ESP32 Forum

ESP32-PICO-KIT using ESP-Now protocol, power consumption and usage issue with 3.5V, 250mA solar panel

I am transmitting 4 photocell (https://grabcad.com/library/5800b-led-photocell-2) values via ADC,
1 IMU value (https://grabcad.com/library/mpu-9255-1) via I2C using the ESP-Now protocol,
from a transmitting ESP32-PICO-KIT module (https://grabcad.com/library/esp32-pico-kit-1)
to a receiving ESP32-PICO-KIT module.

I used this voltage regulator to supply power to my transmitting ESP32 module (https://grabcad.com/library/dd0503ma-ul ... k-module-2).
It has a working range of 3.7V-5V DC.
I am able to power it using a DC power supply that is outputting 3.5V currently.
(https://www.amazon.com/gp/product/B01KJ ... UTF8&psc=1)
The ESP32 module transmits and works successfully.
The DC power supply shows an output voltage of 3.5V, and a current of 100mA.

I have the receiving ESP32 module plugged into my PC and it receives values properly in my Arduino serial monitor.

My problem is I try to power this same module with my 3.5V, 250mA solar panel
https://grabcad.com/library/polycrystal ... a-250-ma-1
even on a bright sunny day and for some reason the values are not transmitting, but the ESP32 module seems to power on.
The receiving module doesn't receive values (they all print out as 0) and I don't get a bytes received confirmation message that I typically get when it is working.

Can some one please explain what might be the issue?
Will putting a super capacitor (what voltage do I use for 3.5V solar panel?) in between the solar panel and voltage regulator help
(If I do this should I put a zener diode or regular diode to protect my small solar panel?)?
Could it be a current spiking issue with the WiFi even though I am using ESP-Now(I thought it has lower power consumption vs. WiFi)?

An ESP32 needs spikes of high current (up to 500mA) when transmitting and calibrating WiFi: your solar panel probably can't deliver it. (Note that solar panel specifications are usually a bit shitty in that the 250mA is likely to be the short-circuit current and 3.5V is likely the open-terminal voltage: you can't actually get both 3.5V on the panel and pull 250mA from it at the same time.)

Adding a capacitor *may* help you here, but it's dependent on the behaviour of the WiFi logic, which is dependent on a lot of other things, so there's no guarantee to be given there.

Is there a way to detect or measure these spikes besides an expensive oscilloscope or expensive fluke like multimeter?
I’ve got a craftsman 82008 multimeter with autoranging. I’m also using ESP Now protocol so I wonder if the power consumption is less and what it actually is including also what the actually spike values are.

I tried to measure current by putting my leads in line in between my power supply and voltage regulator mentioned in the first post and got a readout of 0 amps. I did however put my leads in the 10A port and ground port since I’ve had a bad experience measuring current from the voltage and ground leads and finding out I may have created a short circuit in another project. This is how I’ve also seen it done on YouTube videos. However, I’ve seen a video where someone put in a large resistor or some device of some sort for larger current solar panels. I think they mentioned otherwise it would be unsafe to measure via the multimeter.

My multimeter says it has a 400 mA fuse so I tried to measure V open circuit and I open circuit right now with the multimeter leads in ground and the regular voltage port. Is this okay to do? In 19 degrees Celsius and cloudy weather I get 3v and .09 mA. This is inside the home through my window in the morning.
At least the DC power supply shows on average 100 mA consumption at 3.5 volt with signals being transferred.

https://electronics.stackexchange.com/q ... -capacitor
This was interesting. Although I don’t think I can run my ESP32 Pico kit module lower than 3.3v.
This seems useful too that I found via stack exchange:
https://www.digikey.com/en/articles/a-g ... er-sources

I’ve found Andreas Spiess video on YouTube regarding using the ULP coprocessor for reading ADC readings and i2c readings in deep sleep.
https://www.youtube.com/watch?v=-QIcUTBB7Ww

However I’m using a multidimensional array and coded everything using the Arduino IDE.
It’s hard to find code for using the ULP outside of the espress IDF environment which I still haven’t figure out how to use even after downloading it in Windows. Plus Arduino has so many libraries that are useful.

Sorry, no... power supply stuff is pretty hard with these spiky loads if you cannot guarantee the maximum amount of required power is available at all times. If all you have is a multimeter, you're effectively going to be in the dark; additionally it's quite hard to get the maximum out of a solar cell (you'd have to do MPTT, for instance). You could mess around with capacitors a bit, but do note that adding a cap in parallel with the solar cell might very well not cut it as when the ESP32 drains it, the voltage may quickly go below the voltage needed. That causes the ESP32 to brown out even if the capacitor still is 90% charged.

Hmm... I've attached some images of my setup.

I tried to use 2 and then 3 solar panels in parallel (3.5V, 250 mA) with good day light and still the same results.
It did not send the values. I wonder if I should have tried pressing the reset button on the transmitter side.
Was getting all 0 values on the receiver side.

I also tried measuring current inline and also open circuit current but getting 0 mA values. Am I doing something wrong?
I've measured open circuit current before with my other larger panels, but it should be able to read 250 mA easily for these panels.

Some more images...

Well none of my 3.5V solar panels worked to power it successfully.

I used this one but the reason I like to avoid using it is it is kind of big for my application.
It has a much larger area footprint.
https://grabcad.com/library/4-5-w-solar ... x-165-mm-1

It powers the ESP32-PICO-KIT successfully.
I will see for how long I will get good results based on sun output.
I have about 1 hour left before sunset.

I am trying to look at super capacitors with
minimum Equivalent Series Resistance (ESR),
https://www.sunpower-uk.com/glossary/wh ... tance-esr/
at least 10F,
and at least 2.7 volt,
plus low cost.
I want to either find a super capacitor above 3.3V so I can step it down with a
LDO voltage regulator
I like this one since it has a it has a low quiescient current and low supply current plus it's 1 amp just like the current LDO voltage regulator on the ESP32-PICO-KIT (the current one is AMS1117 I believe).
https://www.digikey.com/product-detail/ ... ND/7228969

or step it up with a voltage booster (but I think this is more inefficient than stepping down).
This is what I remember reading but I might be wrong.

Still have to figure out best blocking diode or bypass diode to use to prevent supercapacitor for destroying solar panel.

Here are working pictures and data (I am no longer getting 0s and receiving data successfully):