Can somone post a link to a description of how 3 phaze power works. My
brother is looking at buying a Felder combination woodworking machine
with 3 4kw motors in 3 phaze and while we both worked for an
electrician as kids we never worked with 3 phaze. If he buys it he's
planing on buying a converter as he can't get 3 phaze power at his
place. He worked in a shop with converter while in college but has
never had to set one up.
Thanks
Karl

wrote in message
...
Can somone post a link to a description of how 3 phaze power works. My
brother is looking at buying a Felder combination woodworking machine
with 3 4kw motors in 3 phaze and while we both worked for an
electrician as kids we never worked with 3 phaze. If he buys it he's
planing on buying a converter as he can't get 3 phaze power at his
place. He worked in a shop with converter while in college but has
never had to set one up.
Thanks
Karl

Hi Karl

Try searching for Three Phase Power in Wikipedia.

Bob Swinney (of this group) can tell you how Rotary Converters work if
you want to make your own 3 phase from a single phase source.

Jerry

On Feb 11, 5:49 pm, "Jerry" wrote:
wrote in message

...

Can somone post a link to a description of how 3 phaze power works. My
brother is looking at buying a Felder combination woodworking machine
with 3 4kw motors in 3 phaze and while we both worked for an
electrician as kids we never worked with 3 phaze. If he buys it he's
planing on buying a converter as he can't get 3 phaze power at his
place. He worked in a shop with converter while in college but has
never had to set one up.
Thanks
Karl

Hi Karl

Try searching for Three Phase Power in Wikipedia.

Bob Swinney (of this group) can tell you how Rotary Converters work if
you want to make your own 3 phase from a single phase source.

Jerry

Will do. Didn't think of that. I asked my brother if he was going to
make a converter but he's looking at buying an electronic one.
Thanks
Karl

wrote in message
...
On Feb 11, 5:49 pm, "Jerry" wrote:
wrote in message

...

Can somone post a link to a description of how 3 phaze power works. My
brother is looking at buying a Felder combination woodworking machine
with 3 4kw motors in 3 phaze and while we both worked for an
electrician as kids we never worked with 3 phaze. If he buys it he's
planing on buying a converter as he can't get 3 phaze power at his
place. He worked in a shop with converter while in college but has
never had to set one up.
Thanks
Karl

Hi Karl

Try searching for Three Phase Power in Wikipedia.

Bob Swinney (of this group) can tell you how Rotary Converters work if
you want to make your own 3 phase from a single phase source.

Jerry

Will do. Didn't think of that. I asked my brother if he was going to
make a converter but he's looking at buying an electronic one.
Thanks
Karl

Hi Karl

I support your brother's decission to buy an "electronic one". I suspect
it will be a device that starts the 3 phase motor spinning then allows the
motor to run on single phase. A 3 phase motor will supply nearly full power
when running on single phase, but it will stall much more easily than when
it has 3 phase power.
If all 3 of your 4 KW motors are spinning at the same time from the same
power connection, you will have made your own 3 phase power within the
unit's wiring anyway.

Jerry

Jerry wrote:

A 3 phase motor will supply nearly full power
when running on single phase, but it will stall much more easily than when
it has 3 phase power.

I see a slight contradiction in this statement.


If all 3 of your 4 KW motors are spinning at the same time from the same
power connection, you will have made your own 3 phase power within the
unit's wiring anyway.

And you only have to feed in 1/3 of the wattage.
Quick, quick! To the patent-office! :-)


Nick
--
The lowcost-DRO:
http://www.yadro.de

"Nick Mueller" wrote in message
...
Jerry wrote:

A 3 phase motor will supply nearly full power
when running on single phase, but it will stall much more easily than
when
it has 3 phase power.

I see a slight contradiction in this statement.


If all 3 of your 4 KW motors are spinning at the same time from the same
power connection, you will have made your own 3 phase power within the
unit's wiring anyway.

And you only have to feed in 1/3 of the wattage.
Quick, quick! To the patent-office! :-)


Nick
--
The lowcost-DRO:
http://www.yadro.de

Hi Nick

I recognize that you are a smart guy, so there is a misunderstanding.
I say that a 3 phase motor can deliver nearly its full name plate rated
power to the load when it is running from a single phase power source. I
suspect that you agree.
I say that a 3 phase motor will stall more easily when running from a
single phase power source than when running from a 3 phase power source.
You certainly agree with that.

I considered that when one of the three motors is spinning, it becomes a
"rotary converter" for the other motors. My thought was (is) when the
system of 3 motors are included in one machine, not all will be loaded
simultaneously. That assumption could easily be an error.

I am open to learn. Where is my thinking wrong?

Jerry

Jerry

On Feb 12, 11:20 am, "Jerry" wrote:
"Nick Mueller" wrote in message

...



Jerry wrote:

A 3 phase motor will supply nearly full power
when running on single phase, but it will stall much more easily than
when
it has 3 phase power.

I see a slight contradiction in this statement.

If all 3 of your 4 KW motors are spinning at the same time from the same
power connection, you will have made your own 3 phase power within the
unit's wiring anyway.

And you only have to feed in 1/3 of the wattage.
Quick, quick! To the patent-office! :-)

Nick
--
The lowcost-DRO:
http://www.yadro.de

Hi Nick

I recognize that you are a smart guy, so there is a misunderstanding.
I say that a 3 phase motor can deliver nearly its full name plate rated
power to the load when it is running from a single phase power source. I
suspect that you agree.
I say that a 3 phase motor will stall more easily when running from a
single phase power source than when running from a 3 phase power source.
You certainly agree with that.

I considered that when one of the three motors is spinning, it becomes a
"rotary converter" for the other motors. My thought was (is) when the
system of 3 motors are included in one machine, not all will be loaded
simultaneously. That assumption could easily be an error.

I am open to learn. Where is my thinking wrong?

Jerry

Jerry

the unloaded RPC motor acts as an LC network and creates the needed
phase shift.

the RPC motor is not being used as it was originally intended as a
LOAD its being used to pass power through it and apply a phase shift
rather than to transform the power into mechanical energy.

The rpc will not generate the third leg properly until it is spinning
at speed. once it is spinning at speed it will take a tiny amount of
power to keep it spinning at speed but that will be insignificant
compared to the load

the 3 motors in the machine are running as loads and are taking power
out of the system rather than generating extra power on the third leg.
and should be treated as loads that remove power

3 Phase power is very desirable. Motors do not suffer velocity modulation
like single single phase motors do and they are more efficient. I am
American, but live in Europe where most homes are fed with 3 phase. It is
wonderful. When I return to the US, I will do my damdest to live where 3
phase is available, but having said that, I do appreciate the single phase
dilemma in the US. My solution would be a Motor Generator set where I would
run a large single phase motor and drive a 3 phase alternator with a very
large flywheel in between. These are very efficient and infinitely more
reliable than an electronic phase converter, as they are very prone to back
EMF caused switch failures with the large inductive loads. I know the
puritans in the group may flame my solution because by using an inductive
motor as a rotory source wwould create a secondary frequency 10% slow due to
inductive slip, but my experience using 60 Hz motors on 50 Hz power has
proven that it works flawlessly and it is definitly the least expensive
solution. Remember that all converters imitate the third phase, but do not
drive the motor in a balanced condition, as this manufactured phase is only
a helper.
Steve


wrote in message
...
Can somone post a link to a description of how 3 phaze power works. My
brother is looking at buying a Felder combination woodworking machine
with 3 4kw motors in 3 phaze and while we both worked for an
electrician as kids we never worked with 3 phaze. If he buys it he's
planing on buying a converter as he can't get 3 phaze power at his
place. He worked in a shop with converter while in college but has
never had to set one up.
Thanks
Karl

"Steve Lusardi" wrote:

3 Phase power is very desirable. Motors do not suffer velocity modulation
like single single phase motors do and they are more efficient. I am
American, but live in Europe where most homes are fed with 3 phase. It is
wonderful.

Most of us would kill for 3ph in the home. It would also make breaker boxes
for industial settings a hell of a lot cheaper.


When I return to the US, I will do my damdest to live where 3
phase is available, but having said that, I do appreciate the single phase
dilemma in the US. My solution would be a Motor Generator set where I would
run a large single phase motor and drive a 3 phase alternator with a very
large flywheel in between. These are very efficient and infinitely more
reliable than an electronic phase converter, as they are very prone to back
EMF caused switch failures with the large inductive loads. I know the
puritans in the group may flame my solution because by using an inductive
motor as a rotory source wwould create a secondary frequency 10% slow due to
inductive slip, but my experience using 60 Hz motors on 50 Hz power has
proven that it works flawlessly and it is definitly the least expensive
solution. Remember that all converters imitate the third phase, but do not
drive the motor in a balanced condition, as this manufactured phase is only
a helper.


I don't know about that slip thing but a motor / generator with a fly wheel
sure would keep the lights from dimming when you switched on your industrial
sized machine out in the back yard polebarn.

Of course that presents the problem where you start up the gen set. Having
worked with a number of mechanical die cut presses, spinning up the flywheel
is the MOAL (mother of all loads). So now you need a soft start VFD as an
input to the motor/genset. Most HSM'ers would just skip the genset and use
the VFD.


Wes

Heh, I remember an 8'x1" capacity shear with a 20 HP motor and the MOAL
flywheel. Had a manual starter: a 2' long lever that you flipped one way
to energize the start windings, wait about 15 seconds then flip it the
other way to energize the run windings. If you needed a break, just make
sure to not wait quite long enough, it would blow the fuses on the run
windings. Of course that meant having to put up with the plant
electrician giving you an earful about your origin, habits, morals, and
destination but a break is a break.
Of course that presents the problem where you start up the gen set. Having
worked with a number of mechanical die cut presses, spinning up the flywheel
is the MOAL (mother of all loads). So now you need a soft start VFD as an
input to the motor/genset. Most HSM'ers would just skip the genset and use
the VFD.


Wes

"Brent" wrote in message
...
On Feb 12, 11:20 am, "Jerry" wrote:
"Nick Mueller" wrote in message

...



Jerry wrote:

A 3 phase motor will supply nearly full power
when running on single phase, but it will stall much more easily than
when
it has 3 phase power.

I see a slight contradiction in this statement.

If all 3 of your 4 KW motors are spinning at the same time from the
same
power connection, you will have made your own 3 phase power within the
unit's wiring anyway.

And you only have to feed in 1/3 of the wattage.
Quick, quick! To the patent-office! :-)

Nick
--
The lowcost-DRO:
http://www.yadro.de

Hi Nick

I recognize that you are a smart guy, so there is a misunderstanding.
I say that a 3 phase motor can deliver nearly its full name plate rated
power to the load when it is running from a single phase power source. I
suspect that you agree.
I say that a 3 phase motor will stall more easily when running from a
single phase power source than when running from a 3 phase power source.
You certainly agree with that.

I considered that when one of the three motors is spinning, it becomes
a
"rotary converter" for the other motors. My thought was (is) when the
system of 3 motors are included in one machine, not all will be loaded
simultaneously. That assumption could easily be an error.

I am open to learn. Where is my thinking wrong?

Jerry

Jerry

the unloaded RPC motor acts as an LC network and creates the needed
phase shift.

the RPC motor is not being used as it was originally intended as a
LOAD its being used to pass power through it and apply a phase shift
rather than to transform the power into mechanical energy.

The rpc will not generate the third leg properly until it is spinning
at speed. once it is spinning at speed it will take a tiny amount of
power to keep it spinning at speed but that will be insignificant
compared to the load

the 3 motors in the machine are running as loads and are taking power
out of the system rather than generating extra power on the third leg.
and should be treated as loads that remove power

Hi Brent

It isnt clear that the OP is considering a Rotary phase converter. A
converter is often a capacitor that is temporarily connected to the 'not
connected leg' of the 3 phase motor. Once the 3 phase motor is spinning, it
will run well with single phase input power while the third leg of the motor
disconnected.

3 phase motors run well when fed single phase, once they have "spun up" to
near their synchronous speed. A 3 phase motor running from single phase
will delliver very nearly its name plate reted power to a load.

Once one 3 phase motor is spinning, any additional motors connected in
parallel with them will see the "spun up" motor as its being a Rotary phase
converter with single phase power applied to their input.

Bob Swinney wrote a good article describing most of the theoritical
aspects of Rotary Converters.

Jerry

wrote:
On Feb 11, 5:49 pm, "Jerry" wrote:

wrote in message

...


Can somone post a link to a description of how 3 phaze power works. My
brother is looking at buying a Felder combination woodworking machine
with 3 4kw motors in 3 phaze and while we both worked for an
electrician as kids we never worked with 3 phaze. If he buys it he's
planing on buying a converter as he can't get 3 phaze power at his
place. He worked in a shop with converter while in college but has
never had to set one up.
Thanks
Karl

Hi Karl

Try searching for Three Phase Power in Wikipedia.

Bob Swinney (of this group) can tell you how Rotary Converters work if
you want to make your own 3 phase from a single phase source.

Jerry


Will do. Didn't think of that. I asked my brother if he was going to
make a converter but he's looking at buying an electronic one.
Thanks
Karl

If you have to ask, you probably really don't want to be mucking with
the making of a rotary phase converter anyways.

The vast majority of what you need to know, is that there are three
wires running into the motor, and if you disconnect two of them and hook
those two up in reverse to where they started, it will cause the motor
to run in the opposite direction to the one it was.

A VFD (Variable Frequency Drive) is a pretty wise choice, if you are
not already fairly familiar with, and well stocked with, three phase
motors. Cost is pretty close to or sometimes less than having to buy a
motor and capacitors to use, as well as the requisite switchgear. If you
can read a simple diagram, and follow it up with connecting the wiring
as per, you should have no troubles. If the VFD is used to simply supply
fixed frequency three phase power off the single phase input, you need
not give it a lot of effort in locating it. With three motors to feed
power to, I would suspect this is the way planned.
If you wish to use the "variable" part of the VFD name, consider where
it will be located, and how the inputs are to be fed to the terminals as
required. Tou could, possibly, incorporate the contlols into a pendant
on the end of a cable that would allow the use of the variable speed
feature as desired, when it is appropriate, and use just fixed speed
when it is a better choice.

If you search Ebay for the phrase "VFD" many of the vendors link to
the makers sites where the manuals can be downloaded from. Worth looking
at a few. They will give you an idea of how simply or complicated it can
be made to be.

Cheers
Trevor Jones

I use a rotary 3-phase and it works nicely. I drive transformers with it
to step-up transformers.

There is so much 2 phase around and in backyards I'm surprised he can't
get the power company to set up a set of transformers for him. I suppose
it is money.


Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


wrote:
On Feb 11, 5:49 pm, "Jerry" wrote:
wrote in message

...

Can somone post a link to a description of how 3 phaze power works. My
brother is looking at buying a Felder combination woodworking machine
with 3 4kw motors in 3 phaze and while we both worked for an
electrician as kids we never worked with 3 phaze. If he buys it he's
planing on buying a converter as he can't get 3 phaze power at his
place. He worked in a shop with converter while in college but has
never had to set one up.
Thanks
Karl
Hi Karl

Try searching for Three Phase Power in Wikipedia.

Bob Swinney (of this group) can tell you how Rotary Converters work if
you want to make your own 3 phase from a single phase source.

Jerry

Will do. Didn't think of that. I asked my brother if he was going to
make a converter but he's looking at buying an electronic one.
Thanks
Karl

Jerry wrote:


I say that a 3 phase motor can deliver nearly its full name plate rated
power to the load when it is running from a single phase power source. Â*I
suspect that you agree.

No. It only draws 1/3 of the current (only one leg connected). Albeit, the
speed is the same.

I say that a 3 phase motor will stall more easily when running from a
single phase power source than when running from a 3 phase power source.
You certainly agree with that.

I a agree. And it stalls easier, because it only has 1/3 the power. You
can't say it has the same power and at the same time say that it stalls
easier.

I considered that when one of the three motors is spinning, it becomes a
"rotary converter" for the other motors.

Draw a diagram how the legs are connected. You'll see that all
the "generator legs" of the same phase are interconnected. If you think
that one leg of one motor is generating power for an other motor, you
invented a perpetuum mobile.


Nick
--
The lowcost-DRO:
http://www.yadro.de

On Feb 12, 1:56 pm, "Jerry" wrote:
"Brent" wrote in message

...



On Feb 12, 11:20 am, "Jerry" wrote:
"Nick Mueller" wrote in message

...

Jerry wrote:

A 3 phase motor will supply nearly full power
when running on single phase, but it will stall much more easily than
when
it has 3 phase power.

I see a slight contradiction in this statement.

If all 3 of your 4 KW motors are spinning at the same time from the
same
power connection, you will have made your own 3 phase power within the
unit's wiring anyway.

And you only have to feed in 1/3 of the wattage.
Quick, quick! To the patent-office! :-)

Nick
--
The lowcost-DRO:
http://www.yadro.de

Hi Nick

I recognize that you are a smart guy, so there is a misunderstanding.
I say that a 3 phase motor can deliver nearly its full name plate rated
power to the load when it is running from a single phase power source. I
suspect that you agree.
I say that a 3 phase motor will stall more easily when running from a
single phase power source than when running from a 3 phase power source.
You certainly agree with that.

I considered that when one of the three motors is spinning, it becomes
a
"rotary converter" for the other motors. My thought was (is) when the
system of 3 motors are included in one machine, not all will be loaded
simultaneously. That assumption could easily be an error.

I am open to learn. Where is my thinking wrong?

Jerry

Jerry

the unloaded RPC motor acts as an LC network and creates the needed
phase shift.

the RPC motor is not being used as it was originally intended as a
LOAD its being used to pass power through it and apply a phase shift
rather than to transform the power into mechanical energy.

The rpc will not generate the third leg properly until it is spinning
at speed. once it is spinning at speed it will take a tiny amount of
power to keep it spinning at speed but that will be insignificant
compared to the load

the 3 motors in the machine are running as loads and are taking power
out of the system rather than generating extra power on the third leg.
and should be treated as loads that remove power

Hi Brent

It isnt clear that the OP is considering a Rotary phase converter. A
converter is often a capacitor that is temporarily connected to the 'not
connected leg' of the 3 phase motor. Once the 3 phase motor is spinning, it
will run well with single phase input power while the third leg of the motor
disconnected.

3 phase motors run well when fed single phase, once they have "spun up" to
near their synchronous speed. A 3 phase motor running from single phase
will delliver very nearly its name plate reted power to a load.

Once one 3 phase motor is spinning, any additional motors connected in
parallel with them will see the "spun up" motor as its being a Rotary phase
converter with single phase power applied to their input.

Bob Swinney wrote a good article describing most of the theoritical
aspects of Rotary Converters.

Jerry

My brother is planing to use one of these of suitable size.
http://www.grizzly.com/products/Stat...-to-7-HP/G5843
Thanks everyone.
Karl

On Tue, 12 Feb 2008 20:22:36 +0100, "Steve Lusardi"
wrote:

3 Phase power is very desirable. Motors do not suffer velocity modulation
like single single phase motors do and they are more efficient. I am
American, but live in Europe where most homes are fed with 3 phase.

Despite you saying you live in Europe, presumably Germany from your
email address I'm not sure where you get the idea that most homes in
Europe are fed with three phase. Some commercial and most industrial
premises are, almost all single occupancy homes aren't, the only real
exceptions are homes that are heated by electricity. Given the cost
of generation with fossil fuels this tends to be those with a
significant proportion of hydro such as Norway.


--

Mike wrote:

address I'm not sure where you get the idea that most homes in
Europe are fed with three phase.

At least that holds true for Germany.
Many don't know that they do have three phases, but a (closer) look at their
fuse box shows it.


Nick
--
The lowcost-DRO:
http://www.yadro.de

"Nick Mueller" wrote in message
...
Jerry wrote:


I say that a 3 phase motor can deliver nearly its full name plate rated
power to the load when it is running from a single phase power source. I
suspect that you agree.
No. It only draws 1/3 of the current (only one leg connected). Albeit, the
speed is the same.


I say that a 3 phase motor will stall more easily when running from a
single phase power source than when running from a 3 phase power source.
You certainly agree with that.

I a agree. And it stalls easier, because it only has 1/3 the power. You
can't say it has the same power and at the same time say that it stalls
easier.

I considered that when one of the three motors is spinning, it becomes a
"rotary converter" for the other motors.

Draw a diagram how the legs are connected. You'll see that all
the "generator legs" of the same phase are interconnected. If you think
that one leg of one motor is generating power for an other motor, you
invented a perpetuum mobile.


Nick
--
The lowcost-DRO:
http://www.yadro.de

Hi Nick

You've made some sort of mistake here somewhere. Thats not your usual
style. Ou, maybe I misunderstand what you are stating when you write "No.
It only draws 1/3 of the current (only one leg connected). Albeit, the
speed is the same."
When a 3 phase motor is running with 2 of it's 3 wires connected to single
phase power, it can be loaded to deliver nearly its FULL name plate rated
power. That means that alot more than 1/3 of the currentfrom the single
phase power.

Nick, I cant draw a diagram of that machine with three, 3 phase motors.
He certainly hasnt posted a diagram. I considered that when one motor is
running after being easily "spun up", it becomes a Rotary Converter for the
other two motors. A 3 phase motor can deliver more than it's name plate
rated power when connected to a Rotary Converter with single phase input
power.

I wonder why you write statements like you do that seem to mock my
statements. Do you think I am stupid? Do you actually think any of
the information I have posted is wrong? Sure, I often make errors while
trying to explain things, but I dont yet recognize any mistakes in any of my
posts to this thread. You might take some time to think about this Rotary
Converter stuff before writing about *my* errors.

Jerry

Jerry

Jerry wrote:

I considered that when one motor is
running after being easily "spun up", it becomes a Rotary Converter for
the other two motors.

You forgot, that the motor's shafts aren't connected. This is a saw (or
such) with three separate motors.
You have to draw a diagram how the three legs of the three motor are
connected. You don't want?
I'll describe it with words:

L1, L2, and L3 are the phases. M1, M2 and M3 are the motors.
L1 is the only phase available, so you connect it to M1L1. M2L1 and M3L3 are
open, because we don't want to let them run. OK so far?
Now the voltage generated in M1L2 and M1L3 goes where? Nowhere, because they
are not connected on M2 and M3 (because we don't want to let them run).

Now we let run all three motors at the same time.
Connections:
M1L1 to M2L1 and M3L1
M1L2 to M2L2 and M3L2
and
M1L3 to M2L3 and M3L3

Now the voltage generated in M1L2 is feed into M2L2 and M3L2 (same for L3).
But at the same time M2 and M3 generate voltage at L2. Now do you really
think that one motor can drive L2 and L3 of the two other motors and at the
same time doesn't lose any energy?
Note that I disregarded losses and was talking about an ideal machine.


Do you actually think any of
the information I have posted is wrong?

Absolutely. :-)

You might take some time to think about this
Rotary Converter stuff before writing about *my* errors.

This ain't a rotary converter!
OP cite:
| ... is looking at buying a Felder combination woodworking
| machine with 3 4kw motors in 3 phaze ...


Nick
--
The lowcost-DRO:
http://www.yadro.de

Nick Mueller wrote:

Mike wrote:

address I'm not sure where you get the idea that most homes in
Europe are fed with three phase.

At least that holds true for Germany.
Many don't know that they do have three phases, but a (closer) look at their
fuse box shows it.


Fuse box? How last millennium!


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

On Feb 11, 7:31*pm, " wrote:
Can somone post a link to a description of how 3 phaze power works. My
brother is looking at buying a Felder combination woodworking machine
with 3 4kw motors in 3 phaze and while we both worked for an
electrician as kids we never worked with 3 phaze. If he buys it he's
planing on buying a converter as he can't get 3 phaze power at his
place. He worked in a shop with converter while in college but has
never had to set one up.
Thanks
Karl

The easiest way to produce 3 phase is to get a 3 phase motor of
about double the capacity that you will need. This motor can then be
"spun up" to the point that single phase (220 in the US) will drive
it. This static motor will create a third phase that is connected to
the 3phase or 'rotary' machine in question.
In the system I use, there are some buck/boost transformers and
'run' type capacitors, as I need very 'clean' 3 phase. This works
pretty well and the less demand/capacity equality you can build in the
better, a good case for overkill, as the larger 3phase motors are
relativly cheap. Things like large compressors need more of a 'fudge'
factor (I use the input from a 25hp to drive my 5hp 3 phase
compressor).
The older, bigger, 3 phase motors are better, as a lot of kinetic
energy in rotating mass is prone to smooth out the produced
electricty. I also advocate the use of pony motors to spin up the
initial 3 phase motor (any other motors in the system start off this-
do the big one first) instead of capacitors supplying the third leg...
especially in large systems!

Hope this helps
Dave G.

"Nick Mueller" wrote in message
...
Jerry wrote:

I considered that when one motor is
running after being easily "spun up", it becomes a Rotary Converter for
the other two motors.

You forgot, that the motor's shafts aren't connected. This is a saw (or
such) with three separate motors.
You have to draw a diagram how the three legs of the three motor are
connected. You don't want?
I'll describe it with words:

L1, L2, and L3 are the phases. M1, M2 and M3 are the motors.
L1 is the only phase available, so you connect it to M1L1. M2L1 and M3L3
are
open, because we don't want to let them run. OK so far?
Now the voltage generated in M1L2 and M1L3 goes where? Nowhere, because
they
are not connected on M2 and M3 (because we don't want to let them run).

Now we let run all three motors at the same time.
Connections:
M1L1 to M2L1 and M3L1
M1L2 to M2L2 and M3L2
and
M1L3 to M2L3 and M3L3

Now the voltage generated in M1L2 is feed into M2L2 and M3L2 (same for
L3).
But at the same time M2 and M3 generate voltage at L2. Now do you really
think that one motor can drive L2 and L3 of the two other motors and at
the
same time doesn't lose any energy?
Note that I disregarded losses and was talking about an ideal machine.


Do you actually think any of
the information I have posted is wrong?




Absolutely. :-)

You might take some time to think about this
Rotary Converter stuff before writing about *my* errors.

This ain't a rotary converter!
OP cite:
| ... is looking at buying a Felder combination woodworking
| machine with 3 4kw motors in 3 phaze ...


Nick
--
The lowcost-DRO:
http://www.yadro.de


Nick, this is silly. You are smart enough to figure this system out.
Why do you insist in not trying to understand. This guy with the three
motor machine only wants to run it on single phase. He doesnt need a
ROTARY CONVERTER. He even told us that he is planning on using a
http://www.grizzly.com/products/Stat...-to-7-HP/G5843.
That is a Static Phase Converter.

I have tried to draw your attention to the fact that each of the three
motors will have three wires, and he will have single phase power supplied
to only two of those wires in each motor. This is not complicated. The
machine has three independent 3 phase motors. Each is driven with single
phase.

I thought it could be beneficial that when one 3 phase motor is spinning
it provides a 3 phase voltage across it's three legs. That makes the first
motor to act as a rotary converter for the second motor.

I thought it would help the OP to know that his 3 phase motors will
deliver nearly full name plate rated power to their loads even when it is
powered by single phase to only two of it's three leads.

You wrote that I dont want to draw a diagram of this machine. You cant
either unless you know something that isnt written in this thread. I dont
know if the motors run simultaneously or in sequence. How do you know how
the motors are wired??? I ask you to think about what you write before you
complain about any mistakes *I* have made. Or, of course, you are invited
to tell me precisely where I have written something that *is* in error.

Jerry

On 2008-02-13, wrote:
On Feb 12, 1:56 pm, "Jerry" wrote:

[ ... ]

It isnt clear that the OP is considering a Rotary phase converter. A
converter is often a capacitor that is temporarily connected to the 'not
connected leg' of the 3 phase motor. Once the 3 phase motor is spinning, it
will run well with single phase input power while the third leg of the motor
disconnected.

[ ... ]

My brother is planing to use one of these of suitable size.
http://www.grizzly.com/products/Stat...-to-7-HP/G5843
Thanks everyone.

What he is planning to use, then, is the equivalent of a
capacitor temporarily connected to to the "not connected" leg of the
motor. This gets it spinning in the right direction and then
disconnects.

The sure indicator here is the range of horsepowers (instead of
"up to X horsepower). This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly. (Of course, the
word "Static" in the name is another clue.

You can perhaps get nearly full horsepower from the motor with
this, but at the cost of running one winding at a much higher current
than it was designed for. It would be more likely to burn out if run at
this level for quite a while, though you can get away with it for short
spurts.

And this is not what *I* would call an "electronic converter".

If you want to do it right, the better way to go (other than
making a rotary converter) is to get a VFD (Variable Frequency Drive), a
truly electronic device which converts the incoming power (single phase
or three phase) to a high DC voltage, and then converts that to true
three phase -- with the added boon of generating the three phase at a
frequency of your choice, so you can run the motor significantly slower
or significantly faster.

When running significantly slower (say about 25% of full speed
or so) you do have the problem that the internal fan in the motor won't
keep it cool enough, but if you wish to run it at such slow speeds for
long periods, you can add an external fan to keep it cool enough. Just
mount it to blow into one end (in the same direction that the internal
fan blows) and you are fine.

I forget what kind of machine tool this was to be used with, but
quite a few benefit from the ability to tune the speed to the task at
hand. For example metal lathes can produce variations in finish quality
as you face from outside towards center or vice versa. The reason for
this is that at certain surface speeds you get buildup of metal on the
cutting tool which will eventually break clear and give good finish for
a short while before building up again. If you can turn the spindle
speed up as you face in towards the center, or down as you face out from
the center to the outside, you can tune away from the speeds which give
the problem. And this is something which you can't do with a step
pulley, since stopping to change belt steps would change the finish at
the point of the stop. (Though if you have a variable speed pulley, you
can do quite well with this.)

I personally would not use a "Static" phase converter, and would
choose either a rotary converter (home shop made) or a VFD (commercially
made). Since I have three VFDs and no Static phase converters, you can
see that I live by that.

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 ---

"DoN. Nichols" wrote in message
...
On 2008-02-13, wrote:
On Feb 12, 1:56 pm, "Jerry" wrote:

[ ... ]

It isnt clear that the OP is considering a Rotary phase converter. A
converter is often a capacitor that is temporarily connected to the 'not
connected leg' of the 3 phase motor. Once the 3 phase motor is
spinning, it
will run well with single phase input power while the third leg of the
motor
disconnected.

[ ... ]

My brother is planing to use one of these of suitable size.
http://www.grizzly.com/products/Stat...-to-7-HP/G5843
Thanks everyone.

What he is planning to use, then, is the equivalent of a
capacitor temporarily connected to to the "not connected" leg of the
motor. This gets it spinning in the right direction and then
disconnects.

The sure indicator here is the range of horsepowers (instead of
"up to X horsepower). This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly. (Of course, the
word "Static" in the name is another clue.

You can perhaps get nearly full horsepower from the motor with
this, but at the cost of running one winding at a much higher current
than it was designed for. It would be more likely to burn out if run at
this level for quite a while, though you can get away with it for short
spurts.

And this is not what *I* would call an "electronic converter".

If you want to do it right, the better way to go (other than
making a rotary converter) is to get a VFD (Variable Frequency Drive), a
truly electronic device which converts the incoming power (single phase
or three phase) to a high DC voltage, and then converts that to true
three phase -- with the added boon of generating the three phase at a
frequency of your choice, so you can run the motor significantly slower
or significantly faster.

When running significantly slower (say about 25% of full speed
or so) you do have the problem that the internal fan in the motor won't
keep it cool enough, but if you wish to run it at such slow speeds for
long periods, you can add an external fan to keep it cool enough. Just
mount it to blow into one end (in the same direction that the internal
fan blows) and you are fine.

I forget what kind of machine tool this was to be used with, but
quite a few benefit from the ability to tune the speed to the task at
hand. For example metal lathes can produce variations in finish quality
as you face from outside towards center or vice versa. The reason for
this is that at certain surface speeds you get buildup of metal on the
cutting tool which will eventually break clear and give good finish for
a short while before building up again. If you can turn the spindle
speed up as you face in towards the center, or down as you face out from
the center to the outside, you can tune away from the speeds which give
the problem. And this is something which you can't do with a step
pulley, since stopping to change belt steps would change the finish at
the point of the stop. (Though if you have a variable speed pulley, you
can do quite well with this.)

I personally would not use a "Static" phase converter, and would
choose either a rotary converter (home shop made) or a VFD (commercially
made). Since I have three VFDs and no Static phase converters, you can
see that I live by that.

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 ---


Hi Don

Why do you write that a static converter with more capacity will have
difficulty starting a smaller motor?
I refer to your statement -
This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly.

Jerry

Jerry wrote:

I thought it could be beneficial that when one 3 phase motor is spinning
it provides a 3 phase voltage across it's three legs. Â*That makes the
first motor to act as a rotary converter for the second motor.

And that is simply wrong. I explained why. You can ignore it if you want.
Two questions to help you understand why you are wrong:
Q1: If only one motor is running and the other two standing still, how can
those two standing motors help to generate the missing phases, especially
considering that they are not connected (they are not running and you don't
want them to run)?

Q2; With all motors running, which motor is generating the missing phases
for which one? Is that M1 for M2 and M2 for M3 and M3 for M1? Or is it the
other way round? Or -in conclusion- how can a motor *at* *the* *same*
*time* both generate and consume the phases made by the other two motors?


You wrote that I dont want to draw a diagram of this machine. Â* Â*You cant
either unless you know something that isnt written in this thread.

Sure I can. There aren't that many possibilities how the motors are
connected to the power.

I dont know if the motors run simultaneously or in sequence.

I explained both scenarios and they both don't help/work.


I ask you to think about what you write
before you complain about any mistakes *I* have made. Â*Or, of course, you
are invited to tell me precisely where I have written something that *is*
in error.

Did you read my answer? What didn't you understand?
Doesn't help to continue the discussion that way.


Nick
--
The lowcost-DRO:
http://www.yadro.de

On Feb 13, 4:36 pm, "DoN. Nichols" wrote:
On 2008-02-13, wrote:

On Feb 12, 1:56 pm, "Jerry" wrote:

[ ... ]

It isnt clear that the OP is considering a Rotary phase converter. A
converter is often a capacitor that is temporarily connected to the 'not
connected leg' of the 3 phase motor. Once the 3 phase motor is spinning, it
will run well with single phase input power while the third leg of the motor
disconnected.

[ ... ]

My brother is planing to use one of these of suitable size.
http://www.grizzly.com/products/Stat...-to-7-HP/G5843
Thanks everyone.

What he is planning to use, then, is the equivalent of a
capacitor temporarily connected to to the "not connected" leg of the
motor. This gets it spinning in the right direction and then
disconnects.

The sure indicator here is the range of horsepowers (instead of
"up to X horsepower). This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly. (Of course, the
word "Static" in the name is another clue.

You can perhaps get nearly full horsepower from the motor with
this, but at the cost of running one winding at a much higher current
than it was designed for. It would be more likely to burn out if run at
this level for quite a while, though you can get away with it for short
spurts.

And this is not what *I* would call an "electronic converter".

If you want to do it right, the better way to go (other than
making a rotary converter) is to get a VFD (Variable Frequency Drive), a
truly electronic device which converts the incoming power (single phase
or three phase) to a high DC voltage, and then converts that to true
three phase -- with the added boon of generating the three phase at a
frequency of your choice, so you can run the motor significantly slower
or significantly faster.

When running significantly slower (say about 25% of full speed
or so) you do have the problem that the internal fan in the motor won't
keep it cool enough, but if you wish to run it at such slow speeds for
long periods, you can add an external fan to keep it cool enough. Just
mount it to blow into one end (in the same direction that the internal
fan blows) and you are fine.

I forget what kind of machine tool this was to be used with, but
quite a few benefit from the ability to tune the speed to the task at
hand. For example metal lathes can produce variations in finish quality
as you face from outside towards center or vice versa. The reason for
this is that at certain surface speeds you get buildup of metal on the
cutting tool which will eventually break clear and give good finish for
a short while before building up again. If you can turn the spindle
speed up as you face in towards the center, or down as you face out from
the center to the outside, you can tune away from the speeds which give
the problem. And this is something which you can't do with a step
pulley, since stopping to change belt steps would change the finish at
the point of the stop. (Though if you have a variable speed pulley, you
can do quite well with this.)

I personally would not use a "Static" phase converter, and would
choose either a rotary converter (home shop made) or a VFD (commercially
made). Since I have three VFDs and no Static phase converters, you can
see that I live by that.

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 ---

Thanks everybody. This should give him the info he needs to decide
what to do.
Karl

Nick, you arent worth my time. You are smart. You have shown that you are
a very capable guy. But, you seem to be closed to thinking that anyone else
can possibly be right unless they agree with you. You seem to have some
misconception that you your knowledge about running 3 phase motors from
single phase, is complete.

If you did have three 3 phase motors in a machine and all fed from one
single phase source, the first motor to spin up can act as the rotary
converter for the others. If you dispute that, you are hopeless.

Jerry (who could teach you something about Rotary
converters if you'd relax and listen carefully).





"Nick Mueller" wrote in message
...
Jerry wrote:

I thought it could be beneficial that when one 3 phase motor is spinning
it provides a 3 phase voltage across it's three legs. That makes the
first motor to act as a rotary converter for the second motor.

And that is simply wrong. I explained why. You can ignore it if you want.
Two questions to help you understand why you are wrong:
Q1: If only one motor is running and the other two standing still, how can
those two standing motors help to generate the missing phases, especially
considering that they are not connected (they are not running and you
don't
want them to run)?

Q2; With all motors running, which motor is generating the missing phases
for which one? Is that M1 for M2 and M2 for M3 and M3 for M1? Or is it the
other way round? Or -in conclusion- how can a motor *at* *the* *same*
*time* both generate and consume the phases made by the other two motors?


You wrote that I dont want to draw a diagram of this machine. You cant
either unless you know something that isnt written in this thread.

Sure I can. There aren't that many possibilities how the motors are
connected to the power.

I dont know if the motors run simultaneously or in sequence.

I explained both scenarios and they both don't help/work.


I ask you to think about what you write
before you complain about any mistakes *I* have made. Or, of course, you
are invited to tell me precisely where I have written something that *is*
in error.

Did you read my answer? What didn't you understand?
Doesn't help to continue the discussion that way.


Nick
--
The lowcost-DRO:
http://www.yadro.de

Jerry wrote:

If you did have three 3 phase motors in a machine Â*and all fed from one
single phase source, the first motor to spin up can act as the rotary
converter for the others. Â* If you dispute that, you are hopeless.

A cite from you:
|Â* If all 3 of your 4 KW motors are spinning at the same time from the
|Â* same power connection, you will have made your own 3 phase power within
|Â* the unit's wiring anyway.

Trying "the moving target-game" now?


Nick
--
The lowcost-DRO:
http://www.yadro.de

On 2008-02-14, Jerry wrote:

"DoN. Nichols" wrote in message
...

[ ... ]

The sure indicator here is the range of horsepowers (instead of
"up to X horsepower). This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly. (Of course, the
word "Static" in the name is another clue.

[ ... ]

Hi Don

Why do you write that a static converter with more capacity will have
difficulty starting a smaller motor?
I refer to your statement -
This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly.

Because the phase shift from the capacitor is a function of the
motor horsepower (and related inductance) the capacitance, and the
frequency. Since the frequency is fixed at either 60 Hz (here) or 50 Hz
(UK) we have the motor inductance/horsepower and the capacitance. Too
small a capacitor will not produce enough phase shift to get the motor
started quickly enough to avoid blowing the capacitor, and too large a
capacitor will generate too much phase shift, again resulting in very
slow motor starting and likely failure.

Note that the static converter was spec'd for a range of
horsepower (in the part of the article now trimmed), not "up to
such-and-so horsepower".

This is a common limitation for a static converter -- at least of
the capacitor and relay style. So -- if the machine tool has three
motors -- one 4 HP, one 2 HP and one 1/2 HP (say for perhaps spindle, feed,
and coolant pump), then while it may start the 4HP motor nicely, it will
fail to start the 1/2 HP coolant pump if that is needed first.
Obviously (in spite of what Nick thinks) once you have the spindle motor
running, it can start the others, but if you need the smallest to start
first (say it also pumps lubricant around to the bearings before you
start moving things) you may have problems. For this, really, an
external rotary converter would be a better bet. Let the static
converter start the rotary, and it can start all of the load motors with
no problems.

Obviously -- if it is a homebuilt static converter, or if the
owner is competent to open it up and replace the capacitor with the
appropriate size for the other motor, then this can be overcome.

Also -- if he is not careful to wire it so the real 240 VAC
comes in to the terminals which feed the control circuitry, he may not
be able to get the spindle motor to start with the static converter
alone.

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 ---

"DoN. Nichols" wrote in message
...
On 2008-02-14, Jerry wrote:

"DoN. Nichols" wrote in message
...

[ ... ]

The sure indicator here is the range of horsepowers (instead of
"up to X horsepower). This is because the capacitor needs to be sized
to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly. (Of course, the
word "Static" in the name is another clue.

[ ... ]

Hi Don

Why do you write that a static converter with more capacity will have
difficulty starting a smaller motor?
I refer to your statement -
This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly.

Because the phase shift from the capacitor is a function of the
motor horsepower (and related inductance) the capacitance, and the
frequency. Since the frequency is fixed at either 60 Hz (here) or 50 Hz
(UK) we have the motor inductance/horsepower and the capacitance. Too
small a capacitor will not produce enough phase shift to get the motor
started quickly enough to avoid blowing the capacitor, and too large a
capacitor will generate too much phase shift, again resulting in very
slow motor starting and likely failure.

Note that the static converter was spec'd for a range of
horsepower (in the part of the article now trimmed), not "up to
such-and-so horsepower".

This is a common limitation for a static converter -- at least of
the capacitor and relay style. So -- if the machine tool has three
motors -- one 4 HP, one 2 HP and one 1/2 HP (say for perhaps spindle,
feed,
and coolant pump), then while it may start the 4HP motor nicely, it will
fail to start the 1/2 HP coolant pump if that is needed first.
Obviously (in spite of what Nick thinks) once you have the spindle motor
running, it can start the others, but if you need the smallest to start
first (say it also pumps lubricant around to the bearings before you
start moving things) you may have problems. For this, really, an
external rotary converter would be a better bet. Let the static
converter start the rotary, and it can start all of the load motors with
no problems.

Obviously -- if it is a homebuilt static converter, or if the
owner is competent to open it up and replace the capacitor with the
appropriate size for the other motor, then this can be overcome.

Also -- if he is not careful to wire it so the real 240 VAC
comes in to the terminals which feed the control circuitry, he may not
be able to get the spindle motor to start with the static converter
alone.

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 ---

Hi Don

I have fallen short on my study in this 3 phase stuff. When I was doing
the testing with my litle dyno on 3 phase motors, I recognized that the
bigger the capacitor I used to spin up even the fractional HP 3 phase
motors, the quicker the motors spun up. I suspect I never approached the
"too much" capacity.
At one time I thought the static converter was a partially useful method
of running 3 phase machines at home, on single phase. But, the more I
learn about them, the more I recognize that they are an excellant device for
most home users for running 3 phase machines.
The only literature I have read related to static converters ghas been
sales brochures. I am a little sceptical of what is written in those sales
papers.

I accumulated some data while dyno testing the effects of 3 phase motors
and rotary convertyers. I saw that a very much smaller idler could spin up
a larger tool motor when the tool motor is spun up while very lightly
loaded. But, as you would expect, the little idler helps little or nothing
to the tool motor's ability to deliver power.

Where can a guy find some good tech info on static converter design?

Thanks for the "heads up" on excess capacity for spinning the 3 phase
motor.

Jerry

On 2008-02-16, Jerry wrote:

"DoN. Nichols" wrote in message
...
On 2008-02-14, Jerry wrote:

[ ... ]

Why do you write that a static converter with more capacity will have
difficulty starting a smaller motor?
I refer to your statement -
This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly.

Because the phase shift from the capacitor is a function of the
motor horsepower (and related inductance) the capacitance, and the
frequency. Since the frequency is fixed at either 60 Hz (here) or 50 Hz
(UK) we have the motor inductance/horsepower and the capacitance. Too
small a capacitor will not produce enough phase shift to get the motor
started quickly enough to avoid blowing the capacitor, and too large a
capacitor will generate too much phase shift, again resulting in very
slow motor starting and likely failure.

Note that the static converter was spec'd for a range of
horsepower (in the part of the article now trimmed), not "up to
such-and-so horsepower".

[ ... ]

Obviously -- if it is a homebuilt static converter, or if the
owner is competent to open it up and replace the capacitor with the
appropriate size for the other motor, then this can be overcome.

Also -- if he is not careful to wire it so the real 240 VAC
comes in to the terminals which feed the control circuitry, he may not
be able to get the spindle motor to start with the static converter
alone.

[ ... ]

Hi Don

I have fallen short on my study in this 3 phase stuff. When I was doing
the testing with my litle dyno on 3 phase motors, I recognized that the
bigger the capacitor I used to spin up even the fractional HP 3 phase
motors, the quicker the motors spun up. I suspect I never approached the
"too much" capacity.

You may not have even reached the level of "right value". :-)
You were perhaps using oil-filled AC capacitors, instead of the
electrolytic motor starting capacitors which are more common in motor
applications -- because they are smaller and they cost a lot less.

Oil-filled AC capacitors are a lot more tolerant of long start
times.

At one time I thought the static converter was a partially useful method
of running 3 phase machines at home, on single phase. But, the more I
learn about them, the more I recognize that they are an excellant device for
most home users for running 3 phase machines.

That depends. If you need to "plug reverse" a motor -- say do
it to a lathe spindle motor when you are threading up to a shoulder to
avoid a crash -- a static converter is useless.

The static converter (one version) is something like this (view
with a fixed pitch font such as Courier to avoid distortion of the
drawing):

(1)--------+ +----------------------------------(A)
| | +-- |
+----------+ | |
| I R | | |
+----------+ | |
o o
| |
(2)-------------------+-----------------------------(B)
|
| C1
+---|(------------------(C)

The block marked "I R" is a current sensing relay. When the motor is
drawing the high current when it is switched onto power with no ability
to start, it is sufficient current to close the contacts. One contact
connects to either (1) or (2) of the 240 VAC input lines (neutral is
ignored, so I did not draw it here). The capacitor (C1) applies
phase-shifted current to the motor terminal (C).

Once the motor spins up to perhaps half of its normal speed, the
relay is no longer seeing enough current, and thus the contacts open,
leaving terminal (C) on the motor totally disconnected.

That's OK for most things, because the single-phase power
applied between (A) and (B) is sufficient to keep the motor spinning at
normal speed -- though if it is loaded to full horsepower rating, the
current through the single winding will be higher than it was designed
for, and the winding will overheat and eventually burn out if you are
running it near its load rating for a long time.

However -- if you want to reverse the motor quickly, you are out
of luck. Normally, a three-phase motor is reversed by interchanging any
two of the three power leads. At that point, the three-phase power will
be trying to turn it the other way and it will reverse *quickly* (and
with a lot of current for a very short period). But, remember that the
(C) feed to the motor goes to nothing as long as the motor is not
drawing a lot of power. And once the motor is spinning, it doesn't care
which way it is going when fed by single phase.

So -- it won't reverse until the relay contacts close, and that
will require a lot of current, such as you get from a stalled motor.
But since it is spinning at normal speed, you won't get that current and
the relay will keep the connection to the (C) terminal open, so the
motor will keep running in the original direction, and your lathe tool
will crash into the shoulder.

A VFD does not want switches between the VFD and the motor, so
you have to ask it to reverse the motor, and that will require it to
slow the motor down and then speed it up in the other direction. Not
quite a fast as just reversing two leads on a real three phase, but
usually quick enough.

A rotary converter (which can be thought of as a static
converter starting a motor (called the idler motor) which then acts to
generate the third phase) can handle plug reversing -- as long as the
idler motor is enough larger than the load motor. I have heard of
attempts to plug reverse with too small an idler motor resulting in
reversing the idler motor instead of the load motor. Plan on at least
1.5 time the load motor rating for the idler motor -- or two times is
even better.

The only literature I have read related to static converters ghas been
sales brochures. I am a little sceptical of what is written in those sales
papers.

Good!

I accumulated some data while dyno testing the effects of 3 phase motors
and rotary convertyers. I saw that a very much smaller idler could spin up
a larger tool motor when the tool motor is spun up while very lightly
loaded. But, as you would expect, the little idler helps little or nothing
to the tool motor's ability to deliver power.

Where can a guy find some good tech info on static converter design?

Not from the makers -- they don't want you to see how simple
what they are selling you is, and how little it would cost for you to
make your own.

BTW That current relay is another reason for the minimum horsepower.
If the motor is two small, even with it stalled it won't draw
enough current to draw in the relay and engage the start
capacitor.

Some may be built using voltage sensing relays, waiting for
enough voltage to come back from terminal C instead of current sensing
relays -- or perhaps even a timer which just assumes that the motor must
have started by now and thus disengages the capacitor. All of this is
doing just what the centrifugal switch in a motor built for single phase
does.

If you want to study circuits which do what a static converter
does -- look at the home-brew plans for rotary converters -- they often
use the "static converter" design to start the idler.

And good rotary converter designs add oil-filled AC capacitors
to tune the output of the rotary converter for better balanced three
phase. You need to adjust the total capacitance according to the idler
motor, and ideally with the load motor connected too, so you are tuning
for best balance when under load.

Now -- I have seen mention of static converters which use a
tapped inductor to accomplish the phase shift instead of a capacitor.
That might avoid the need to switch out the third phase as soon as the
motor is spun up -- but it certainly increases the cost of
construction. Basically -- if you have difficulty lifing a static
converter, it is probably an inductor-based one, and may be better.

But personally, I like the VFD for most home shop conversion,
since it lets you tune the speed. The only place where I would consider
the rotary converter better is when you have a lot of three phase motors
on a single machine (which I believe is what started this). And of
course real three phase from the power company is even better -- if you
can get it.

Thanks for the "heads up" on excess capacity for spinning the 3 phase
motor.

You're welcome.

Good Luck,
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 ---

"DoN. Nichols" wrote in message
...
On 2008-02-16, Jerry wrote:

"DoN. Nichols" wrote in message
...
On 2008-02-14, Jerry wrote:

[ ... ]

Why do you write that a static converter with more capacity will have
difficulty starting a smaller motor?
I refer to your statement -
This is because the capacitor needs to be sized to
the horsepower of the motor which it is being used with. Too large a
motor or too small a motor will not start properly.

Because the phase shift from the capacitor is a function of the
motor horsepower (and related inductance) the capacitance, and the
frequency. Since the frequency is fixed at either 60 Hz (here) or 50 Hz
(UK) we have the motor inductance/horsepower and the capacitance. Too
small a capacitor will not produce enough phase shift to get the motor
started quickly enough to avoid blowing the capacitor, and too large a
capacitor will generate too much phase shift, again resulting in very
slow motor starting and likely failure.

Note that the static converter was spec'd for a range of
horsepower (in the part of the article now trimmed), not "up to
such-and-so horsepower".

[ ... ]

Obviously -- if it is a homebuilt static converter, or if the
owner is competent to open it up and replace the capacitor with the
appropriate size for the other motor, then this can be overcome.

Also -- if he is not careful to wire it so the real 240 VAC
comes in to the terminals which feed the control circuitry, he may not
be able to get the spindle motor to start with the static converter
alone.

[ ... ]

Hi Don

I have fallen short on my study in this 3 phase stuff. When I was
doing
the testing with my litle dyno on 3 phase motors, I recognized that the
bigger the capacitor I used to spin up even the fractional HP 3 phase
motors, the quicker the motors spun up. I suspect I never approached
the
"too much" capacity.

You may not have even reached the level of "right value". :-)
You were perhaps using oil-filled AC capacitors, instead of the
electrolytic motor starting capacitors which are more common in motor
applications -- because they are smaller and they cost a lot less.

Oil-filled AC capacitors are a lot more tolerant of long start
times.

At one time I thought the static converter was a partially useful
method
of running 3 phase machines at home, on single phase. But, the more I
learn about them, the more I recognize that they are an excellant device
for
most home users for running 3 phase machines.

That depends. If you need to "plug reverse" a motor -- say do
it to a lathe spindle motor when you are threading up to a shoulder to
avoid a crash -- a static converter is useless.

The static converter (one version) is something like this (view
with a fixed pitch font such as Courier to avoid distortion of the
drawing):

(1)--------+ +----------------------------------(A)
| | +-- |
+----------+ | |
| I R | | |
+----------+ | |
o o
| |
(2)-------------------+-----------------------------(B)
|
| C1
+---|(------------------(C)

The block marked "I R" is a current sensing relay. When the motor is
drawing the high current when it is switched onto power with no ability
to start, it is sufficient current to close the contacts. One contact
connects to either (1) or (2) of the 240 VAC input lines (neutral is
ignored, so I did not draw it here). The capacitor (C1) applies
phase-shifted current to the motor terminal (C).

Once the motor spins up to perhaps half of its normal speed, the
relay is no longer seeing enough current, and thus the contacts open,
leaving terminal (C) on the motor totally disconnected.

That's OK for most things, because the single-phase power
applied between (A) and (B) is sufficient to keep the motor spinning at
normal speed -- though if it is loaded to full horsepower rating, the
current through the single winding will be higher than it was designed
for, and the winding will overheat and eventually burn out if you are
running it near its load rating for a long time.

However -- if you want to reverse the motor quickly, you are out
of luck. Normally, a three-phase motor is reversed by interchanging any
two of the three power leads. At that point, the three-phase power will
be trying to turn it the other way and it will reverse *quickly* (and
with a lot of current for a very short period). But, remember that the
(C) feed to the motor goes to nothing as long as the motor is not
drawing a lot of power. And once the motor is spinning, it doesn't care
which way it is going when fed by single phase.

So -- it won't reverse until the relay contacts close, and that
will require a lot of current, such as you get from a stalled motor.
But since it is spinning at normal speed, you won't get that current and
the relay will keep the connection to the (C) terminal open, so the
motor will keep running in the original direction, and your lathe tool
will crash into the shoulder.

A VFD does not want switches between the VFD and the motor, so
you have to ask it to reverse the motor, and that will require it to
slow the motor down and then speed it up in the other direction. Not
quite a fast as just reversing two leads on a real three phase, but
usually quick enough.

A rotary converter (which can be thought of as a static
converter starting a motor (called the idler motor) which then acts to
generate the third phase) can handle plug reversing -- as long as the
idler motor is enough larger than the load motor. I have heard of
attempts to plug reverse with too small an idler motor resulting in
reversing the idler motor instead of the load motor. Plan on at least
1.5 time the load motor rating for the idler motor -- or two times is
even better.

The only literature I have read related to static converters ghas been
sales brochures. I am a little sceptical of what is written in those
sales
papers.

Good!

I accumulated some data while dyno testing the effects of 3 phase
motors
and rotary convertyers. I saw that a very much smaller idler could spin
up
a larger tool motor when the tool motor is spun up while very lightly
loaded. But, as you would expect, the little idler helps little or
nothing
to the tool motor's ability to deliver power.

Where can a guy find some good tech info on static converter design?

Not from the makers -- they don't want you to see how simple
what they are selling you is, and how little it would cost for you to
make your own.

BTW That current relay is another reason for the minimum horsepower.
If the motor is two small, even with it stalled it won't draw
enough current to draw in the relay and engage the start
capacitor.

Some may be built using voltage sensing relays, waiting for
enough voltage to come back from terminal C instead of current sensing
relays -- or perhaps even a timer which just assumes that the motor must
have started by now and thus disengages the capacitor. All of this is
doing just what the centrifugal switch in a motor built for single phase
does.

If you want to study circuits which do what a static converter
does -- look at the home-brew plans for rotary converters -- they often
use the "static converter" design to start the idler.

And good rotary converter designs add oil-filled AC capacitors
to tune the output of the rotary converter for better balanced three
phase. You need to adjust the total capacitance according to the idler
motor, and ideally with the load motor connected too, so you are tuning
for best balance when under load.

Now -- I have seen mention of static converters which use a
tapped inductor to accomplish the phase shift instead of a capacitor.
That might avoid the need to switch out the third phase as soon as the
motor is spun up -- but it certainly increases the cost of
construction. Basically -- if you have difficulty lifing a static
converter, it is probably an inductor-based one, and may be better.

But personally, I like the VFD for most home shop conversion,
since it lets you tune the speed. The only place where I would consider
the rotary converter better is when you have a lot of three phase motors
on a single machine (which I believe is what started this). And of
course real three phase from the power company is even better -- if you
can get it.

Thanks for the "heads up" on excess capacity for spinning the 3 phase
motor.

You're welcome.

Good Luck,
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 ---

Hi Don

You have alot of information on Converters. I began a study a few years
ago by building a dyno and using Excel to make charts of HP while running 3
phase motors from a single phase line. Don Foreman taught me lots and lots
about all the stuff I built and tested. he is world class instructor. I
have disassembled the dyno but keep the set of four 200 mic electrolytics in
parallel that I can apply to the unfed motor lead thru a solid state switch.
I use the capacitors to spin up 3 phase motors here at home. I wont be
surprised if i sometime fail to spin up a small 3 phase motor due to the
excess capacity.
I have several VFDs in systems I work on. So, I do like them and have
used alot for stuff I've built. I even repaired a 120 KW solid state
converter last week. It is fixed frequency at 60 Hz in and 400 Hz out.
The problem is 'I dont know what I did to make it work'. Thats not too
satisfying, but the unit did get shipped after I disassembled part of it and
then put it back together.
But, the more I learn about "Static Converters", the more I respect their
value to home use where space and budget is a factor.

Jerry

Capacitors cant store enuf energy to be used to convert single phase

to 3 phase , you must use rotary machines to store the energy .

Its real simple , a motor is powered to store energy , which it
delivers

to a phase wire on a 3 phase motor , you simply control the energy

applied to the single phase so it can deliver this energy , but
delayed

to the 3 phase motor .

The more energy needed , the larger the rotating mass of the single
phase

motor .


motors and transformers can be modeled as a magnetizing inductance in
parallel

with a leakage induct'+resistive load .

At no load , all current flows thru magnetizing induct' .... bad
P.F. ,

so you pay more to the electric company .

But as the current flows to the load , which is series to the leakage
induct'

the P.F. improves to 85% ( cause the load is resistive , not induct'
as the L-induct is ).

The stored energy is in the Leakage induct' , and it is effecient .

But it needs a large heavy rotor to deliver that energy to a 2nd
motor .

It also needs a small air gap , to reduce the reluctance of the path
from

stators to the rotor .

we need to move above 400 hz , to get higher power , but that means
diameter

of motor also increases .

"werty" wrote in message
...

Capacitors cant store enuf energy to be used to convert single phase

to 3 phase , you must use rotary machines to store the energy .

Its real simple , a motor is powered to store energy , which it
delivers

to a phase wire on a 3 phase motor , you simply control the energy

applied to the single phase so it can deliver this energy , but
delayed

to the 3 phase motor .

The more energy needed , the larger the rotating mass of the single
phase

motor .


motors and transformers can be modeled as a magnetizing inductance in
parallel

with a leakage induct'+resistive load .

At no load , all current flows thru magnetizing induct' .... bad
P.F. ,

so you pay more to the electric company .

But as the current flows to the load , which is series to the leakage
induct'

the P.F. improves to 85% ( cause the load is resistive , not induct'
as the L-induct is ).

The stored energy is in the Leakage induct' , and it is effecient .

But it needs a large heavy rotor to deliver that energy to a 2nd
motor .

It also needs a small air gap , to reduce the reluctance of the path
from

stators to the rotor .

we need to move above 400 hz , to get higher power , but that means
diameter

of motor also increases .

Hi Werty

I find no fault in what you write here. But, there is a situation where
3 phase motors can be run nicely when connected to single phase. And, it
requires only that a capacitor be temporily connected from one of the single
phase lines to the "not connected" third wire from the 3 phase motor. That
temporary connection of the capacitor gets the 3 phase motor spinning so it
can then deliver appreciable power.
The capacitor doesnt need to store power. It is quickly "bumped across"
the two terminals of the motor wires. The major benefit from having a VFD
or a Rotary Converter would be to get the tool motor to delive close to its
name plate rated power to a load for extended times.

Jerry

Nick Mueller wrote:



L1, L2, and L3 are the phases. M1, M2 and M3 are the motors.
L1 is the only phase available, so you connect it to M1L1. M2L1 and M3L3 are
open, because we don't want to let them run. OK so far?


No this is where your analysis falls apart.

A single phase supply is TWO count 'em TWO wires, i.e. L1 AND L2


Now the voltage generated in M1L2 and M1L3 goes where? Nowhere, because they
are not connected on M2 and M3 (because we don't want to let them run).

When you run any ONE of the 3 motors, it will generate a phantom
voltage on the 3rd leg. YOu have to get that one running first (some
how), then it can act as the (sort of RPC) to start the other two.

You also seem to be missing the difference between a motor that is
running, but UNLOADED, and one that is disconnected. You consistently
seem to assume that an unloaded motor is a stopped motor.


Now we let run all three motors at the same time.
Connections:
M1L1 to M2L1 and M3L1
M1L2 to M2L2 and M3L2
and
M1L3 to M2L3 and M3L3

Now the voltage generated in M1L2 is feed into M2L2 and M3L2 (same for L3).
But at the same time M2 and M3 generate voltage at L2. Now do you really
think that one motor can drive L2 and L3 of the two other motors and at the
same time doesn't lose any energy?
Note that I disregarded losses and was talking about an ideal machine.

OF COurse it loses energy, that is how the 3rd phase gets developed.
But the energy loss is supplied by the "Real" phase pair.

jk

On 2008-02-17, Jerry wrote:

"DoN. Nichols" wrote in message
...
On 2008-02-16, Jerry wrote:

[ ... ]

Hi Don

I have fallen short on my study in this 3 phase stuff. When I was
doing
the testing with my litle dyno on 3 phase motors, I recognized that the
bigger the capacitor I used to spin up even the fractional HP 3 phase
motors, the quicker the motors spun up. I suspect I never approached
the
"too much" capacity.

You may not have even reached the level of "right value". :-)
You were perhaps using oil-filled AC capacitors, instead of the
electrolytic motor starting capacitors which are more common in motor
applications -- because they are smaller and they cost a lot less.

Oil-filled AC capacitors are a lot more tolerant of long start
times.

[ ... ]

You have alot of information on Converters. I began a study a few years
ago by building a dyno and using Excel to make charts of HP while running 3
phase motors from a single phase line. Don Foreman taught me lots and lots
about all the stuff I built and tested. he is world class instructor. I
have disassembled the dyno but keep the set of four 200 mic electrolytics in
parallel that I can apply to the unfed motor lead thru a solid state switch.

Hmm ... that is enough to handle rather large horsepower motors.

I use the capacitors to spin up 3 phase motors here at home. I wont be
surprised if i sometime fail to spin up a small 3 phase motor due to the
excess capacity.
I have several VFDs in systems I work on. So, I do like them and have
used alot for stuff I've built. I even repaired a 120 KW solid state
converter last week. It is fixed frequency at 60 Hz in and 400 Hz out.
The problem is 'I dont know what I did to make it work'. Thats not too
satisfying, but the unit did get shipped after I disassembled part of it and
then put it back together.

An interesting device -- and something which I would like to
have -- except much smaller -- to run an old gyrocompass and an
artificial horizon which want 115 VAC 400 Hz. Probably on the order of
20 W each.

But, the more I learn about "Static Converters", the more I respect their
value to home use where space and budget is a factor.

I'm not too sure about the budget matter. The price from
vendors seems to be not too different from that for a VFD from eBay or
one of the good dealers -- at least until you get into seriously high
horsepower ratings.

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 ---

On 17 Feb 2008 00:35:01 GMT, "DoN. Nichols"
wrote:

On 2008-02-16, Jerry wrote:



At one time I thought the static converter was a partially useful method
of running 3 phase machines at home, on single phase. But, the more I
learn about them, the more I recognize that they are an excellant device for
most home users for running 3 phase machines.

I agree, Jerry; static converters get an undeserved bad rap. I have
three machines (mill, lathe, surface grinder) that benefit from VFDs,
but my vertical band saw, belt sander, and one bench grinder run
happily on a static converter. (And, yes, turning one of those
machines on will help start a motor that the converter would otherwise
not start.)

I do have a large rotary converter, and can easily switch between the
static and rotary, but rarely find it necessary to run the (noisy)
rotary.


That depends. If you need to "plug reverse" a motor -- say do
it to a lathe spindle motor when you are threading up to a shoulder to
avoid a crash -- a static converter is useless.


And yet it works. I ran a Bridgeport for many years on a static
converter and regularly plug reversed when power tapping. A friend who
has a commercial shop without access to 3-phase runs 4 BPs on static
converters, and has for as long as I can remember. Plug reversing
isn't a problem for him, either.

Here's what Phase-A-Matic has to say:
**********************************************
Next, you must determine whether to use a Regular or Heavy Duty
Converter. Keep in mind you can always use a
Heavy Duty Converter in place of a Regular Duty model. However, there
are some applications for which you
should always recommend Heavy Duty Converters. They a

1. Frequent starting or instant reversing (more than once a minute).
2. Unattended equipment, such as air compressors.
3. Long, heavy starting cycles, such as lathes without a clutch,
flywheel driven equipment, etc.
4. If jogging is required.
5. If there is a chance of the motor being stalled during use
(woodworking equipment, etc.)

********************************************

--
Ned Simmons

jk wrote:

No this is where your analysis falls apart.

A single phase supply is TWO count 'em TWO wires, i.e. L1 AND L2

A single phase is one phase and neutral.


Nick
--
The lowcost-DRO:
http://www.yadro.de

On Feb 18, 4:14*am, Nick Mueller wrote:
jk wrote:
No this is where your analysis falls apart.

A single phase supply is TWO count 'em TWO wires, i.e. L1 AND L2

A single phase is one phase and neutral.

Nick

US residential power is single-phase 240VAC from a center-tapped
transformer.
120V single phase is hot to neutral, 240V is hot to hot.

Nick Mueller wrote:

jk wrote:

No this is where your analysis falls apart.

A single phase supply is TWO count 'em TWO wires, i.e. L1 AND L2

A single phase is one phase and neutral.


Only if that side is connected as a neutral. You have a LOT to learn
about electricity and electronics.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida