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Generator for LEDs

R

Ryan

Jan 1, 1970
0
For a few weeks I have been pondering a scheme to rig up a lot of LED
running lights on my bicycle frame for night time illumination.

At first I was going to use a 9v and then sets of 3-4 in series with a
resistor, but as the voltage of the battery drops, the current seems to
drop so much that I don't know what effect it has on luminosity.

I have no formal electronics education, it's all been from doing and
reading.

I recently purchased a cheap shake-up LED flashlight and I've seen
advertised the crank kind.

It seems I should be able to fashion a generator out of the wheel using
magnets on the spokes, or else pull a small motor out of something and
use that. As I understand from the archives, I need to find a motor
with a magnet rather than an electric field. Would a hard drive magnet
work for the spokes?

If I cause a DC motor to turn, does it output DC power, or AC power? I
thought since a magnet moves first toward, and then away from the
windings (or vise-versa) then this creates first a negative and then
positive voltage; a sine wave rather. Is this correct?

Can the magnets pass next to those windings or do they have to pass
through the middle of it?

Do those flashlights use a special capacitor? I notice it still has
power even several days later. I would expect a capacitor to be
drained?

So, I envsion a battery-free setup with a dozen or so LEDs fashioned
onto the frame (very minimal hardware and very low budget) and one or
more capacitors to keep supplying the current when I have to stop.

If the magnet idea isn't feasible, then I want to make a generator, but
not the impossible to pedal tire eaters I remember from the 1980s. I
used to spin motors from capsela toys and watch them make power.

If a DC motor consumes X watts at its RPM, does it produce approximately
that many watts if made to spin at that same RPM? I presume I need to
determine my current demand which I think will be 20mA times the number
of LEDs and then find a motor to accomodate this. Is a motor's output
voltage dependent on its RPM or is it steady? Would a floppy drive,
CD-ROM, or hard drive have a suitable motor? What about trimming off
the blades of a computer case fan and using that as a motor, or is there
something in an old VCR I could use?

It seems so difficult to design this circuit because voltage can be so
dynamic and from the LED calculators I've used, this has a dramatic
effect on the current the LED uses. I don't want to burn them up, but
I want them to be bright.

I don't know much about regulation, but if that is the answer, should I
regulate voltage, or current?

As I understand, making them flash necessitates a transistor or two,
which is probably beyond me and probably beyond the scope of this
project.

I appreciate any pointers you can offer.

-Ryan
 
J

John Popelish

Jan 1, 1970
0
Ryan said:
For a few weeks I have been pondering a scheme to rig up a lot of LED
running lights on my bicycle frame for night time illumination.

At first I was going to use a 9v and then sets of 3-4 in series with a
resistor, but as the voltage of the battery drops, the current seems to
drop so much that I don't know what effect it has on luminosity.

I have no formal electronics education, it's all been from doing and
reading.

I recently purchased a cheap shake-up LED flashlight and I've seen
advertised the crank kind.

It seems I should be able to fashion a generator out of the wheel using
magnets on the spokes, or else pull a small motor out of something and
use that. As I understand from the archives, I need to find a motor
with a magnet rather than an electric field. Would a hard drive magnet
work for the spokes?

If I cause a DC motor to turn, does it output DC power, or AC power? I
thought since a magnet moves first toward, and then away from the
windings (or vise-versa) then this creates first a negative and then
positive voltage; a sine wave rather. Is this correct?

Can the magnets pass next to those windings or do they have to pass
through the middle of it?

Do those flashlights use a special capacitor? I notice it still has
power even several days later. I would expect a capacitor to be
drained?

So, I envsion a battery-free setup with a dozen or so LEDs fashioned
onto the frame (very minimal hardware and very low budget) and one or
more capacitors to keep supplying the current when I have to stop.

If the magnet idea isn't feasible, then I want to make a generator, but
not the impossible to pedal tire eaters I remember from the 1980s. I
used to spin motors from capsela toys and watch them make power.

If a DC motor consumes X watts at its RPM, does it produce approximately
that many watts if made to spin at that same RPM? I presume I need to
determine my current demand which I think will be 20mA times the number
of LEDs and then find a motor to accomodate this. Is a motor's output
voltage dependent on its RPM or is it steady? Would a floppy drive,
CD-ROM, or hard drive have a suitable motor? What about trimming off
the blades of a computer case fan and using that as a motor, or is there
something in an old VCR I could use?

It seems so difficult to design this circuit because voltage can be so
dynamic and from the LED calculators I've used, this has a dramatic
effect on the current the LED uses. I don't want to burn them up, but
I want them to be bright.

I don't know much about regulation, but if that is the answer, should I
regulate voltage, or current?

As I understand, making them flash necessitates a transistor or two,
which is probably beyond me and probably beyond the scope of this
project.

I appreciate any pointers you can offer.

-Ryan
You might well build a simple AC generator that uses a magnet (or
several) mounted on the wheel, with a pickup cpil mounted on the
frame. The pickup coil needs to be designed to have an iron core
(made of laminations from a transformer or ferrite, to keep eddy
currents low) such that it nearly bridges across the poles of the
magnet as it goes by. This will drive a big pulse of flux through the
core and generate a significant voltage across any coil wound around
that flux. You should be able to connect pairs of LEDs in anti
parallel, so one lights when the current goes one way, and the other
lights when the current rebounds the other way. How many of these
pairs you can connect in series depends on the number of turns on the
coil, and how strong the magnets are.
 
R

Ryan

Jan 1, 1970
0
You might well build a simple AC generator that uses a magnet (or
several) mounted on the wheel, with a pickup cpil mounted on the


Thanks John, you are always very helpful in this group.

Can this be any old magnet, or does it need to be made of anything in
particular? How close must it pass to the coil? I presume the
magnetic intensity influences voltage?

Do I want to use tiny wire for the coil so that I can make more
windings? Could I rip thin wire like what is found on the back of a
speaker cone and make a coil from that? Could I wrap it around an ink
pen body or what? Does the radius of this coil matter?

When you say a core of ferrite, is this the stuff you find on the end of
a monitor data cord? Should I wind around one of those or perhaps
through one of those?

If I pull a transformer out of something, does this serve as two pickup
coils already?



that flux. You should be able to connect pairs of LEDs in anti
parallel


If I power them with AC current, does the resistor become less important
since it is effectively pulsed width duty cycle? I presume I could also
add two capacitors in the same fashion to store energy for each
"direction" of current?



pairs you can connect in series depends on the number of turns on the


I presume more turns equal more voltage, not unlike the rule of a
transformer?


coil, and how strong the magnets are.

Is the magnetic field "falloff" curve for any object the same? For
example, can one type of metal attract from a farther distance than
another type of metal given that they have the same measured amount of
magnetism?


-Ryan
 
J

John Popelish

Jan 1, 1970
0
Ryan said:
Thanks John, you are always very helpful in this group.

Can this be any old magnet, or does it need to be made of anything in
particular? How close must it pass to the coil? I presume the
magnetic intensity influences voltage?

The more powerful the magnet, the larger the output. The (open
circuit) voltage is proportional to he rate of change of flux passing
through the coil, and also proportional to the number of turns.
Do I want to use tiny wire for the coil so that I can make more
windings? Could I rip thin wire like what is found on the back of a
speaker cone and make a coil from that? Could I wrap it around an ink
pen body or what? Does the radius of this coil matter?

As I said, the coil should be wound around a good core material, like
laminations recovered from a small transformer. Wire can also be
recovered from a transformer (or wall wart power supply or relay). In
fact, a relay with the coil on a bobbin may be all you need.

The idea is to have the magnet go past the core so that the core
almost touches both poles of the magnet, so it intercepts a large
fraction of the magnets flux. If you have access to old lawn mowers,
you may be able to adapt the magneto coil that is mounted near the fly
wheel.
When you say a core of ferrite, is this the stuff you find on the end of
a monitor data cord? Should I wind around one of those or perhaps
through one of those?

If you can think of a way to have this core bridge the passing poles
of the magnets, it would work.
If I pull a transformer out of something, does this serve as two pickup
coils already?

No. A transformer has the coils wound around the center lag of a
closed magnetic path.

If you can slide the E and I laminations out of the coil, and then
reassemble all the E's through the coil from one side, you end up with
a magnetic structure with 3 poles (a big center one with the coils
around it, and a smaller pole on each side). This structure can be
used to intercept the flux from a passing magnet as it slides past the
three poles.
If I power them with AC current, does the resistor become less important
since it is effectively pulsed width duty cycle? I presume I could also
add two capacitors in the same fashion to store energy for each
"direction" of current?

The impedance of the coil limits the current. Whether this keeps the
current low enough to not damage the LEDs depends on the number of
turns and the strength of the magnets. Some experimentation is called
for. With a direct connection, you will get a flash each time a
magnet goes past. if you rectify the pulses and store them in a
capacitor, then you can dump power continuously through a string of
LEDs and a series resistor. If you use the DC to charge a small
rechargeable battery, you can have a glow, even when you stop.
I presume more turns equal more voltage, not unlike the rule of a
transformer?

Yes, same concept. But more voltage implys less current, so you can
limit the current to a safe value (and drive more LEDs in series) by
raising the voltage.
Is the magnetic field "falloff" curve for any object the same? For
example, can one type of metal attract from a farther distance than
another type of metal given that they have the same measured amount of
magnetism?

The distance is related to the strength of the field produced by the
magnet, the distance between the poles, and the permeability of the
material being attracted.

Larger magnets (bigger distance between the poles) produce larger flux
patterns. Really good magnets would be neodymium iron boron types.
These are sold in great variety on Ebay. But they are powerful enough
that larger ones will collect scrap metal as you ride.
 
J

Jasen Betts

Jan 1, 1970
0
For a few weeks I have been pondering a scheme to rig up a lot of LED
running lights on my bicycle frame for night time illumination.

At first I was going to use a 9v and then sets of 3-4 in series with a
resistor, but as the voltage of the battery drops, the current seems to
drop so much that I don't know what effect it has on luminosity.

I have no formal electronics education, it's all been from doing and
reading.

I recently purchased a cheap shake-up LED flashlight and I've seen
advertised the crank kind.

It seems I should be able to fashion a generator out of the wheel using
magnets on the spokes, or else pull a small motor out of something and
use that. As I understand from the archives, I need to find a motor
with a magnet rather than an electric field. Would a hard drive magnet
work for the spokes?

they used to make generators for that purpose that were driven by a friction
wheel of the tyre.
If I cause a DC motor to turn, does it output DC power,

DC, kind of noisy DC, but DC.
thought since a magnet moves first toward, and then away from the
windings (or vise-versa) then this creates first a negative and then
positive voltage; a sine wave rather. Is this correct?

yes, but the contacts in the motor reverse that sine wave where it crosses 0V
Can the magnets pass next to those windings or do they have to pass
through the middle of it?

through the middle is best. next to will work to a lesser extent.
Do those flashlights use a special capacitor? I notice it still has
power even several days later. I would expect a capacitor to be
drained?

possibly a rechargable battery?
So, I envsion a battery-free setup with a dozen or so LEDs fashioned
onto the frame (very minimal hardware and very low budget) and one or
more capacitors to keep supplying the current when I have to stop.

If the magnet idea isn't feasible, then I want to make a generator, but
not the impossible to pedal tire eaters I remember from the 1980s. I
used to spin motors from capsela toys and watch them make power.

If a DC motor consumes X watts at its RPM, does it produce approximately
that many watts if made to spin at that same RPM?

no, at best about 60% of the amount it consumes. probably much less.

I presume I need to
determine my current demand which I think will be 20mA times the number
of LEDs and then find a motor to accomodate this. Is a motor's output
voltage dependent on its RPM or is it steady?

it depends on the RPM.
Would a floppy drive,
CD-ROM, or hard drive have a suitable motor? What about trimming off
the blades of a computer case fan and using that as a motor, or is there
something in an old VCR I could use?

All those motors have electronic switching instead of the comutator that the
toy motors you experimented with had. you'd need to remove the switching
circuit and replace it with a rectifier bridge.
It seems so difficult to design this circuit because voltage can be so
dynamic and from the LED calculators I've used, this has a dramatic
effect on the current the LED uses. I don't want to burn them up, but
I want them to be bright.

use the generator to charge the capacitor and use a regulator to control the
putput.
I don't know much about regulation, but if that is the answer, should I
regulate voltage, or current?

ideally you should hook the diodes up in series and reguulate current
this may require boosting the voltage..
As I understand, making them flash necessitates a transistor or two,
which is probably beyond me and probably beyond the scope of this
project.

voltage boosting regulators are more complex still.


A good motor to use could be the head motor from a 5.25" floppy drive
they're nice and big (so potentially have a good output) and give 40 pulses
per rotation. you could probably drive one fast enough to light LEDs with a
using a cog that engages the spokes near the hub...


FWIW the turntable motor from a microwave oven can produce hundereds
of volts when turned by hand... if you could somehow drive one of them
from an axle you could have CCFL lighting on your bike :)

Bye.
Jasen
 
J

Jasen Betts

Jan 1, 1970
0
Thanks John, you are always very helpful in this group.

Can this be any old magnet, or does it need to be made of anything in
particular? How close must it pass to the coil? I presume the
magnetic intensity influences voltage?

Do I want to use tiny wire for the coil so that I can make more
windings? Could I rip thin wire like what is found on the back of a
speaker cone and make a coil from that? Could I wrap it around an ink
pen body or what? Does the radius of this coil matter?

When you say a core of ferrite, is this the stuff you find on the end of
a monitor data cord? Should I wind around one of those or perhaps
through one of those?

Around, could work through won't

the idea is to make a path from the north to the south pole of the magnet
out of metal (or ferrite etc) and have the path pass through the turns of
copper then move the magnet round...
If I pull a transformer out of something, does this serve as two pickup
coils already?

If you can cut one of then ends off it it would work, some tranformers come
apart quite easily.
If I power them with AC current, does the resistor become less important
since it is effectively pulsed width duty cycle? I presume I could also
add two capacitors in the same fashion to store energy for each
"direction" of current?

no, you can still burn them out with AC if you feed them enough...
I presume more turns equal more voltage, not unlike the rule of a
transformer?

yes.


Bye.
Jasen
 
A

Andy Baxter

Jan 1, 1970
0
Ryan said:
For a few weeks I have been pondering a scheme to rig up a lot of LED
running lights on my bicycle frame for night time illumination.

At first I was going to use a 9v and then sets of 3-4 in series with a
resistor, but as the voltage of the battery drops, the current seems to
drop so much that I don't know what effect it has on luminosity.

A current regulator isn't that hard to build - see my earlier thread on
luxeon LEDs for various circuits you might be able to adapt.
It seems so difficult to design this circuit because voltage can be so
dynamic and from the LED calculators I've used, this has a dramatic
effect on the current the LED uses. I don't want to burn them up, but
I want them to be bright.

I don't know much about regulation, but if that is the answer, should I
regulate voltage, or current?

For LEDs, you want to regulate current. Using a resistor in series is a
trick people use when they know they have a stable fixed voltage source.
 
Q

quietguy

Jan 1, 1970
0
You might like to have a look at Silicon Chip Feb 2004 - they describe a few
human powered torches using small stepper motors to power led torches - might
find some useful ideas there

It would seem not too hard to rig a motor so it is driven off a bike wheel
instead of being hand cranked

David
 
M

Mark Healey

Jan 1, 1970
0
I've been pondering the same thing. That's what brought me to this group.
I initially planed on using a bunch of hard drive magnets glued around the
rim but then remembered the brakes. I also decided that it would be best
to have the rig near the hub so it doesn't interfere with removing the
wheel as much.
You might like to have a look at Silicon Chip Feb 2004 - they describe a
few human powered torches using small stepper motors to power led
torches - might find some useful ideas there

I took one apart and it's not a stepper, it's just a regular DC motor.
This is what gave me the idea. I actually plan to cannibalize the
circuitry of the wind up flashlight and just turn my wheel into a
motor/generator. The cool thing is that my flashlight has a rectifier
already in it.
It would seem not too hard to rig a motor so it is driven off a bike
wheel instead of being hand cranked

Actually it is. They make generators that rub against the tire but drag a
lot. They also make hubs with generators in them but they cost a lot.

You don't want to drive anything with the spokes, that will bend them
eventually. There is no room between the hub and the fork ends to attach
anything.
 
D

Don Bruder

Jan 1, 1970
0
I've been pondering the same thing. That's what brought me to this group.
I initially planed on using a bunch of hard drive magnets glued around the
rim but then remembered the brakes. I also decided that it would be best
to have the rig near the hub so it doesn't interfere with removing the
wheel as much.
You might like to have a look at Silicon Chip Feb 2004 - they describe a
few human powered torches using small stepper motors to power led
torches - might find some useful ideas there

I took one apart and it's not a stepper, it's just a regular DC motor.
This is what gave me the idea. I actually plan to cannibalize the
circuitry of the wind up flashlight and just turn my wheel into a
motor/generator. The cool thing is that my flashlight has a rectifier
already in it.
It would seem not too hard to rig a motor so it is driven off a bike
wheel instead of being hand cranked

Actually it is. They make generators that rub against the tire but drag a
lot. They also make hubs with generators in them but they cost a lot.

You don't want to drive anything with the spokes, that will bend them
eventually. There is no room between the hub and the fork ends to attach
anything.[/QUOTE]

Wind a couple "pancake" coils to mount on the forks, then clip magnets
to the spokes, lined up with the coils. Rectify the coil output. Presto!
:)
 
M

Mark Healey

Jan 1, 1970
0
I've been pondering the same thing. That's what brought me to this group.
I initially planed on using a bunch of hard drive magnets glued around the
rim but then remembered the brakes. I also decided that it would be best
to have the rig near the hub so it doesn't interfere with removing the
wheel as much.


I took one apart and it's not a stepper, it's just a regular DC motor.
This is what gave me the idea. I actually plan to cannibalize the
circuitry of the wind up flashlight and just turn my wheel into a
motor/generator. The cool thing is that my flashlight has a rectifier
already in it.


Actually it is. They make generators that rub against the tire but drag a
lot. They also make hubs with generators in them but they cost a lot.

You don't want to drive anything with the spokes, that will bend them
eventually. There is no room between the hub and the fork ends to attach
anything.

Wind a couple "pancake" coils to mount on the forks, then clip magnets
to the spokes, lined up with the coils.[/QUOTE]

I'm looking for something that will have the coils in it that I can
cannibalize. It's just more satisfying that way.
Rectify the coil output. Presto!

Why? The flashlight circuitry already has a rectifier.
 
D

Don Bruder

Jan 1, 1970
0
Mark Healey said:
I'm looking for something that will have the coils in it that I can
cannibalize. It's just more satisfying that way.


Why? The flashlight circuitry already has a rectifier.

My bad - didn't notice that part.
 
D

Don Bruder

Jan 1, 1970
0
Actually I was hoping someone would know what I could cannibalize the coil
from.


Old AM radio loopsticks with the ferrites removed, perhaps? Then again,
those might be too fragile to be useful for any significant current
without cooking themselves.
 
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