Recently I bought myself this 14W USB Foldable
Solar Power Charger for a price of 35€ because
as you might know from my previous videos
I love utilizing solar power and charging
my phone with it on the go just sounded awesome.
After unpacking the product and having a closer
look at it I have to say that I really do
like its overall quality.
The solar cells seem well protected and the
fabric with all of its stitches looks pretty
amazing.
The only question left was whether it could
truly output the claimed 2.4A at 5V which
is why I headed into my garden to unfold the
solar charger.
After then hooking up a USB extension cable
along with a USB tester and ultimately my
smartphone we can see that the solar charger
only outputs a current of half an amp at 5V.
But don’t judge about the solar charger
just yet because my extension cable was actually
the problem.
Without it my phone was charging with 1.2A
at 5V which sadly though was still not even
half of the advertised output power.
But in the end I have to say that I still
like the product even with lower output power
but I started asking myself whether I could
create a similar of course more crude solar
power charger that costs around the same but
outputs more power which is what we will be
finding out in this episode of DIY or Buy.
Let’s get started
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First off in order to create a solar power
charger we obviously need some solar cells.
I got those 35 solar cells from Ebay for a
price of only 30€ and since I will later
only be using 10 of them, the required cells
cost me around 8.6€.
Apparently they can output a maximum of 4W
at an efficiency of 17% and they come with
dimensions of 156 by 156mm.
But aside from those information we do not
know anything else about the cells like their
open circuit voltage or their short circuit
current.
So to do a bit of testing I got myself solar
cell tapping wire, a flux pen and solder.
To add the wire to the cell we have to apply
flux to the front lines and then use some
solder to bond the wire to it.
After I did this for two lines on the front
side, I repeated this procedure for the back
side and after I connected the front wires
and back wires with one another, I got a test
cell that we can work with.
I laid it in the sun light in my garden and
connected my positive multimeter probe to
the back wires and my GND probe to the front
wires.
And as you can see we are dealing with an
open circuit voltage of around 0.56V.
And by using the current measurement feature
of my multimeter, I was able to measure a
short circuit current of only around 2.8A
which was a bit weird.
The reason is that the short circuit current
is theoretically the maximum current a solar
cell can output at which the voltage is almost
zero.
But even if the voltage would be the open
circuit voltage then the power would never
reach 4W and according to other 4W solar cells,
their short circuit current is almost at 9A
instead of just 3.
So I was not sure whether I got bamboozled
or whether my setup was faulty but I got no
other choice than to use my ordered cells
because getting new ones would take forever
so let’s just hope for the best.
And by the way I tried utilizing the three
lines of the solar cell and sadly that did
not change anything.
But anyway for now we need to increase the
open circuit voltage of 0.56V to something
around 5V for my smartphone.
For that we need to put a few cells in series
in order to increase the output voltage.
10 of them should do the trick but we should
not directly connect the solar panels to my
phone since the voltage can shift depending
on the sun light and possibly destroy something.
Instead we need some kind of regulator that
outputs a constant 5V.
I decided on this buck boost converter that
you can get for rather cheap.
As a first test, I hooked it up to my lab
bench power supply set to 8V and continued
by adjusting its output voltage to 5V.
After then soldering a chopped up micro USB
cable to its output and plugging that into
my phone we can see that it charges with a
current draw of around 1.4A.
The awesome thing about such a buck boost
converter is that the input voltage can vary
below or above the desired output voltage
without affecting it.
So 10 of those cells in combination with the
buck boost converter will be my setup which
brings us to the next question on how to protect
the cells from mechanical stress because they
are super brittle.
In my DIY solar panel video I used a technique
of encapsulating the cells in epoxy resin
but if you are following me on Twitter then
you know that this story did not end well.
In my opinion the problem was that the metal
frame was too big and held too many cells
inside which reduced the mechanical stability
of each.
A solution for that problem would be to create
a small frame for each cell and encapsulate
it in there in order to get a nice sturdy
cell.
So I designed this frame in fusion 360 which
I 3D printed 10 times with my two Prusa 3D
printers and some red and blue PLA filament.
As soon as all the frames were done, I got
myself this 2 component transparent epoxy
resin.
As a first test I mixed up a small batch of
it through the help of a stirrer and then
popped all the air bubbles with the help of
some hot air.
Then I poured a bit of the resin into a frame,
distributed it evenly, positioned a solar
cell on top of the spacers to which I obviously
already added tapping wire and then finished
this procedure by adding more resin on top
which I then also distributed evenly.
And after letting the resin dry for a day
I have to say that the finished cell was mechanically
pretty strong and according to the electrical
measurements in the sun light, the voltage
and current values were only altered slightly.
That means it was time to solder tapping wire
to 9 more cells and encapsulating all of them
inside the 3D printed frames just like I described
it before.
And just like we got 10 finished cells ready
for soldering.
My tactic was to lay 2 cells on top of each
other, shorten the tapping wire, and solder
them together at the end of the two wires.
Then I placed the next cell on top but with
the other side facing up and repeated this
process.
You basically have to constantly alter the
orientation of the cells in order to later
be able to pull them apart like an accordion.
And as soon as all the series connections
were done you can of course use some rubber
bands in order to keep the folded up system
together.
And after adding the buck boost converter
to the output, it was finally time to truly
test my DIY 5V portable solar charger in my
garden and as you can see it can charge up
my phone even during a clouded day with a
current of around 0.7A.
And in direct sunlight we get a charging current
of 1.35A which was apparently limited by my
phone.
So to measure the maximum power of my system
I hooked it up directly to a constant load
and performed a couple of tests.
As you can see it can reach a maximum power
of 26W which is certainly not bad if we consider
that my DIY version cost around the same as
the commercial version.
Of course you have to invest some time and
there is still a lot of room for improvement
like maybe a fabric protection or a hinge
system that relieves the wires and folds the
cells up more nicely.
But even after considering all of those factors
I still have to say that for me this time
DIY is the winner.
And with that being said let me know what
you think in the comment section below.
As always thanks for watching, don’t forget
to like, share, subscribe and hit the notification
bell.
Stay creative and I will see you next time.
