reversing AC motors?
 

Hi,
I'm looking around motor for a grinder. someone pointed out that
compressor-duty motors are non-reversible. I didn't think this an
issue previously, but it occurs to me that if I build a buffing wheel
opposite the grinder, off the same motor, for each to run in the proper
rotation I would have to reverse the rotation of the motors.

Assuming a conventional, reversible motor (I'm not on the question
of compressor motor or not here), does this involve rewiring the motor
each time? Even if just 10 minutes of work, it would be a nuisance;
since it would not just be a one-time rewiring, but every time I want
to switch between machines. Could I build a simple device that would
rewire it by flipping a switch, if this is the case?


btw, how much more efficient is 3 phase over 2? It seems a
converter is affordable off of ebay, and it looks like it would make
every subsequent motor cheaper, and/or more efficient and
smoother-running?

thanks!
-Bernard Arnest

reversing AC motors?
 

Why would they run in opposite directions? You want a grinding wheel to
run so that the grinding face is traveling down, that is the same as a
buffing wheel, down and away from you.
--
Steve W.

"Bernard Arnest" wrote in message
oups.com...
Hi,
I'm looking around motor for a grinder. someone pointed out that
compressor-duty motors are non-reversible. I didn't think this an
issue previously, but it occurs to me that if I build a buffing wheel
opposite the grinder, off the same motor, for each to run in the
proper
rotation I would have to reverse the rotation of the motors.

Assuming a conventional, reversible motor (I'm not on the question
of compressor motor or not here), does this involve rewiring the motor
each time? Even if just 10 minutes of work, it would be a nuisance;
since it would not just be a one-time rewiring, but every time I want
to switch between machines. Could I build a simple device that would
rewire it by flipping a switch, if this is the case?


btw, how much more efficient is 3 phase over 2? It seems a
converter is affordable off of ebay, and it looks like it would make
every subsequent motor cheaper, and/or more efficient and
smoother-running?

thanks!
-Bernard Arnest




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reversing AC motors?
 

Exactly. Because they are on opposite sides of the same stand/motor, to
conserve space.

reversing AC motors?
 

On 20 Apr 2006 07:45:45 -0700, "Bernard Arnest"
wrote:

Exactly. Because they are on opposite sides of the same stand/motor, to
conserve space.
You are sleeping, Bernard.
*** Posted via a free Usenet account from http://www.teranews.com ***

reversing AC motors?
 

I dunno the context of the comment that compressor-rated motors aren't
reversible, but that comment isn't accurate.
Compressor-rated motors, as well as any other specific type of motor
may be reversible.

I can understand that an air compressor manufacturer might specify a
single direction of rotation, because a reversible motor wouldn't be
required for their particular application, and the motors would cost
less than a reversible version of the same model of motor (fewer power
leads and/or terminals, lower cost).
This would result in the availability of non-reversible
compressor-rated motors, but there are many of the same which are
reversible.
Generally, any type of motor that wasn't produced for a specific
appliance/machine application, will be available as a reversible model.


I think the application you're contemplating is a motor located between
two separate shafts/arbors, and each shaft intended for a different
use.
In the assumed application, the nuts securing the grinding and buffing
wheels may loosen when the motor is started, if there is no
consideration given to preventing that.

On a typical single shaft arbor, the mounting/securing nuts are
separately left and right hand threaded, since the arbor is always run
in one direction only.
Placing your wheels on opposite ends of a single shaft would probably
be easier to implement (most certainly safer). Then there would be no
need to reverse the motor direction.

Compressor-duty motors are built/intended for high starting and running
torque, but aren't absolutely required for grinding or buffing
applications. Another type of motor would be adequately sufficient,
although a c-r motor would also provide very good performance.

Switching reversible motors to run in either direction isn't extremely
complicated if the motor is a reversible model. There was an in-depth
discussion within the last week concerning this same topic, here in
RCM.

Motor efficiency is related to running hours, to be of any major
significance. For cost-effectiveness, one might consider 3-phase power
as less costly, as 3-phase motors are generally cheaper to purchase.

WB
...............

Bernard Arnest wrote:
Hi,
I'm looking around motor for a grinder. someone pointed out that
compressor-duty motors are non-reversible. I didn't think this an
issue previously, but it occurs to me that if I build a buffing wheel
opposite the grinder, off the same motor, for each to run in the proper
rotation I would have to reverse the rotation of the motors.

Assuming a conventional, reversible motor (I'm not on the question
of compressor motor or not here), does this involve rewiring the motor
each time? Even if just 10 minutes of work, it would be a nuisance;
since it would not just be a one-time rewiring, but every time I want
to switch between machines. Could I build a simple device that would
rewire it by flipping a switch, if this is the case?


btw, how much more efficient is 3 phase over 2? It seems a
converter is affordable off of ebay, and it looks like it would make
every subsequent motor cheaper, and/or more efficient and
smoother-running?

thanks!
-Bernard Arnest

reversing AC motors?
 

OK I think I see what you plan on doing now. Your thinking of putting
the motor in the middle and having two separate units mounted to run off
of it, kind of like a small lineshaft arrangement. with equipment
located to the front/back of the motor.

In that case I would not bother with reversing the motor. I would just
run either a reversing 1:1 gearbox on one item or twist the belt driving
one shaft. That way they all run the same direction and you won't have
problems with loosening of the retaining nuts.
--
Steve W.
Life is not like a box of chocolates
it's more like a jar of jalapenos-
what you do today could burn your ass tomorrow!


"Bernard Arnest" wrote in message
oups.com...
Exactly. Because they are on opposite sides of the same stand/motor,
to
conserve space.





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reversing AC motors?
 

Compressor duty motors are commonly built with no access to the leads
necessary to reverse them. They are considered 'specific purpose' and
built as cheaply as possible. They are also usually not rated for
continuous duty.

Wild Bill wrote:
I dunno the context of the comment that compressor-rated motors aren't
reversible, but that comment isn't accurate.
Compressor-rated motors, as well as any other specific type of motor
may be reversible.

I can understand that an air compressor manufacturer might specify a
single direction of rotation, because a reversible motor wouldn't be
required for their particular application, and the motors would cost
less than a reversible version of the same model of motor (fewer power
leads and/or terminals, lower cost).
This would result in the availability of non-reversible
compressor-rated motors, but there are many of the same which are
reversible.
Generally, any type of motor that wasn't produced for a specific
appliance/machine application, will be available as a reversible model.


I think the application you're contemplating is a motor located between
two separate shafts/arbors, and each shaft intended for a different
use.
In the assumed application, the nuts securing the grinding and buffing
wheels may loosen when the motor is started, if there is no
consideration given to preventing that.

On a typical single shaft arbor, the mounting/securing nuts are
separately left and right hand threaded, since the arbor is always run
in one direction only.
Placing your wheels on opposite ends of a single shaft would probably
be easier to implement (most certainly safer). Then there would be no
need to reverse the motor direction.

Compressor-duty motors are built/intended for high starting and running
torque, but aren't absolutely required for grinding or buffing
applications. Another type of motor would be adequately sufficient,
although a c-r motor would also provide very good performance.

Switching reversible motors to run in either direction isn't extremely
complicated if the motor is a reversible model. There was an in-depth
discussion within the last week concerning this same topic, here in
RCM.

Motor efficiency is related to running hours, to be of any major
significance. For cost-effectiveness, one might consider 3-phase power
as less costly, as 3-phase motors are generally cheaper to purchase.

WB
..............

Bernard Arnest wrote:

Hi,
I'm looking around motor for a grinder. someone pointed out that
compressor-duty motors are non-reversible. I didn't think this an
issue previously, but it occurs to me that if I build a buffing wheel
opposite the grinder, off the same motor, for each to run in the proper
rotation I would have to reverse the rotation of the motors.

Assuming a conventional, reversible motor (I'm not on the question
of compressor motor or not here), does this involve rewiring the motor
each time? Even if just 10 minutes of work, it would be a nuisance;
since it would not just be a one-time rewiring, but every time I want
to switch between machines. Could I build a simple device that would
rewire it by flipping a switch, if this is the case?


btw, how much more efficient is 3 phase over 2? It seems a
converter is affordable off of ebay, and it looks like it would make
every subsequent motor cheaper, and/or more efficient and
smoother-running?

thanks!
-Bernard Arnest

reversing AC motors?
 

Hi,
Regarding nuts loosening, I was considering just taking the belt off
one machine and transferring to the other, wouldn't take but a second,
so that it would only be running one at a time. But good point, I
forgot about that.

I didn't realize I could just twist the belt; wouldn't there be
friction where it crosses itself, and/or other premature wear? Or
maybe not? That would certainly be a straightforward solution.


thanks!
-Bernard Arnest

reversing AC motors?
 

In article ,
says...
Compressor duty motors are commonly built with no access to the leads
necessary to reverse them. They are considered 'specific purpose' and
built as cheaply as possible. They are also usually not rated for
continuous duty.


That may be true of the motor that comes on a cheap compressor, but if
you ask for a compressor duty motor from, for example, Leeson or Baldor
it'll probably have a larger frame, higher insulation class, and higher
breakdown torque than a general purpose motor. If single phase, it will
also be reversible.

Ned Simmons

reversing AC motors?
 

LOTS of equipment out there with twisted belts. Also many with a twisted
idler and two belts when you only have a short distance. In that
situation you use a double sheave pulley and tip it 45 degrees to keep
crossover from occurring.

--
Steve W.

"Bernard Arnest" wrote in message
oups.com...
Hi,
Regarding nuts loosening, I was considering just taking the belt off
one machine and transferring to the other, wouldn't take but a second,
so that it would only be running one at a time. But good point, I
forgot about that.

I didn't realize I could just twist the belt; wouldn't there be
friction where it crosses itself, and/or other premature wear? Or
maybe not? That would certainly be a straightforward solution.


thanks!
-Bernard Arnest




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reversing AC motors?
 

There may be LOTS of machinery using twisted belts but it is still
considered bad practice. Twisted V belts should be heavily derated and
make sure there is LOTS of space between adjacent pulleys.

Steve W. wrote:
LOTS of equipment out there with twisted belts. Also many with a twisted
idler and two belts when you only have a short distance. In that
situation you use a double sheave pulley and tip it 45 degrees to keep
crossover from occurring.

reversing AC motors?
 

Bernard Arnest wrote:
I'm looking around motor for a grinder. someone pointed out that
compressor-duty motors are non-reversible. I didn't think this an
issue previously, but it occurs to me that if I build a buffing wheel
opposite the grinder, off the same motor, for each to run in the proper
rotation I would have to reverse the rotation of the motors.

DON'T DO IT!!! The threads on the shafts are such that the acceleration
of the motor at switch on tends to _tighten_ the nuts. Reversing the
motor would then tend to loosen them. This causes the grinding wheel to
become an unidentified flying object until after it hits someone.

Ted

reversing AC motors?
 

On Sat, 22 Apr 2006 21:24:53 GMT, Ted Edwards
wrote:

Bernard Arnest wrote:
I'm looking around motor for a grinder. someone pointed out that
compressor-duty motors are non-reversible. I didn't think this an
issue previously, but it occurs to me that if I build a buffing wheel
opposite the grinder, off the same motor, for each to run in the proper
rotation I would have to reverse the rotation of the motors.

DON'T DO IT!!! The threads on the shafts are such that the acceleration
of the motor at switch on tends to _tighten_ the nuts. Reversing the
motor would then tend to loosen them. This causes the grinding wheel to
become an unidentified flying object until after it hits someone.

Ted
A simple jam nut will avoid this - been doing it this way for 40+
years.
Gerry :-)}
London, Canada

reversing AC motors?
 

On my 16 speed import drill press (of which only about 3 sperds are useful)
w/ a capacitor/centrifugal starting circuit (that clicks out at speed), I
discovered that if you disconnect the starting circuit, the motor stalls,
but will spin in either direction you set it in by hand, and then continue
in that direction when the motor circuit connected.
Yeah, a little rustic....

I figger this could be wired in properly, as single phase lathe motors w/
centrifugal switches are reversible.
And in those, if you attempt to reverse the motor before the centrifugal
switch drops out, it will continue in the same direction even tho the handle
was thrown in the reverse direction!
I screwed up more than a few tapped holes that way. :)

Often the techs at the motor mfr can be helpful w/ this.
As can small motor winding shops. Bring it to them disassembled, I'll bet
they can point to the "right wires" in about 2 seconds--no charge. Proly
just need a dpdt switch from radio shack (two 3-way wall switches will work
in a pinch).
--
Mr. P.V.'d
formerly Droll Troll
"Bernard Arnest" wrote in message
oups.com...
Hi,
I'm looking around motor for a grinder. someone pointed out that
compressor-duty motors are non-reversible. I didn't think this an
issue previously, but it occurs to me that if I build a buffing wheel
opposite the grinder, off the same motor, for each to run in the proper
rotation I would have to reverse the rotation of the motors.

Assuming a conventional, reversible motor (I'm not on the question
of compressor motor or not here), does this involve rewiring the motor
each time? Even if just 10 minutes of work, it would be a nuisance;
since it would not just be a one-time rewiring, but every time I want
to switch between machines. Could I build a simple device that would
rewire it by flipping a switch, if this is the case?


btw, how much more efficient is 3 phase over 2? It seems a
converter is affordable off of ebay, and it looks like it would make
every subsequent motor cheaper, and/or more efficient and
smoother-running?

thanks!
-Bernard Arnest