Guides
Charge controller guides covering MPPT vs PWM efficiency, amperage and voltage sizing, and battery chemistry settings.
Why this page exists
Most kit solar systems include a PWM charge controller because it's cheaper. For small, matched-voltage systems this is fine. But if your panel voltage is higher than your battery voltage — common with any 12V system using modern 36-cell or 60-cell panels — a PWM controller is throttling your harvest significantly. An MPPT controller recovers that wasted power by stepping down voltage and converting it to usable current.
The amperage sizing question is also consistently underestimated. A charge controller rated for 20A connected to an array that can produce 30A will clip output. This page explains how to calculate the current your array can deliver and match it to the right controller.
Charge controllers worth searching on eBay
MPPT and PWM controllers for 12V, 24V, and 48V off-grid solar systems. We earn a small commission on qualifying sales; your price is unchanged. Full disclosure.
MPPT Charge Controller
The correct choice for any system with panel voltage significantly higher than battery voltage, or for arrays above ~200W. Efficiency typically 93–98%. Verify max PV input voltage (VOC) — this is the number that will destroy the controller if exceeded on a cold morning.
View on eBay →
Solar Charge Controller
General search across both MPPT and PWM controllers. Filter by system voltage (12V/24V/48V) and amperage. Look for units with a clear display showing current PV power, battery voltage, and charging state — this makes diagnosing system issues much easier.
View on eBay →
PWM Charge Controller
Works well when panel nominal voltage closely matches battery voltage — typically 12V panels with a 12V battery. Lower cost, simpler, adequate for small systems up to about 150W. Beyond that, the efficiency loss vs MPPT makes MPPT worth the premium.
View on eBay →
40A MPPT Controller
A popular size for 400–600W arrays on 12V systems or 800–1,200W on 24V systems. Brands like Renogy, Victron, and EPever are commonly cited — verify the unit has a genuine LiFePO4 charge profile if you're running lithium batteries.
View on eBay →
Charge Controller with Display
Controllers with an integrated LCD or LED display showing real-time PV voltage, battery voltage, charging current, and state of charge. Valuable for verifying your system is operating correctly and diagnosing shading or wiring issues.
View on eBay →