Charge Controller Selection and Configuration

The charge controller is the brain of your solar power system - it manages battery charging, prevents overcharge and deep discharge, and in MPPT controllers, optimizes power extraction from the solar panel. Choosing the right charge controller significantly affects system efficiency and longevity.

PWM vs. MPPT: Which to Choose

Recommendation: Use MPPT for any permanent deployment. The efficiency gain pays for the cost premium within 1-2 years in most climates, and MPPT controllers last longer and provide better battery protection.

Victron SmartSolar MPPT 75/10: The Standard Choice

The Victron SmartSolar 75/10 ($45-55, as of 2026-06-08) is the most popular choice for LoRa mesh solar nodes:

• Input: up to 75V open-circuit panel voltage, 10A max battery charge current
• Supports 12V and 24V battery systems
• Bluetooth monitoring via Victron Connect app - see real-time voltage, current, and charge state from your phone
• Load output: switched 15A continuous output (short-circuit proof) with built-in low-voltage disconnect that protects the battery. Note the 10A figure is the battery charge current rating, not the load output rating.
• Temperature compensation for accurate charging - this adjusts charge voltage for lead-acid chemistry; LiFePO4 does not use it, so disable it even in cold climates (see configuration below)

# Victron MPPT configuration for LiFePO4 battery (12V system):
Charge algorithm: Li-Ion
Absorption voltage: 14.4V (range 14.2-14.6V; do not float here)
Float voltage: 13.5V
Low voltage disconnect: 12.0V (operating LVD for longevity, ~10-20% SoC remaining; this is NOT 80% DOD protection. The hard BMS under-voltage cutoff is lower, ~10-10.8V)
Temperature compensation: Disabled for LiFePO4 (temp compensation is a lead-acid feature)

# For LiPo (3.7V single cell, 4.2V max):
# Use a TP4056 Li-Ion charger module, not a Victron
# Victron 75/10 is designed for 12V+ systems

Load Output vs. Direct Battery Connection

Most MPPT controllers have a "load output" - a switched output that turns off automatically when the battery voltage drops below a set threshold:

• Advantages of load output: Built-in low-voltage disconnect protects battery; the controller manages when to power the node vs. when to conserve battery for recovery
• Disadvantages: Load output current limit (typically 10-15A) may not support higher-power loads; adds a small voltage drop (0.1-0.5V)

Best practice: Connect your node through the load output for automatic low-voltage protection. Connect any monitoring equipment (Pi) directly to the battery with its own cutoff relay if the Pi exceeds the load output current limit.

Solar Panel Tilt Optimization

# A good annual-average tilt is approximately equal to your latitude.
# (A common refinement is latitude * ~0.76 per NREL studies, since the
# true annual optimum is somewhat below latitude.) The latitude * 0.9
# + offset formulas you may see elsewhere are season-specific (winter),
# not the annual-maximum rule.

# Annual-average examples (tilt ~ latitude):
# Portland (45.5°N): ~45 degrees from horizontal
# Dallas (32.8°N): ~33 degrees
# Phoenix (33.4°N): ~33 degrees
# Chicago (41.8°N): ~42 degrees

# For winter optimization (maximize December-February output):
# Tilt angle = latitude + 15 degrees

# For snow-shedding (prevents accumulation that blocks panel):
# Tilt angle = 45 degrees minimum; 60 degrees ideal in heavy snow climates