Electric motor reversing question
 

All,

I am adding a motor to a mini lathe and have a wiring question. The
motor I have is reversible. I can add a switch to the circuit to
switch polarity and change rotation direction. Here is the question:

Can I switch the motor from forward to backward when the motor is
already turning? Or do I need to cut power and stop the rotation
first, before switching direction and reapplying power?

Thanks,
Joe Fleming - San Diego

Electric motor reversing question
 

"Joe Fleming" wrote: (clip) Or do I need to cut power and stop the
rotation first, before switching direction and reapplying power?
^^^^^^^^^^^^^^^^
Cut power first. The safest thing would be to use a three-position switch
that will not pass through center without stopping.

Electric motor reversing question
 

yes

most likely if you switch while running nothing at all will happen, but to
be on the safe side, let the motor stop before starting it in the reverse
direction



"Joe Fleming" wrote in message
ups.com...
All,

I am adding a motor to a mini lathe and have a wiring question. The
motor I have is reversible. I can add a switch to the circuit to
switch polarity and change rotation direction. Here is the question:

Can I switch the motor from forward to backward when the motor is
already turning? Or do I need to cut power and stop the rotation
first, before switching direction and reapplying power?

Thanks,
Joe Fleming - San Diego




--
Posted via a free Usenet account from http://www.teranews.com

Electric motor reversing question
 

A polarity reversing switch will instantly change the direction of the
motor, regardless of whether it is in motion or not. This is
incredibly dangerous. Think of how much strain you put in the motor
spinning at XXXX rpms and you instantaneously make it turn the other
direction. The jolt to the setup would be unnerving.

Now think of having something chucked up, and you switch directions at
the flip of a switch. The inertia that a spinning piece of wood might
have spinning at a modest rate (say 2000 rpms) that is in effect being
slammed into a dead stop (and at the same instant - reversed!) would
throw just about anything off the chuck/faceplate/centers. And with a
10 - 20 pound piece of wood on the spindle, how much force would be
retained by the launched wood, and how much would it take to bend the
lathe spindle shaft or break your tailstock?

There is a guy in our turning club that has a motor assembly he bought
somewhere that has a variable speed reverse. He said that when he
doesn't remember to stop 100%, it sounds like a pistol shot when he
just hits reverse. I can't how that is a good thing...

Robert

Electric motor reversing question
 

Joe
When I put a reversing switch on a motor I use one that has a "dead"
position in the center so that I can not forget to turn the motor off before
changing direction. On the other hand I am a devote coward who hates pain to
himself or the lathe :-)

--
God bless and safe turning
Darrell Feltmate
Truro, NS Canada
www.aroundthewoods.com

"Joe Fleming" wrote in message
ups.com...
All,

I am adding a motor to a mini lathe and have a wiring question. The
motor I have is reversible. I can add a switch to the circuit to
switch polarity and change rotation direction. Here is the question:

Can I switch the motor from forward to backward when the motor is
already turning? Or do I need to cut power and stop the rotation
first, before switching direction and reapplying power?

Thanks,
Joe Fleming - San Diego

Electric motor reversing question
 

A polarity reversing switch will instantly change the direction of the
motor, regardless of whether it is in motion or not.

Well.... sort of. That is only true when reversing a DC motor or a three-phase
motor. Reversing a single-phase motor will do nothing since the 'reversing' is
done on the starter circuitry to get it initially spinning in the direction you
want.

This is
incredibly dangerous.

Somewhat true for motors that can reverse while turning. The danger is if your
stock is mounted with a screwed on faceplate or chuck. The sudden, opposite
torque can unscrew it. Of course, it may also tighten it even further depending
on the threading and rotation direction.

If a lathe can handle starting torque then it can handle the same torque that is
applied when reversing.

Dan

Electric motor reversing question
 

wrote: A polarity reversing switch will instantly
change the direction of the motor, (clip)
Then Dan Bollinger wrote: Reversing a single-phase motor will do nothing
since the 'reversing' is
done on the starter circuitry to get it initially spinning in the direction
you want.
^^^^^^^^^^^^^^^^^
First, Nailshooter, regardless of what type of motor it is, it will never
instantly reverse. It may start to decelerate rapidly--but I think Dan is
right: once a single phase motor is up to speed, the direction of rotation
is not controlled by the wiring.

The thing that could be harmful in this situation would be this: You turn
the motor off, and as it slows down, the starting windings kick in. If you
chose to reenergize the windings for reverse rotation before it stops
completely, the motor would draw higher than normal starting current. If
this did not kick the breaker, it could damage the motor, or shorten the
life of the starting switch.

My main concern is not the mechanical lathe parts--it is the effect of
higher than normal current during reversal.

Plan on stopping the motor, for all of the above reasons.

Electric motor reversing question
 

The thing that could be harmful in this situation would be this: You turn the
motor off, and as it slows down, the starting windings kick in. If you chose
to reenergize the windings for reverse rotation before it stops completely,
the motor would draw higher than normal starting current.

Leo, I don't see how this is so. Even if it did draw more to overcome stopping
and then reversing (which I doubt), it would be a small increment because by the
time a 1725 rpm motor's starting circuitry could kick in it's rpm would be down
to about 2-300 rpm. That's not a lot of torque to overcome.

And, my experience with reversing a motor that uses starter circuitry is that it
must be at 0 rpm otherwise the motor just spins back up in the same old
direction, making it a moot point anyway.

Finally, I have yet to have a problem with reversing such a motor including one
connected to a very massive 18" sanding wheel. The 1.5 Hp motor takes about 5
seconds to get it up to speed. That's a large starting torque by anyone's
measure. And I've flipped that reversing switch at all rpms until I learned that
it needed to coast to a stop first. Not once did the thermal switch open or the
'magic smoke' leave the motor.

I've worked in factories and shops all my life and I have yet to replace a motor
because it was reversed improperly or too often.

Unless someone can come up with a significant history or evidence of what you
are talking about I'm just going to write this off as something for Mythbusters
to call 'busted!'

Dan

Electric motor reversing question
 

Thanks everyone for the information. I can tell by the questions that
I didn't provide enough information, and I have OK - I want to be extra
clear.

A. My Stubby lathe has a 3-phase motor on a controller that allows me
to switch the motor direction while the lathe is spinning. the
controller, I presume brakes the rotation down to zero rpm, and then
starts rotation in the opposite direction. I do not stop the spinning
before switching directions. Once in a great while the braking torque
does cause a chuck to unscrew, but I generally tighten the chuck so
this does not happen. The slow down and speed up are rather gradual.
there is no "hard slam" reversing going on. So, this is my experience
with reversing on a lathe.

B. The motor for my mini lathe is a single phase 110 motor that has
wiring to allow rotation in both directions. I will not have a
controller. It will be wired directly to 110 AC through whatever
switch(es) I install.

So, based upon all the great responses, here are my more precise
questions:

1. If I flip the polarity on the switch to instantly reverse motor
direction, does the motor gradually slow down, then gradually speed up
in the other direction, or does the motor attempt to slam direction
changes? In other words, to avoid slamming direction change, I must
allow the rotation to stop before re-energizing the motor in the
opposite direction?

2. If I flip the polarity on the switch to instantly reverse motor
direction, does this damage the motor? In other words, to avoid motor
damage, I must allow the rotation to stop before re-energizing the
motor in the opposite direction?

Assuming the slamming effect is what happens and/or that motor damage
happens, then I will use some sort of three position set-up where I
turn off rotation in one direction. Wait until the rotation stops,
then re-energize the motor for reverse rotation.

Thanks again.
Joe Fleming



Darrell Feltmate wrote:
Joe
When I put a reversing switch on a motor I use one that has a "dead"
position in the center so that I can not forget to turn the motor off before
changing direction. On the other hand I am a devote coward who hates pain to
himself or the lathe :-)

--
God bless and safe turning
Darrell Feltmate
Truro, NS Canada
www.aroundthewoods.com

"Joe Fleming" wrote in message
ups.com...
All,

I am adding a motor to a mini lathe and have a wiring question. The
motor I have is reversible. I can add a switch to the circuit to
switch polarity and change rotation direction. Here is the question:

Can I switch the motor from forward to backward when the motor is
already turning? Or do I need to cut power and stop the rotation
first, before switching direction and reapplying power?

Thanks,
Joe Fleming - San Diego

Electric motor reversing question
 

joe - for your mini, if you flip the switch, one of three things will
happen:

1. nothing - the motor will continue to run in the same direction - this is
what happens with my reviersible grinder, for example - if the motor is
turning more than a few RPM, it will just keep going. Many motors are
bi-directional on the run-windings and use the start winding to make them go
in the desired direction.

2. it will go BANG-POOF!! and will hurt itself, probably by smoking one of
the windings or the capacitor when it attempts to revese instantly.
You can do this instant reverse with a 3 phase motor (my mill does this to
actuate the rapids), but most 110V single phase motors won't do this. You
just MIGHT get lucky, but personally, I wouldn't push my luck.

3. it might actually reverse instantly. If this happens on a wood lathe,
you will also nearly instantly unscrew the chuck or whatever is on the
spindle, much to your annoyance. One can get away wtih this on metal lathes
because when you do it (like when tapping) you are going much much slower
(10 RPM or 20 RPM, not 2,000)


I use a center off DPDT switch to control the motor on my mini lathe, I
strongly suggest you consider the same.



"Joe Fleming" wrote in message
ups.com...
Thanks everyone for the information. I can tell by the questions that
I didn't provide enough information, and I have OK - I want to be extra
clear.

A. My Stubby lathe has a 3-phase motor on a controller that allows me
to switch the motor direction while the lathe is spinning. the
controller, I presume brakes the rotation down to zero rpm, and then
starts rotation in the opposite direction. I do not stop the spinning
before switching directions. Once in a great while the braking torque
does cause a chuck to unscrew, but I generally tighten the chuck so
this does not happen. The slow down and speed up are rather gradual.
there is no "hard slam" reversing going on. So, this is my experience
with reversing on a lathe.

B. The motor for my mini lathe is a single phase 110 motor that has
wiring to allow rotation in both directions. I will not have a
controller. It will be wired directly to 110 AC through whatever
switch(es) I install.

So, based upon all the great responses, here are my more precise
questions:

1. If I flip the polarity on the switch to instantly reverse motor
direction, does the motor gradually slow down, then gradually speed up
in the other direction, or does the motor attempt to slam direction
changes? In other words, to avoid slamming direction change, I must
allow the rotation to stop before re-energizing the motor in the
opposite direction?

2. If I flip the polarity on the switch to instantly reverse motor
direction, does this damage the motor? In other words, to avoid motor
damage, I must allow the rotation to stop before re-energizing the
motor in the opposite direction?

Assuming the slamming effect is what happens and/or that motor damage
happens, then I will use some sort of three position set-up where I
turn off rotation in one direction. Wait until the rotation stops,
then re-energize the motor for reverse rotation.

Thanks again.
Joe Fleming



Darrell Feltmate wrote:
Joe
When I put a reversing switch on a motor I use one that has a "dead"
position in the center so that I can not forget to turn the motor off
before
changing direction. On the other hand I am a devote coward who hates pain
to
himself or the lathe :-)

--
God bless and safe turning
Darrell Feltmate
Truro, NS Canada
www.aroundthewoods.com

"Joe Fleming" wrote in message
ups.com...
All,

I am adding a motor to a mini lathe and have a wiring question. The
motor I have is reversible. I can add a switch to the circuit to
switch polarity and change rotation direction. Here is the question:

Can I switch the motor from forward to backward when the motor is
already turning? Or do I need to cut power and stop the rotation
first, before switching direction and reapplying power?

Thanks,
Joe Fleming - San Diego





--
Posted via a free Usenet account from http://www.teranews.com

Electric motor reversing question
 

"Dan Bollinger" wrote: (clip) Unless someone can come up with a significant
history or evidence of what you are talking about I'm just going to write
this off as something for Mythbusters to call 'busted!'
^^^^^^^^^^^^^^^^^
Dan, based on your experience, and the fact that your logic is better than
my logic, I'm BUSTED.

Electric motor reversing question
 

B. The motor for my mini lathe is a single phase 110 motor that has
wiring to allow rotation in both directions. I will not have a
controller. It will be wired directly to 110 AC through whatever
switch(es) I install.

1. If I flip the polarity on the switch to instantly reverse motor
direction, does the motor gradually slow down, then gradually speed up
in the other direction,

No, that requires a VFD controller.

or does the motor attempt to slam direction
changes?

It can't slam if it is a reversible capacitor start induction motor commonly
used on shop equipment like Grainger item 4k144.. The reversing switch changes
the polarity of the starting capacitor. When the motor is running, the starting
capacity is not energized, hence reversing it has no effect on the running
motor.

In other words, to avoid slamming direction change, I must
allow the rotation to stop before re-energizing the motor in the
opposite direction?

See above. In order to achieve reverse rotation the motor must be turned off
and allowed to stop then turned back on. When you reverse the capacitor makes no
difference.

2. If I flip the polarity on the switch to instantly reverse motor
direction, does this damage the motor?

How can it? See above.

In other words, to avoid motor
damage, I must allow the rotation to stop before re-energizing the
motor in the opposite direction?

No, to avoid motor damage don't hit it with an 8 pound sledge hammer. To
reverse the motor, see above.

Assuming the slamming effect is what happens and/or that motor damage
happens,

What slamming effect? There is no slamming effect with this motor unless of
course you are using the MOTOR as an 8 pound sledge hammer!

then I will use some sort of three position set-up where I
turn off rotation in one direction. Wait until the rotation stops,
then re-energize the motor for reverse rotation.

You can use a center-off three position switch if you like but it will be a
waste of money. A regular old DPDT switch will work just fine to revers the
capacitor. To turn the lathe on and off (regardless of rotation) just use the
switch that came with the lathe.

What I do is mount a toggle reversing switch in a little housing attached to the
motor wiring cover when the motor is accessible. See Grainger item 2x660, Motor
Switch Mounting Box

Dan

Electric motor reversing question
 

Dan, based on your experience, and the fact that your logic is better than my
logic, I'm BUSTED.

Write to the guys at Mythbusters, maybe they'll purchase your idea! They like
to blow things up. :)

Electric motor reversing question
 

Leo Lichtman wrote:

First, Nailshooter, regardless of what type of motor it is, it will never
instantly reverse. It may start to decelerate rapidly--but I think Dan is
right: once a single phase motor is up to speed, the direction of rotation
is not controlled by the wiring.


That is good to know. I never said that the fellow's machine I was
referencing that heard the loud bang was single phase, it may or may
not be. So if you are right and motors react completely the same
"regardless" of what type of motor it is, if ALL act the way you say
under all set up conditions, it sounds like I may have heard some
baloney over here.

I will see him at the next meeting and ask him if he was pulling my
leg. You know how some can't resist an exaggeration to tell a good
story. He doesn't seem the type, but...

Joe - I hope you let us know what you decide and why.

Robert

Electric motor reversing question
 

"Dan Bollinger" wrote in message
...
The reversing switch changes
the polarity of the starting capacitor. When the motor is running, the
starting capacity is not energized, hence reversing it has no effect on
the running motor.

That's it! All it sees is a power interruption until it's coasted down
enough to kick in the centrifugal switch. Sees 120 of those every minute
anyway. Once the switch is in you enter the zone of uncertainty where
issues are sometimes decided after an exchange of smoke signals....

Now how about one rigged with a start/run capacitor.

Electric motor reversing question
 

Dan Bollinger wrote:

I've worked in factories and shops all my life and I have yet to replace a motor
because it was reversed improperly or too often.

Well, I have, reversing a motor that has either a improperly rated (or
no) overload and the wrong accel/decel settings - then you get "arcing
and sparking and (still) popping the breaker" and sometimes motor
smoke; do it often enough (or with enough load) and the motor will be
toasted - 37 years aerospace industrial electronics. Unlike many
single phase motors, a 3-phase AC motor CAN be reversed instantly but
is VERY likely to pop the overload and/or burn the motor. I've seen
the after affects of a motor reversed at speed and load - 2" thick
shafts twisted, couplings bent and, somtimes, motors toasted. There is
even a type of welding that uses stored inertia, try reversing that
systems motor at speed (less than 100 RPM). Any system that lets you
reverse a motor at speed and load, without a decel/accel curve, is
poorly designed.

Also, brushed (AC or DC) motors (think router) can be reversed
instantly, but, again, you're likely to either pop the overload or
smoke the motor; mostly the brushes/commutator. I've got a blender
that uses a router motor that has a reversing switch - the whole
blender jumps and twists and you get major arcing when it is used.

BrianC

Electric motor reversing question
 

All,

Thanks for all the great information. Here is what I have decided to
do:

Two switches: one to turn power on/off. One to reverse the direction.
I thought about a three position switch, but I don't want the chance
that I flip the switch right past the "off" position to the other "on"
position and cause problems.

Joe

============================
Brian C wrote:
Dan Bollinger wrote:

I've worked in factories and shops all my life and I have yet to replace a motor
because it was reversed improperly or too often.

Well, I have, reversing a motor that has either a improperly rated (or
no) overload and the wrong accel/decel settings - then you get "arcing
and sparking and (still) popping the breaker" and sometimes motor
smoke; do it often enough (or with enough load) and the motor will be
toasted - 37 years aerospace industrial electronics. Unlike many
single phase motors, a 3-phase AC motor CAN be reversed instantly but
is VERY likely to pop the overload and/or burn the motor. I've seen
the after affects of a motor reversed at speed and load - 2" thick
shafts twisted, couplings bent and, somtimes, motors toasted. There is
even a type of welding that uses stored inertia, try reversing that
systems motor at speed (less than 100 RPM). Any system that lets you
reverse a motor at speed and load, without a decel/accel curve, is
poorly designed.

Also, brushed (AC or DC) motors (think router) can be reversed
instantly, but, again, you're likely to either pop the overload or
smoke the motor; mostly the brushes/commutator. I've got a blender
that uses a router motor that has a reversing switch - the whole
blender jumps and twists and you get major arcing when it is used.

BrianC

Electric motor reversing question
 

joe - you are in a location with good surplus stores - look around them -
there is a type of three position switch that forces you to stop in the
center position, don't remember the name of them, but if you find one
surplus (generally mil surplus) they won't cost much more (if any) than any
other switch.


"Joe Fleming" wrote in message
oups.com...
All,

Thanks for all the great information. Here is what I have decided to
do:

Two switches: one to turn power on/off. One to reverse the direction.
I thought about a three position switch, but I don't want the chance
that I flip the switch right past the "off" position to the other "on"
position and cause problems.

Joe





--
Posted via a free Usenet account from http://www.teranews.com

Electric motor reversing question
 

Thanks Bill



William Noble wrote:
joe - you are in a location with good surplus stores - look around them -
there is a type of three position switch that forces you to stop in the
center position, don't remember the name of them, but if you find one
surplus (generally mil surplus) they won't cost much more (if any) than any
other switch.


"Joe Fleming" wrote in message
oups.com...
All,

Thanks for all the great information. Here is what I have decided to
do:

Two switches: one to turn power on/off. One to reverse the direction.
I thought about a three position switch, but I don't want the chance
that I flip the switch right past the "off" position to the other "on"
position and cause problems.

Joe





--
Posted via a free Usenet account from http://www.teranews.com

Electric motor reversing question
 

Joe Fleming wrote:
B. The motor for my mini lathe is a single phase 110 motor that has
wiring to allow rotation in both directions. I will not have a
controller. It will be wired directly to 110 AC through whatever
switch(es) I install.

Whether or not it can be reversed at speed or not depends on the type
of motor it is: single phase induction motors canNOT be reversed at
speed (these are the most common type on a single phase system),
brushed (AC or DC) motors (think router) CAN be reversed instantly, at
speed, but then you're likely to either pop the overload or smoke the
motor; mostly the brushes/commutator. I've got a blender that uses a
router motor that has a reversing switch - the whole blender jumps and
twists and you get major arcing when it is used.

How to tell if your motor has brushes? Look at the near end the wires
go in, does it have two knobs or screw slots of non-metallic stuff,
then it is probably brushed and can be reversed at speed.

Electric motor reversing question
 

Here is an industrial motor reversing drum switch with center off position. Some
of these will do a single phase motor, other only a 3-phase motor. This one does
both.

Search eBay for item #120076756054

Dan

"Joe Fleming" wrote in message
ups.com...
All,

I am adding a motor to a mini lathe and have a wiring question. The
motor I have is reversible. I can add a switch to the circuit to
switch polarity and change rotation direction. Here is the question:

Can I switch the motor from forward to backward when the motor is
already turning? Or do I need to cut power and stop the rotation
first, before switching direction and reapplying power?

Thanks,
Joe Fleming - San Diego

Electric motor reversing question
 

any switch that will reverse a 3 phase motor can be used on a single phase
motor, you will just have unused contacts
"Dan Bollinger" wrote in message
m...
Here is an industrial motor reversing drum switch with center off
position. Some of these will do a single phase motor, other only a 3-phase
motor. This one does both.

Search eBay for item #120076756054

Dan

"Joe Fleming" wrote in message
ups.com...
All,

I am adding a motor to a mini lathe and have a wiring question. The
motor I have is reversible. I can add a switch to the circuit to
switch polarity and change rotation direction. Here is the question:

Can I switch the motor from forward to backward when the motor is
already turning? Or do I need to cut power and stop the rotation
first, before switching direction and reapplying power?

Thanks,
Joe Fleming - San Diego





--
Posted via a free Usenet account from http://www.teranews.com

Electric motor reversing question
 

any switch that will reverse a 3 phase motor can be used on a single phase
motor, you will just have unused contacts

You might be right about that. It's been a long time since I've used one of
these. Now its VFD all the way!

Dan

Electric motor reversing question
 

vfds are great, of course I have one machine with three motors, one has a 27
speed gearbox, the other has 18, if I remember right, and the third has only
on/off - so that would be 2 VFDs or one capacitor and one relay to make a
static inverter and then the larger (6 hp) motor acts as the ponly motor for
the others. One of the other motors, a 2 HP relies on instant reversing to
make the machine movement go from "slow" to "fast", and a VFD can't do that.
(note, t his machine is not a wood lathe) So, whether to use VFD depends
on the specific situation
"Dan Bollinger" wrote in message
m...
any switch that will reverse a 3 phase motor can be used on a single
phase motor, you will just have unused contacts

You might be right about that. It's been a long time since I've used one
of these. Now its VFD all the way!

Dan





--
Posted via a free Usenet account from http://www.teranews.com