Tablesaw motor overheating - causes?
Michael J. "Mike" McCabe
Here's the latest. The power source is an outlet in my garage a long way
(70') from the panel. My voltmeter says 119-126 volts. I run my 5hp
compressor on this circuit without problems. (They have not been running
concurrently.)
The motor does not have brushes. The motor drives the blade via a cog belt.
There is no binding at the blade or in the motor. Everything is clean and
the blade is installed correctly.
When I start the saw it powers right up. The motor gets hot enough to to
start smoking in less than a minute. There is a mild vibration. There is
plenty of cutting power.
Today I bought an amp meter. When I start the saw the draw jumps to about
20 amps for a fraction of a second and drops to about 6. (The 5 hp
compressor draws about 18 at start and drops to 8 in about a second.
-----Original Message-----
Michael J. "Mike" McCabe wrote in message
<01bd870e$76df27b0$7d7db39b@mccabe1>...
>
>I have an old DeWalt tablesaw with a 2hp (13AMP) motor. It overheats in
>just a few seconds. I replaced the stator ($170) with no change in
>symptoms. I know virtually nothing about motors. I was told that the rotor
>is usually never the problem so I'm at a loss. It seems the options are:
>
> 1. The new stator was defective.
> 2. The rotor is defective.
> 3. Something in the switch is defective. (The switch has a capacitor and a
>?relay? involved.
>
>
>Any help on troubleshooting will be appreciated.
John J. Auchincloss
I would check the 'cog-drive' very carefully.
--
Regards, "Jack" of All Trades
Only an opinion: experienced; but an opinion none the less.
Michael J. "Mike" McCabe wrote in message <6laasg$sue$1@nnrp3>...
Sam Goldwasser
What is the voltage at the outlet while the motor is running?
Did you ever determine if the starting switch is operating correctly?
6 A doesn't sound that bad since the actual power consumption is probably
much less than this would indicate due to the low power factor of an inductive
load. Maybe I will go and measure my table saw current......
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In article <6laasg$sue$1@nnrp3> "Michael J. \"Mike\" McCabe" <mcc...@swbell.net> writes:
Here's the latest. The power source is an outlet in my garage a long way
(70') from the panel. My voltmeter says 119-126 volts. I run my 5hp
compressor on this circuit without problems. (They have not been running
concurrently.)
The motor does not have brushes. The motor drives the blade via a cog belt.
There is no binding at the blade or in the motor. Everything is clean and
the blade is installed correctly.
When I start the saw it powers right up. The motor gets hot enough to to
start smoking in less than a minute. There is a mild vibration. There is
plenty of cutting power.
Today I bought an amp meter. When I start the saw the draw jumps to about
20 amps for a fraction of a second and drops to about 6. (The 5 hp
compressor draws about 18 at start and drops to 8 in about a second.
-----Original Message-----
Michael J. "Mike" McCabe wrote in message
Tony Burton
Mike,
You might check the voltage at the saw with the saw running but
following your description of the problem (it overheats in a few
seconds) it doesn't sound like it is low line problem.
My suspicion is that something in the motor is defective.
Does the motor overheat with the belt disconnected?
TonyB.
Sam Goldwasser
This doesn't sound like a cord problem,
--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
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In article <gnge1.4031$v72.9...@news1.jacksonville.net> "john" <mobi...@emi.net> writes:
have you tried moving the saw closer to a outlet and see if it is getting
hot. using 70' of cord is losing alot of amperage. what gauge extension cord
are you using. look at the amp rating on the saw compared to the compressor.
the saw is more than likely more. but try moving the saw closer and see if
there is a overheat problem then. if so get a electrical outlet out to where
you are working or get a much bigger cord. john
Michael J. "Mike" McCabe wrote in message <6laasg$sue$1@nnrp3>...
LBHistand
Hi Mike,
Bet I know what you would like to do with this saw motor about now. Anyway,
it's a good problem. Got us all thinking.
What is the history of this motor? Has it ever run properly for you, or did
you recently aquire it? Has it ever run properly with it's present 120V
hookup?
Sounds like maybe a wiring problem in the motor connection box. Most larger
motors can be connected several different ways. Is it a dual voltage motor?
On the name plate what is stamped after Phase or Ph? Should be 1 (single).
What are the voltage ratings?
Six amps sounds low to me for a 2hp motor, even at a no-load condition. Is it
wired for 220v ? If so it may run but will effectively be electrically
overloaded at any mechanical load.
Is the motor actually geting hot to the touch? Where is the smoke comming
from? Are you sure it is comming from the windings?
Len
Terry Spragg
The current readings don't sound like they are way out in left field. The
voltage, if read at the motor end of the circuit while the motor is cutting
sounds good enough. A bad wire, plug, receptacle or switch would probably get
hot too.
Have you ascertained that the motor fan blades are ok, and that air cooling
channels are not blocked, say with sawdust?
Most motors have a thermal cutout, often identified by a manual reset button,
if it got too hot, it would shut off, if automatic, it would then start again
after it cooled. Large motors do get very warm, but not smoking hot. If it's
really getting that hot, why did it not 'thermal out?'
The capacitor is usually switched by the centrifugal starting switch on the
shaft inside the motor after startup, to provide max torque at start. Once
the motor is turning fast enough, the centrifugally operated switch should
either connect or disconnect the capacitor or auxiliary windings, depending on
motor type, possibly through a relay, if that is what is really present. If
it is not right near the shaft, it could be a relay controlled by the
centrifugal switch, that switches the capacitor or windings.
The capacitor or auxiliary windings and start switch is used to increase
starting torque and to run the motor at a lower power during high rpm
operation.
Your multimeter may be able to measure the capacitor's value, once it is
disconnected at one end. The value is marked on the side. 5 uF would be 5
microfarads. It MUST be an alternating current (AC), non-polarised capacitor.
In any case, the capacitor is easiest to change, and cheapest. Do it. It will
likely be about 350 volt AC 5 microfarad capacitor, available cheap at any
decent motor repair shop.
Examine the centrifugal start switch / actuator, on the shaft, it should be
apparent (at least to an experienced eye) if the contacts are damaged, or if
it is broken or binding, or stuck open or closed. If there are no brushes,
your start switch is a mechanical arrangement which, when spun up, moves an
actuator to change the switch contacts mounted nearby, inside the motor.
Sometimes contacts weld themselves closed, and can be broken open, often to
operate perfectly for years afterwards, sometimes not. Sometimes they burn or
corrode, and won't close, even though they look like they do. It sounds like
you don't know how to check a relay, and apparently, you don't trust your
motor repair shop, mabey for good reason, if they sold you a stator you don't
need, or you bought one on 'spec', but someone is gonna have to check or
replace it, and / or the start (centrifugal) switch. The relay (if there
really is one, I doubt it) should be easy to change (3 or 4 wire connections),
but the centrifugal switch / actuator is probably a bit of a pain and messy,
but not impossible. It may need to be special ordered, to fit the motor,
there is quite a variety.
You can either keep diddling around yourself, or find a trustworthy motor
tech. Sounds like you bought the most expensive part first. It'll be non
returnable, of course, and a dishonest tech may fix the capacitor, or start
switch and not charge you, saying that he replaced the stator under warranty,
no charge, having realised the healthy profit from an unneccesary part sale,
instead of a cheaper part, or quick fix, possibly out of spite if you didn't
trust him to fix your motor in the first place. You might want to place an
inobtrusive mark on the stator to find out if he does that. (I'm an old tech,
who's heard a lot of stories.) You could also replace the stator after he
'replaces' it to see if there was a problem in there in the first place.
Enlist a witness, and have him busted for fraud if you catch him. Most techs
are honest, but like car mechanics or apples, there are a few bad ones.
Induction rotors almost never fail, but are difficult to check without
replacing. I suggest you check out the start switch / actuator, ?relay?, and
capacitor. If all that fails, request a warranty replacement stator, or let
a tech do it. This all presumes the bearings turn freely, and no motor parts
are rubbing inside, except for the start switch / actuator and that someone
didn't recently (like, just before it started to overheat) incorrectly change
connections in the power connection terminal area, say from 110 to 220 volt
operation, if the motor is of a type that can be wired for either voltage, or
direction.
Terry K
Jack Swedberg
One more possibility is that the bearing seals have failed and you have
sawdust and/or other contaminants in you motor bearings.
Easy to check: By hand (NO POWER) rotate the blade.
Do you notice any friction?
If the motor bearings are bad, you will notice either a constant resistance
to rotation
and/or if a cyclic resistance, it is possible that your motor shaft is
bent.
One requires a bearing set replacement, the other a motor shaft
replacement.
Best regards,
Jack
Sam Goldwasser
First we need to establish where the smoke is coming from. Is one or more
motor windings gettings so hot in a minute? Or is it from some mechanical
problem like bad bearings?
Michael J. "Mike" McCabe
Terry;
Thanks for taking the time to help me with this.
MMc
Terry Spragg wrote in message <6lfgkh$rab$1...@garnet.nbnet.nb.ca>...
David Scheer
Michael J. "Mike" McCabe wrote:
> >When I start the saw it powers right up. The motor gets hot enough to to
> start smoking in less than a minute. There is a mild vibration. There is
> plenty of cutting power.
> >Any help on troubleshooting will be appreciated.
Every one knows motors run on smoke! when the smoke leaks out they dont run, try
replacing the smoke :-) David
cbesch
before you spend another 170 dollars on any parts take it to a friendly
starter generator place or a place that repairs electric motors and they
will bench test it and find the short for a lot less than 170.00
dollars................good luck...s,gregg
Niels Henriksen
The moter will overheat for 2 reasons.
1) The load is excessive of motor rating.
2) Short in windings.
1) The load can be from trying to cut to large woods or there is excessive friction
causing the overload.
Run motor for 1/2 minute and check were heat is comming from. Bearing or interal to
motor.
If bearing replace.
2) Not much to due here. There may be a short within some of the windings that for
the most part is still malking motor work but casuing certain winding sections to
overheat.
It will only get worse.
Sam Goldwasser
Supposedly, he:
replaced the stator (the part with the windings) and
this happens unloaded.
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John Normile
Is there any other evidence of overheating than smoke from the new
stator? Have you actually checked the temp. rise?
I have missed some threads but if the amp draw is not excessive the
motor MAY not be overheating. Sometimes the magnet wire has oil on it
from the winding operation. If this is not removed it will smoke.
This might be the smoke you see.
John
danh...@millcomm.com
In <357ED974...@sos.pwgsc.gc.ca>, Niels Henriksen <henr...@sos.pwgsc.gc.ca> writes:
>The moter will overheat for 2 reasons.
>1) The load is excessive of motor rating.
>2) Short in windings.
3) Short in armature
4) Insufficient voltage
5) Wiring error
Question: When the stator winding was replaced, were you sure to get one
with the same voltage rating?
Dan Hicks
Hey!! My advice is free -- take it for what it's worth!
http://www.millcomm.com/~danhicks
Sam Goldwasser
I think he is running on 110 - what could be lower than 110? Attempting to
run a 220 V motor on 110 could result in overheating under load (there
wouldn't be much torque either) but unloaded AND drawing a reasonable
current?
There is some piece of the puzzle we haven't seen yet!
--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Latest Sam stuff: http://www.repairfaq.org/sam/
Lasers: http://www.repairfaq.org/sam/lasersam.htm
http://www.misty.com/~don/lasersam.html
Michael J. "Mike" McCabe
It's FIXED!!!!! I replaced the capacitor and the problem went away.
I want to thank everyone for the invaluable advice.
MMc
>There is some piece of the puzzle we haven't seen yet!
>
>--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
> Latest Sam stuff: http://www.repairfaq.org/sam/
> Lasers: http://www.repairfaq.org/sam/lasersam.htm
> http://www.misty.com/~don/lasersam.html
>
>
>In article <6lnkfl$e31$3...@supernews.com> danh...@millcomm.com writes:
>
> In <357ED974...@sos.pwgsc.gc.ca>, Niels Henriksen
<henr...@sos.pwgsc.gc.ca> writes:
> >The moter will overheat for 2 reasons.
> >1) The load is excessive of motor rating.
> >2) Short in windings.
>
> 3) Short in armature
> 4) Insufficient voltage
> 5) Wiring error
Ernie
>Here's the latest. The power source is an outlet in my garage a long way
>(70') from the panel. My voltmeter says 119-126 volts. I run my 5hp
>compressor on this circuit without problems. (They have not been running
>concurrently.)
>
>The motor does not have brushes. The motor drives the blade via a cog belt.
>There is no binding at the blade or in the motor. Everything is clean and
>the blade is installed correctly.
>
>When I start the saw it powers right up. The motor gets hot enough to to
>start smoking in less than a minute. There is a mild vibration. There is
>plenty of cutting power.
>
>Today I bought an amp meter. When I start the saw the draw jumps to about
>20 amps for a fraction of a second and drops to about 6. (The 5 hp
>compressor draws about 18 at start and drops to 8 in about a second.
>
>
>-----Original Message-----
>Michael J. "Mike" McCabe wrote in message
><01bd870e$76df27b0$7d7db39b@mccabe1>...
>>
>>I have an old DeWalt tablesaw with a 2hp (13AMP) motor. It overheats in
>>just a few seconds. I replaced the stator ($170) with no change in
>>symptoms. I know virtually nothing about motors. I was told that the rotor
>>is usually never the problem so I'm at a loss. It seems the options are:
>>
>> 1. The new stator was defective.
>> 2. The rotor is defective.
>> 3. Something in the switch is defective. (The switch has a capacitor and a
>>?relay? involved.
>>
>>
>>Any help on troubleshooting will be appreciated.
>
>
>
>
All of the symptoms you describe indicate the voltage to the motor
under peak loading is below motor rating. Check the volts at the
motor and the amp draw at peak loading. Are they out of line with
motor rating. Your problem will go away if you move closer to the
power panel or usae a larger cable. What size cable are you using.
ES in Midland, Texas
P.Groepper
low voltage can be a nightmare. Here in Europe we are all (except UK, I
think) wired with 240 V (1 phase) or 400 Volt (3 phase). All my
stationary machines (incl. 1 deWalt 1600S) in my shop are 3 phase 400
Volt and never any overheating occurred. They are also cheaper, than
monophase machines.
Same frustration occurred in cars in the 60-s, when some still had 6
Volt circuits.
Conclusion: Try, if possible, higher voltage and 3 phases. At least next
time, you buy a machine. But I am not familiar with your specific
voltage circumstances.
regards, Peter (Europe, the Netherlands)
--
Ziggy
Heat is often generated from friction. How are the bearings in the
motor? If dry, this could be the source of your heat. Check the motor
shaft for scarring or a burnt look where the bearing surface contacts
the motor shaft. This is particularly true for the oillite type
bearing- looks like a pourous copper or gold color.
Ernie wrote in message <6mci14$a...@bgtnsc03.worldnet.att.net>...
Mark Brueggeman
Ernie wrote:
Since your 5 HP air compressor runs OK on the same line, it seems doubtful
that the problem is low line voltage. The way to check it is to monitor the
line voltage at the saw (preferably right at the motor, if this is possible),
while the saw is under load. If you have at least 110 volts under load, then
the problem is not low voltage. If you do have a voltage drop, it could be
caused by a defective switch or splice in the saw itself.
If you have plenty of voltage at the motor, under load, then the problem is the
motor itself. Vibration indicates a mechanical problem, although other
possibilities include a shorted rotor or a defective starting capacitor.
Rick
> >> 1. The new stator was defective.
> >> 2. The rotor is defective.
> >> 3. Something in the switch is defective. (The switch has a
> capacitor and a
> >>?relay? involved.
> >>
> >>
> >>Any help on troubleshooting will be appreciated.
> >
> >
I had a similar problem several years ago. I believe the relay had stuck
and wasn't letting the capacitor (condensor) drop out. That held the
starting coil on and caused things to behave similar to your problems.
The parts were so cheap I replaced them both and the problem went away.
Good luck!
Rick in St Louis
bennett blumenkopf
Let see what you have: The line voltage seems to be OK with a load so I doubt
that the cable run is offering much in the way of offensive resistance. The motor
idles at @ 6 amps and since power is proportional to current squared and voltage
it doesn't seem that your motor is loading heavily at idle. The capacitor is a
start-up cap that would cause the motor to not reach speed if it were open. If it
were shorted, it would get hot and not the motor. Open field windings woul cause
you to lose power and show up as excesive loading while working the motor. Does
the motor get hot when idling? If so, I'll bet the field windings have shorted.
You can buy a new motor for less than the $170.00 that you payed for the stator.
I suggest that you take the motor to a moto shop and have them check the
inductance and impedence of the field windings. Hope this helps.
Mark Harper