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DC motors for wind power

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Bart Bervoets

Jan 1, 1970
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Does anyone have any large permanent magnet motors that could be used to
build a few micro wind turbines?

Bart Bervoets
 
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JB

Jan 1, 1970
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Bart Bervoets said:
Does anyone have any large permanent magnet motors that could be used to
build a few micro wind turbines?

Bart Bervoets

There are some home made wind power generators that work a lot better. Most
motors are built for torque and are supposed to turn a lot faster than a
wind turbine, means what little power you have gets eaten up in a
transmission. Current state of the art has permanent magnets securely
mounted to a disk directly driven by the turbine and the stator windings
mounted stationary to the housing.
 
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Bryce

Jan 1, 1970
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Meat said:
Find some old DC generators from autos before they started using an
alternator. Don't know what you would use for a prop maybe some custom
thing out of a polymer like a spinner for a child's toy.

A DC generator generates an AC waveform that is mechanically rectified
by the commutator and brushes. Isn't it better to eliminate the comm
and brushes (maintenance and friction losses) and rectify with diodes?
That's what an alternator does, although its field is rotating while
the DC motor/generator field is stationary.
 
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JB

Jan 1, 1970
0
Arfa Daily said:
IIRC, alternators run faster than car engine speed so that means a
lossy transmission from a slow propeller with a lot of drive torque.
BTW, you'd get AC and then rectify to DC... not quiet clear from your
post where your "AC" and "DC" should be.
Good luck!
Cheers,
Roger

The drive pulley on my alternator is about the same size as the one on the
engine, so alternator speed should be roughly equivalent to engine speed. I
don't know whether modern car alternators still use rotating coils and slip
rings, or rotating magnets and static coils, but either way, I wouldn't have
expected there to have been a lot more mechanical losses than in the modern
wind turbine alternators. You don't need to have a car alternator turning
too fast before it reaches regulated voltage output, but I guess if you
wanted to get much actual power from it, you might need to get it going
quite fast, in which case, what you say about gearbox losses will of course,
be true.

I'm not quite sure where you are having trouble understanding what I was
saying about AC and DC. The op's original header said "DC motors for wind
power". If you use a DC motor backwards, or indeed an old car generator - or
dynamo if you like - to produce your wind driven output, then that output
will be DC. No rectification required. That satisfies what he was asking.
If, on the other hand, you use a rotating magnet, fixed stator coil
generator, then this will be an alternator, and will produce AC, which will
require rectifying to get to his originally stated requirement, yes ?

Arfa
My mistake. I was thinking he was looking for some useful output rather
than experimenting with toy motors for a science fair project. Most toy
motors will make some power if you can spin it.

Useful output demands that you design and build your own or buy the
equipment store bought for the purpose. Using automotive components
requires optimizing the turbine some how to provide adequate torque at high
RPM. The idea is to reduce the losses to the minimum AND design optimize
the turbine AND the generator to the available wind. Also bear in mind that
higher voltages reduce ohmic losses in electrical transmission.

One of the more useful designs for automotive generators and alternators,
was the modified 55 gallon drum turbine on wheel bearings with belt drive.
 
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Bryce

Jan 1, 1970
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Meat said:
Doesn't an alternator need a voltage on the field to make voltage and
then you regulate the field to regulate the output?

I guess the choice would be up to the OP and his design to store/use
the end product.

An alternator (or, for that matter, a DC generator) need some magnetic
field to sweep windings through. There's usually enough residual
magnetic field in the iron from earlier running to get things started.
The alternator on my standby-power set does this. If the residual
is too small or gone, you gotta "flash" the machine with a brief
current pulse from a storage battery to restore the residual.

Superman would use kryptonite instead.
 
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David Nebenzahl

Jan 1, 1970
0
A DC generator generates an AC waveform that is mechanically rectified
by the commutator and brushes.

No, an *alternator* does that (which is why it's so called). A generator
just generates plain old DC. Like the ones on old VWs. No diodes.

Dunno how efficient they are compared with alternators, though.
 
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David Nebenzahl

Jan 1, 1970
0
David Nebenzahl said:
[someone else wrote]
A DC generator generates an AC waveform that is mechanically rectified
by the commutator and brushes.
No, an *alternator* does that (which is why it's so called). A generator
just generates plain old DC. Like the ones on old VWs. No diodes.

The clue is in the commutator. That is a mechanical switch which does
approx. the same as the diodes in an alternator. If the dynamo
intrinsically produced DC it would merely need slip rings as in an
alternator.

What in the world are you talking about? "Mechanical switch"?

The commutator is a set of rotary contacts. My VW (old 6-volt one) had a
generator with a commutator. Produced DC without any diodes.
 
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Bryce

Jan 1, 1970
0
David said:
David Nebenzahl said:
[someone else wrote]

A DC generator generates an AC waveform that is mechanically rectified
by the commutator and brushes.
No, an *alternator* does that (which is why it's so called). A generator
just generates plain old DC. Like the ones on old VWs. No diodes.

The clue is in the commutator. That is a mechanical switch which does
approx. the same as the diodes in an alternator. If the dynamo
intrinsically produced DC it would merely need slip rings as in an
alternator.

What in the world are you talking about? "Mechanical switch"?

The commutator is a set of rotary contacts. My VW (old 6-volt one) had a
generator with a commutator. Produced DC without any diodes.
Alternators contain a pair of slip rings, one brush contacting each ring
to transfer the generated AC voltage to the output terminals. A generator
has a commutator that is made up of many copper segments separated by
insulating strips. One or more pairs of brushes ride on the commutator.
Armature coils are connected between comm bar pairs. As the generator
rotates, the coils sweep through a stationary magnetic field and
electromagnetic induction creates an AC voltage across the comm bars
which are cleverly arranged so that the positive and negative brushes
cross over the right bars at the right time to convert AC to DC without
diodes.

Old cars used generators 'cuz power diodes were in short supply a
hundred years ago. Automotive alternators became practical around
1960, thanks to silicon power diodes. Alternators are less costly
to manufacture and are more rugged.

Bryce
 
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Bart Bervoets

Jan 1, 1970
0
If you look on ebay you'll see many used treadmill PMDC motors
sold for this use.

Yes, so i now noticed, there are some solutions but alas a bit bulky.
I did some research already and have experimented with car alternators,
i got so far i can make one that charges at 400rpm but the wind is
too unpredictable and the field coil needs to be energized all the time
which drains your battery in dead moments, rather a pm alternator as
suggested as i don't feel much for having to build a dynamo from start,
but hey, if i have to...
But i did buy some motors on ebay as suggested, they are treadmill
motors.
Someone else suggested the use of a motor off an electrical bicycle,
benefit is that it's weatherproof.
I just thought someone here could sell me some instead
of on eekbay.
What i would like is an easy off the shelf solution, but i can see
that there isn't really one.
Thanks everybody for the input on this.

Bart
 
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Bryce

Jan 1, 1970
0
Bart said:
Yes, so i now noticed, there are some solutions but alas a bit bulky.
I did some research already and have experimented with car alternators,
i got so far i can make one that charges at 400rpm but the wind is
too unpredictable and the field coil needs to be energized all the time
which drains your battery in dead moments, rather a pm alternator as
suggested as i don't feel much for having to build a dynamo from start,
but hey, if i have to...
But i did buy some motors on ebay as suggested, they are treadmill
motors.
Someone else suggested the use of a motor off an electrical bicycle,
benefit is that it's weatherproof.
I just thought someone here could sell me some instead
of on eekbay.
What i would like is an easy off the shelf solution, but i can see
that there isn't really one.
Thanks everybody for the input on this.

Bart

Wind turbine kits which include everything except the tower and the wind are
available ... but at a price.

PM alternators avoid the need for field excitation, but now you need some
other way to efficiently regulate output voltage as turbine speed changes.

No need to keep the field energized when the turbine isn't turning. A bit
of control electronics solves that.

A local college just announced an associate degree program in wind power.
I wonder whether the diploma comes with a pair of wooden shoes!

Bryce
 
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Bart Bervoets

Jan 1, 1970
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Thanks for the links and as always a great story.

As well thanks from me, i know about otherpower but
i think i come right anyway.

Bart Bervoets
 
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GregS

Jan 1, 1970
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Yeah I have a 4000 watt standby AC generator that rely's on residual
magnetism. There are two types a brushed type (through which you would
flash the field with a 6 volt lantern battery) and a non-brushed type
that I forget at the moment how you get it going when the residual is
gone. But I can almost 99.9% guaranty you that if I remove the field
connection on my Harley that the alternator would produce zero
volktage.

I fooled with a funny little generator my brother gave me. It had little power.
To get it started it had a separate brushed section to get DC. Push a little
button to get it going.

I'm thinking I want to build a wind generator.

Too bad around here, we have miles of rivers, but ZERO water driven
energy. They have new turbins out that you put in rivers and get
some energy. Yeasr ago they did not even think of that. They still
don't.

greg
 
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GregS

Jan 1, 1970
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I fooled with a funny little generator my brother gave me. It had little power.
To get it started it had a separate brushed section to get DC. Push a little
button to get it going.

I'm thinking I want to build a wind generator.

Too bad around here, we have miles of rivers, but ZERO water driven
energy. They have new turbins out that you put in rivers and get
some energy. Yeasr ago they did not even think of that. They still
don't.

Now I'm feeling awfull about all the nice big DC motors I,ve thrown away.

greg
 
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David Nebenzahl

Jan 1, 1970
0
[someone else wrote]

A DC generator generates an AC waveform that is mechanically rectified
by the commutator and brushes.

No, an *alternator* does that (which is why it's so called). A generator
just generates plain old DC. Like the ones on old VWs. No diodes.

The clue is in the commutator. That is a mechanical switch which does
approx. the same as the diodes in an alternator. If the dynamo
intrinsically produced DC it would merely need slip rings as in an
alternator.

What in the world are you talking about? "Mechanical switch"?

The commutator is a set of rotary contacts. My VW (old 6-volt one) had a
generator with a commutator. Produced DC without any diodes.

The output voltage at the comm is DC not a 'switched by windings and
com bar AC'.

So you agree that a generator (motor used in reverse, i.e., driven
instead of driving, with a commutator instead of slip rings) produces DC
without rectification, not AC, correct? That was my point.

I'm not disputing that the current direction in a generator reverses
with each set of commutator bars contacted by the brushes, so I guess in
that sense one could consider the commutator a "mechanical switch". I
just regard it as the way the thing is wired to produce DC.
 
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GregS

Jan 1, 1970
0
The problem with rivers is that without a falls, there's no vertical
head to run a high speed turbine or Pelton wheel:
<http://en.wikipedia.org/wiki/Pelton_wheel>
This is usually solved by building a dam, which has profound
aesthetic, ecological, and environmental issues. It is possible to
use a fully immersed low speed turbine, but to get enough energy from
the usual slow flow rate and high volume river, the number of turbines
and/or their size tend to be large. For example:
<http://en.wikipedia.org/wiki/Kaplan_turbine>

Also:
<http://en.wikipedia.org/wiki/Water_turbine>
<http://www.homepower.com/basics/hydro/>

Another problem is that the power output of the water turbine is
directly proportional to the head and to the flow rate. Unlike the
wind turbine, where the output is proportional to the cube of the air
speed, water power generators tend to become very large at higher
power outputs. Where the flow rate is minimal, the usual solution is
a higher dam.

There are problems with everything. Here is what is being done tomorrow.

http://www.hydrogreenenergy.com/technology.html


greg
 
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Sjouke Burry

Jan 1, 1970
0
David said:
David Nebenzahl said:
[someone else wrote]

A DC generator generates an AC waveform that is mechanically rectified
by the commutator and brushes.
No, an *alternator* does that (which is why it's so called). A generator
just generates plain old DC. Like the ones on old VWs. No diodes.
The clue is in the commutator. That is a mechanical switch which does
approx. the same as the diodes in an alternator. If the dynamo
intrinsically produced DC it would merely need slip rings as in an
alternator.

What in the world are you talking about? "Mechanical switch"?

The commutator is a set of rotary contacts. My VW (old 6-volt one) had a
generator with a commutator. Produced DC without any diodes.
Wow, A miracle, please show us how!!!
In about fifty years of work in the field, this would be the
first time to see one.
 
S

Sjouke Burry

Jan 1, 1970
0
Arfa said:
Sjouke Burry said:
David said:
On 7/27/2009 11:26 PM Dave Plowman (News) spake thus:

[someone else wrote]

A DC generator generates an AC waveform that is mechanically rectified
by the commutator and brushes.
No, an *alternator* does that (which is why it's so called). A
generator just generates plain old DC. Like the ones on old VWs. No
diodes.
The clue is in the commutator. That is a mechanical switch which does
approx. the same as the diodes in an alternator. If the dynamo
intrinsically produced DC it would merely need slip rings as in an
alternator.
What in the world are you talking about? "Mechanical switch"?

The commutator is a set of rotary contacts. My VW (old 6-volt one) had a
generator with a commutator. Produced DC without any diodes.
Wow, A miracle, please show us how!!!
In about fifty years of work in the field, this would be the
first time to see one.

A generator with a commutator i.e. a car dynamo from days of yore, *does*
produce DC, and does it without diodes, courtesy of the switching action of
that commutator. I can't imagine how you've never seen one, as back in the
fifties and sixties - that is fifty years ago - that's about the only type
of generator that was fitted to car engines ...

Arfa
Read the previous response, where he says that the commutator does not
switch (windings).
 
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Bart Bervoets

Jan 1, 1970
0
Now I'm feeling awfull about all the nice big DC motors I,ve thrown away.

Last year i trashed a big comp tape drive, so i know that feeling.
But one would not get me far anyway, i need quite a few.

Bart
 
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