why make ac then change to dc

[artv]

here we go again....? couldn't you make one rotor all north mags and the other all souths?.wouldn't this produce dc with the right wiring configuration then you wouldn't lose any voltage at the diodes and just charge your batteries directly. Also would this arrangement not make for a more uniform magnetic field ......the north rotor pulling towards the south.........thanx for any input.........artv                                                                                                                       

[Boss]

I think it is the change from north to south which causes the greatest flux
I hope that helps

[wooferhound]

It's the Change in magnetic strength at the coil that produces voltage.
Changing from North to South creates the maximum change that is possible.

Also you want to create a Magnetic Circuit to channel the Flux.
Putting all Magnetic Norths on one rotor would prevent the Circuit from forming.

[artv]

how would puting alll the N/S opposite each other kill the flow

[bob g]

it won't kill the magnetic circuit as it relates to cutting through the coils
but it will dramatically reduce it.

here is why

the magnets on one plate will be north, and south on the opposing

on the north plate the south pole of the magnet will be sucked up to the steel
 
that south pole needs to find a north pole to complete a magnetic circuit, but none exists
with your arrangement, all the magnets on that plate are north facing toward the airgap
and south to the plate.

thats one part of the problem

the other is the voltage will certainly always surge positive with each passing of the magnet pairs, but
it will go heavy negative when the magnets pass because the current collapses and induces a reverse voltage in the coil

the end result is a very ragged alternating current that will need rectification to get back to DC

DC generators get away without diodes because they use mechanical rectification by means of the commutator and brushes
although the result is still pulsating it is always a pulsating DC current out the leads.

what you are contemplating would be a waste of magnets and wire, let alone your time. it will work in a fashion but will still require diodes
and the output will be perhaps as low as 1/4 or less that of a conventional design using standard magnetic circuit construction.

ymmv,  and my opinion only

bob g

[Flux]

You are thinking of the homopolar generator that produces dc instead of ac, it has never turned out to be a practical idea and can't be built without brushes, even then it is a messy contraption and has made little headway.

All practical generators produce ac in the coils, dc machines use commutators and brushes but in reality this is nothing more than a mechanical synchronous rectifier and it is now generally easier to substitute a silicon rectifier and use a 3 phase alternator.

Yes you can indeed use all N poles on one disc and all south poles on the other, it can still work and work reasonably effectively but you need a different coil layout, the final result is however no different , it still produces ac in the coils.

This and control and all the other issues has been sorted out many years ago, materials change but fundamental ideas don't , it has all been done before. recent stuff is all on the internet but much of the early work has been forgotten and I see examples nearly daily where ideas 150 years old are being re invented.

Flux

[bob g]

reinvention?

isn't that the truth, even the much loved aircore alternator made its original debut back in the 1880s
only thing different with the ones built here and elsewhere is the use of neo magnets which i am sure
the originator would have used in had they been available.

an excellent book on early alternator and generator development is

Dynamo-electric machinery
a manual for students of electrotechniics
by silvanus p. thompson
(my copy is from 1893, but there is an earlier and several later publish editions)

anyone thinking about alternator design would be well advised to get a copy of this book, most especially if he thinks he
has designed something new. 

aside from new materials there is really not much new under the sun.

bob g

[artv]

thanx for the replies ......bobg you said when the mags pass it will be a positive surge then go heavy neg because of the collapsing field but if the mags are all tight together wouldn't it be a constant postive surge without the feild ever collapsing...........my thinking is with all the mags the same polarity nnnnn.....the fields would repel each other on the north rotor forcing them to the south rotor..........in the arrangement nsns on the rotor it seems to me that the flux is forming semi circles as well as drawing towards its counterpart....wasting half the flux........I'm also thinking the arrangment of mags are on the outside of the rotor say 10"dia. with the 2nd rotor 11.5" 5/8 layer of short strands of wire 1/4 longer than length of magnet (rectangles), copper ring  to connect the leads......or would the leads have to be hooked in a certian sequence................"your either laughing or scared"............lol ...artv

[ghurd]

if the mags are all tight together wouldn't it be a constant postive surge without the feild ever collapsing...........my thinking is with all the mags the same polarity nnnnn.....

Without a changing field, relative to the coils, there is no voltage produced.
Otherwise, we could just lay a magnet on a coil.
G-

[artv]

In the book I have it says "moving a conducter perpindicular to the north south  magnetic field causes electron flow" at 90`in one direction only it dosen't say anything about "changing feilds"...........the designs here ...."and very good ones I might add"....."like I know anything ha ha....sorry the dots are just me thinking.........the designs here    push electrons up the left and down the right on the coils in the proper sequence or vice a versu   "changing fields " (south mag enters left leg of coil while north hits right side, thus producing flow in the same direction.............??

[Flux]

That book and similar ones causes infinite confusion, this is the basic starting point in the early  cgs days.

The whole thing causes so much confusion that I keep trying to persuade people to forget it. In real life you can't have a single conductor moving through a uniform field. As soon as you connect something to its ends you make a loop and the volts in the connecting leads cancel the volts in the wire.That is why the homopolar generator has to have brushes.

In a real generator you think in terms of flux linking a coil and this can only occur when there is a change of magnet polarity. Forget that book and stop dreaming up impossible ideas, it will lead nowhere unless you have sufficient basic knowledge to understand it in greater depth and from your questions you don't.

I am not trying to discourage original thought, just trying to steer you away from concepts that go nowhere.

Flux

[artv]

not to worry I don't get discouraged the book I have shows in the diagram that the armature as a single strand (I realize you need many strands ) formed in a loop with the leads being the outputs....at 0degrees 0induced voltage at 90 degrees max volts  180 degrees 0volts  270 degrees max -volts 360 degrees complete cycle..... sine wave .Here the designs used in three phase gens you make three sine waves equally spaced ....correct? The dc gen produces +volts at 90 degrees and 270 degrees .In both cases you climb from 0volts to max volts in 1/4 rev at these positions the armature is cutting the magnetic field the greatest. Is this right or should I just go and burn this book ......after all what good is a book if it teaches you the wrong basic ideas....If this is correct then designing an armature that cuts magnetic field at max at all times seems to be what we should be aiming for....?

[ghurd]

"moving a conducter perpindicular to the north south  magnetic field causes electron flow" at 90`in one direction only it dosen't say anything about "changing feilds".......the designs here    push electrons up the left and down the right on the coils in the proper sequence or vice a versu   "changing fields " (south mag enters left leg of coil while north hits right side, thus producing flow in the same direction.............??

Flux said "think in terms of flux linking a coil and this can only occur when there is a change of magnet polarity."

Think about a transformer.  The coils are linked.  They are not "(south mag enters left leg of coil while north hits right side)"

Connect a transformer to DC.  The output will be a voltage spike, then nothing.  Shortly after, the primary coils melt.

G-

[bob g]

if you want to read a book on alternator/generator design get the one i mentioned, they are available used from various sources
on ebay and amazon (and others) for not a lot of money.

if for no other reason than to go back in time and see just how many different designs were tried, which were successful and why, which were
unsuccessful and why , and...

when you think you have thought up some new design it is humbling to go to that book and realize that over 100 years ago there were others that already tried it and either succeeded or failed.

the back of the book as a couple dozen fold out plates that are just downright beautiful in my opinion, illustrating a time when it was not enough
to build a machine that was functional but it must also be beautiful in form.  mine are in such poor condition that i am considering removing them
and reproducing them in larger format and frame a few examples to hang on my walls.

aside from that, there are very few books on the subject of alternator or generator design that are clearly laid out and useful in understanding
proper design, most illustrate in such an elementary way so as to be about useless.

my opinion only

from about 1880 to 1895 was the golden age of alternator generator and motor design, during those years there were hundreds of men
all of which were engineers of some sort, working for several dozen very competitive companies designing and testing machines. these men
worked long hours coming up with different designs 8-10 hrs per day, probably an equal amount of time off the clock and many would wake at
night to pencil out a design that might be keeping them up and interfering with their sleep.  they not only did this during those years
but most did it their whole lives.

its really hard for me to imagine that a diy'er in 2010 is going to come up with any design that is different and anywhere near as successful
let alone more successful than anything that was done before by those me way back when. with the exception of improved materials there
really has been no new alternator or generator design in the last 100 years that i know of, and i would really like to know of a single example.

this does not mean a diy'er should quit thinking or dreaming, quite the contrary. what i am saying is one might be better served to go back
and study those golden years and get an appreciation of what was done back then. what would be more useful would be the reapplication of
a particular design to a task at hand, such as has taken place with the aircore alternator that has changed diy windpower over the last several years.

bob g

[artv]

great replies from all of you ....I will get one of those books .. bob g.....thanx ...been looking already..with 12 mags and 9 coils in the 10' turbine the dans built, once its connected together you basiclly have three coils .......correct ?thereby three phase offset by 30degrees/phase.So once were spinning the mags every 10 degrees hits max voltage..........is this right??

[fabricator]

Transporting DC any distance takes a lot larger wire so it is more expensive, Tesla and Westinghouse beat out Edison for that reason, that and all the linemen getting fried by high voltage DC.

[boB]

This idea will work for a quick moment until you run out of flux to satisfy Faraday's law.


And DC ~IS~ the preferred mode for transmitting power long distances, or thousands of miles.

http://en.wikipedia.org/wiki/High-voltage_direct_current

boB

[fabricator]

That's what I get for believin the history channel.

[boB]

That's what I get for believin the history channel.

If I saw some of the same stuff you may have seen, that WAS correct about AC being better for long distances
 because at that time (Tesla and Edison's time), they didn't have all the nice voltage conversion
semiconductors and stuff that we have today.  AC could just be up and down converted using transformers.

That works great from Niagra Falls to NY City or wherever it was they sent it.  Buffalo NY maybe ?

It just depends on how far you want to send the electricity.  LONG ways, DC, semi long ways, AC.

  That's my take on it anyway.

boB

[Perry1]

if you want to read a book on alternator/generator design get the one i mentioned, they are available used from various sources
on ebay and amazon (and others) for not a lot of money.

if for no other reason than to go back in time and see just how many different designs were tried, which were successful and why, which were
unsuccessful and why , and...

You can view the entire book on goggle books here, definetely worth a bookmark.

http://books.google.com/books?id=-MVIAAAAMAAJ&pg=PA200&lpg=PA200&dq=Dynamo-electric+machinery+a+manual+for+students+of+electrotechniics+by+silvanus+p.+thompson&source=bl&ots=qgOx3IB7HX&sig=S4bQR2C9J1irAPSeKCiZWnVG22k&hl=en&ei=g0jWS6mFDIT48AbhssSqDw&sa=X&oi=book_result&ct=result&resnum=2&ved=0CA4Q6AEwAQ#v=onepage&q&f=false

Perry

[artv]

If I hold a piece of coil wire, in amagnetic field,....then create motion ,........ this will induce a voltage(emf)..........in the conductor.....current only occurs when you attach resistance......such as a load.......when you attach this load .........the draw of the current leaves behind" swirls"aka eddy currents..........its like a boat in the water ............these eddies fight ,..or resisit ,...against the energy that creates it........for every action  ther is a reaction............artv

[willib]

This idea will work for a quick moment until you run out of flux to satisfy Faraday's law.


And DC ~IS~ the preferred mode for transmitting power long distances, or thousands of miles.

http://en.wikipedia.org/wiki/High-voltage_direct_current

boB

I question that link ..

That goes against everything i learned in school about power transmission ..

I thought THAT transmission argument was was settled years ago when Edison wanted to use DC .

We even proved mathematically That the transmission of electric power was more efficient using AC than DC.

[bob g]

it used to be much more efficient to transport AC over long distance, using very high voltages and step down
transformers at the end, but

with the advent of power electronics, it is now more efficient to transport extremely high DC voltages over very long
distances, and convert to AC downrange

seems like this was decided about 20 years ago, with some lines of 1 million volts DC being used over very long distances.

bob g

[DamonHD]

HVDC (High Voltage Direct Current) avoids capacitive and inductive (coupling) losses of AC, plus means that you can run the cable at maximum rating all the time not just twice per cycle, AND makes it possible to couple separate unsynchronised grids which is especially useful over greater distances: what's not to like?  B^>

Rgds

Damon

[zap]

seems like this was decided about 20 years ago

bob g

I think it was realized in the '50s HVDC had it's advantages in certain situations and as you say, with power electronics other benefits are offered which can be played against AC.
Smaller right-of-ways, less conductors, less insulators...