protection should not be required regularly, it is just to prevent burning out the motor in the event that something goes wrong, Such as stalling the motor or over loading it to the point that it slows down.? On Monday, December 30, 2019, 04:44:24 PM EST, Robert Downs via Groups.Io <wa5cab@...> wrote: I’ll comment that if the motor is a 1750 RPM nominal and ?routinely loads down to 1250 RPM, either the ?motor id/was too small, the blade pressure is too high, or something else is wrong.? Because my original motor and the replacement (after stupidly letting it run unattended) didn’t/don’t slow down much at all.? So there may be a real problem that you are trying to put a bandaid on instead of fixing. ?
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Re: motor acted funny the other day
Sound like a simple IEC (cheap) motor
starter either manual or magnetic with a properly sized adjustable motor
overload would be an easy solution.
?
While speed sensing sounds like a fun project
and I am all for neat projects, simple straight forward solution is to add a
motor overload. Oh, and did I mention this is also a recognized industrial
solution to the problem. Check our Automation Direct.
?
gary
?
?
Normally such motor protection is done by monitoring
current, not speed. Current is relatively easy and cheap to monitor, speed not
so much. The easiest and cheapest way would be to put in a fuse. If the cost of
fuses becomes an issue, the problem is not being addressed. The protection
should not be required regularly, it is just to prevent burning out the motor
in the event that something goes wrong, Such as stalling the motor or over loading
it to the point that it slows down.?
On Monday,
December 30, 2019, 04:44:24 PM EST, Robert Downs via Groups.Io
<wa5cab@...> wrote:
I’ll
comment that if the motor is a 1750 RPM nominal and ?routinely loads down
to 1250 RPM, either the ?motor id/was too small, the blade pressure is too
high, or something else is wrong.? Because my original motor and the
replacement (after stupidly letting it run unattended) didn’t/don’t slow down
much at all.? So there may be a real problem that you are trying to put a
bandaid on instead of fixing.
?
?
?
??? ??? that
could prob be done pretty with a Arduino & someone that knows how to
program it
??? ???
animal
On
12/29/2019 11:03 PM, John Vreede wrote:
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Yeah
I've thought about that too Jerry.
Do you have any particular sensor in mind?
I wonder if a sensor on the motor might be better, as its the motor you're
trying to protect.
If it loads up so the motor rpm drops to 1250rpm, it will stall almost
immediately it drops any lower, so a sensor that cuts the power between 1300
and 1250 rpm would be ideal.? There must be an electric/electronic
solution.? Anyone out there who can comment? - jv??
|
Re: motor acted funny the other day
Normally such motor protection is done by monitoring current, not speed. Current is relatively easy and cheap to monitor, speed not so much. The easiest and cheapest way would be to put in a fuse. If the cost of fuses becomes an issue, the problem is not being addressed. The protection should not be required regularly, it is just to prevent burning out the motor in the event that something goes wrong, Such as stalling the motor or over loading it to the point that it slows down.?
On Monday, December 30, 2019, 04:44:24 PM EST, Robert Downs via Groups.Io <wa5cab@...> wrote:
I’ll comment that if the motor is a 1750 RPM nominal and ?routinely loads down to 1250 RPM, either the ?motor id/was too small, the blade pressure is too high, or something else is wrong.? Because my original motor and the replacement (after stupidly letting it run unattended) didn’t/don’t slow down much at all.? So there may be a real problem that you are trying to put a bandaid on instead of fixing. ? ?
From: [email protected] [mailto:[email protected]] On Behalf Of mike allen
Sent: Monday, December 30, 2019 11:20
To: [email protected]
Subject: Re: [4x6bandsaw] motor acted funny the other day ? ??? ??? that could prob be done pretty with a Arduino & someone that knows how to program it ??? ??? animal On 12/29/2019 11:03 PM, John Vreede wrote: Yeah I've thought about that too Jerry.
Do you have any particular sensor in mind?
I wonder if a sensor on the motor might be better, as its the motor you're trying to protect.
If it loads up so the motor rpm drops to 1250rpm, it will stall almost immediately it drops any lower, so a sensor that cuts the power between 1300 and 1250 rpm would be ideal.? There must be an electric/electronic solution.? Anyone out there who can comment? - jv??
|
Re: motor acted funny the other day
I’ll comment that if the motor is a 1750 RPM nominal and ?routinely loads down to 1250 RPM, either the ?motor id/was too small, the blade pressure is too high, or something else is wrong.? Because my original motor and the replacement (after stupidly letting it run unattended) didn’t/don’t slow down much at all.? So there may be a real problem that you are trying to put a bandaid on instead of fixing. ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of mike allen
Sent: Monday, December 30, 2019 11:20
To: [email protected]
Subject: Re: [4x6bandsaw] motor acted funny the other day? ??? ??? that could prob be done pretty with a Arduino & someone that knows how to program it ??? ??? animal On 12/29/2019 11:03 PM, John Vreede wrote: Yeah I've thought about that too Jerry.
Do you have any particular sensor in mind?
I wonder if a sensor on the motor might be better, as its the motor you're trying to protect.
If it loads up so the motor rpm drops to 1250rpm, it will stall almost immediately it drops any lower, so a sensor that cuts the power between 1300 and 1250 rpm would be ideal.? There must be an electric/electronic solution.? Anyone out there who can comment? - jv??
|
Re: motor acted funny the other day
??? ??? that could prob be done pretty with a Arduino &
someone that knows how to program it
??? ??? animal
On 12/29/2019 11:03 PM, John Vreede
wrote:
toggle quoted message
Show quoted text
Yeah I've thought about that too Jerry.
Do you have any particular sensor in mind?
I wonder if a sensor on the motor might be better, as its the
motor you're trying to protect.
If it loads up so the motor rpm drops to 1250rpm, it will stall
almost immediately it drops any lower, so a sensor that cuts the
power between 1300 and 1250 rpm would be ideal.? There must be an
electric/electronic solution.? Anyone out there who can comment? -
jv??
|
Re: motor acted funny the other day
If you're just trying to protect the motor, that
works.? I'm looking at adding the relay power switch so it doesn't
sometimes turn back on when you lift up the arm.? When you're 200
cuts into the day you're not as alert and could get hurt.
Then around the 300th cut in this job the blade popped off.? It
turns out there was a wad of plastic fluff hidden that jammed the
blade.
So I thought a wheel sensor would be good and easy to add to the
power relay I haven't built yet.
I normally make boards from scratch, but for one-off jobs like
this I will probably start using the NANO boards.? At less than $2
delivered I can't beat the price.?
The only thing I'd need to get is the debugging pod from
MicroChip, I would highly prefer to program in a real IDE and not
use the Arduino thing.
On 12/30/19 3:36 AM, Aaron Brace wrote:
What about a simple motor controller with overload
protection (aka a heater)?
--
Jerry Durand, Durand Interstellar, Inc.
tel: +1 408 356-3886
|
Jerry Durand
John Vreede
Walter Townsend