Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor. I've heard varying opinions on the subject.
Having thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it
is not connected directly to the supply. The flywheel doesn't change
this. Nor will it change the steady speed at which the rotor turns, so
unless it has some averaging effect on a cycle-by-cycle basis which I
haven't considered, it won't affect the quality of the three phase
output when the convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load
motor. As far as I can see (on the most simplistic level), the motor
with the most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get
a flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

In article , Christopher Tidy says...

Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.

There is no experimental data on this subject as far as I can see.

I have seen coherent, cogent arguments from respected folks
that support both views - one that it will help, the other that it
will hinder.

Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.

Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.

Those two preceeding statements are pure paraphrase on my part, and
I of course apologize if I have mis-represented anyones comments.
But there's no empirical data out there as far as I can tell.

It wouldn't be that hard to instrument and measure.

Jim


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==================================================

jim rozen wrote:
In article , Christopher Tidy says...

Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.


There is no experimental data on this subject as far as I can see.

I have seen coherent, cogent arguments from respected folks
that support both views - one that it will help, the other that it
will hinder.

Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.

Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.

Then maybe one needs a "dual-mass" flywheel like they are putting on the
diesel pickups now.

In article ,
Rex B wrote:

[...]

Then maybe one needs a "dual-mass" flywheel like they are putting on the
diesel pickups now.

That sounds like an interesting thingy. Got any details on it?

--
B.B. --I am not a goat! thegoat4 at airmail dot net

On 3 Jan 2006 13:58:38 -0800, jim rozen
wrote:

In article , Christopher Tidy says...

Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.

There is no experimental data on this subject as far as I can see.

I have seen coherent, cogent arguments from respected folks
that support both views - one that it will help, the other that it
will hinder.

Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.

Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.

Those two preceeding statements are pure paraphrase on my part, and
I of course apologize if I have mis-represented anyones comments.
But there's no empirical data out there as far as I can tell.

It wouldn't be that hard to instrument and measure.

Jim

Some kinetic energy is necessary for the thing to work, but my bet is
that the rotor has more than enough and more would not help.

Kinetic energy is necessary for the idler to produce power in the
third leg during parts of the cycle when less or none is being drawn
from the mains. Energy is also stored in the magnetic field, but its
ebb and flow is in quadrature with third leg power. This is a
cycle-by-cycle event: it accelerates (accumulates energy) during
part of each cycle and decelerates (gives up energy) during other
parts of each cycle. The result is speed ripple, which would be
greater for rotors with small moments of inertia.

The power levels drawn and delivered are a function of slip speed
which governs both stator current and induced emf -- back emf in the
case of the driven windings and generated emf in the case of the third
leg. As the third leg produces more countertorque from higher
current flow thru it, the rotor will slow until slipspeed has
increased to the point where enough power is drawn from the mains to
regain equilibrium.

Observers (Jerry and Fitch) have said they didn't note much change in
idler slipspeed with varying loads. However, resolution of 1% or
better would be necessary to see speed variations because the slip
speed range from no load to full load in most induction motors is
only a few percent at most.

On 3 Jan 2006 13:58:38 -0800, jim rozen
wrote:

Those who suggest a flywheel is bad say that rotary converters
deliver transient power to the generated phase by allowing the rotor to
slip, and a flywheel prevents this.

Those who suggest a flywheel is good say that that flywheels store
rotational energy and will this is made available to transient loads.

Those two preceeding statements are pure paraphrase on my part, and
I of course apologize if I have mis-represented anyones comments.
But there's no empirical data out there as far as I can tell.

It wouldn't be that hard to instrument and measure.

Jim

Dont forget a nice heavy rotor IS a flywheel.

Gunner

The aim of untold millions is to be free to do exactly as they choose
and for someone else to pay when things go wrong.

In the past few decades, a peculiar and distinctive psychology
has emerged in England. Gone are the civility, sturdy independence,
and admirable stoicism that carried the English through the war years
.. It has been replaced by a constant whine of excuses, complaints,
and special pleading. The collapse of the British character has been
as swift and complete as the collapse of British power.

Theodore Dalrymple,

Regarding plug reversing, I recently rewired an older BP head. I was surprised
to see considerable evidence of arcing near the contacts in the drum switch. I
figured that plug reversing it was the reason - a LOT of current flows, and
motors with all their inductance do NOT like current changes. So regardless of
what you do with your phase convertor, I strongly suggest that you not plug
reverse anything using a drum switch unless that switch is extremely heavily built.

I know of no value in adding rotary mass. The armature of an idler motor is
already quite a bit of rotary mass.

GWE

Christopher Tidy wrote:

Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor. I've heard varying opinions on the subject.
Having thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it
is not connected directly to the supply. The flywheel doesn't change
this. Nor will it change the steady speed at which the rotor turns, so
unless it has some averaging effect on a cycle-by-cycle basis which I
haven't considered, it won't affect the quality of the three phase
output when the convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load
motor. As far as I can see (on the most simplistic level), the motor
with the most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get
a flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

Christopher Tidy wrote...

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.

A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.

That's my understanding. Perhaps one of the old regulars can explain it
better. Is Fitch still around? I seem to remember his doing some tests on
this very thing a few years back.

Jim

Jim Wilson wrote:

Thanks for all the responses.

A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.

I'm not sure about this. Yes, it will take longer for the rotor's speed
to fall, but surely the stored energy will be dissipated by driving
extra current through the load?

Best wishes,

Chris

On Tue, 3 Jan 2006 22:53:42 +0000 (UTC), Christopher Tidy
wrote:

Jim Wilson wrote:

Thanks for all the responses.

A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.

I'm not sure about this. Yes, it will take longer for the rotor's speed
to fall, but surely the stored energy will be dissipated by driving
extra current through the load?

Yes, but power is the rate of energy flow. The amount of power it
can produce for the third leg (energy delivered per cycle) is a
function of slip speed, and field strength hence stator current which
is also a function of slip speed.

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network. IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits. Such circuits are "tuned" via
capacitance placed in series.

Bob Swinney
"Jim Wilson" wrote in message
.net...
Christopher Tidy wrote...

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor.

A flywheel would reduce, not increase, the idler's ability to respond to
load changes. When the electrical load on the idler increases, the
idler's rate of rotation falls (I.e., the slip increases). This raises
the current draw from the single phase source. The higher winding current
increases the strength of the rotating magnetic field in the idler, which
pushes the generated third leg voltage up. The upshot of all this is that
the response rate of the third leg voltage to electrical load changes is
inversely related to the inertia of the idler's armature.

That's my understanding. Perhaps one of the old regulars can explain it
better. Is Fitch still around? I seem to remember his doing some tests on
this very thing a few years back.

Jim

In article , Robert Swinney says...

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network. IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits. Such circuits are "tuned" via
capacitance placed in series.

Granted this kind of tuning is the very *first* thing one would do
before considering flywheels.

I specifically recall Gary Coffman claiming they would reduce transient
response, and yet there's a considerable group of well-informed
individuals on the practical machinist board who say they improve
matters.

I have to say I find *both* sides to be persuasive, at least at the
'hand-waving' level.

My suspicion is that flywheels probably help up to a point, if one
models the rotor as having zero mass to start with. And that the
optimum flywheel size will wind up being about one rotor unit in
size! This is what a former boss of mine calls 'the schwarz law
of the initial maximum.'

Ie, if it works the first time you set it up, anything you do to it
after that makes it work worse.

:^)

Jim


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==================================================
please reply to:
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==================================================

On 3 Jan 2006 16:04:40 -0800, jim rozen
wrote:

In article , Robert Swinney says...

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network. IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits. Such circuits are "tuned" via
capacitance placed in series.

Granted this kind of tuning is the very *first* thing one would do
before considering flywheels.

I specifically recall Gary Coffman claiming they would reduce transient
response, and yet there's a considerable group of well-informed
individuals on the practical machinist board who say they improve
matters.

I have to say I find *both* sides to be persuasive, at least at the
'hand-waving' level.

My suspicion is that flywheels probably help up to a point, if one
models the rotor as having zero mass to start with. And that the
optimum flywheel size will wind up being about one rotor unit in
size! This is what a former boss of mine calls 'the schwarz law
of the initial maximum.'

Ie, if it works the first time you set it up, anything you do to it
after that makes it work worse.

:^)

We just call that syndrome "fix it 'til it's broke".

Snarl

Robert Swinney wrote...
IMO, you need to lose the thinking of a RPC as being a form of generator.

Hrm. Is this in response to my post, or Christopher's? I don't think I
view a RPC as a generator at all. Perhaps it's more like a rotating
transformer.

snip

It would be aprox. the same to put the flywheel on the
load motor instead.

Most of what you said seemed reasonable (I snipped all the
unobjectionable parts), but this statement can only be true under limited
conditions. There would be a large difference in performance between the
two systems for example when plug reversing is used.

Cheers,

Jim

"Jim Wilson" wrote in message
.net...
Robert Swinney wrote...
IMO, you need to lose the thinking of a RPC as being a form of generator.

Hrm. Is this in response to my post, or Christopher's? I don't think I
view a RPC as a generator at all. Perhaps it's more like a rotating
transformer.

snip

It would be aprox. the same to put the flywheel on the
load motor instead.

Most of what you said seemed reasonable (I snipped all the
unobjectionable parts), but this statement can only be true under limited
conditions. There would be a large difference in performance between the
two systems for example when plug reversing is used.

Cheers,

Jim

FWIW, you might view a plug reverse of the load motor as the worst case
flywheel effect.

Bob Swinney

On Tue, 3 Jan 2006 17:20:12 -0600, "Robert Swinney"
wrote:

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate in
order to supply current throughout. Part of the RPC is the load motor. The
idler generates nothing without the load as part of a network.

Sure it does. With the idler spinning, a voltage is generated in
the third leg that is in quadrature to line voltage, even if there are
no capacitors anywhere. Transformer action can not produce a
quadrature voltage so it must be (and is) generated by the rotating
rotor field -- which always is in quadrature with the stator field.

IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can be
viewed as series resonant circuits.

If there are capacitors. But idlers without any run caps still work.
In fact, they work quite well if they're large enough.

I agree, using large motors simplifies everything! You get the
advantage of great kinetic energy with very understressed component
parts. I favor a pony to "spin up" the first started (should be
largest by 1.5) motor.

"Don Foreman" wrote in message
...
On Tue, 3 Jan 2006 17:20:12 -0600, "Robert Swinney"
wrote:

IMO, you need to lose the thinking of a RPC as being a form of generator.
It isn't. Think more of the RPC as a network in which parts of it rotate
in
order to supply current throughout. Part of the RPC is the load motor.
The
idler generates nothing without the load as part of a network.

Sure it does. With the idler spinning, a voltage is generated in
the third leg that is in quadrature to line voltage, even if there are
no capacitors anywhere. Transformer action can not produce a
quadrature voltage so it must be (and is) generated by the rotating
rotor field -- which always is in quadrature with the stator field.

No load, no generation, Don. An idler running with no load motor does not
constitute a RPC. The network and supported current flow through that
network makes a RPC. Remember the idler is running as a single-phase
machine and the 3rd leg is open, that is, until it is connected into a RPC.

IMO, a
flywheel on the idler cannot act as anything more than additional dynamic
load on the network. It would be aprox. the same to put the flywheel on
the
load motor instead. Forget flywheels and spend the money on enhancing the
idler-load network with proper capacitance. Complex current flows in all
parts of the RPC. In simplistic terms, the idler-load current paths can
be
viewed as series resonant circuits.

If there are capacitors. But idlers without any run caps still work.
In fact, they work quite well if they're large enough.

OK. So they aren't series resonant circuits when there are no run caps -
granted. But the interconnection of idler and load and their associated
current paths are the same, even without run caps.

In article , Robert Swinney says...

No load, no generation, Don. An idler running with no load motor does not
constitute a RPC. The network and supported current flow through that
network makes a RPC. Remember the idler is running as a single-phase
machine and the 3rd leg is open, that is, until it is connected into a RPC.

No current flow, yes. But the third leg does come up in voltage, even
when open circuited. While it won't do any work, folks would be tempted
to say that the third leg is indeed "generated" even when it's open
circuited. Another one of those semantic mine fields....

Jim


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==================================================
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==================================================

Don sez:
" Sure it does. With the idler spinning, a voltage is generated in
the third leg that is in quadrature to line voltage, even if there are
no capacitors anywhere. Transformer action can not produce a
quadrature voltage so it must be (and is) generated by the rotating
rotor field -- which always is in quadrature with the stator field."

I'm not sure what you mean, Don. You said "Transformer action can not
produce a quadrature voltage so it must be (and is) generated by the
rotating rotor field -- which always is in quadrature with the stator
field".

Firstly, I don't understand why the issue must be complicated by bringing
the rotor field into the picture. It is well known the stator field and
rotor field are more or less locked into rotation at the same speed, but it
is incongruous to speculate the rotor field is solely responsible for the
stator field's third leg voltage. Remember we are essentially talking about
a single phase motor here with an open coil connected to the center point of
the line-fed main winding. I respectfully submit the third leg voltage is
not in quatrature with line voltage. The only way for that to be a true
statement would be in the special case of a precise amount of capacitance
connected from one line side to the end of the 3rd leg coil; an amount of
capacitance (start cap if you will) necessary to achieve an exact 90 degree
phase shift between line voltage and the 3rd. leg.

Bob Swinney

Robert Swinney wrote:
IMO, you need to lose the thinking of a RPC as being a form of generator.

Bob Swinney

In my opinion you need to realize that a RPC is an induction generator.


As far as flywheels are concerned, a flywheel will keep the slip angle
from changing as quickly. So a RPC without a flywheel will draw power
from the mains more quickly when the load is increased. Score points
for that side. On the other hand, a RPC with a flywheel will draw
power from the flywheel when the load is increased as well as from the
mains. So score points for the other side.

In the real world, it does not make much difference as the change in
speed of the RPC should be slight, and therefore only a small amount of
power can be drawn from the flywheel. Having a flywheel would help
with an undersized RPC when the load motor is plugged.


Dan

Dan sez:
" In my opinion you need to realize that a RPC is an induction generator."

Dan, I know you have some experience with induction generators so I'll ask
you to respectfully consider that:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

wrote in message
oups.com...

Robert Swinney wrote:
IMO, you need to lose the thinking of a RPC as being a form of generator.

Bob Swinney



As far as flywheels are concerned, a flywheel will keep the slip angle
from changing as quickly. So a RPC without a flywheel will draw power
from the mains more quickly when the load is increased. Score points
for that side. On the other hand, a RPC with a flywheel will draw
power from the flywheel when the load is increased as well as from the
mains. So score points for the other side.

In the real world, it does not make much difference as the change in
speed of the RPC should be slight, and therefore only a small amount of
power can be drawn from the flywheel. Having a flywheel would help
with an undersized RPC when the load motor is plugged.


Dan

Sorry, Dan - Make that overdrive via overspeed from the prime mover to make
an induction generator. The induction generator (one made from a common
induction motor) will generate when excited by the mains and when its rotor
is driven by external means to a speed exceeding that of the motor's
synchronous speed. Slip is said to be negative under these conditions.

Bob Swinney
"Robert Swinney" wrote in message
...
Dan sez:
" In my opinion you need to realize that a RPC is an induction
generator."

Dan, I know you have some experience with induction generators so I'll ask
you to respectfully consider that:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive
from the AC mains in order to generate. Tht is not done in any fashion in
a RPC. The RPC is a load on the mains, not a supplier to the mains.
Again, I'll say, we need lose the idea of a RPC being a generator. Think
of it as more of a converter; well, that's part of it's name now isn't it?

Bob Swinney

wrote in message
oups.com...

Robert Swinney wrote:
IMO, you need to lose the thinking of a RPC as being a form of
generator.

Bob Swinney



As far as flywheels are concerned, a flywheel will keep the slip angle
from changing as quickly. So a RPC without a flywheel will draw power
from the mains more quickly when the load is increased. Score points
for that side. On the other hand, a RPC with a flywheel will draw
power from the flywheel when the load is increased as well as from the
mains. So score points for the other side.

In the real world, it does not make much difference as the change in
speed of the RPC should be slight, and therefore only a small amount of
power can be drawn from the flywheel. Having a flywheel would help
with an undersized RPC when the load motor is plugged.


Dan

On Fri, 6 Jan 2006 16:43:51 -0600, "Robert Swinney"
wrote:

Dan sez:
" In my opinion you need to realize that a RPC is an induction generator."

Dan, I know you have some experience with induction generators so I'll ask
you to respectfully consider that:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

A fella by the name of Swinney said elsewhere that idler and load
motor function both as generators and loads. True statement.

Emf is produced in all three windings of the idler. In the driven
windings, those connected to the mains, that emf is slightly less than
applied voltage so the current in those windings is (Vline -
Vemf)/Zwnding. A similar but phase-displaced emf is also produced
in the third leg. This emf can then drive (supply power to) the
third leg of the load motor which also is not connected to the mains.

So neither the idler nor the load are generators from the perspective
of the mains, but the idler, regardless of what else you may call it,
does supply current and power to the load motor's third leg.

I would therefore argue that the idler alone is a rotary phase
converter (RPC) because it produces a voltage on its third leg that
is of different phase from the mains voltage whether or not it has a
load connected to it. It isn't a rotary power converter (also RPC)
unless there is a load connected, because if there is no load
connection then the idler's third leg has no current so there is no
different-phase power.

In either case, this different phase is not exactly right in
magnitude or phase to make the result balanced threephase, though if
the idler is big enough (low impedance) it'll be pretty close. This
is because the IZ drops in the driven windings of the idler are
different in polarity wrt the emf than is the case in the third leg.

The discrepancy can be reduced with capacitors, at least for a
particular load motor and particular mechanical or useful load.

Unfortunately when I learned about electric motors, I was taught that
an electric motor GENERATES a back emf because there is a magnetic
field which is cutting conductors.
So my view of say a motor is somewhat different from yours. If you
have an electric motor and you increase the load, the speed drops
slightly, the back emf drops, and the current drawn goes up. If you
decrease the load, the speed increases, the back emf goes up, and the
current drawn goes down. If you decrease the load until it is
negative, ( ie mechanical power is being applied to the motor ) , the
back emf goes up until it is more than the applied emf, and the current
drawn goes negative. That is current goes into the mains. That is an
induction generator. Works whether the motor is a single phase motor
or a three phase motor.

If you have three phase motor and get it running on single phase power,
things are a bit more complicated. But you still get a back emf
generated, and on the terminal that is unconnected to the power there
is a back emf, but there is no forward emf. So you can draw current
from that terminal.

Consider this. If you get a three phase motor running on single phase,
you can use it to produce mechanical power. So the way I think of a
RPC is as a three phase motor running on single phase, with some of the
mechanical power being used to drive an induction generator.

I am a bit confused by your statement about overdrive from the AC
mains. Mostly by the word "overdrive". As I see it a RPC is connected
to the AC mains, so I think it would be excited by overdrive from the
AC mains. However an induction generator does not have to be connected
to the AC mains in order to work. You can use a gasolene engine to
drive an induction motor and generate electric power with no connection
to the mains. It just is just sensitive to the amount of power you
draw and does not regulate the voltage at all well.

To further confuse you, you can build a very nice RPC by using a single
phase motor to drive a three phase motor via a belt drive adjusted so
mechanical power is going into the three phase motor. Now if you apply
single phase power to the three phase motor, it will act as a three
phase induction generator. If you do this use an adjustable pulley on
one of the motors and measure the current drawn by the single phase
motor. Adjust the pulleys so the current drawn by the single phase
motor is close to but below rated nameplate current when the RPC is
driving whatever load you are going to drive. As you might suspect
such a RPC produces voltages that are very closely balanced.

So I still analyse a RPC as an induction generator. Trying to analyse
it as some sort of transformer, I have a lot of problems figuring out
one ever gets anything that is not still in phase with the original
single phase mains. And how one calculates what the phase angle is
going to be.

I amy not be able to convince you that this is a valid way to analyse
RPC's, but it works for me.


Dan




Robert Swinney wrote:
Dan sez:
" In my opinion you need to realize that a RPC is an induction generator."

Dan, I know you have some experience with induction generators so I'll ask
you to respectfully consider that:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

wrote in message
oups.com...

Robert Swinney wrote:
IMO, you need to lose the thinking of a RPC as being a form of generator.

Bob Swinney



As far as flywheels are concerned, a flywheel will keep the slip angle
from changing as quickly. So a RPC without a flywheel will draw power
from the mains more quickly when the load is increased. Score points
for that side. On the other hand, a RPC with a flywheel will draw
power from the flywheel when the load is increased as well as from the
mains. So score points for the other side.

In the real world, it does not make much difference as the change in
speed of the RPC should be slight, and therefore only a small amount of
power can be drawn from the flywheel. Having a flywheel would help
with an undersized RPC when the load motor is plugged.


Dan

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

Robert Swinney wrote:
Dan sez:
" In my opinion you need to realize that a RPC is an induction generator."

Dan, I know you have some experience with induction generators so I'll ask
you to respectfully consider that:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney



I am sorry but thinking of RPC's the way I do just seems to make sense.
When I learned about motors, I learned that they generate a back emf
because they have a rotating magnetic field and conductors that cut the
magnetic field. And if you increase the load on a motor, it slows
slightly and the back emf drops and the current rises. And if you
decrease the load the back emf increases and the current decreases.
Now consider decreasing the load even more, so that the load is
negative. ( putting mechanical power into the motor trying to make it
run faster than synchronous speed ) The back emf increases and the
current goes negative. That is current is being supplied by the motor
to the mains. So as I see it a motor can work from locked rotor to
being driven. ( Don't try locked rotor for very long unless you have a
AC servo motor ) Same physics for all cases.

Now this happens whether the motor is a single phase motor or a three
phase motor.

Now what happens when you have a three phase motor and run it on just
one phase?
After you get it started, it will run on single phase power. You still
have a rotating magnetic field, and windings for three phases. So the
rotating magnetic field generates a back emf in all the windings. So
you consume power from the single phase, but generate three phase
power.

Incidently you do not have to have an induction motor connected to the
mains in order for it to work as an induction generator. It just will
not work with a large variety of loads.

Another by the way. One of the better ways to make a RPC is to connect
a single phase motor to a three phase motor using an adjustable belt
drive. You monitor the current going into the single phase motor and
adjust the drive so the current is at or below name plate current when
driving the three phase load. Recommended ( by me ) for driving three
phase machines as surface grinders that are sensitive to unbalanced
three phase power.
In that case it is pretty obvious that you have a three phase induction
generator being driven by a single phase motor.

You may find this way of analysing a RPC as weird, but it works for me.
I have problems understanding RPC's as transfomers that produce a
voltage that is not in phase with the input voltage. And it lets me
think about how a flywheel would affect a RPC.


Dan

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

Robert Swinney wrote:

An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney


In school I was taught that a motor generates a back emf because there
is a rotating magnetic field whose flux cuts the windings in the motor.
When a motor is running and you increase the load, the motor slows
slightly and the back emf drops so the net voltage increases causing
the current to increase. If you decrease the load the speed increases,
the back emf rises, net voltage drops and current drops. If you
decrease the load until it is negative, the back emf increases until it
is above the input emf, and the current goes negative. That is current
flows from the motor to the mains.

Now this works for both single phase and three phase motors from locked
rotor to being an induction generator. ( Don't try locked rotor for
very long unless you have an AC servo motor ) It even works for a
three phase motor running on just one phase. In that case the motor
consumes single phase power, but still generates back emf in all
windings. Which results in generating three phase power. Because the
back emf is less than the mains voltage, the voltage is not balanced.
But this can be improved by either adding capacitors.

So now you can at least see how I analyse RPC's. It isn't the only
way, but it works for me and maybe Don Young and Pentagrid. ( Speak up
if you disagree ).

As an aside issue, an induction generator will work without being
connected to the mains.
You can google and find some references to this as regards using an
induction motor driven by a small gas engine for operating ham field
stations. It is load sensitve.

And as another aside, you can build a fine RPC using a single phase
motor connected to a three phase motor via a adjustable belt drive. Two
terminals of the three phase motor are also connected to the mains. You
adjust the belt drive so the current drawn by the single phase motor is
at or below name plate rated current while the RPC is supplying three
phase power to whatever needs three phase power. I happen to think
this approach is good for things as surface grinders where good three
phase power is needed.


Dan

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

I hope this message actually gets posted. My last two attempts failed.
I am hoping the problem has something to do with cookies and posting
through Google.

When I learned about motors, I was taught that a motor generates a back
emf because there is a rotating magnetic field cutting the conductors
in the winding. When a motor is running the back emf is close the
applied voltage and the amount of current drawn is proportional to the
net emf / the inductance and resistance of the winding. Increase the
load on the motor and the speed decreases, back emf goes down, net
voltage goes up, and current goes up. Decrease the load and the speed
increases, net voltage goes down and current goes down. Decrease the
load some more until it is negative ( mechanical power going into the
motor ) speed increases, net voltage goes negative ( back emf is
larger that applied voltage ) and the current goes negative ( power
goes into the mains ).

This works from locked rotor to induction generator for single phase
and three phase motors. Just don't try the locked rotor for very long
unless you have an AC servo motor.

Now when you have a three phase motor running on single phase power, it
still works. A back emf is generated that keeps the net voltage across
the terminal connected to the mains from being very large. But you
also have a back emf generated in the windings that connect to the
terminal that is not connected to the mains. Not quite as large as the
emf from the mains, but nearly as large. So you have single phase
power being consumed and three phase power being generated.

This may not be the only way to analyse a RPC, but it works for me, and
I think it works for Don Young and Pentagrid. Speak up if you
disagree.

A couple of aside issues. An induction generator will work without
being connected to the mains. Google enough and you will find some web
sites that talk about using an induction motor and a lawn mower type
engine to power field ham radio stations. Such a generator is load
sensitive.

Also a rather nice RPC can be made using a single phase motor to drive
a three phase motor using an adjustable belt drive. Both motors are
connected to the mains and the belt drive adjusted so the current to
the single phase motor is at or below the nameplate current when
supplying three phase power to the load. I think this type of RPC will
supply three phase power that is more balanced and therefore suitable
to run things as surface grinders that are sensitive to harmonics in
the power.

Dan


Robert Swinney wrote:


An induction motor is a consumer, not a generator. As you know true
induction generators (induction motors) have to be excited by overdrive from
the AC mains in order to generate. Tht is not done in any fashion in a RPC.
The RPC is a load on the mains, not a supplier to the mains. Again, I'll
say, we need lose the idea of a RPC being a generator. Think of it as more
of a converter; well, that's part of it's name now isn't it?

Bob Swinney

The only reason I can see for a flywheel to be advantageous is if you
were spinning the rpc up by hand before cutting in the power to lessen
the duration of high current draw.

On Tue, 3 Jan 2006 21:07:42 +0000 (UTC), Christopher Tidy
wrote:


I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get
a flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.


I won't touch the theoretical discussions on this thread. However I
thought I might mention that if you wanted to experiment cheaply I'm
sure you can find a used cast iron pulley in large enough diameter to
serve as your flywheel. Preferably a multi-groove pulley.

Wayne Cook
Shamrock, TX
http://members.dslextreme.com/users/waynecook/index.htm

Wayne Cook wrote:
On Tue, 3 Jan 2006 21:07:42 +0000 (UTC), Christopher Tidy
wrote:



I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get
a flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.



I won't touch the theoretical discussions on this thread. However I
thought I might mention that if you wanted to experiment cheaply I'm
sure you can find a used cast iron pulley in large enough diameter to
serve as your flywheel. Preferably a multi-groove pulley.

Thanks for that thought, Wayne. It actually entered my head a month or
two ago, but for some reason I'd forgotten about it again. I have a
couple of two-groove cast iron pulleys which fit this motor. Each weighs
about 10 lb and is about 8" in diameter. I'm not sure if I can fit two
on the shaft, but it'll certainly take one.

It seems like there is no data regarding flywheels on RPC idlers. A few
people have suggested that it may help with plug reversing (which is
what I was thinking) but it seems unclear what the effect will be while
the convertor is running in a steady state. My motor already has a
pretty heavy rotor (about 8" diameter), but the energy stored will be
reduced by the fact that it spins fairly slowly (940 rpm). My aim is to
get the best performance out of a convertor with a limited idler size.

If I get chance to experiment with a flywheel and acquire some data, I
will. Thanks for all the input.

Chris

Since the running idler and load motors are directly connected in parallel,
wouldn't plug reversing with identical motors and no mechanical load have an
equal chance of reversing either motor? When running free, it seems to me
that either motor could be considered to be the source or load for the third
phase leg. I tend to believe that the idler requires more mechanical inertia
than the load to maintain the best functioning.

If an induction motor does not "generate", is induced counter EMF imaginary
and the use of common induction motors as generators impossible? There are
many ways to understand and describe how things work and I like to think of
the RPC as simply a running induction motor with the magnetized rotor
inducing EMF not only into the line energized windings (counter EMF) but
also into the unenergized and phase displaced windings. Note that, when
disconnected and still turning, an induction motor still has voltage across
its windings and loading this voltage with "braking" resistors will
mechanically load the rotor. I do not claim that this is the only way to
describe it or that any description can change the operating principles
involved.

Don Young
"Christopher Tidy" wrote in message
...
Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to a
rotary phase convertor. I've heard varying opinions on the subject. Having
thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it is
not connected directly to the supply. The flywheel doesn't change this.
Nor will it change the steady speed at which the rotor turns, so unless it
has some averaging effect on a cycle-by-cycle basis which I haven't
considered, it won't affect the quality of the three phase output when the
convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load motor.
As far as I can see (on the most simplistic level), the motor with the
most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get a
flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

Don Young sez:

"Since the running idler and load motors are directly connected in parallel
.. . ."

You are right about there being "many ways to understand and describe how
things work" but the concept of an idler and load motor's respective
windings being in parallel is not one of them.

Bob Swinney

"Don Young" wrote in message
...
wouldn't plug reversing with identical motors and no mechanical load have
an equal chance of reversing either motor? When running free, it seems to
me that either motor could be considered to be the source or load for the
third phase leg. I tend to believe that the idler requires more mechanical
inertia than the load to maintain the best functioning.

If an induction motor does not "generate", is induced counter EMF
imaginary and the use of common induction motors as generators impossible?
There are many ways to understand and describe how things work and I like
to think of the RPC as simply a running induction motor with the
magnetized rotor inducing EMF not only into the line energized windings
(counter EMF) but also into the unenergized and phase displaced windings.
Note that, when disconnected and still turning, an induction motor still
has voltage across its windings and loading this voltage with "braking"
resistors will mechanically load the rotor. I do not claim that this is
the only way to describe it or that any description can change the
operating principles involved.

Don Young
"Christopher Tidy" wrote in message
...
Hi all,

I'm trying to figure out if there is any benefit in adding a flywheel to
a rotary phase convertor. I've heard varying opinions on the subject.
Having thought about it myself, I've reached the following conclusions:

(i) The sag in voltage on the third line is caused by the fact that it is
not connected directly to the supply. The flywheel doesn't change this.
Nor will it change the steady speed at which the rotor turns, so unless
it has some averaging effect on a cycle-by-cycle basis which I haven't
considered, it won't affect the quality of the three phase output when
the convertor is running in a steady state.

(ii) It might be an advantage when trying to plug reverse the load motor.
As far as I can see (on the most simplistic level), the motor with the
most kinetic energy will win.

I can't seem to find any used flywheels to fit my motor, but I can get a
brand new flywheel for £40. I'm not sure if it is worth it in order to
satisfy my scientific curiousity. If I get a different motor, I can get a
flywheel for next to nothing, but that will involve lots of effort,
bartering and deals in order to get a motor which isn't quite so cool.

Any opinions and arguments? Thoughts would be appreciated...

Best wishes,

Chris

On Wed, 4 Jan 2006 00:12:38 -0600, "Robert Swinney"
wrote:

Don Young sez:

"Since the running idler and load motors are directly connected in parallel
. . ."

You are right about there being "many ways to understand and describe how
things work" but the concept of an idler and load motor's respective
windings being in parallel is not one of them.

Bob Swinney

Hey, Bob, what about delta-wound motors? Sure looks parallel to me!

Hey, Don, it sounds like you are beginning to go off half cocked, sort of
"Iggy style".

Do this: Visualize 2 deltas connected in "parallel" if you will..
Obviously the current paths through the branches, where the lines are
connected, are in parallel. Now look at the common point where the other 2
legs of both deltas connect together. Those points are no more in parallel
than they would be if they were between two wyes.

It may be helpful to look at the configuration in its wye equivalent. Same
thing. All this speaks to the very complex current flow in an idler and
load connected as a RPC. Two 3-phase induction motors running on the same
3-phase line do not constitute a RPC. A RPC is two 3-phase induction motors
running on single-phase current. Capacitor augmentation assists in tuning
the network such that it appears to be operating from a 3-phase line.

Bob Swinney



"Don Foreman" wrote in message
...
On Wed, 4 Jan 2006 00:12:38 -0600, "Robert Swinney"
wrote:

Don Young sez:

"Since the running idler and load motors are directly connected in
parallel
. . ."

You are right about there being "many ways to understand and describe how
things work" but the concept of an idler and load motor's respective
windings being in parallel is not one of them.

Bob Swinney

Hey, Bob, what about delta-wound motors? Sure looks parallel to me!