Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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  #1   Report Post  
SRF
 
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I'm setting up a hobby machine shop and am getting into the issue of 3 phase
motors. Most of the motors are going to be in the 1 to 3 horsepower range.
For motors of this size, why would I want to have make three phase power to
run these machines instead of just swapping out the motors for single phase?

Thanks.
Steve.



  #2   Report Post  
Tom Gardner
 
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If you can swap out the motors for less than it will cost to get a
converter...go for it.
I'm sure that many others will respond and this is the place to be for
converter and other power related questions.


"SRF" wrote in message
...
I'm setting up a hobby machine shop and am getting into the issue of 3

phase
motors. Most of the motors are going to be in the 1 to 3 horsepower

range.
For motors of this size, why would I want to have make three phase power

to
run these machines instead of just swapping out the motors for single

phase?

Thanks.
Steve.





  #3   Report Post  
jim rozen
 
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In article , SRF says...

I'm setting up a hobby machine shop and am getting into the issue of 3 phase
motors. Most of the motors are going to be in the 1 to 3 horsepower range.
For motors of this size, why would I want to have make three phase power to
run these machines instead of just swapping out the motors for single phase?


Well, I can tell you why I chose to put in a home-made
rotary converter: one of the machines I bought had a
two speed pole changing, three phase motor, and I wanted
to keep that motor in place. For the lathe, I found
that real three phase provides the advantage of plug
(instant) reversing.

And then later, I found I purchased yet another (hardinge)
machine with a similar two speed motor.

The cost of the phase converter itself was miniscule
compared with the cost of changing those three motors,
or installing a VFD for each machine - aside from the
convenience aspects.

Jim

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  #4   Report Post  
Grant Erwin
 
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Three phase motors are an order of magnitude cheaper.
Machines powered by three phase motors have inherently less vibration.
(Think about it - 120 times every second the power applied to a single
phase machine is instantaneously *zero* ..)
Many industrial motors e.g. motors that come on a Bridgeport mill are
much better quality than cheap single phase replacements.

Good question!

Grant Erwin

SRF wrote:
I'm setting up a hobby machine shop and am getting into the issue of 3 phase
motors. Most of the motors are going to be in the 1 to 3 horsepower range.
For motors of this size, why would I want to have make three phase power to
run these machines instead of just swapping out the motors for single phase?

Thanks.
Steve.




  #5   Report Post  
John Manders
 
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"SRF" wrote in message
...
I'm setting up a hobby machine shop and am getting into the issue of 3

phase
motors. Most of the motors are going to be in the 1 to 3 horsepower

range.
For motors of this size, why would I want to have make three phase power

to
run these machines instead of just swapping out the motors for single

phase?

Thanks.
Steve.

There are a number of answers.
As others have said, industrial 3 phase motors are much better made than the
cheap single phase equivalents.
Used 3 phase machinery is generally cheaper than single phase stuff.
You only need to make one converter instead of buying a number of separate
motors so the total cost is less.
A number of machines use non standard motors so replacing them is difficult.
The answer quoting 120 times per second that the power is zero made me think
a bit. The first reaction was to realise that you are on 60 Hz mains and we
(UK) are on 50 Hz. The other thought was that a single phase motor doesn't
actually rely on single phase as such but it makes another phase by use of
an inbuilt capacitor. This second phase is frequently of a lower power than
the primary phase though hence 3 phase is generally a better motor.

John




  #6   Report Post  
DoN. Nichols
 
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In article ,
John Manders wrote:

"SRF" wrote in message
m...
I'm setting up a hobby machine shop and am getting into the issue of 3

phase
motors. Most of the motors are going to be in the 1 to 3 horsepower

range.
For motors of this size, why would I want to have make three phase power

to
run these machines instead of just swapping out the motors for single

phase?

Thanks.
Steve.

There are a number of answers.
As others have said, industrial 3 phase motors are much better made than the
cheap single phase equivalents.


Amen!

Used 3 phase machinery is generally cheaper than single phase stuff.


Again amen.

You only need to make one converter instead of buying a number of separate
motors so the total cost is less.


Correct -- or you can set up a VFD (Variable Frequency Drive) to
generate three phase at the machine, which offers you the advantage of
being able to fine-tune the motor speed (while it is running) to
eliminate chatter.

I would suggest that for machines which have only steps in their
speed selection (e.g. gears or belts and step pulleys), the VFD is
preferred, while for those with variable speed pulleys, and for running
multiple machines at a minimum initial investment, a home-built rotary
converter (built around a larger three-phase motor, some capacitors, and
some voltage-sensitive relays) would be the better choice.

For long-term operating cost, the VFD will put more of your
energy budget directly into the motor, but the initial investment is
greater.

*My* choice is VFDs. I have two machines which currently have
three-phase motors, and a third three-phase motor ready to go into my
lathe to replace the existing single-phase motor.

A number of machines use non standard motors so replacing them is difficult.
The answer quoting 120 times per second that the power is zero made me think
a bit. The first reaction was to realise that you are on 60 Hz mains and we
(UK) are on 50 Hz. The other thought was that a single phase motor doesn't
actually rely on single phase as such but it makes another phase by use of
an inbuilt capacitor. This second phase is frequently of a lower power than
the primary phase though hence 3 phase is generally a better motor.


Well ... that depends on the motor. There are some single-phase
motors (capacitor-run motors, and hysteresis-synchronous motors (which
would be found on audio turntables and tape recorder decks, not on
machine tools)), but most found on machine tools are only capacitor
*start* motors -- the manufactured second phase is present only when the
motor is at a standstill, or very low speeds, just to get it started in
a desired direction, and more quickly. If you are starting in under
load, it is possible to spin a motor by hand, then switch on the power,
and do entirely without the starting capacitor. And once the motor is
up to speed, the starting capacitor and winding are disconnected
automatically, so you are back to the once per 120th of a second (or
once per 100th of a second in the UK) zero power point.

For surface grinders in particular, the three phase motors
produce a much better finish than the single-phase ones -- thanks to the
vibration introduced by the zero-power points.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
  #7   Report Post  
wmbjk
 
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"SRF" wrote in message
...

I'm setting up a hobby machine shop and am getting into the issue of 3

phase
motors. Most of the motors are going to be in the 1 to 3 horsepower

range.
For motors of this size, why would I want to have make three phase

power to
run these machines instead of just swapping out the motors for single

phase?

Thanks.
Steve.


Here's a site with some info.
http://www.processcontroltechnologie...seinverter.htm My only
experience is with the Toshiba S7. A very cool product, but probably in
the $800 range. This is the best I could do for a picture
http://www.lbelec.com/toshiba/drives.html It's the one shown in the palm
of a hand. Contact TK Electric at 702 293-2310 if you need more info.
Why would you want one? Smaller wire sizes, variable speed, variable
torque, slow startup, safety cutoffs, etc. Not really needed for
woodworking I don't think, and you wouldn't be able to make use of most
of the sophisticated programming anyway if you were running multiple
motors. Although if you have enough motors, perhaps adding one new
device would be easier than swapping them all.

Wayne


  #8   Report Post  
jim rozen
 
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In article , DoN. Nichols says...

I would suggest that for machines which have only steps in their
speed selection (e.g. gears or belts and step pulleys), the VFD is
preferred, while for those with variable speed pulleys, and for running
multiple machines at a minimum initial investment, a home-built rotary
converter (built around a larger three-phase motor, some capacitors, and
some voltage-sensitive relays) would be the better choice.


At the face of it this would seem to be the case,
but the really odd part is, folks who have some
machines like the monarch 10EE, or the lathe with
the variable speed drive that everyone dislikes
(I think this is either a rockwell, or a delta,
or maybe it was both) seem to say, the varispeed
drive is a major pain, and they always retrofit
with a VFD. But the folks with step belt machines
like southbend or the older hardinges, seem to
get along fine with step belts.

Where the VFD really shines though, IMO is in a
drill press. Just *so* handy for getting the right
speed.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

  #9   Report Post  
DoN. Nichols
 
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In article ,
jim rozen wrote:
In article , DoN. Nichols says...

I would suggest that for machines which have only steps in their
speed selection (e.g. gears or belts and step pulleys), the VFD is
preferred, while for those with variable speed pulleys, and for running
multiple machines at a minimum initial investment, a home-built rotary
converter (built around a larger three-phase motor, some capacitors, and
some voltage-sensitive relays) would be the better choice.


At the face of it this would seem to be the case,
but the really odd part is, folks who have some
machines like the monarch 10EE, or the lathe with
the variable speed drive that everyone dislikes
(I think this is either a rockwell, or a delta,
or maybe it was both) seem to say, the varispeed
drive is a major pain,


I've seen a lot about the problems with the hydraulic variable
speed lathes produced by Clausing. It seems that they are just getting
to be old enough to have problems with the hydraulics by now.

My Clausing is a 1957 one with the step pulleys. And there are
times when I would like to be able to reach out to a knob and tune the
speed without interrupting the cut. I also would like the ability to
reverse the spindle without having to wait for the motor to coast down
to near a stop (when I'm tapping with the turret), hence the desire for
a three phase motor, and a VFD (with the reversing being done by
commanding the VFD to reverse, not by switching the motor windings. I
can get away with that with the vastly oversized (e.g. 30A) VFD which is
currently running the 1HP motor on the Nichols horizontal mill, but I
could not do so with a VFD which is a closer match to the motor's
horsepower.

As for the Monarch 10EE -- that is because the electronics for
the older ones is getting to be rather expensive to keep going
(replacing the big old thyratrons to drive the motor), and some of the
newer replacement electronics is showing up as rather fragile. Probably
the best in terms of long-term service is the old motor-generator style,
which I used to use at work.

A friend in the local metalworking club (CAMS) has recently done
a marvelous job of marrying a three-phase motor to the original gearbox
in his 10EE -- to be driven from a VFD, of course.

and they always retrofit
with a VFD. But the folks with step belt machines
like southbend or the older hardinges, seem to
get along fine with step belts.


If it were not for the turret tapping work, I could probably do
without the upgrade, but I must admit to not always selecting just the
right speed for a given operation, thanks to having to squat down to
access the motor lever and belt for the changes. :-)

Where the VFD really shines though, IMO is in a
drill press. Just *so* handy for getting the right
speed.


That is something which I need to do some of these days. But I
also have a hefty permanent magnet DC motor and a matching speed
controller, which I may use for the purpose instead.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
  #10   Report Post  
Richard Ferguson
 
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I have been hearing about VFDs and other types of solid state controls.
The Phase Inverter seems not to offer variable speed, but lots of
features. I presume similar units are available with variable speed.

However, it would seem to me that you would need a specific variable
speed drive for each tool, that you would not want to walk to the corner
to adjust the speed. That could get pricy.

To me the most practical (cheapest) thing would be to have one convertor
for the whole shop, asuming that you might eventually have multiple
devices with 3-phase motors.

The way I understand it, the alternatives go something like this.

1. Static rotory converter, simple, only gives 2/3 power, probably costs
around $100 for under 5 hp. Probably could be shared by several machines.

2. Rotary converter - full power, could be cheap if you use an old 3
phase motor to make your own, or more expensive if you buy one new.
Could be noisy. Often shared by multiple machines.

3. Phase inverter - solid state, I think that you said $700. I think
that you said that they could be shared, but you lose some of the
sophisticated features in that case.

4. Variable Frequency Drive - the top of the line solution, provides
electronic variable speed control. I would assume the top price. I
would guess that with some machines, you might want to run part of the
machine with the VFD, while running other parts with straight 3-phase
power, like the controls. It would seem unlikely that one would share
the VFD, but maybe some people do.

What is the price range here? Which of these solutions can be shared
between multiple devices? Am I wrong about what I said above? I am
trying to make sure that I understand.

Richard



wmbjk wrote:

"SRF" wrote in message
...

I'm setting up a hobby machine shop and am getting into the issue of 3

phase
motors. Most of the motors are going to be in the 1 to 3 horsepower

range.
For motors of this size, why would I want to have make three phase

power to
run these machines instead of just swapping out the motors for single

phase?

Thanks.
Steve.


Here's a site with some info.
http://www.processcontroltechnologie...seinverter.htm My only
experience is with the Toshiba S7. A very cool product, but probably in
the $800 range. This is the best I could do for a picture
http://www.lbelec.com/toshiba/drives.html It's the one shown in the palm
of a hand. Contact TK Electric at 702 293-2310 if you need more info.
Why would you want one? Smaller wire sizes, variable speed, variable
torque, slow startup, safety cutoffs, etc. Not really needed for
woodworking I don't think, and you wouldn't be able to make use of most
of the sophisticated programming anyway if you were running multiple
motors. Although if you have enough motors, perhaps adding one new
device would be easier than swapping them all.

Wayne



  #11   Report Post  
william_b_noble
 
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you can get a VFD drive for anywhere from around $400 to any large number
you care to mention - my wood turning lathe has one built into it. You can
get some basic information at Minarik (did I spell that right? they have a
web site, www.minarikcorp.com ) and look at their offerings. You can find
the things surplus cheaply, if you know how to work on electronics.

http://www.phase-a-matic.com/ is a source for static and rotary inverters -
I'm told that their static inverter is around $100


"Richard Ferguson" wrote in message
...
I have been hearing about VFDs and other types of solid state controls.
The Phase Inverter seems not to offer variable speed, but lots of
features. I presume similar units are available with variable speed.

However, it would seem to me that you would need a specific variable
speed drive for each tool, that you would not want to walk to the corner
to adjust the speed. That could get pricy.

To me the most practical (cheapest) thing would be to have one convertor
for the whole shop, asuming that you might eventually have multiple
devices with 3-phase motors.

The way I understand it, the alternatives go something like this.

1. Static rotory converter, simple, only gives 2/3 power, probably costs
around $100 for under 5 hp. Probably could be shared by several machines.

2. Rotary converter - full power, could be cheap if you use an old 3
phase motor to make your own, or more expensive if you buy one new.
Could be noisy. Often shared by multiple machines.

3. Phase inverter - solid state, I think that you said $700. I think
that you said that they could be shared, but you lose some of the
sophisticated features in that case.

4. Variable Frequency Drive - the top of the line solution, provides
electronic variable speed control. I would assume the top price. I
would guess that with some machines, you might want to run part of the
machine with the VFD, while running other parts with straight 3-phase
power, like the controls. It would seem unlikely that one would share
the VFD, but maybe some people do.

What is the price range here? Which of these solutions can be shared
between multiple devices? Am I wrong about what I said above? I am
trying to make sure that I understand.

Richard



wmbjk wrote:

"SRF" wrote in message
...

I'm setting up a hobby machine shop and am getting into the issue of 3

phase
motors. Most of the motors are going to be in the 1 to 3 horsepower

range.
For motors of this size, why would I want to have make three phase

power to
run these machines instead of just swapping out the motors for single

phase?

Thanks.
Steve.


Here's a site with some info.
http://www.processcontroltechnologie...seinverter.htm My only
experience is with the Toshiba S7. A very cool product, but probably in
the $800 range. This is the best I could do for a picture
http://www.lbelec.com/toshiba/drives.html It's the one shown in the palm
of a hand. Contact TK Electric at 702 293-2310 if you need more info.
Why would you want one? Smaller wire sizes, variable speed, variable
torque, slow startup, safety cutoffs, etc. Not really needed for
woodworking I don't think, and you wouldn't be able to make use of most
of the sophisticated programming anyway if you were running multiple
motors. Although if you have enough motors, perhaps adding one new
device would be easier than swapping them all.

Wayne



  #12   Report Post  
John Manders
 
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However, it would seem to me that you would need a specific variable
speed drive for each tool, that you would not want to walk to the corner
to adjust the speed. That could get pricy.

A lot (if not all) VFD's can use remote speed setting. A 2 or 3 core flex to
a potentiometer will do the job. This can then be taken to the machine in
use on it's long lead. Remote stop/start/reverse controls are also
incorporated into many VFD's.
As a thought, I suppose that a VFD could be coupled to a lathe Digital Read
Out to set the speed according to the diameter of the work. That way, the
linear cutting speed is kept constant as the workpiece diameter is reduced.
Very handy for facing cuts. Lots of you will no doubt tell be that this is
already the case somewhere.

John


  #13   Report Post  
PeterKe
 
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Folks - I'm curious, and would welcome if someone could explain
something for me. I notice on this and many other threads that when
the topic of making three phase power from single phase comes up,
often the use of an idler motor is proposed.

My question is. If you don't need the variable speed function ( ie use
a VFD ) why the use of a separate idler motor?

- I have a three phase motor on my drill press and I simply hooked it
up in Steinmetz connection - single phase supply across one motor line
and a suitably sized run cap ( about 50uf per hp ) from neutral to the
third motor phase. Admittedly the starting torque isn't great, but
most machine tools start on light-load conditions, and if it is a
problem it is simple to arrange for an extra start cap to be switched
in during startup.

Its not that I'm advocating one method over another, but the use of
idler motors seems so general that I'm assuming I've missed a point
somewhere along the way, and would like it if someone could explain
the pro's and con's

Peter


"wmbjk" wrote in message ...
"SRF" wrote in message
...

I'm setting up a hobby machine shop and am getting into the issue of 3

phase
motors. Most of the motors are going to be in the 1 to 3 horsepower

range.
For motors of this size, why would I want to have make three phase

power to
run these machines instead of just swapping out the motors for single

phase?

Thanks.
Steve.


Here's a site with some info.
http://www.processcontroltechnologie...seinverter.htm My only
experience is with the Toshiba S7. A very cool product, but probably in
the $800 range. This is the best I could do for a picture
http://www.lbelec.com/toshiba/drives.html It's the one shown in the palm
of a hand. Contact TK Electric at 702 293-2310 if you need more info.
Why would you want one? Smaller wire sizes, variable speed, variable
torque, slow startup, safety cutoffs, etc. Not really needed for
woodworking I don't think, and you wouldn't be able to make use of most
of the sophisticated programming anyway if you were running multiple
motors. Although if you have enough motors, perhaps adding one new
device would be easier than swapping them all.

Wayne

  #14   Report Post  
jim rozen
 
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In article , PeterKe says...

- I have a three phase motor on my drill press and I simply hooked it
up in Steinmetz connection - single phase supply across one motor line
and a suitably sized run cap ( about 50uf per hp ) from neutral to the
third motor phase. Admittedly the starting torque isn't great, but
most machine tools start on light-load conditions, and if it is a
problem it is simple to arrange for an extra start cap to be switched
in during startup.

Its not that I'm advocating one method over another, but the use of
idler motors seems so general that I'm assuming I've missed a point
somewhere along the way, and would like it if someone could explain
the pro's and con's


I like to plug reverse my machines' motors on frequent
occasion, and using an individual phase converter consisting
of another run cap, or even another starting capacitor and
potential relay, does not allow that.

Each machine would have to have its electrics modified
to do what you propose, whereas I can simply stick the
idler motor (bought at zero expense) away in a crawl
space and start it when needed. Then I can buss the
3~ supply wherever I want in the shop.

Also running motors as you suggest, with a static
(capacitor type) phase converter - and that's what
a commercial static phase converter is - does not
allow the full hp rating of the motor to be used.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

  #15   Report Post  
jim rozen
 
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In article , Richard Ferguson says...

I have been hearing about VFDs and other types of solid state controls.
The Phase Inverter seems not to offer variable speed, but lots of
features. I presume similar units are available with variable speed.

However, it would seem to me that you would need a specific variable
speed drive for each tool, that you would not want to walk to the corner
to adjust the speed. That could get pricy.


In principle one *could* run low voltage control lines to each
machine, and switch them so whatever machine you are running
has the active lines. Sounds like a major nosebleed to me
though.

To me the most practical (cheapest) thing would be to have one convertor
for the whole shop, asuming that you might eventually have multiple
devices with 3-phase motors.


This is what I do, with a simple idler motor setup:

http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg

http://www.metalworking.com/DropBox/_2000_retired_files/conv.txt

(the text should be annotated to include the *real* current
draw when idling, which is about 200 watts)

1. Static [] converter, simple, only gives 2/3 power, probably costs
around $100 for under 5 hp. Probably could be shared by several machines.


The static converters are special sized for each machine, you
can't run a large machine with a small converter, or a small
machine from a large static converter.

2. Rotary converter - full power, could be cheap if you use an old 3
phase motor to make your own, or more expensive if you buy one new.
Could be noisy. Often shared by multiple machines.


Cost for mine: free, except for the wire and wiring devices.
It's so quiet I can forget that it's running and accidentally
leave it on.

3. Phase inverter - solid state, I think that you said $700. I think
that you said that they could be shared, but you lose some of the
sophisticated features in that case.

4. Variable Frequency Drive - the top of the line solution, provides
electronic variable speed control. I would assume the top price. I
would guess that with some machines, you might want to run part of the
machine with the VFD, while running other parts with straight 3-phase
power, like the controls. It would seem unlikely that one would share
the VFD, but maybe some people do.


I haven't seen any phase inverters that don't also incorporate
variable speed options. At least for the smaller ones I've
seen. YMMV.

What is the price range here?


Zero to hundreds of dollars, depending on size of load.

Which of these solutions can be shared
between multiple devices?


All of them to some degree or another. Easiest seems to
be the single point idler motor setup, for this factor.

Am I wrong about what I said above? I am
trying to make sure that I understand.


You pretty much understand the issues.

Jim

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please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
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  #16   Report Post  
Charles A. Sherwood
 
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4. Variable Frequency Drive - the top of the line solution, provides
electronic variable speed control. I would assume the top price. I



You can buy NEW VFDs for reasonable prices.
For example dealers electric sells a Teco 2HP for $246.
Price is dependent on size.
www.dealerselectric.com

I have a Teco 1HP on my surface grinder and 2HP on my lathe.
I have a Boston Fincor on my mill. VFDs are the way to go.
chuck
  #17   Report Post  
Dan Caster
 
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The reasons people use idler motors is to increase the starting and
running torque. A three phase motor run on single phase power will
produce about 2/3 rds the power it would produce on three phase power.
Also with an idler motor you can reverse the motor rapidly ( well
maybe ). Used three phase motors are pretty cheap, so using one is
not a lot of money. But as you say, you don't have to.

Dan


(PeterKe) wrote in message

My question is. If you don't need the variable speed function ( ie use
a VFD ) why the use of a separate idler motor?



Its not that I'm advocating one method over another, but the use of
idler motors seems so general that I'm assuming I've missed a point
somewhere along the way, and would like it if someone could explain
the pro's and con's

Peter


  #18   Report Post  
DoN. Nichols
 
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Default Motor Phases

In article ,
Richard Ferguson wrote:
I have been hearing about VFDs and other types of solid state controls.
The Phase Inverter seems not to offer variable speed, but lots of
features. I presume similar units are available with variable speed.

However, it would seem to me that you would need a specific variable
speed drive for each tool, that you would not want to walk to the corner
to adjust the speed. That could get pricy.

To me the most practical (cheapest) thing would be to have one convertor
for the whole shop, asuming that you might eventually have multiple
devices with 3-phase motors.


Yep -- and if you have a single machine which can seriously
benefit from the variable speed, put a VFD on that one item. That can
be powered from a rotary converter, or from a single-phase line, with
the possibility that you will want a slightly higher rating (depending
on the manufacturer and model) to run it from single-phase.

The way I understand it, the alternatives go something like this.

1. Static rotory converter, simple, only gives 2/3 power, probably costs
around $100 for under 5 hp. Probably could be shared by several machines.


Static and rotary don't belong in the same breath. A "static
converter" is (usually) a set of starting capacitor and a
voltage-sensitive relay which uses the capacitor to only start the motor
spinning in the proper direction, and then switches it out. (There are
some versions which have tapped inductors as part of the system which is
a bit more flexible, but a *lot* more expensive. The static converter's
drawbacks a

a) Only gives you 2/3 of the motor's nameplate horsepower
as you have already noted.

b) The voltage-sensitive relay and the sizing of the
capacitors is right for only a narrow range of
horsepower, and may also have problems starting a motor
under load. If you have multiple tools with differing
horsepowers, you may not be able to use a single static
converter for all of them.

One advantage is that is is probably the least expensive bought
purely at *new* prices.

Another is that it can be used as part of a rotary converter
built from an old motor -- used to start the motor.

2. Rotary converter - full power, could be cheap if you use an old 3
phase motor to make your own, or more expensive if you buy one new.
Could be noisy. Often shared by multiple machines.


There are techniques for starting them other than the one
mentioned under "static converter", including:

a) "self-starting": where the tuning capacitors are a
compromise value which gets the motor spinning without
any switching at all.

b) "Pony motor": A smaller motor is connected with belt
to the converter motor, to get it started spinning, and
then the belt is thrown by raising the pony motor to
slack the belt.

c) A pull rope, used to start the motor spinning, just
before switching on the power.

Note that a rotary converter is better made self starting, either
from the inclusion of the parts of a static converter, or from
self-starting capacitor balance. One reason for this is that if
you walk out of the shop leaving something running (even just
the rotary converter), and power drops for long enough for the
converter to spin down, when it returns, the motor will sit
there humming and drawing excess current. If the circuit
breakers are properly sized, it will pop the breaker.
Otherwise, it might fry the motor without a self-starting mode.

Note also that a rotary converter can be made better (for a
given size) by "tuning" (the addition of run capacitors -- not
the starting capacitors) to optimize the balance of voltages and
currents in the generated phase to match the other two.

An additional step beyond tuning is a power-factor correction
capacitor across the line power leads coming into the converter,
best done *after* the rest of the tuning. This minimizes the
out-of-phase current which flows into the idler motor, which may
not affect your electricity costs with home power, though it can
if you are being charged commercial rates. However, it *can*
trip circuit breakers if you are close to the rating, which can
be a nuisance.


3. Phase inverter - solid state, I think that you said $700. I think
that you said that they could be shared, but you lose some of the
sophisticated features in that case.


Hmm ... not sure about this -- I think that it is the same as a
VFD, and the prices need not be that high -- unless you are into
the serious horsepower range. That is probably a brand-new
price for the current model -- which is more than you need.

4. Variable Frequency Drive - the top of the line solution, provides
electronic variable speed control. I would assume the top price. I
would guess that with some machines, you might want to run part of the
machine with the VFD, while running other parts with straight 3-phase
power, like the controls. It would seem unlikely that one would share
the VFD, but maybe some people do.


I have shared one VFD -- but it is an oversize one for my shop.
It is a 30A one (7.5 HP running from single phase). However, I
now have individual VFDs on a per-machine basis.

One way to avoid running to the corner for each change is to
remote the controls. Most VFDs have terminals which offer you
the ability to stop it, start it in forward or reverse, and
adjust the speed with a potentiometer. These wires should be
run in a shielded cable -- especially if the reach is more than
just a few feet. Just make the cable long enough to reach to
the worst-case location machine.

Note that you *don't* want to switch the motor leads at the
machine when running from a VFD, as the spikes created can zap
the output transistors. Instead, you command the VFD to start,
stop, and reverse -- ideally from controls mounted on the
machine.

If there are electronics on the machine (e.g. a CNC machine, or
one equipped with a DRO, you do *not* want to power those parts
through the VFD, as they may not handle the variable frequency
gracefully -- let alone the variable voltage which comes with
the slower speeds.

What is the price range here?


I'll let others specify the prices of the other systems, and I
will deal with the kind of prices which *can* be found for VFDs -- if
you are lucky, and don't insist on new. That 30A VFD which I mentioned
above cost me $100.00 -- at a hamfest perhaps five years ago.

The other VFDs that I have cost around $300.00 each (some
adjustment, as one was 3HP and the other 2HP rated running from single
phase). These were when a local individual, looking for a VFD to power
his own machines, got to talking with Mitsubishi USA at the right time.
It turns out that the had just come out with a new line, slightly
smaller footprint, and a few more features (beyond what is needed for a
HSM type -- more for industrial controls). He was able to buy a large
number of them for a good bulk price, and was selling them locally for
equally good prices.

Then, someone at Mitsubishi got the idea of selling the VFDs on
eBay -- usually bringing in more money, though still well below the
price of the current models.

There are at least two web locations which sell VFDs -- both
used, and new, for good prices. The one which I remember is
http://www.dealerselectric.com. I'm sure that someone else will point
to the other source.

A VFD from one of these sources (even eBay) can cost you less
than a commercially-built rotary converter, though unless you luck into
one at a hamfest as I did, it will be hard to beat the price of a rotary
built from used parts.

Which of these solutions can be shared
between multiple devices? Am I wrong about what I said above? I am
trying to make sure that I understand.


Most of the above *can* be shared -- with some compromises with
some. For running multiple machines, a good oversized rotary converter
is probably the best bet. A "static converter" is the least likely to
be a good choice for this, especially if you have a wide range of
horsepower ratings for your machines. A VFD can work, with the remoted
control box, as long as you don't need to run more than one machine at a
time, but it can be a nuisance as you move from machine to machine.

Now to see what others have posted.

Good Luck,
DoN.



--
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  #19   Report Post  
Gary Coffman
 
Posts: n/a
Default Motor Phases

On 21 Oct 2003 23:20:39 -0400, (DoN. Nichols) wrote:
2. Rotary converter - full power, could be cheap if you use an old 3
phase motor to make your own, or more expensive if you buy one new.
Could be noisy. Often shared by multiple machines.


There are techniques for starting them other than the one
mentioned under "static converter", including:

a) "self-starting": where the tuning capacitors are a
compromise value which gets the motor spinning without
any switching at all.

b) "Pony motor": A smaller motor is connected with belt
to the converter motor, to get it started spinning, and
then the belt is thrown by raising the pony motor to
slack the belt.


No need to throw the belt, just switch the power off to the pony and let
it freewheel.

c) A pull rope, used to start the motor spinning, just
before switching on the power.

Note that a rotary converter is better made self starting, either
from the inclusion of the parts of a static converter, or from
self-starting capacitor balance. One reason for this is that if
you walk out of the shop leaving something running (even just
the rotary converter), and power drops for long enough for the
converter to spin down, when it returns, the motor will sit
there humming and drawing excess current. If the circuit
breakers are properly sized, it will pop the breaker.
Otherwise, it might fry the motor without a self-starting mode.


Always use a contactor to supply power to the rotary. The contactor
is activated with a momentary push button, then it is held in by auxillary
contacts on the contactor. If the power fails, the contactor releases,
and won't re-engage until you push the start button again. This way,
if the power fails, the converter will be *cold* until you manually restart
it after the power returns. You'll also want a normally closed push
button in series with the contactor coil. This is your stop button.

Gary
  #20   Report Post  
jim rozen
 
Posts: n/a
Default Motor Phases

In article , Gary Coffman says...

No need to throw the belt, just switch the power off to the pony and let
it freewheel.


I remove the belt, Gary, because it reduces the noise output
of the converter setup by about a factor of three. The
belt and pony motor spinning makes a fair racket.

Always use a contactor to supply power to the rotary. The contactor
is activated with a momentary push button, then it is held in by auxillary
contacts on the contactor. If the power fails, the contactor releases,
and won't re-engage until you push the start button again. This way,
if the power fails, the converter will be *cold* until you manually restart
it after the power returns. You'll also want a normally closed push
button in series with the contactor coil. This is your stop button.


This is also excellent advice. Unless one is willing
to be absolutely fanatic about never leaving a converter
that is not controlled by a contactor, it's the way to go.

If a large idler motor spins down and then power is re-applied,
there's going to be some smoke, someplace. If one is lucky,
it will be in the fuses or circuit breakers.

Jim

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  #21   Report Post  
Gary Coffman
 
Posts: n/a
Default Motor Phases

On 22 Oct 2003 11:23:48 -0700, jim rozen wrote:
In article , Gary Coffman says...

No need to throw the belt, just switch the power off to the pony and let
it freewheel.


I remove the belt, Gary, because it reduces the noise output
of the converter setup by about a factor of three. The
belt and pony motor spinning makes a fair racket.


My converter uses a 15 hp idler, and the pony is a 3/4 hp
single phase motor. Frankly, I can't tell the difference with
the belt on or off. Most of the windage is in the big idler.

Because the running speeds of the two motors aren't exactly
the same, there's a bit of a squeal when the big idler first gets
power and the pony is switched off (I have the switches
interlocked). But that's all.

Gary
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