why doesn't my permanent magnet alternator work?

[matthew]

i just build a small permanent magnet alternator just to see if i
could do it and make some electricity, however i can't get the
alternator to work. i've included some pictures so you can see how i
constructed, wired etc the alternator.

http://www4.ncsu.edu/~mjdunay/pictures/pma5.jpg
a wiring drawing

http://www4.ncsu.edu/~mjdunay/pictures/pma6.jpg
the actual alternator

i can spin the alternator up pretty quickly but the little LED i put
in doesn't even flicker but i'm hoping it's something simple that i
over looked. to the best of my knowledge i think i've wired the thing
correctly and i've checked all the connections many times. the
magnetic poles are switched every other magnet and the coils are
wrapped in opposite directions. could my LED not work with an AC
current? do i not have a thick enough gauge magnet wire? is the
space between the magnets and the iron filings too far? have i wired
it correctly? the magnet part of the alternator spins quite evenly
(maybe only swaying a 1/16") so i don't think thats it. i definitly
would think that the magnets are strong enough to create some kind of
flicker but i just don't know. any help would be great.

also if anyone knows of a cheap place to get magnet wire on the net
let me know.

thanks
matthew

 

[Ian Stirling]

i just build a small permanent magnet alternator just to see if i
could do it and make some electricity, however i can't get the
alternator to work. i've included some pictures so you can see how i
constructed, wired etc the alternator.

magnetic poles are switched every other magnet and the coils are
wrapped in opposite directions. could my LED not work with an AC
current? do i not have a thick enough gauge magnet wire? is the
space between the magnets and the iron filings too far? have i wired
it correctly? the magnet part of the alternator spins quite evenly
(maybe only swaying a 1/16") so i don't think thats it. i definitly
would think that the magnets are strong enough to create some kind of
flicker but i just don't know. any help would be great.

You can kill the LED by supplying voltage the wrong way round.
Do you own a multimeter?

--
http://inquisitor.i.am/ | mailto:[email protected] | Ian Stirling.
---------------------------+-------------------------+--------------------------
Lord, grant me the serenity to accept that I cannot change, the
courage to change what I can, and the wisdom to hide the bodies
of those I had to kill because they pissed me off. - Random

 

[John Popelish]

i just build a small permanent magnet alternator just to see if i
could do it and make some electricity, however i can't get the
alternator to work. i've included some pictures so you can see how i
constructed, wired etc the alternator.

http://www4.ncsu.edu/~mjdunay/pictures/pma5.jpg
a wiring drawing

http://www4.ncsu.edu/~mjdunay/pictures/pma6.jpg
the actual alternator

i can spin the alternator up pretty quickly but the little LED i put
in doesn't even flicker but i'm hoping it's something simple that i
over looked. to the best of my knowledge i think i've wired the thing
correctly and i've checked all the connections many times. the
magnetic poles are switched every other magnet and the coils are
wrapped in opposite directions. could my LED not work with an AC
current?

You should get a flicker every time the voltage peaks above 2 volts in
one of the directions.

do i not have a thick enough gauge magnet wire?

Until you get current moving, you don't need thickness.

is the space between the magnets and the iron filings too far?

Closer would be a lot better. Are the coils backed up with a
magnetically permeable short from one magnet to the ones on each
side? The idea is to get the magnetic path from one side of each
magnet to its other side to contain as little air as possible. This
means that all the magnets could be mounted on a disk of iron (since
this field does not reverse, the conductivity of the iron will not
circulate eddy current). And there should be a second iron path
through the coils, that bridges from one to each of its neighbors
(another disk) behind them, but this iron sees alternating field, so
its conductivity will act like a shorted turn that circulates
current. This iron arrangement creates complete flux loops through
each magnet and both of its neighbors. It also creates quite a bit of
axial force between the rotating disk and the stationary one. This is
why this structure is usually made as one cylinder rotating inside
another, so that the forces from opposites cancel, rather than being
transmitted through the shaft. Another way to keep the magnetic
forces out of the shaft is to put magnets that attract each other on
both sides of the coils, and either rotate the magnets or the coils.
In either case the attractive force of the magnets is transmitted only
through the structure that holds them spaced away from the coils, not
through the generator bearings.

have i wired it correctly?

I would try connecting the coils in series for more voltage, instead
of in parallel (for more current). Start with the LED across a single
coil, and make sure when you series the next one, it gets brighter,
not dimmer. This will prove the series sequence needed. Any series
parallel combination can be used to trade current for voltage, as long
as all parallel units are identical (or opposite polarity and reverse
wired. This all assumes that the number of magnets and the number of
coils are equal.

the magnet part of the alternator spins quite evenly
(maybe only swaying a 1/16") so i don't think thats it.
Agreed.

i definitly would think that the magnets are strong enough to create some kind of flicker but i just don't know. any help would be great.

also if anyone knows of a cheap place to get magnet wire on the net
let me know.

It goes for about $4 per pound on Ebay.

 

[John Larkin]

i just build a small permanent magnet alternator just to see if i
could do it and make some electricity, however i can't get the
alternator to work. i've included some pictures so you can see how i
constructed, wired etc the alternator.

http://www4.ncsu.edu/~mjdunay/pictures/pma5.jpg
a wiring drawing

http://www4.ncsu.edu/~mjdunay/pictures/pma6.jpg
the actual alternator

i can spin the alternator up pretty quickly but the little LED i put
in doesn't even flicker but i'm hoping it's something simple that i
over looked. to the best of my knowledge i think i've wired the thing
correctly and i've checked all the connections many times. the
magnetic poles are switched every other magnet and the coils are
wrapped in opposite directions. could my LED not work with an AC
current? do i not have a thick enough gauge magnet wire? is the
space between the magnets and the iron filings too far? have i wired
it correctly? the magnet part of the alternator spins quite evenly
(maybe only swaying a 1/16") so i don't think thats it. i definitly
would think that the magnets are strong enough to create some kind of
flicker but i just don't know. any help would be great.

also if anyone knows of a cheap place to get magnet wire on the net
let me know.

thanks
matthew

Are all your coils in phase?

22 isn't a lot of turns, and your magnetic paths have a huge amount of
air gap.

I've lit an LED by dropping a magnet through a coil, maybe 300 turns a
couple of inches in diameter.

John

 

[Ben Bradley]

In sci.electronics.design, John Larkin

Are all your coils in phase?

Looking at the outputs of two coils at a time with a dual-trace
scope would verify this.

22 isn't a lot of turns, and your magnetic paths have a huge amount of
air gap.

Now I see, the 22 turns is from the top drawing in pma5.jpg it says
"22 rappings for each coil." Also, this diagram shows the eight coils
wired in parallel. That would be good for higher current, but it
probably provides much less than a volt (unless the rotor is spun
faster than you would reasonably want to spin it). Putting the coils
in series might give enough voltage to light the LED, but might also
give enough reverse voltage to damage it. A parallel diode going the
other direction should protect it.
Use an AC voltmeter or DMM on the lowest AC scale to measure the
output voltage. Compare it with the output voltage calculated from the
number of turns, magnet strength, gap size and rotor speed, and
appropriate equations. This would be at least as good an exercise in
electromagnetics as was building the alternator to begin with, and
would let you calculate things like how many turns you should put on
each coil to get a certain voltage at a certain RPM. I have no doubt
the "appropriate equations" are just a few google searches away.