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Sure you’ve seen LED torches. But not like these!
Our Fantastic
HUMAN-POWERED LED TORCHES!
by Julian Edgar
Drum-roll, please! We’d like to introduce our new DIY humanpowered electric torches. Using a deceptively simple design, a
slow turn the handle is enough to give a quite amazing output.
D
EPENDING ON how you choose
to build the torch, you can have
anything from a pencil beam
with a range of at least 50 metres (and
incredibly, it will light reflectors at
well over five times that distance!) to
a broad and diffuse light source perfect
as a general purpose torch.
Plus, you don’t need to turn the
handle continuously; the light itself is
ultra-white; and we would expect such
a torch to last for, well, nearly ever.
And, to top it all off, if you play your
cards right, the torch can also cost you
very, very little to put together…
The Design Basics
So what’s inside these humanpowered torches? Just four basic
components: a stepper motor, which
generates the power to run the thing;
a rectifier, which converts the AC
(alternating current) from the stepper
56 Silicon Chip
motor into DC (direct current), which
the LED needs; capacitors, which store
the power; and finally the LED itself,
which produces the light.
Stepper Motor
The driving force in any of the designs is a stepper motor, driven as an
alternator.
Stepper motors are used in electric
typewriters, printers, photocopiers,
faxes – a whole range of goods. They
are most easily identified as a stepper
because of the large number of wires
that come out of the motor – usually six
leads. When you turn the shaft, you’ll
also feel a ‘cogging’ motion.
The huge benefit of using a stepper
motor to produce the power (rather
than the conventional brushed DC
generator) is that the rotational speed
needed is much, much slower. In fact,
a stepper motor can be turned 10-15
times slower than a conventional
motor-turned-generator.
So using a stepper motor in this
application means that you can completely dispense with the gearbox – not
only does that reduce noise and cost,
it also decreases effort, as even a good
gearbox has noticeable frictional losses. Longevity is also greatly enhanced.
And you shouldn’t have to pay
much for the stepper motor – not if you
get it from inside a discarded printer,
electric typewriter, fax, photocopier
or similar.
Scrounging the steppers
The stepper motors used here came
from laser printers and fax machines
(each around $5 at jumble sales), while
an old electric typewriter (for example,
a daisy wheel design) can yield three
or four suitable steppers. Steppers
are available in many different sizes
www.siliconchip.com.au
– smaller motors will generally yield
less power than larger motors.
Rectification
Either four diodes or two bridge rectifiers are used to turn the AC output of
the stepper motor into the DC that the
LED and storage capacitor pack need.
Pretty well any small diodes can
be used – they can be salvaged from
equipment (the PC board from the
aforementioned discarded electric
typewriter had no less than 16 suitable
diodes!) or they can be bought new for
nearly nothing.
The wiring approach that you use
depends on the stepper motor that you
have at hand – more on this below.
Capacitor Storage
The low current draw of the LED
makes something else possible – shortterm energy storage. Using capacitors
within the torch serves two functions:
1: it smoothes out the pulsing coming
from the alternator, which otherwise
causes the LED to flicker; and
2: it allows the LED to stay on for a
short time after you stop cranking
How long the LED stays on for depends on how much capacitance you
can squeeze inside the box. For example, using four 4700µF 16V electrolytic
caps (ie 18,800µF total), typically gives
a usable beam for about three seconds
after you stop cranking – and the LED
beam will stay dimly glowing for much
longer. The latter means that it’s easy
to find the torch in the dark if you put
it down.
The heart of the hand-cranked LED torch is a stepper motor. Several different
types are shown here – these can typically be obtained from discarded electric
typewriters and printers, amongst other goods.
However, if you decide to invest a
little more money and use a supercapacitor (eg, the RS Components’
339-6843 1 Farad designs), the torch
will produce a dim beam all night
without any further cranking!
LEDs
The torches use white LEDs rather
than conventional bulbs. LEDs are
starting to replace incandescent bulbs
in many applications.
Until very recently, even highintensity LEDs were really marginal
in high-output torches – the amount
of light produced was simply not
great enough for any distant viewing.
However, that limitation can now be
Using Stepper Motors To Generate DC
Stepper motors use a multi-pole alternator design with four phases. When used as a
motor, the computer puts a pulse of current
into each phase coil in turn, moving the
shaft on one step. As with a DC permanent
magnet motor, driving the motor’s shaft
makes it work as a generator – in this case
causing pulses of current to come out of
the windings.
The developed current is AC, going
positive as a magnet pole approaches a coil
and then negative as it goes away again.
Usually there are four phases at 90-degree
intervals so when one comes down to zero,
the next one has reached maximum. This
is a benefit as it means the output can be
rectified to produce much smoother DC
with hardly any gaps, but it means these
www.siliconchip.com.au
motors have a scarily large number of wires
coming out. Luckily, it’s quite easy to figure
out which way around they are by using a
resistance meter (preferably digital), and
getting them the wrong way around won’t
do any damage.
The most common type of stepper has
six wires coming out. The six wire stepper
is actually two motors on one shaft, so the
six wires can immediately be separated
into two groups of three. Each group will
have some connection to each other, but
no connection to any of the other group. In
each group, one wire is the common and the
other two are the opposite ends of a winding
which will give out oppositely-phased AC.
In terms of resistance, the reading from
the common to either end will be half the
reading across the two ends. Having found
the common on one set, you can use the
same process to find the common in the
other one. All four windings will have almost
exactly the same resistance.
The majority of steppers are six wire,
but there are other varieties. Five wire ones
are easy; the two commons on the six wire
have already been connected together for
you, which makes things easier. Eight wire
ones are just like a six wire but with all the
windings separate, and four wire ones are
half of an eight wire one (or half a six wire
one with the two windings separate).
Courtesy of www.c-realevents.demon.co.uk/steppers/stepmotor.htm
- used with permission
February 2004 57
Fig.1: most stepper
motors that can
be salvaged from
old equipment use
this type of wiring
configuration.
Finding out which
wire is which can
be done with a
multimeter.
overcome by (a) using very bright
white LEDs, and (b) using first-class
coated optics to develop a very well
focused beam.
The great advantage of using a LED
is that its current draw is so low. The
disadvantages (and of course, there
are also disadvantages…) is that the
LED costs more than an incandescent
bulb, and in the final analysis, doesn’t
produce as much light as a hard-driven
filament lamp. However, we’re immensely pleased with how strong the
beams of these torches are, especially
considering that the effort put into
turning the handle is really quite low.
Focusing Lens
A key ingredient in getting a good
beam is the use of a focusing lens.
High intensity LEDs are already very
directional – some light comes out of
the side of the LED but the vast majority is aimed straight out of the front.
So while a reflector is good to channel
the minor amounts of light scattering
out the sides, it’s much more important to focus the beam that’s already
being formed.
The best lens that we have found
is formed from some of the glass elements from an old standard 35mm
SLR camera lens. These days, with
the advent of digital cameras and with
pretty well all SLR cameras being sold
with zoom lenses, the standard lens is
unloved and unwanted. In short, you
can buy them secondhand for nearly
nothing.
For example, one of these torch
designs uses a lens formed from the
reversed rear section of a 50mm f2
Ricoh lens. (Note that the ‘speed’ of
the lens – ie in this case a maximum
aperture of f2 – is important as the
‘faster’ the lens, the larger will be its
glass bits.) Using what was once a very
good quality lens (ie, much better than
a cheap plastic magnifying glass or
58 Silicon Chip
Fig.2: the simplest way
of getting DC out of a
stepper motor is to link
the two commons to the
‘minus’ terminal and
then connect the four live
phases through small
diodes to provide the
positive output.
similar) gives plenty of light transmission and also allows for the focusing
of a tight beam. After all, how many
commercial torches use high quality,
low dispersion, coated glass optics!
Organising the Bits
1. Finding the Stepper
The first step is to find a suitable
stepper motor that can be used to
generate the power the LED needs. Digging through discarded equipment, it’s
not hard to come up with four or five
steppers of different sizes and outputs.
A quick way of sorting out the
better ones for the torch application
is to firstly go for the larger motors
(but which are still small enough to
fit in your designated box), and then
select those which most easily light
a white LED wired directly to two of
the output wires. (Despite the stepper producing AC when wired like
this, the LED will still light when the
stepper is turned – it will just flicker
a lot). You will need to find a stepper
where even when the shaft is turned
quite slowly (eg, 1-2 turns a second),
the LED shines brightly.
The experimentation that you do
should be with a LED similar to that
which you intend using in your final
design – LEDs vary in their current
requirements. For example, the Luxeon Star 1-watt models (available
in Australia from Prime Electronics
(www.primelectronics.com.au) or the
Alternative Technology Association
(www.ata.org.au/leds.htm) certainly
can’t be brought to full illuminance by
a small stepper but that same stepper
can work quite well with a conventional white LED. The Jaycar ZD1780
6000mcd LED is suitable for use with
many small steppers, for example. The
physically larger the stepper, the more
Fig.3: if you want to generate
a higher voltage for the same
cranking speed, you’re usually
better off using this circuit
which uses two bridge rectifiers.
likely that you will be able to drive a
high-current LED.
2. Wiring Approaches
There are two wiring approaches
that can be taken when building
the torch – these are shown in Figs.
2&3 in the “Using Stepper Motors to
Generate DC” breakout box. Fig.2 is
the most common approach but Fig.3
has a distinct advantage in some applications – often it will increase the
voltage available from the stepper.
Deciding which approach is better
for your application requires some
further experimentation. First, use a
multimeter to find out which wire is
which, then wire the stepper to the
LED as is shown in Fig.2.
The next step is to turn the stepper
as fast as you will ever be able to (you
can use a bulldog clip to make a temporary clamp around the shaft of the
motor to act as the attachment for a test
handle) and measure the voltage being
developed as the LED is powered up.
In addition, turn the shaft more
slowly (that is, at a comfortable speed)
and view the LED brightness. The ideal
www.siliconchip.com.au
Step by Step: Making a Narrow Beam Torch
We selected a rigid plastic box as
Using a holesaw, a hole was then
1Electronics
the enclosure for the design – Jaycar
11
cut in one end of the box. The two
Cat. HB-6122 at $7.25. It
halves of the box were then separated,
is made from high impact ABS, uses a
tongue-and-groove seal around the lid,
and is dust and hoseproof. Importantly
to hand-holding comfort, it has rounded
edges and corners.
first step was to mount the
2usingThe
stepper motor in the lid of the box,
the two screws that originally
held the stepper in place inside the
laser printer.
Next, the lens/reflector package needed to
3disassembled
be organised. This Ricoh camera lens was
and it was found that the rear
lens elements (mounted in a sub-assembly)
gave good results when placed about 20mm
from the LED. The assembly is reversed in
orientation to that used in the original camera lens.
torch was then disassembled,
4Athesmall
reflector removed…
…and the reflector
5
opening for the
bulb carefully drilled out (jn small steps) until
the LED was a tightish push-fit. (The reflector
isn’t critical but it adds a ring of light around
the main beam.)
The pump-lid of a plastic
6having
container of skin cream was then selected as
a hole in one end about right for the reflector
and a length about right for the LED-to-lens distance.
The lid was disassembled
7opened-up
and the hole in the cap
a little with a round
file so that the reflector sat nicely in it.
8
The threaded top of the skin-cream container was then cut off, cleaned-up and then
screwed back down inside the lid, holding the
reflector firmly and securely in place.
The holder from the
9
camera lens was filed
from its original semi-circular shape until it was
about the same diameter as the reflector holder
(that’s the former skin cream cap, remember!).
Good quality elec10
trical tape was then wrapped around the
lens/reflector assembly, holding the two pieces
together. Large diameter heatshrink could also
have been used for this purpose.
www.siliconchip.com.au
the lens/reflector assembly inserted,
and the box temporarily re-assembled
to check that the lens/reflector assembly
was held firmly in place. It was.
The capacitors were placed into
12
position next, being held in place
inside the lid with double-sided tape.
The diodes were soldered to the four
13
stepper motor outputs, making sure
that all their bands were furthest from
the stepper motor, then the wiring was
completed. Note that the capacitors are
polarised – their negative terminal is shown
by a line of negative (-) symbols down the side of each of their bodies
and they must be connected around the right way.
The final design is quite a
14
tight fit – as you can see here,
there’s only just enough room for all
of the bits.
The hand crank was made from
15
a piece of polypropylene plastic
kitchen chopping board. This material
has a distinct advantage in this application: if a carefully-sized hole is drilled in
the material, it can then be forced over
the stepper motor shaft giving a good
non-slip fit. In the case of the stepper motor shown here, a small
diameter cog was already in place on the shaft and so the push-fit of
the crank is even more secure.
At the other end of the crank, a
17
high quality knob was made by
using two ball-bearing pulleys, previ-
ously found inside an electric typewriter.
Sandwiched together and with a couple
of washers under them, they give an
easily-grasped knob which has excellent
quality bearings built right in.
Note that the distance
18
centre-to-centre between
the knob and the motor shaft (ie
the working length of the crank)
is very important to the ‘feel’ of
the device: you should experiment with this distance until the
leverage suits your preferences.
February 2004 59
La Crème de la Crème – the big-buck design
This torch is the big buck design – it uses
an expensive 1-watt(!) Luxeon Star/O LED
and super capacitor energy storage.
As you’d expect, in operation it’s also the
most impressive of the designs, able to light
a room or create a swathe of light outside
that – for example – is ideal for walking.
Despite the fact that extra focusing optics
would have given this torch an incredible
beam reach, it was decided to use only the
Luxeon built-in lens and reflector, resulting
in a very even 20° beam.
When held close to a digital light meter, a
reading of over 34,000 lux can be recorded!
In practice, when walking down a road at
night, the full width of the road is illuminated
with a range of six metres or so.
The torch uses for its body a plastic housing that was originally one of the satellite
speaker enclosures in a PC sound system.
The knob is a ball-bearing equipped cog
(with the teeth mostly sanded away) that
was salvaged from an old fax machine.
Both wiring approaches were tried
and the simple diode rectification
gave the best output for the least
The output of a focused
cranking effort. Inside, a 0.47µF
beam or Luxeon Star
electrolytic capacitor and a 1 farad
LED torch is sufficient to
super capacitor are used for energy
storage.
cause eye discomfort and
This is an enormously impressive
possibly eye damage.
torch. In fact, the only downside
Do not look directly into
is that generating a full watt by a
the torch, and don’t shine
Warning!
the beam into anyone else’s
eyes at a close distance.
hand-cranked mechanism is hard to
do quietly – despite the direct drive,
the stepper motor makes a whirring
noise when being turned. The size of
the required stepper also makes this
torch the heaviest of the designs – it
weighs 600 grams – but the sheer light
output is just staggering.
Very few people can believe that a
simple turn of the handle can produce
this much light – especially from a
LED!
If you want the best, you have to be prepared to pay for
it. This torch uses the VERY bright LUXEON Star/O LED
and a supercapacitor. But its performance is exceptional!
60 Silicon Chip
www.siliconchip.com.au
A Broad Beam Torch
After my partner saw the results of the narrow
beam torch, She-Who-Must-Be-Obeyed decided
that when out walking she wanted a torch that would
light up the area immediately in front of her – that
is, producing a very broad, diffuse beam.
This meant that a focusing lens was not required,
so creating more room inside the box for storage
capacitors – nine 4700µF capacitors were installed,
giving a total capacitance of 42,300µF. Secondly, it
was preferred that the torch weigh less than the first
design, so in this model a smaller stepper motor
was used. It was also decided to fit two of the high
intensity LEDs, rather than just one.
The stepper motor is easily able to drive two
LEDs (and probably more as well), and without the
dramas of trying to integrate multiple LEDs into a
reflector-and-lens system, it was easy enough to
use two.
However, when wired with separate rectifying
diodes, the smaller stepper proved to have a lower
voltage output than the larger stepper used in the
focus-beam torch. This meant that the crank had to be
wound very fast to get a good light output, so a revision
was made to the wiring. Two bridge rectifiers were then
used (ie, Fig.3’s wiring approach).
In practice this resulted in the voltage rising to 3.2V at an
easy cranking speed – and peaking at 3.4V when the short
handle was being turned as quickly as possible. While the
effort in turning the handle rose when this alternative wiring configuration was adopted, it is still quite easy to turn.
In some respects, the handle is actually easier to use
when working against the slight resistance – before, it
was almost free-wheeling. A very short handle was fitted
(about 10mm centre-to-centre), with its knob formed by
three sealed ball bearings from discarded video cassette
recorder video heads.
In a small room with a white ceiling and walls, the twoLED torch will dimly illuminate the whole room. Following
outcome is a peak voltage of around
3.5V – that’s what is needed by the LED
– and a ‘slow turn’ voltage as close to
this as possible. (In fact, of course, it’s
the peak current – rather than the voltage – that should be limited, but if the
stepper being turned flat-out develops
only around 3.5V, in real use the LED
will be well within its ratings.)
Matching the stepper motor to the
LED in this way removes the need for
a dropping resistor, saving valuable
energy – energy, remember, that’s being put in by you!
If the voltage that you see during the
test is well below 3.5V, try the wiring
approach shown in Fig.3. Often (but
not always!), this will increase the
www.siliconchip.com.au
an outside path at night, the torch casts a soft white glow
that extends about five metres ahead and a metre or so
either side of the path. In fact, the light output is similar to
a small fluorescent lantern.
Interestingly, with the LEDs sticking out of the front of
the torch, any light being produced by them is more easily
seen than in the focusing torch design (where the LED is
buried from view behind a lens). In fact, the LEDs in this
torch stay faintly glowing for a very long time after the
handle has stopped turning – in pitch darkness, they can
be seen for over six hours – and that’s without using any
expensive super capacitors!
This characteristic, and the diffuse spread of light that
it develops, makes this an ideal torch for moving around
a house at night when the lights are off, walking down a
dark footpath, or for use as an emergency torch during
blackouts.
voltage output of the stepper motor. If
neither approach yields a high enough
voltage when powering the LED of
your choice, select another stepper
and try again.
In our testing of more than 50 stepper motors salvaged from used con-
sumer goods, we’ve not seen a stepper
motor that, when cranked in this way,
produced well in excess of 3.5V – so
your chances of overpowering the LED
are slim. On the other hand, probably half of these motors had enough
‘oomph’ to drive a conventional white
Emergency?
These human-powered LED torches have some really good emergency
applications. The light is visible from a very long distance (especially if you
build it to have a narrow, focussed spot beam) and the torch will never get a
flat battery. Because of the direct-drive system, the quality bearings used in
stepper motors, and the LED light source, the torches should also have an
almost unlimited life.
February 2004 61
If the LED torch is constructed with precision focusing optics, a very intense,
narrow beam is formed. This lens assembly uses elements from a discarded
50mm SLR camera lens and gives excellent long-range performance.
LED to a high brightness. In short, a
great many small salvageable steppers
are ideal for white LED torches.
3. Optics
Once you have found the right combination of LED and stepper, you will
need to make some decisions about the
optics. There are three basic choices:
• A narrow, intense beam – this requires a series of lenses, preferably an
optical assembly from a 35mm camera
lens as described above.
• A broad, bright beam – usually,
a single lens can be used to achieve
this – eg, a single element from a
35mm camera lens or a good standalone glass lens; eg, a quality magnifying glass. Alternatively, a very
62 Silicon Chip
high quality LED lens-and-reflector
combination (such as the Luxeon
Star/O 1W white LED) can be used.
• A diffused, relatively dim beam
– in this case, one or two LEDs can
be mounted ‘bare’; ie, without any
optics at all.
Think through the choice carefully
– the utility of the final torch for the
application that you have in mind is
dramatically affected by the decision
on optics.
4. Storage Capacitors
The type and number of storage
capacitors that you use depends on
how much room you’ve got inside your
box – and how much you want to pay.
Electrolytic capacitors are the ones to
go for and if you select those with a
lower working voltage, the size of the
capacitor becomes smaller for a given
capacitance. In other words, a 1000µF
16V capacitor is physically much
smaller than a 1000µF 63V capacitor.
Since we’re working with only 3-4V,
the lower voltage capacitor is fine.
Basically, the more capacitance that
you can squeeze in, the better – which
brings us to super capacitors.
While these mighty marvels are
available from a variety of sources,
extensive testing showed that the
cheaper super caps give poor results
– we recommend the RS Components
339-6843 1 Farad component. Note
also that a super cap used on its own
won’t work very well –you should always have a conventional electrolytic
capacitor as well, of as high a capacitance as will fit in the box.
You might be wondering how all
these capacitors are connected – again
it’s very easy, with the capacitors wired
in parallel to both each other and the
LED. No current limiting resistors,
no zenor diodes, nothing. It works
extremely well and wastes no energy.
Conclusion
Despite being very simple in design
and construction, these torches really
cut it. They’re effective and cheap,
working well in both general-purpose
and specialised applications.
Not one of the many people who
have seen the prototypes was unimpressed – in fact most people had to
have the torch removed from them by
force, so intent were they on winding
the handle and shining the torch into
SC
dark places!
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