Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
Thankyou everyone! Great information.
I think I've got enough of a handle now to move forward.
I talked it over with Vlad (a mad Russian Academy of Sciences scientist/friend) who has set up lots of Ardueno devices, so got that angle covered Jerry.
We're going to test a device next week with any luck. I'll let you know how we get on - jv
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
What is a "motor heater"? Why is a heater needed in a situation where the motor tends to overload thermally?
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
¡°So maybe 1 second before the control circuit cuts the power. Is that too long a time to wait?¡±
You need two time delays. The first disables the stall protection until the motor gets up to speed. The second timer shuts the motor off after detecting a stall event.
Allowable stall time varies with motor design. A typical value is 10 seconds from a cold start and 8 seconds from a hot start. There is typically a specified number of starts for a time interval. Too many starts in a short period can damage the motor unless specifically designed for repetitive starting duty. There is no way of knowing what the parameters are for these Chinese motors. Using up to 5 seconds should be fine but I would use a lower value and raise it if it gives nuisance trips.
¡°So maybe 1 second before the control circuit cuts the power. Is that too long a time to wait?¡±
?
There is an additional consideration.? How long does the motor take to come up to a speed above your ¡°threshold¡±?
That needs to be significantly faster than your threshold value.
?
?
¡°An optical sensor on the motor fan could be rigged to give many more pulses per rev,¡±
While optical should be reliable enough, in the general case I would go with sensing the shaft. Not all motors have an accessible fan.
?
While there are multiple ways to control it, an Arduino with a ¡°relay shield¡±, or Ras Pi sort is probably the easiest to implement these days.
?
You COULD however use a 555 Timer, configured as a one shot, triggered by your sensor, feeding a solid state relay.
?
?
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
"You COULD however use a 555 Timer, configured as a one shot, triggered by your sensor, feeding a solid state relay."
A switch and timer will work. It will need to be reset at some point. It will not be as sensitive or adjustable as current sensing.?
¡°So maybe 1 second before the control circuit cuts the power. Is that too long a time to wait?¡±
?
There is an additional consideration.? How long does the motor take to come up to a speed above your ¡°threshold¡±?
That needs to be significantly faster than your threshold value.
?
?
¡°An optical sensor on the motor fan could be rigged to give many more pulses per rev,¡±
While optical should be reliable enough, in the general case I would go with sensing the shaft. Not all motors have an accessible fan.
?
While there are multiple ways to control it, an Arduino with a ¡°relay shield¡±, or Ras Pi sort is probably the easiest to implement these days.
?
You COULD however use a 555 Timer, configured as a one shot, triggered by your sensor, feeding a solid state relay.
?
?
?
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
¡°So maybe 1 second before the control circuit cuts the power. Is that too long a time to wait?¡±
?
There is an additional consideration.? How long does the motor take to come up to a speed above your ¡°threshold¡±?
That needs to be significantly faster than your threshold value.
?
?
¡°An optical sensor on the motor fan could be rigged to give many more pulses per rev,¡±
While optical should be reliable enough, in the general case I would go with sensing the shaft. Not all motors have an accessible fan.
?
While there are multiple ways to control it, an Arduino with a ¡°relay shield¡±, or Ras Pi sort is probably the easiest to implement these days.
?
You COULD however use a 555 Timer, configured as a one shot, triggered by your sensor, feeding a solid state relay.
?
?
?
OUR EMAIL ADDRESSES HAVE CHANGED
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Electrical Reliability Services, VERTIV
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
A three-phase motor overload will not properly protect a single-phase motor if you use only one pole. The overload units are calibrated for current in all three poles. You can use it if you daisy chain all three poles together or some combination of neutral and phase so that all the poles have current. Otherwise, the overload will operate at a much higher current because they will not see mutual heating from the adjacent poles. See:
?
?
¡°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??¡°
?
Yes, you can buy a brand new Nema size 00 Motor starter for single phase motors.
? They are NOT however cheap.
?
Expect to pay anywhere from $70 to $300.
?
You can also use an appropriately sized 3 phase one, just using a single phase of the unit.
?
A motor starter consists of a Contactor (really a heavy duty relay) that does the switching,
and an overload relay, that senses the current, and some controls.
These can be added to any motor. They are completely external to them.
You nit the start button, that energizes the contactor, which seals in, and the motor starts,
when the OL relay sees too much current for too long, it opens the seal in circuit, and the contactor opens.
?
The motors with built in protection have a device built in to the windings that acts (sort of)
as the relay and contactor combined. They actually provide better protection (since they sense
the ACTUAL temperature of the motor winding, rather than a guess at it) but are not as durable (IMO).
?
In EITHER case, NEITHER provide short circuit protection, so you need that in your circuit as well.
(but it is probably there already)
?
?
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
Chris wrote
¡°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.¡±
?
Do you LIKE hacksawing large quantities of steel (or whatever)?
If the answer is NO, then yes buy one, if it meets your needs.
?
Most of this discussion centers around the assumption of people wanting to walk away from the saw while it is working
And partly making it cut faster.
Another element is that the original motor that comes with them are usually utter crap.
My saw had the original motor, when I got it (used), and worked well for years, but got HOT when cutting for extended periods.
And I mean ¡°too hot to touch¡± hot.
Eventually it gave up the ghost.
The replacement motor (UL listed, but used) barely gets warm under the same sort of usage.
OTOH, I am still pretty much right there while it is cutting.
?
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Re: motor acted funny the other day
John Wrote
¡°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.¡°
?
Of course the thermistors or RTDs are no better at lag, and have the same placement issues.
?
And when talking about the ¡°larger¡± motors here, well I usually do not see advanced protection like
the thermal replica relays [or electronic motor relays] applied till we are talking about motors rated in 100s or 1000s of HP.
[Even then the protection is really an estimated educated guess at what the worst case? temp in the motor is.]
?
As John indicates, though protecting against stall can be problematic,
mostly because every time you start, that IS a stall condition.
A stall condition that you don¡¯t want to trip for.
I will however disagree that overloads do not protect against stall.
They just will not always do so without allowing for some insulation damage.
?
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
Agree that NEMA motor starters, bought new, have gotten
absurdly expensive.?? Even the little toggle-switch
style.? But they are pretty easily scrounged.? (You have to
expect to buy heaters to suit the application., but for a 120 volt single
phase motor you only need one heater, even if the starter has positions
for 2 or 3.)
I expect you could get the international style (IEC) for a few bucks,
mail order from China.??? These don't use replaceable
heaters but are adjustable over a range.
Note that a "motor starter" is a combination contactor and
overload relay in the same box.
For sure you can use a plug fuse to protect the motor.? And you can
put it into a porcelain or plastic lampholder costing $1, or the handy
box cover with the tin lid.?? Check the price of fuses,
though.
None of this will stop the saw in case of a broken or derailed
blade.? That probably requires some sort of motion sensor, as
discussed.? But is it necessary?? If a blade breaks or comes
off, the saw will just sit there with the motor idling.? No real
hazard to operator or machine. At least, this is my experience.
Don't use a motor with an auto-reset protector ("Klixon")
without bypassing it, or replacing it with the ;manual reset (red button)
type.? You don't want the motor restarting unexpectedly.
am
At 10:59 AM 1/2/2020 -0500, you wrote:
toggle quoted message
Show quoted text
a) NEMA motor starters would be
adaptable, but at a price comparable to the whole saw (this makes it a
non-starter for me).
John,
? ? ?? ? ? ?? ? ? ?? I hate to sound like a broken record
here, but the simple time delay fuse solution can be a very effective
method of providing motor overload protection for motors that either
don't have it integrated or arent very good. Quote from Bussman:
"Motor protection fuses are usually used in conjunction with branch
circuit protection. The fuse is often located in a box cover unit. Plug
fuses provide a compact and inexpensive method to prevent damage to
electrical motors. They help reduce downtime and lower maintenance costs
by opening the circuit when a dangerous overload is present. When used
for residential branch circuit protection, fuses are typically located in
the main fuse panel."
? ? ?? Check out this page:
? ? ?? They are offered in sizes as small as 1.25A, so you can size
the fuse exactly to the motor and provides effective overload protection.
Would not do anything for the blade falling off, this would be more for a
stall situation. However, it is cheaper than a starter with heater, and
fits in a small handy box so could be bolted right to the leg of the saw
if you want.
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
¡°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??¡°
?
Yes, you can buy a brand new Nema size 00 Motor starter for single phase motors.
? They are NOT however cheap.
?
Expect to pay anywhere from $70 to $300.
?
You can also use an appropriately sized 3 phase one, just using a single phase of the unit.
?
A motor starter consists of a Contactor (really a heavy duty relay) that does the switching,
and an overload relay, that senses the current, and some controls.
These can be added to any motor. They are completely external to them.
You nit the start button, that energizes the contactor, which seals in, and the motor starts,
when the OL relay sees too much current for too long, it opens the seal in circuit, and the contactor opens.
?
The motors with built in protection have a device built in to the windings that acts (sort of)
as the relay and contactor combined. They actually provide better protection (since they sense
the ACTUAL temperature of the motor winding, rather than a guess at it) but are not as durable (IMO).
?
In EITHER case, NEITHER provide short circuit protection, so you need that in your circuit as well.
(but it is probably there already)
?
?
?
OUR EMAIL ADDRESSES HAVE CHANGED
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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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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
a) NEMA motor starters would be adaptable, but at a price comparable to the whole saw (this makes it a non-starter for me). John, ??? ??? ??? I hate to sound like a broken record here, but the simple time delay fuse solution can be a very effective method of providing motor overload protection for motors that either don't have it integrated or arent very good. Quote from Bussman: "Motor protection fuses are usually used in conjunction with branch circuit protection. The fuse is often located in a box cover unit. Plug fuses provide a compact and inexpensive method to prevent damage to electrical motors. They help reduce downtime and lower maintenance costs by opening the circuit when a dangerous overload is present. When used for residential branch circuit protection, fuses are typically located in the main fuse panel." ??? Check out this page: ??? They are offered in sizes as small as 1.25A, so you can size the fuse exactly to the motor and provides effective overload protection. Would not do anything for the blade falling off, this would be more for a stall situation. However, it is cheaper than a starter with heater, and fits in a small handy box so could be bolted right to the leg of the saw if you want.
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
If all you need is to cut off below a certain rotation speed, you could use a simple LM555 circuit driving a relay.? You would want to use a tiny bit of dual edge detection so no matter if the sensor stopped in the ON or OFF position the timer would still time out.
I've found now that using a small 8 pin processor is cheaper and easier than LM555 circuits.? I used to use the LM555 all the time when I worked on factory production equipment a few era ago.
Now I'm figuring I'll just use the Arduino NEO boards since they're about $1.90 each delivered.? The ICE for it isn't expensive and it's easy to erase the Arduino firmware it comes with so you have all the memory for your use.
---
Jerry Durand
Durand Interstellar, Inc.
This seems to be getting a bit off topic (well the one we hijacked it too, of motor protection, anyway).
Jerry is looking for something to protect the motor against stalls, detect broken blades and slipping belts, I'm really only interested in stalls as I can put up with the others.
From what I'm hearing:?
a) NEMA motor starters would be adaptable, but at a price comparable to the whole saw (this makes it a non-starter for me).
b) thermal overloads (which a lot of aftermarket motors (eg Grizzly) have std, but are not an EOM fitment) are buried in the guts of the motor, so not retrofitable.? They will protect against burning your shop down, but may not be quick enough to protect the motor (again not what I really wanted).
c) that leaves motion sensing (rather than current sensing?) as the only cheap(ish) option.
Then the decision is to sense at the motor or at the driven band wheel.
a) if using the spokes of the driven band wheel, the time to sense that the wheel has stopped changes with the gearing.? It is longest between pulses in low speed (three pulses per revolution (with a?neo magnet on each spoke) with the wheel doing 32rpm at 1250rpm stall speed on 50HZ .? That means the drive wheel takes ~2 sec per rev, so there is 2/3 of a second before the next spoke doesn't arrive when it stalls, plus whatever delay you'd build in so it's not always tripping.? So maybe 1 second before the control circuit cuts the power. Is that too long a time to wait? (can Jim/John/Jerry pls comment). If 1 second is ok, then this is viable.
b) An optical sensor on the motor fan could be rigged to give many more pulses per rev, (60 or 100 or whatever) and so cut down the reaction time, but Jerry's experience says these are unreliable.
c) I suppose a plate could be fixed to the back of the driven wheel with as many magnets as are needed to give an adequate response time.
Then, is there a simple circuit that would control this? (I don't like the sound of Arduino but I could learn!) - jv
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
This seems to be getting a bit off topic (well the one we hijacked it too, of motor protection, anyway).
Jerry is looking for something to protect the motor against stalls, detect broken blades and slipping belts, I'm really only interested in stalls as I can put up with the others.
From what I'm hearing:?
a) NEMA motor starters would be adaptable, but at a price comparable to the whole saw (this makes it a non-starter for me).
b) thermal overloads (which a lot of aftermarket motors (eg Grizzly) have std, but are not an EOM fitment) are buried in the guts of the motor, so not retrofitable.? They will protect against burning your shop down, but may not be quick enough to protect the motor (again not what I really wanted).
c) that leaves motion sensing (rather than current sensing?) as the only cheap(ish) option.
Then the decision is to sense at the motor or at the driven band wheel.
a) if using the spokes of the driven band wheel, the time to sense that the wheel has stopped changes with the gearing.? It is longest between pulses in low speed (three pulses per revolution (with a?neo magnet on each spoke) with the wheel doing 32rpm at 1250rpm stall speed on 50HZ .? That means the drive wheel takes ~2 sec per rev, so there is 2/3 of a second before the next spoke doesn't arrive when it stalls, plus whatever delay you'd build in so it's not always tripping.? So maybe 1 second before the control circuit cuts the power. Is that too long a time to wait? (can Jim/John/Jerry pls comment). If 1 second is ok, then this is viable.
b) An optical sensor on the motor fan could be rigged to give many more pulses per rev, (60 or 100 or whatever) and so cut down the reaction time, but Jerry's experience says these are unreliable.
c) I suppose a plate could be fixed to the back of the driven wheel with as many magnets as are needed to give an adequate response time.
Then, is there a simple circuit that would control this? (I don't like the sound of Arduino but I could learn!) - jv
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
??? ??? I bought a blade at Lowes for my saw , it's a Bosch ,
don't remember the teeth count but it's eatin everything I throw
at it nicely . think it was @ $13.00
??? ??? animal
On 1/1/2020 5:09 PM, Paul Loyd wrote:
toggle quoted message
Show quoted text
For what it is worth, I have had a Harbor Freight 4x6 for about 3
years. I have cut a lot of steel, brass and aluminum with no
problems at all. I'm still on the original blade. I run it on the
slowest speed for everything.
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
For what it is worth, I have had a Harbor Freight 4x6 for about 3 years. I have cut a lot of steel, brass and aluminum with no problems at all. I'm still on the original blade. I run it on the slowest speed for everything.
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
??? ??? second thing to do is open the gear box & check for
oil . these are things to do with any 4x6 ya buy
??? ??? animal
On 1/1/2020 5:39 PM, Jerry Durand
wrote:
toggle quoted message
Show quoted text
One thing I'd be sure of, when you receive it
verify that the arm goes straight up and down.? Occasionaly
they'll ship one where the hinge holes are off.? This is VERY
hard to fix by yourself, best to swap for another one.? But,
most of these work fine.
I had to swap mine simply because the FedEx
delivery guy was by himself and they didn't issue him a hand
truck/dolly.? So, he simply shoved the box out the back of the
truck to fall onto the street.? He then dragged it to my door
where I sent it back.? I met him at the truck for the next trip
and we carried it to the house.
---
Jerry Durand
Durand Interstellar, Inc.
On Jan 1, 2020, at 17:13, mike allen < animal@...> wrote:
??? ??? the saws are pretty ok , but like anything from HF
"if it plugs in yer gonna have problems at sometime " motors
are pretty easy to come by
??? ??? animal
On 1/1/2020 4:49 PM, Chris
Hibbert wrote:
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.
?
¡°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.
?
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EMAIL ADDRESSES HAVE CHANGED
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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
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
One thing I'd be sure of, when you receive it verify that the arm goes straight up and down.? Occasionaly they'll ship one where the hinge holes are off.? This is VERY hard to fix by yourself, best to swap for another one.? But, most of these work fine.
I had to swap mine simply because the FedEx delivery guy was by himself and they didn't issue him a hand truck/dolly.? So, he simply shoved the box out the back of the truck to fall onto the street.? He then dragged it to my door where I sent it back.? I met him at the truck for the next trip and we carried it to the house.
---
Jerry Durand
Durand Interstellar, Inc.
On Jan 1, 2020, at 17:13, mike allen < animal@...> wrote:
toggle quoted message
Show quoted text
??? ??? the saws are pretty ok , but like anything from HF "if it
plugs in yer gonna have problems at sometime " motors are pretty
easy to come by
??? ??? animal
On 1/1/2020 4:49 PM, Chris Hibbert
wrote:
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.
?
¡°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
?
?
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.
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Re: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
??? ??? the saws are pretty ok , but like anything from HF "if it
plugs in yer gonna have problems at sometime " motors are pretty
easy to come by
??? ??? animal
On 1/1/2020 4:49 PM, Chris Hibbert
wrote:
toggle quoted message
Show quoted text
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.
?
¡°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
?
?
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: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
I have a Buffalo that is 37 years old and has sawn tons
of material. Using Lennox Bi-M metal blades it still cuts fast and true.
?
It still has the original motor which says
it is 3/4HP on the label but more likely a stretch to 1/2HP. I recently had 100
pieces of 2" pre hardened 1144 Stressproof to cut 6" long for 4 axis machining
into Barrel Cams. The saw would cut about 35 to 40 pieces and the internal
thermal overload would shut it down until it cooled. After an half hour or 45
minutes it would start up and go again. If I had a lot of this to do, I would
3D print an end bell fan shroud for an electric fan to cool the motor.
?
My saw while not a Harbor Freight and made
in Taiwan
a long time ago is like the old Timex watch commercial, "It takes a
licking and keeps on ticking!".
?
gary
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]]
On Behalf Of Chris Hibbert
Sent: Wednesday, January 01, 2020
6:50 PM
To: [email protected]
Subject: 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.
On Jan 1, 2020, at 3:01
PM, JimKlessig@... <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@...
?
?
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 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: [ExternalEmail] Re: [4x6bandsaw] motor acted funny the other day
On 1/1/2020 6:49 PM, Chris Hibbert wrote: 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.
? Don't let it worry you . I did burn up a motor on mine , but it was my own fault . One should no more leave a saw cutting unattended than one should walk away from a lathe making a cut . I knew my motor was getting weak , it hung in a cut and I didn't notice until all the magic smoke had escaped . And I was standing within a few feet ... but occupied on the lathe . This is actually more rare than it sounds , those who have burned one up are usually those who use their saw a LOT . ?-- ? Snag Shade-tree part time hack machinist and full time hillbilly .
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John Vreede
Jerry Durand