Imported from GitHub: HarveyBates/mptt-solar-charger · commit f1b35e5 · license MIT

Description

MPTT solar charge controller for 18650 cells.

README

mptt-solar-charger

MPTT solar charge controller based around the LT3652IMSE solar charge controller / battery management IC.

Features

• Barrel jack or solar input 5 - 32 V
• Reverse polarity protection (input)
• Input/output current and voltage monitoring (INA219 IC) over I2C
• Float voltage of 4.2 V
• Battery management:
  • 1000 mA charge current
  • Thermistor shut-off (-10 to +60 degrees Celcius)
  • Indicator LED will flash when fully charged
• Various fault LED's

Schematic

Schematic can be found here

Notes from schematic

Note 1.

Resistor divider VINREG

Resistor divider determines shut-off voltage for LT3652 under low-light conditions. When charging VINREG should be greater than 2.7 V (VINREG > 2.7 V).

$\frac{R_{IN1}}{R_{IN2}} = \frac{min(V_{IN})}{2.7} - 1$

where:

$min(V_{IN}) = 10 ; \text{volts}$

therefore:

$\frac{R_{IN1}}{R_{IN2}} = \frac{9.0}{2.7} - 1 = 2.3\dot{3}$

$R_{IN1} = 220 ; K\Omega$

$R_{IN2} = 100 ; K\Omega$