#383 Cheap and simple Solar Power for our small Projects (ESP32, ESP8266, Arduino)

Adding cheap and simple solar power to 
our small outdoor projects removes the   need to save energy or recharge batteries. 
Today we will enhance a simple 50 cents   Li-Ion charger board to do exactly that.
Grüezi YouTubers. Here is the guy with the   Swiss accent. With a new episode and fresh 
ideas around sensors and microcontrollers.   Remember: If you subscribe, you 
will always sit in the first row.  To extend battery life, we usually deep-sleep our 
devices and use quality components that consume   minimal energy. Because this is not simple and 
still needs recharging the batteries from time   to time, I changed to using solar energy 
for all my outdoor projects. Much simpler!  What do we need to do so?
– An appropriate solar panel  – A small battery to survive periods without sun
– A simple battery charging device including   overvoltage and deep discharge protection
– A simple voltage regulator  – And, because we are not beginners on this 
channel, I show you how you can add a power path  Let s start with the most important 
part: Our device we want to power.   For this video, I assume it is an ESP32.

But you 
can use any other board as long as its voltage is   3.3 volts. If you want to use a 5-volt 
device, you need to add a step-up converter.  The first question we have to answer is:   How much energy does the device 
use per year. To get this number,   you have to measure its current consumption 
over time and do some calculations. Luckily,   solar power is very cheap these days, and we do 
not need exact numbers. We can use rules of thumb.  My light sensor, for example, wakes up every 
10 minutes and transmits its values to Wi-Fi.   A simple rule of thumb says that an ESP needs 
below 10 seconds to connect and transfer values   via Wi-Fi. Then it sleeps. During the busy time, 
it consumes around 100mA. The energy consumption   for one cycle is 100mAx10sec = 1000mAs. For an 
hour, it is six times more.

Converted in normal   battery speech, this is 1.7mAh. The Deep-sleep 
current is so small that we can forget it.   For a year it consumes 365x24x1.66mAh = 14 600 
mAh at 3.3 volts. More or less five full 18650   batteries without solar charging. This is the 
minimal energy our solar panel has to deliver.   Of course, we use a bigger panel to be safe and 
to account for losses everywhere in the process.   In video #142, I showed how you could calculate 
the typical power output of a solar panel   at your geographical location. Today we make it 
simpler: We use one of those small and cheap 5 or   6 volt panels. It is too big for Switzerland 
and therefore should work for most locations   with similar loads. Maybe you even find a smaller 
one if you live in a country with more sun.  Because we have enough solar power, we only need 
a small battery to cover nights and bad weather.   Because the battery has to provide peak current 
for the ESP32, I suggest using one of those   small batteries.

Most Li-Ion batteries will 
work. You even could use LiFePo4 batteries.   Then you would need a different charger board 
but could omit the 3.3-volt regulator. If you   want to do a proper calculation for the battery 
size, you also find the formulas in video #142.  What is next? We have to charge the battery, 
of course. In video #155, we did investigations   and found that, for low-power applications, 
no sophisticated MPPT charger is needed to get   decent performance. A simple TP4056 charger chip 
works fine. But we have to tweak it a little.  Fortunately, we get such boards that not 
only offer a charger chip but also two chips   to protect batteries from deep discharge. 
In video #160, you can see how they work.  This is the standard diagram of such boards.

The 
TP4056 makes sure the battery is charged with   a proper charging curve. This means it uses 
a defined charging current up to 4.2 volts.   Below around 3 volts, this current 
is reduced to about 10% to safely   recover the battery from under voltage.
The DW01, together with the FS8205 FETs, switches   the load off when the battery is below about 2.5 
volts. Excellent! We quickly check the datasheet   of the TP4056. The maximum input voltage of the 
chip is 8 volts which fit our 6-volt solar cell,   and its maximum charging current is 1 ampere. 
For sure enough for our small solar panel.  So we can connect this board directly to the solar 
panel. But we have to take one thing into account:   The curve of a typical solar panel. 
They have a point where they deliver   maximum power. If we draw more current, 
for example, the power will decrease.  The datasheet of the charger board reveals 
that they chose a charging current of 1000mA.   Which sounds great but cannot be delivered by a 
typical panel used in this setup. This is why its   power can drop.

You have to check with your panel 
if this happens, and if so, we have to find a way   to reduce the maximum current to a suitable value.
The datasheet of the TP4056 shows how. If   we change this resistor to, for example, 
10kOhms, the charging current is only 130mA.   Much better for our small panel. To do 
so, we have to replace this tiny resistor.   Good luck! I am too old for such tricks 
and have to do it like Indiana Jones:   I solder a 20k potentiometer from pin 2 to 
ground. Now I can adjust the charging current   to maximum current when the panel is in full 
sun. Problem solved! Our charger is finished,   and we can go on with the ESP board. The 
fully charged battery delivers 4.2 volts   and, if discharged, around 3 volts. The ESP32 is 
only rated up to 3.6 volts, and below 3 volts,   it becomes unstable. We have to keep this in mind.
Most ESP32 boards sold run on 5 volt USB and have   additional components like a USB to serial chip 
on board. This is why I tend to use such a simple   PCB with a simple WROOM module. Unfortunately, it 
does not provide a 3.3-volt regulator.

From other   videos, we know that the HT7333 is good enough 
for this purpose. And fortunately, if we cut its   middle leg, it perfectly fits here and connects 
to the ground and 3.3 volts. The battery voltage   can be connected to its cooling area on the other 
side of the chip. I even can add a 10uF tantalum   cap to make sure we comply with the datasheet. 
You see, my old hacker soul is still at work  Now our beloved ESP32 is protected 
against battery voltages above 3.6 volts,   and our solar-charged project is ready to rumble.
But, as usual on this channel, we want more.   I add a battery monitor to all of my projects. 
With this simple voltage divider connected to   the regulator's input voltage, we can monitor 
the battery voltage with an ADC pin.

The voltage   divider is needed to reduce the maximum voltage 
of 4.2 volts to below 3.3 volts for the ESP32 and   below one volt for the ESP8266. Its values are not 
critical because we can calibrate it in software.   All my devices include measured battery voltage 
in the values transmitted. I display them for   reference, and you even could use them 
for an alarm if something went wrong.  The second addition is a little more complex. As 
said before, the TP4056 charges the battery with   a low current if it is below 2.9 volts. If we have 
a closer look at our setup, we see what happens:   The battery and the ESP32 run in parallel, 
and the current coming from the TP4056   is divided into two parts.

So the battery does not 
get the needed charging and stays below 2.9 volts   for a long time, or even forever. 
Not very good for a remote location.  Of course, you can prevent this situation 
by ensuring you never end here. This is how   I usually do it. With a too large solar panel 
and with monitoring the voltage, I feel safe.  But what can be done to avoid this situation in 
any case? We can add two diodes here and here.   If our solar panel delivers energy, its voltage is 
high, and the needed current flows directly to the   ESP. If we use a Schottky diode, the voltage drop 
is less than 0.3 volts. This power path removes   the battery from powering the load if solar energy 
is available. It also blocks this current if no   solar energy is produced. If current is left, it 
flows into the TP4056 and charges the battery.  This diode prevents solar current from going 
directly into the battery. It would be a   safety issue because it can go up to 6 volts.
There is another advantage of this concept:   Without a power path, the load is always powered 
by the battery.

As said before, the TP4056 charges   the battery up to 4.2 volts and stops charging, 
and only restarts at a lower voltage. This means   that your battery is continuously cycled a 
little and this might influence its lifetime.  The power path seems to be a simple and perfect 
solution! Unfortunately, it has a caveat:   This voltage drop across the diode reduces the 
usable battery capacity. The ESP stops working   even if the battery voltage is still ok.
If we replace the diode with a P-channel FET,   the voltage drop is nearly zero, and the problem 
is solved. Excellent! Also, here I add the three   components to the charger board. Of course, 
it would be cool if the manufacturer would add   these components to its standard board. 
It would not be too difficult, I think.  Let s test the setup in full sun: The panel 
delivers nearly 130mA without the ESP32   connected.

If we connect it, the panel delivers 
143mA and the voltage at the ESP32 is 4.5 volts.   A clear indication that out power path works. If I 
turn the solar panel to simulate night, the ESP32   gets its power from the battery at around 3.5 
volts. So the battery is not yet fully charged.  We now have simple and cheap solar 
power for all our small devices.   It even works without deep sleep if you increase 
the solar panel size and adjust the charging   current accordingly. Just make sure you stay 
below 8 volts. Otherwise, you fry the TP4056.  What should we remember?
– A small solar panel can   easily power our ESP or similar boards
– We only need a small battery   to survive periods without sun
– If we use 6 volts solar panels, we can   use a simple and cheap TP4056 battery charger 
which includes all needed protection circuits  – To protect our 3.3-volt chips, usually, we 
have to add an LDO regulator like the HT7333  – Adding a power path makes our solution nearly 
professional.

Unfortunately, the way I built it   was less professional but highly efficient
Now, summer can come!  As always, you find all the 
relevant links in the description.  I hope this video was useful or 
at least interesting for you.   If true, please consider supporting the channel 
to secure its future existence. Thank you! Bye.

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