ESP32-S3 Based Logger

 I have revised the April 2024 logger concept, the breadboard of the unit is shown in Figure 1 below.

Figure 1. Logger V2 breadboard.

This time around I used ChatGPT extensively to advise for which modules to include, their wiring, and to write all the required ADE sketches.  I switched from the using the ESP32 Dev Kit to a ESP32 S3 Dev Kit.  The old ESP32 wasn't all that bad but the S3 unit is easier to use and is a later version.  The main modules used are: 

• ESP32 S3 Dev Kit: used so far for control of sensors, logging and control of OLED display
• SPI microSD module: used to record time, battery voltage, and battery current once per second. Data is recorded into a csv file.
• SSD1306 OLED display:  used to display current battery voltage and current, and current time.
• DS3231 Real Time Clock module:  used to generate time stamps for data points
• ADS1115 16-bit ADC: used to measure battery voltage
• INA226 current monitor: used to measure high-side batter current.

So far I've used the unit in conjunction with my UC2906 based charger, along with my dummy load and SLA battery to record a couple of battery charge and discharge curves. 

Figure 2.  SLA battery 0.95A discharge curve

Figure 2 shows the discharge curve using a 13.5 ohm load (nominal 888 mA load).  The current was constant at about 0.95 amp.  Voltage started to fall precipitously at approximately 4.25 hours.  The discharge experiment was halted after 4.4 hours when battery voltage dropped below 11.3V.  Note the noise free quality of the data.  Approximately 4.1 AH of charge was removed, giving (7.2-4.1)/7.2 = 43% capacity remaining. 

Figure 3 shows the measured charge curve following the previous discharge curve.  Note that the current curve is negative, in accordance with the assumption of positive current coming out of the battery and negative current going into the battery.

1. In the first hour the charger was turned off.  Discharged voltage was approximately 12.2V. 
2. At about 1.2 hours the charger is turned on and goes into the bulk (constant current) phase.  The current is set to 0.64A.  This phase lasts about 5 hours. 
3. At about 6.4 hours the charging goes into the absorption phase (constant voltage).  In this phase the current tapers toward zero.   For the UC2906 the transition from this phase to float phase occurs at Imax/10, in this case Imax is 0.64A.  The actual transition occurred at 0.069A. 
4. At about 11.5 the charger entered the float phase, dropping the float voltage to 13.5V.  Initial float charge current was 0.025A.  Integrating the current curve using Excel yields a total of 4.4AH charged into the battery.