At first energy harvesting sounds like a topic
related to free energy which is a subject
that is flooded with fake designs of machines
that supposedly create more output power than
they require on the input which makes them
perpetual motion machines.
But of course there does not exist such a
machine which is why I even exposed two designs
of such fake machines in my free energy BS
video.
But what is energy harvesting then, you might
ask?
Well let’s imagine we got an IOT system
which for example consists of a microcontroller
and a sensor.
The microcontrollers job is to power up every
hour, get the sensors current measurement
which can be for example the temperature,
send this data out to a receiver and then
go into deep sleep.
Let’s imagine this system needs 3.3V and
draws 10mA for 1 second while gathering the
data and sending it but otherwise the system
only draws 3uA in deep sleep.
That means such a common LiPo battery with
a capacity of 7.4Wh could theoretically power
the IOT system for around 44 years which sounds
good at first.
But have fun replacing perhaps thousands of
those batteries all around your factory after
practically speaking 10 years and maybe half
or more of those batteries will probably be
dead and cannot be reused.
So wouldn’t it be awesome to just harvest
energy from nearby available energy sources
like the sun light, mechanical vibrations,
heat or radio frequencies and power our IOT
systems with that.
And I know this sounds a bit crazy but it
is partly easily possible and I will test
it out in this video to find out whether energy
harvesting makes any sense at all.
Let’s get started!
INTRO
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First off I have to say that using sun light
to power electronics is certainly not crazy
nowadays and widely known as a photovoltaic
system.
I even made several videos about the topic
like building a photovoltaic off grid system
in my garage or creating my own solar panel
and that is why I will not talk much further
about this topic in this video.
But let me just say that you can get such
a small solar panel for relatively cheap and
they can easily output more than enough power
for our imaginary IOT circuit.
With that out of the way let’s move on to
mechanical vibrations which you can commonly
find in factories due to motors and a good
example for that in your household is your
washing machine which I will be using as a
test subject in a second.
Before doing that though we have to think
about what makes up an energy harvesting system.
At the beginning we obviously need a harvester
which turns our source energy into raw electrical
energy.
Then we need a conversion circuit that takes
our raw electrical energy which was maybe
an AC voltage and turns it into a DC voltage
which we can then use to charge up the next
part of the system, the energy storage.
This can be a normal or supercapacitor with
enough capacity to power the last part of
the system, the electronic load.
And now that we are familiar with the basic
structure let’s try to come up with a complete
system for the mechanical vibration energy.
As a harvester we can use such a piezoelectric
disc which after soldering wires to its two
plates outputs an AC waveform whenever we
hit it.
But as you can see such a tiny disc cannot
really output big voltage spikes which we
will definitely need.
That is why I got myself a bigger disc which
can certainly output higher voltages.
Next we need a conversion circuit which turns
the AC voltage into a DC voltage and for that
we need such a full bridge rectifier circuit
which I created with the help of four 1N5822
Schottky diodes.
Those diodes are suitable for this job since
they feature a low forward voltage and they
also work with high frequencies.
So after hooking up the rectifier to the disc,
all we have to figure out was a suitable capacitor
value for which I firstly chose a 22uF one
as a test.
After hooking that up to the rectifiers output
and then connecting my oscilloscope probes
to it, I hit the disc with the handle of one
of my screw drivers continuously and as you
can see the voltage went up to a value of
5V within just 7 seconds.
The gathered energy was even sufficient to
power a 5mm red LED for a brief moment which
is why I wanted to push this system even further
by hooking up a 220uF capacitor.
As you can see the voltage took a quite a
bit longer to increase up to 5V but this time
we can let the LED light up longer and even
a tiny bit continuously which was a very good
sign.
So as a final test I used double sided tape
to attach the disc to my washing machine,
selected the spin option and hit start.
As you can see on the oscilloscope the voltage
climbed super slowly and never reached values
to illuminate the LED.
By switching to a smaller capacitor value,
the rise time did decrease quite a bit but
hitting the disc was certainly more effective.
But nevertheless even though the last test
was not perfect, I strongly believe that mechanical
vibrations could power our IOT system.
And with that being said let’s move on to
heat for which we can use a Peltier Module
as a harvester.
When we heat up one side of it while keeping
the other cool, then the module will output
a DC voltage which we can hopefully use.
The real life example in a factory would simply
be an oven or something similar and a good
example for excess heat at home would be my
induction cooking field right after I am done
preparing my meal.
With a temperature of around 80 degrees Celsius
it should be able to deliver a bit of energy
which is why I simply placed the Peltier module
on it, onto which I then positioned a pot
for cooling the other side.
Sadly though the module only output around
1V which was not enough for my red LED but
by simply connecting two Peltier modules in
series we can easily reach a high enough voltage
and also draw enough power to light up the
LED without a problem which is why I think
that using heat as an energy source for an
IOT system is definitely possible.
But if you do not believe me yet then feel
free to watch my video about creating a thermoelectric
generator.
And that brings us to the last energy source,
radio frequencies which was the energy source
I was most skeptical of.
I mean yes, according to this picture of the
United States Frequency Allocations, there
seems to be lots of radio frequencies around
us all so there should be some that we can
use.
But the problem is that you need a specifically
designed antenna for a certain frequency bands
and your rectifier also needs to be able to
work with such high frequencies and let’s
not forget that you need to live near a radio
frequency broadcaster to get any useful power.
So no matter which RF energy harvester circuit
from google images you try out, you will most
likely never get any decent results which
why I can say that RF energy harvesting will
with high probability not power our IOT system.
But nevertheless in the end we can say that
having 3 of 4 energy harvesting options to
work out in a positive way is definitely not
a bad result.
And nowadays there even exist energy harvesting
ICs like this UB20M one I received from the
University of Bristol.
By hooking up an IR photodiode to its input
and connecting an LED and power source to
its output we can see that by using a TV remote
the IC switches its output on and off according
to the infrared light sent out by the TV remove.
The reason is that the IC is actually powered
by the energy of the infrared light and turns
on its output as soon as a threshold voltage
value on the input is reached.
That means instead of leaving your TV in standby
mode, in which the TV still draws a small
amount of power, we could use such an IC in
order to decrease the TVs standby power even
further and thus saving energy.
And I hope that with this final example you
now understand that energy harvesting is a
real electronics topic nowadays and very important
for certain applications.
I hope you enjoyed this video, if so don’t
forget to like, share, subscribe and hit the
notification bell.
Stay creative and I will see you next time.
