Hybrid Car – More Fun with Less Gas

A few idiots in these groups believe Wind Generator must have PMA (permanent magnet) Motor. - Page 7

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Posted by Richardson on July 6, 2009, 3:18 am
 


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Agreed, however to assist the retard, it would be better to speak the
language that they understand, so they don't have to worry about rectifying
the output.





Posted by daestrom on July 7, 2009, 9:50 pm
 
harry wrote:

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Boy, where did you get that nonsense.  DC motor is the name given to a
particular type of machine that uses DC power to work.  It doesn't work
worth a hoot on AC.  Similarly take an AC induction motor and hook it up
to a DC supply and tell me how many times in spins.

Likewise its awfully difficult to get AC out of a DC generator.  Whereas
  most modern car alternators are just AC generators with a rectifier
built in to convert it to DC.


*SOME* motors are much easier to use as generator than others.  Running
/ regulating an induction generator without an AC supply is quite
difficult.  But using a synchronous motor as an AC generator is a snap.
  Likewise it's just about impossible to get AC from a DC generator.
Despite your silly statement that 'they are all AC'.


DC generators can still put out smoother power than rectified AC unless
you want to go to 9-phase AC generator or higher.  The 'principles' are
more than just claiming 'they are all AC'.

daestrom

Posted by clare on July 8, 2009, 3:05 am
 wrote:


The reason PM alternators are used are GOOD reasons. The load does not
need to go through  brushes and commutators like in a DC generator,
nor does feild current need to be fed  through brushes and slip-rings
like in an automotive type alternator.

This CAN be addressed , as it has been by several motorcycle
manufacturers, by building an alternator with the feild coil FIXED and
the rotor feild cores, open ended, rotating around the coil and inside
the stator. They have more air gap, so are less efficient than
rotating coil alternators, but have the advantage of being more easily
controlled.
A Hybrid alternator could easily be built that would have a relatively
weak permanent magnet rotating feild, with a fixed coil that would add
magnetic flux when the rotor was spun fast enough to produce a
specified minimum output voltage, and the feild current could be
reduced to limit the output of the alternator at higher speeds.


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No idea where you are coming from on this. Power is
power.Mechanically, torque at RPM. Higher torque or higher RPM means
more power.

Electrically power is EMF(voltage) times current(amperage) and is
measured in Watts or volt-amps

The reason automotive style electromagnet feild alternators generally
do NOT make sense is because they generally require an electrical
power source to get them started (to provide feild flux) which must
not be applied  until the device is spinning fast enough, with enough
torque available, to produce more power than the feild flux consumes.

Makes for complex controls and regulation, compared to a PWM system.

Beg to differ with you, man.
Delco Remy made DC "starterators" which were used as both motors and
generators and were brush type DC devices. Used on Many Kohler as well
as other engines. Belt driven - 6 or 12 volt.

Actually, there are such devices as "universal" motors, which are
simply wound feild brush type motors, the same as DC motors, but with
laminated iron pole shoes and armature cores to reduce eddy currents.
Any series or shunt DC motor WILL run on AC, but unless they have the
laminated cores they are quite inefficient and run hot on AC.

Not NECESSARILY true. DC permanent magnet motors have been built with
"variable flux" which make the motor speed and torque adjustable. Most
would be AXIAL flux motors (printed circuit or "pancake" armatures)
and the variable flux is acheived by moving the magnets further from,
or closer to, the armature.. Could also be radial flux with tapered
feild magnet and tapered armature . Shift the feild to vary the
magnetic flux.
Same thing can be done with a PM generator.



Well, technically, INSIDE, they ARE all AC. The generator commutator
rectifies the AC produced in the armature windings, bringing DC out.
In a motor, the commutator acts as a mechanical "inverter" providing
AC to the armature windings from the DC supply.

The reason DC generators CAN produce smoother DC is because of the
number of segments on the commutator - analogous to the number of
phases on an alternator. Running the alternator fast enough to provide
the same frequency of commutation (rectification) as the DC generator
could provide cleaner power than the DC generator because there would
me NO arcing in the "rectifier" (commutuator) section.


Posted by harry on July 8, 2009, 7:43 pm
 
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You are a very ignorant boy.  ALL rotating machines work on AC. It's
usually in the bit that spins though not neccesarily so.
DC "motors" are fitted with a clever MECHANICAL  INVERTER called a
"commutator and brushes" that makes DC into AC.
 This same device can also function as a  RECTIFIER so that the same
machine can run as a "generator" outputting DC.
But in every rotating electrical machine  there is AC.

The "Alternator" used in a car outputs DC doesn't it?  In this case it
is rectified by means of diodes.  They are not as smart bcause they
won't work  as an inverter. Though this of course is irrelevant in the
use it is put to.

Why do we use alternators in cars instead of the old "dynamos"?
Because the alternator has no commutator it can be driven faster and
will generate at lower speeds.  If you drove a dynamo at those speeds
the commutator would explode due to centrifugal force.
You can check this out, the pulley on an alternator is half the size
of a pulley on a dynamo.
Also diodes are cheaper to make than commutators & require no
maintenance.


Posted by daestrom on July 11, 2009, 2:46 pm
 harry wrote:

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Ha!  Some arm-chair 'theorist' is telling me about DC machinery!  What a
laugh.  How many 150 hp, 270V DC motors have you rebuilt?  Standard gear
on submarines boy.

As far as your 'all motors work on AC', you don't apply AC to the motor
terminals you apply DC.  Period.

But since you want to try and split hairs, consider this.  THe current
in the wire under the N pole of the stator is *always* flowing in the
same direction.  The current in the wire under the 'S' pole is always
flowing in the opposite direction.  Sounds like 'direct current' to me.

The wire is replaced with another one as the machine rotates, but the
current is always flowing in the same direction under a given magnetic
pole.  If it weren't, the thing wouldn't spin.


You're probably one of those few that insist the term 'generator' only
applies to machines that output DC and 'alternator' applies to all AC
machines.  What a joke.  Get out and work on some multi-megawatt
machines and let us know what the manufacturer calls them. (hint, the
machine in power plants is called a 'turbine-generator', not
'turbine-alternator')


Irrelevant to your other nonsense.

daestrom

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