So, I have been buying, selling and scrapping 3 phase motors in the
last couple of years. I even made (and sold) a 15 HP phase converter a
couple of months ago. That worked out great financially.

All of this made me think: what exactly is the difference between a
motor and a generator? Can a circuit of some kind be added to a
regular 3 phase motor so that it converts mechanical energy input into
electrical energy output?

For example, a phase converter is actually a "generator": if two of
its "legs" are excited with single phase input, it "generates" third
phase that is shifted 120 degrees.

This, obviously, does not qualify as a standalone generator, since it
requires snigle phase input on L1-L2.

But can this motor somehow excite itself to generate electricity?

i

On 11/16/2013 6:50 PM, Ignoramus26083 wrote:
So, I have been buying, selling and scrapping 3 phase motors in the
last couple of years. I even made (and sold) a 15 HP phase converter a
couple of months ago. That worked out great financially.

All of this made me think: what exactly is the difference between a
motor and a generator? Can a circuit of some kind be added to a
regular 3 phase motor so that it converts mechanical energy input into
electrical energy output?

For example, a phase converter is actually a "generator": if two of
its "legs" are excited with single phase input, it "generates" third
phase that is shifted 120 degrees.

This, obviously, does not qualify as a standalone generator, since it
requires snigle phase input on L1-L2.

But can this motor somehow excite itself to generate electricity?

I think that they can, but with some issues. You have to spin them up
with externally supplied power, or at least get it biased up, so it
generates the stator field. The power factor sucks.

Look up self excited induction generator or self excited squirrel cage
generator. A solar energy place I talked to a few years ago was planning
on using them. In the process of studying for the interview, it appeared
to me that there are several better choices, but they do work.

BobH

Ignoramus26083 fired this volley in
:

But can this motor somehow excite itself to generate electricity?

Short answer, "No." Not unless it was a permanent-magnet motor or had a
wound armature fed through slip rings or a commutator. There has to be
something to excite the fields initially. Common AC motors use reverse-
EMF in the armature to repel the fields, but the armature gets its
excitation from the field windings.

So-called "universal" motors can act as generators, so long as they
either retain some residual magnetism in their fields, or have a DC
supply to provide excitation until they can supply their own through a
rectifier.

Lloyd

On 2013-11-17, BobH wrote:
On 11/16/2013 6:50 PM, Ignoramus26083 wrote:
So, I have been buying, selling and scrapping 3 phase motors in the
last couple of years. I even made (and sold) a 15 HP phase converter a
couple of months ago. That worked out great financially.

All of this made me think: what exactly is the difference between a
motor and a generator? Can a circuit of some kind be added to a
regular 3 phase motor so that it converts mechanical energy input into
electrical energy output?

For example, a phase converter is actually a "generator": if two of
its "legs" are excited with single phase input, it "generates" third
phase that is shifted 120 degrees.

This, obviously, does not qualify as a standalone generator, since it
requires snigle phase input on L1-L2.

But can this motor somehow excite itself to generate electricity?

I think that they can, but with some issues. You have to spin them up
with externally supplied power, or at least get it biased up, so it
generates the stator field. The power factor sucks.

You spin a generator with mechanical power, for example a gasoline
engine.

Look up self excited induction generator or self excited squirrel
cage generator. A solar energy place I talked to a few years ago was
planning on using them. In the process of studying for the
interview, it appeared to me that there are several better choices,
but they do work.

I believe that if I excite one leg with DC, it will statr producing
AC. Right?

PS...
Bob's right that they _can_ be made to self-excite with a DC supply to kick
them, and DC external circuitry to continue the excitation, but their
energy density sucks.

Lloyd

Ignoramus26083 fired this volley in
:

I believe that if I excite one leg with DC, it will statr producing
AC. Right?

Ayup... with lousy efficiency, because it's only the decaying flux in the
armature passing AWAY from the excitation and under the next field that
would transfer energy to the other fields.

Works... yes... efficient, not.

LLoyd

Ignoramus26083 wrote:

So, I have been buying, selling and scrapping 3 phase motors in the
last couple of years. I even made (and sold) a 15 HP phase converter a
couple of months ago. That worked out great financially.

All of this made me think: what exactly is the difference between a
motor and a generator? Can a circuit of some kind be added to a
regular 3 phase motor so that it converts mechanical energy input into
electrical energy output?

The home power crowd has used big induction motors as alternators
for years. One big problem is you have poor/no control of frequency.
You spin the motor at somewhat above synchronous speed, and you
get a frequency lower than the actual rotor speed, due to slip.
It works exactly like the induction motor except everything is
reversed. It is called an induction alternator. There area
couple other problems with this system. It will not self-excite
under load, and if momentarily overloaded output will collapse and
you will have to remove all load to get the alternator re-excited.
To maintain excitation, you need to put substantial capacitor
banks across the terminals. You adjust output voltage by adjusting
the resistive load on it, I think, and adjust frequency by varying
RPM. If the motor was a 1750 RPM motor, the slip at rated load was
50 RPM, so you'd spin it at 1850 RPM to get something close to 60
Hz out.

If you Google induction alternator and maybe some things related
to off-grid power, you should turn up plenty of info.

Jon

Ignoramus26083 wrote:


I believe that if I excite one leg with DC, it will statr producing
AC. Right?
No, it will burn out. That's DC injection braking, what most VFDs
use for the final stage of stopping a motor. It may be necessary
to blip some DC on an induction alternator to get it excited,
but apparently with a cap back across the windings, they usually
will self-excite as long as there's no load on it.

Jon

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
PS...
Bob's right that they _can_ be made to self-excite with a DC supply to
kick
them, and DC external circuitry to continue the excitation, but their
energy density sucks.

Lloyd


They'll self excite just fine from residual magnetism. Single phase C2C
induction generators made from standard 3 phase motors are very common in
small scale hydro projects.

http://www.who.int/management/Induct...droSchemes.pdf

On Saturday, November 16, 2013 9:03:47 PM UTC-5, Lloyd E. Sponenburgh wrote:

But can this motor somehow excite itself to generate electricity?



Short answer, "No."

Lloyd

Short answer , "yes ".


Dan

On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus26083 fired this volley in
:

But can this motor somehow excite itself to generate electricity?

Short answer, "No." Not unless it was a permanent-magnet motor or had a
wound armature fed through slip rings or a commutator. There has to be
something to excite the fields initially. Common AC motors use reverse-
EMF in the armature to repel the fields, but the armature gets its
excitation from the field windings.

So-called "universal" motors can act as generators, so long as they
either retain some residual magnetism in their fields, or have a DC
supply to provide excitation until they can supply their own through a
rectifier.

And what if I excite one leg with DC (supply DC to L1-L2)?

i

On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
PS...
Bob's right that they _can_ be made to self-excite with a DC supply to kick
them, and DC external circuitry to continue the excitation, but their
energy density sucks.

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

i

On 2013-11-17, Jon Elson wrote:
Ignoramus26083 wrote:


I believe that if I excite one leg with DC, it will statr producing
AC. Right?
No, it will burn out. That's DC injection braking, what most VFDs
use for the final stage of stopping a motor. It may be necessary
to blip some DC on an induction alternator to get it excited,
but apparently with a cap back across the windings, they usually
will self-excite as long as there's no load on it.

Jon

So, what is a difference between a 3 phase generator and a 3 phase motor?

Ignoramus26083 fired this volley in
:

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

If you excite all three windings, yes.

LLoyd

On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus26083 fired this volley in
:

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

If you excite all three windings, yes.

Right. If I connect the motor to the grid, and run it at above the
synchronous speed, it will feed energy to the grid and I can get paid
for it (or reduce my electric bill).

But what if there is no electrical grid, can I somehow make it excite
itself?

i

On 2013-11-17, Ignoramus26083 wrote:
On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus26083 fired this volley in
:

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

If you excite all three windings, yes.

Right. If I connect the motor to the grid, and run it at above the
synchronous speed, it will feed energy to the grid and I can get paid
for it (or reduce my electric bill).

But what if there is no electrical grid, can I somehow make it excite
itself?

i

In a way, if I may say, I want to not take NO for an answer, at least
for a while.

i

On Sat, 16 Nov 2013 20:35:37 -0600, Ignoramus26083
wrote:

On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
PS...
Bob's right that they _can_ be made to self-excite with a DC supply to kick
them, and DC external circuitry to continue the excitation, but their
energy density sucks.

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

Similar to what you're talking about, see these 12v systems.

Look at some of the hand powered generators on YouTube, Ig. Take an
old automotive alternator and create backup power from it.

http://www.prestowind.com/ American made systems. Good pricing.
Perfect to back up a solar/battery power system.

--
We are always the same age inside.
-- Gertrude Stein

Ignoramus26083 wrote:

On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
PS...
Bob's right that they _can_ be made to self-excite with a DC supply to
kick them, and DC external circuitry to continue the excitation, but
their energy density sucks.

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

i
There's a guy on the Colorado River that is many miles from the
grid. But, he has guaranteed water rights to some insane number
of cubic feet / second of the river included in his deed.
So, he built a micro hydro system. He used a modest 3 phase
induction motor, banks of caps to ensure excitation, and a
huge tapped resistor grid to regulate the thing. I think there
was a flyball governor that controlled RPM by throttling the
water flow. He apparently had this running for at least a decade
when I read about it in the Mother Earth News back in the '70s.
Apparently his regulation was so good electric clocks ran accurately,
and only needed resetting every few weeks. he sold excess power
to his neighbor. Since the electricity was free, he used it for
EVERYTHING, electric resistive heating, etc.

There are neighborhood micro hydro systems in various off-grid
areas of the US that have been running for years, although they
may not be quite as sophisticated as the Colorado river one.

Jon

Ignoramus26083 wrote:


And what if I excite one leg with DC (supply DC to L1-L2)?

i
You get a brake. No DC is needed, just the capacitors.

Jon

Ignoramus26083 wrote:

On 2013-11-17, Jon Elson wrote:
Ignoramus26083 wrote:


I believe that if I excite one leg with DC, it will statr producing
AC. Right?
No, it will burn out. That's DC injection braking, what most VFDs
use for the final stage of stopping a motor. It may be necessary
to blip some DC on an induction alternator to get it excited,
but apparently with a cap back across the windings, they usually
will self-excite as long as there's no load on it.

Jon

So, what is a difference between a 3 phase generator and a 3 phase motor?
Absolutely no difference between an induction motor and an induction
alternator, except the cap bank for excitation.

Now, a real 3-phase alternator has a DC winding in the rotor
and a regulating device to control that DC excitation based on
output voltage and phase angle. Modern portable generators
use permanent magnets in the rotor and get rid of the regulator.

An induction AC motor uses the field of the stator to create an
induced field in the shorting bars of the rotor. This requires
the stator current to always have a lagging power factor.
The principle of the induction alternator is to get the same
induced field in the rotor by making the stator always have
leading current in it. (Everything has to be backwards as the
direction of power flow is backward.) Placing capacitors
across the line terminals assures a leading power factor, and
that will keep the alternator excited. Then, you have to
apply a load to the alternator to prevent the voltage from
soaring. You may also have to cut capacitors in and out
as load varies.

All electrical machine are supposed to be reversible.

Jon

On 2013-11-17, Jon Elson wrote:
Ignoramus26083 wrote:

On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
PS...
Bob's right that they _can_ be made to self-excite with a DC supply to
kick them, and DC external circuitry to continue the excitation, but
their energy density sucks.

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

i
There's a guy on the Colorado River that is many miles from the
grid. But, he has guaranteed water rights to some insane number
of cubic feet / second of the river included in his deed.
So, he built a micro hydro system. He used a modest 3 phase
induction motor, banks of caps to ensure excitation, and a
huge tapped resistor grid to regulate the thing. I think there
was a flyball governor that controlled RPM by throttling the
water flow. He apparently had this running for at least a decade
when I read about it in the Mother Earth News back in the '70s.
Apparently his regulation was so good electric clocks ran accurately,
and only needed resetting every few weeks. he sold excess power
to his neighbor. Since the electricity was free, he used it for
EVERYTHING, electric resistive heating, etc.

There are neighborhood micro hydro systems in various off-grid
areas of the US that have been running for years, although they
may not be quite as sophisticated as the Colorado river one.

Jon

That's interesting. Let's say that RPM of the rotor is a regulatd
value. Do you recall how he used resistors and capacitors to regulate
AC? It seems like a good project to do and write up about.

i

On 11/16/2013 7:42 PM, Larry Jaques wrote:
On Sat, 16 Nov 2013 20:35:37 -0600, Ignoramus26083
wrote:

On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
PS...
Bob's right that they _can_ be made to self-excite with a DC supply to kick
them, and DC external circuitry to continue the excitation, but their
energy density sucks.

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

Similar to what you're talking about, see these 12v systems.

Look at some of the hand powered generators on YouTube, Ig. Take an
old automotive alternator and create backup power from it.

http://www.prestowind.com/ American made systems. Good pricing.
Perfect to back up a solar/battery power system.

--
We are always the same age inside.
-- Gertrude Stein

It's been 40 years, so I can't give you any details...but I
remember something about the optimum angle between the field and the
armature being different whether a device is used as a motor
or a generator.

On 2013-11-17, Jon Elson wrote:
Ignoramus26083 wrote:

On 2013-11-17, Jon Elson wrote:
Ignoramus26083 wrote:


I believe that if I excite one leg with DC, it will statr producing
AC. Right?
No, it will burn out. That's DC injection braking, what most VFDs
use for the final stage of stopping a motor. It may be necessary
to blip some DC on an induction alternator to get it excited,
but apparently with a cap back across the windings, they usually
will self-excite as long as there's no load on it.

Jon

So, what is a difference between a 3 phase generator and a 3 phase motor?
Absolutely no difference between an induction motor and an induction
alternator, except the cap bank for excitation.

Now, a real 3-phase alternator has a DC winding in the rotor
and a regulating device to control that DC excitation based on
output voltage and phase angle. Modern portable generators
use permanent magnets in the rotor and get rid of the regulator.

An induction AC motor uses the field of the stator to create an
induced field in the shorting bars of the rotor. This requires
the stator current to always have a lagging power factor.
The principle of the induction alternator is to get the same
induced field in the rotor by making the stator always have
leading current in it. (Everything has to be backwards as the
direction of power flow is backward.) Placing capacitors
across the line terminals assures a leading power factor, and
that will keep the alternator excited. Then, you have to
apply a load to the alternator to prevent the voltage from
soaring. You may also have to cut capacitors in and out
as load varies.

All electrical machine are supposed to be reversible.

Jon

Thanks. This actually makes sense. It would seem that it is
straightforward to build a 3 phase alternator to produce power, as you
described.

It may require some initial flashing to get started from black start,
but it will work. At the same time, such a system would be difficult
to regulate for constant voltage as load varies.

On Sat, 16 Nov 2013 18:57:16 -0700, BobH wrote:

On 11/16/2013 6:50 PM, Ignoramus26083 wrote:
So, I have been buying, selling and scrapping 3 phase motors in the
last couple of years. I even made (and sold) a 15 HP phase converter a
couple of months ago. That worked out great financially.

All of this made me think: what exactly is the difference between a
motor and a generator? Can a circuit of some kind be added to a regular
3 phase motor so that it converts mechanical energy input into
electrical energy output?

For example, a phase converter is actually a "generator": if two of its
"legs" are excited with single phase input, it "generates" third phase
that is shifted 120 degrees.

This, obviously, does not qualify as a standalone generator, since it
requires snigle phase input on L1-L2.

But can this motor somehow excite itself to generate electricity?

I think that they can, but with some issues. You have to spin them up
with externally supplied power, or at least get it biased up, so it
generates the stator field. The power factor sucks.

Look up self excited induction generator or self excited squirrel cage
generator. A solar energy place I talked to a few years ago was planning
on using them. In the process of studying for the interview, it appeared
to me that there are several better choices, but they do work.

BobH

When I was an undergrad induction generators were considered the bee's
knees for wind power because they didn't require synchronization.

Technology has marched on since then, by a few decades.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

Ignoramus26083 wrote:



That's interesting. Let's say that RPM of the rotor is a regulatd
value. Do you recall how he used resistors and capacitors to regulate
AC? It seems like a good project to do and write up about.

i
I think the deal was that the power output had to be constant.
So, if he wasn't using much power in the middle of the night, the
resistors had to absorb the maximum power he would use during the
day. There are probably more intelligent (efficient) ways to
regulate it. But, his energy input was free and constant, so
he didn't care.

Jon

On Sat, 16 Nov 2013 19:42:20 -0800, Larry Jaques
wrote:

On Sat, 16 Nov 2013 20:35:37 -0600, Ignoramus26083
wrote:

On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
PS...
Bob's right that they _can_ be made to self-excite with a DC supply to kick
them, and DC external circuitry to continue the excitation, but their
energy density sucks.

For me, number one question is whether it is possible to get decent AC
(1 or 3 phase), with some excitation. Efficiency is a secondary question.

Similar to what you're talking about, see these 12v systems.

Not really as the auto "alternator" is just a small A.C. generator
complete with a DC excieted rotor which is used to control output. The
D.C. output comes from rectifiers.


Look at some of the hand powered generators on YouTube, Ig. Take an
old automotive alternator and create backup power from it.

http://www.prestowind.com/ American made systems. Good pricing.
Perfect to back up a solar/battery power system.
--
Cheers,

John B.

On Saturday, November 16, 2013 8:50:33 PM UTC-5, Ignoramus26083 wrote:


For example, a phase converter is actually a "generator": if two of

its "legs" are excited with single phase input, it "generates" third

phase that is shifted 120 degrees.



This, obviously, does not qualify as a standalone generator, since it

requires snigle phase input on L1-L2.



But can this motor somehow excite itself to generate electricity?



i

If you connect a internal combustion engine to a " phase converter " , and arrange the gearing between the phase converter and the engine so the engine puts power into the system, you will have a three phase generator. Could be useful if you wanted to run a honking big three phase welder and did not have an electric outlet that would provide enough power for the welder.

Dan

On Sat, 16 Nov 2013 22:39:47 -0600, Ignoramus26083
wrote:

On 2013-11-17, Jon Elson wrote:
Ignoramus26083 wrote:

On 2013-11-17, Jon Elson wrote:
Ignoramus26083 wrote:


I believe that if I excite one leg with DC, it will statr producing
AC. Right?
No, it will burn out. That's DC injection braking, what most VFDs
use for the final stage of stopping a motor. It may be necessary
to blip some DC on an induction alternator to get it excited,
but apparently with a cap back across the windings, they usually
will self-excite as long as there's no load on it.

Jon

So, what is a difference between a 3 phase generator and a 3 phase motor?
Absolutely no difference between an induction motor and an induction
alternator, except the cap bank for excitation.

Now, a real 3-phase alternator has a DC winding in the rotor
and a regulating device to control that DC excitation based on
output voltage and phase angle. Modern portable generators
use permanent magnets in the rotor and get rid of the regulator.

An induction AC motor uses the field of the stator to create an
induced field in the shorting bars of the rotor. This requires
the stator current to always have a lagging power factor.
The principle of the induction alternator is to get the same
induced field in the rotor by making the stator always have
leading current in it. (Everything has to be backwards as the
direction of power flow is backward.) Placing capacitors
across the line terminals assures a leading power factor, and
that will keep the alternator excited. Then, you have to
apply a load to the alternator to prevent the voltage from
soaring. You may also have to cut capacitors in and out
as load varies.

All electrical machine are supposed to be reversible.

Jon

Thanks. This actually makes sense. It would seem that it is
straightforward to build a 3 phase alternator to produce power, as you
described.

It may require some initial flashing to get started from black start,
but it will work. At the same time, such a system would be difficult
to regulate for constant voltage as load varies.

But a generator based on an induction motor won't work WELL, and it
won't work efficiently. It's a kludge, and you have to play with it
every time, and you'll be flashing the field every time going "C'mon
baby! One more time..." You can't sell a generator built like that.

If you want to make electricity every time it starts, you can get
pre-made generator heads that bolt up to suitable gasoline or diesel
engines easily, and there are adaptors available if you want to use a
repurposed automobile engine. The tricky part then becomes finding
the right bellhousing adapter plate and coupling, a proper governor
system and interfacing the engine controls to it.

This is why the Generator Duty small engines have both an internal
oil-bath Flyweight Governor driven off the camshaft that holds right
at 1800 or 3600 RPM +/- 1% or 2%, and a fan-vane style Overspeed off
the cooling fan that cuts off if it overspeeds roughly 125% - enough
to keep the engine from grenading.

And the Generator Duty engines also have a taper-shaft with threaded
counterbore on the end, facing a 4-bolt flange cast into the engine
case face so the generator head bolts right on. And the engine has
oversized main bearings because those special generator heads only
have one ball bearing on the outboard end.

On 16 Nov 2013, Ignoramus26083
posted some :

So, I have been buying, selling and scrapping 3 phase motors in the
last couple of years. I even made (and sold) a 15 HP phase converter a
couple of months ago. That worked out great financially.

All of this made me think: what exactly is the difference between a
motor and a generator? Can a circuit of some kind be added to a
regular 3 phase motor so that it converts mechanical energy input into
electrical energy output?

For example, a phase converter is actually a "generator": if two of
its "legs" are excited with single phase input, it "generates" third
phase that is shifted 120 degrees.

This, obviously, does not qualify as a standalone generator, since it
requires snigle phase input on L1-L2.

But can this motor somehow excite itself to generate electricity?

i


With a little help certainly.

See instructions for both 3 PH and 1 PH at link below. It does work
although I'd use a DMV in conjunction with his "light bulb test".

http://www.redrok.com/cimtext.pdf

On Saturday, November 16, 2013 8:04:47 PM UTC-8, Jon Elson wrote:

So, what is a difference between a 3 phase generator and a 3 phase motor?

Absolutely no difference between an induction motor and an induction
alternator, except the cap bank for excitation.

There's a VERY BIG difference in a standard AC motor (squirrel-cage
hysteresis type) and a generator or alternator. The rotating core
of the motor is not connected with any kind of wiring to create a field
in that core, and the residual magnetism of that core is very low.

A large truly synchronous induction motor, however, DOES have slip rings,
or a commutator, and can be made to generate electricity. So can
a small synchronous motor (permanent magnet type).

All electrical machine are supposed to be reversible.

Yes, and no; the problem here is that the core is magnetizable with
continuous application of external field (powered by the AC that drives
the stator), but becomes demagnetized easily (and if the rotor isn't
magnetized, it's symmetric: it has no poles, so no generation of electricity).

Bruce L. Bergman (munged human readable) wrote:



But a generator based on an induction motor won't work WELL, and it
won't work efficiently. It's a kludge, and you have to play with it
every time, and you'll be flashing the field every time going "C'mon
baby! One more time..." You can't sell a generator built like that.

Actually, most of the wind turbines made in the last few years
use induction alternators. Now, I can easily believe these were
made SPECIFICALLY for this use, so that might make a big
difference.

They are now transitioning to permanent magnet alternators with
electronic converters for startup and then invert power
back to the mains.

Jon

Jon Elson fired this volley in
:

Actually, most of the wind turbines made in the last few years
use induction alternators. Now, I can easily believe these were
made SPECIFICALLY for this use, so that might make a big
difference.


Y'think?

I stick with my original answer. The short answer is "NO!"

You _can_ generate power with an induction motor, but everything about it
is wonky, including the phase angles, the frequency at optimum
efficiency, and the amount of power per horsepower you'll get.

It's just not worth it, unless you find a PM armature motor, or an
authentic slip-ring, wound-armature type. It's a silly waste of time to
make what you can buy for less than your hourly rate.

Lloyd

Ignoramus26083 wrote:
So, I have been buying, selling and scrapping 3 phase motors in the
last couple of years. I even made (and sold) a 15 HP phase converter a
couple of months ago. That worked out great financially.

All of this made me think: what exactly is the difference between a
motor and a generator? Can a circuit of some kind be added to a
regular 3 phase motor so that it converts mechanical energy input into
electrical energy output?

a generator tends to be fed DC power to setup the magnetic field to get
things going. Induction motors don't need this. An induction "motor" with
a DC winding is an alternator.

For example, a phase converter is actually a "generator": if two of
its "legs" are excited with single phase input, it "generates" third
phase that is shifted 120 degrees.

This, obviously, does not qualify as a standalone generator, since it
requires snigle phase input on L1-L2.

But can this motor somehow excite itself to generate electricity?

yes, under some conditions, but it's as others said, wonky in behavior and
not useful outside of experimenting out of curiosity.

You could use an alternator as a motor, but again, it's not optimal and
just something you might do for fun.

On Saturday, November 16, 2013 10:12:00 PM UTC-5, Ignoramus26083 wrote:
On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:

Ignoramus26083 fired this volley in

:



For me, number one question is whether it is possible to get decent AC

(1 or 3 phase), with some excitation. Efficiency is a secondary question.



If you excite all three windings, yes.



Right. If I connect the motor to the grid, and run it at above the

synchronous speed, it will feed energy to the grid and I can get paid

for it (or reduce my electric bill).



But what if there is no electrical grid, can I somehow make it excite

itself?



i

As an engineering student I was on a tour of one of the Roseton NY power plants.
Got to look through a small window at the astonishingly small alternator at the end of the turbine shaft.

Stuck onto the end of the alternator shaft was an even smaller excitation generator.

On 2013-11-18, Cydrome Leader wrote:
Ignoramus26083 wrote:
So, I have been buying, selling and scrapping 3 phase motors in the
last couple of years. I even made (and sold) a 15 HP phase converter a
couple of months ago. That worked out great financially.

All of this made me think: what exactly is the difference between a
motor and a generator? Can a circuit of some kind be added to a
regular 3 phase motor so that it converts mechanical energy input into
electrical energy output?

a generator tends to be fed DC power to setup the magnetic field to get
things going. Induction motors don't need this. An induction "motor" with
a DC winding is an alternator.

For example, a phase converter is actually a "generator": if two of
its "legs" are excited with single phase input, it "generates" third
phase that is shifted 120 degrees.

This, obviously, does not qualify as a standalone generator, since it
requires snigle phase input on L1-L2.

But can this motor somehow excite itself to generate electricity?

yes, under some conditions, but it's as others said, wonky in behavior and
not useful outside of experimenting out of curiosity.

You could use an alternator as a motor, but again, it's not optimal and
just something you might do for fun.

Thanks. This makes sense.

i

It is possible to a asynchronous generator/motor auto-excite utilizing the
same VA rating of generation with capacitors. but the voltage and
frequency is hard to control this way.
with no eletrical grid it is better to utilize a permanent magnetic
generator. with a electronic inverter or an generator/motor with rotor
field coil, with the last it is possible to lock the generator speed same
to mains frequency, and control the voltage regulating the field current,
very like the car alternator.

but to close circuity with the mains will be necessary to sync the phase.

the permanent magnet has better efficiency.

Regards,
Suns

On Mon, 18 Nov 2013 19:31:44 -0200, wrote:

On Saturday, November 16, 2013 10:12:00 PM UTC-5, Ignoramus26083 wrote:
On 2013-11-17, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:

Ignoramus26083 fired this
volley in

:



For me, number one question is whether it is possible to get decent
AC

(1 or 3 phase), with some excitation. Efficiency is a secondary
question.



If you excite all three windings, yes.



Right. If I connect the motor to the grid, and run it at above the

synchronous speed, it will feed energy to the grid and I can get paid

for it (or reduce my electric bill).



But what if there is no electrical grid, can I somehow make it excite

itself?



i

As an engineering student I was on a tour of one of the Roseton NY power
plants.
Got to look through a small window at the astonishingly small alternator
at the end of the turbine shaft.

Stuck onto the end of the alternator shaft was an even smaller
excitation generator.


--
Using Opera's mail client: http://www.opera.com/mail/

"F. George McDuffee" wrote in
message ...

HealthSherpa.com, which is just two weeks old, allows a user
to simply input their zip code and view all the health plans
available to them.
snip

Note this is a UK paper. Why isn't this all over the US
media?


The excuse I heard was that such a site would reveal the alarmingly
high raw cost and couldn't adjust for subsidies without the user's
data. Mustn't frighten the herd, you know.

On Tuesday, November 19, 2013 7:29:54 PM UTC-5, Lloyd E. Sponenburgh wrote:
Induction motors - that are designed to be motors - make lousy generators,

regardless of how well 'tuned' their capacitive excitations circuits are,

if they're used for any varying loads, or - for the most part - on any

inductive loads.



They're about useless for anything but purely resistive loads like

incandescent lights or resistive-limited battery charging.



Lloyd

You are right if you are talking about using an induction motor for a stand alone generator. But they work well if they are being used to feed power into the electric grid.

Dan

Ignoramus26083 wrote:



Thanks. This actually makes sense. It would seem that it is
straightforward to build a 3 phase alternator to produce power, as you
described.
Ah, finally found a serious reference on this, with actual
documented operation.
http://www.iea.lth.se/publications/T...H-IEA-1058.pdf

This was a bit bigger gear than you probably were thinking of,
275 KVA.

Jon

On Sat, 16 Nov 2013 20:03:47 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Ignoramus26083 fired this volley in
m:

But can this motor somehow excite itself to generate electricity?

Short answer, "No." Not unless it was a permanent-magnet motor or had a
wound armature fed through slip rings or a commutator. There has to be
something to excite the fields initially. Common AC motors use reverse-
EMF in the armature to repel the fields, but the armature gets its
excitation from the field windings.

So-called "universal" motors can act as generators, so long as they
either retain some residual magnetism in their fields, or have a DC
supply to provide excitation until they can supply their own through a
rectifier.

Lloyd
Not true. Induction motors CAN be used as generators Usually using a
bank of capacitors. Look up induction generators.