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
