Squonk writes about this scalable solar charger he’s located:
The most common solar charger consists of a Schottky diode to prevent the battery from draining into the PV panel and a shunt regulator that effectively short circuits the panel once the battery is fully charged.
An unconventional, scalable high efficiency 12V solar power system and battery charge controller with low voltage cutout to protect the battery. (ideal for systems of 50W or less).
One problem with this approach is diode losses and the resulting heat. If a 50W 12V panel supplies 4A to the battery, the Schottky diode will drop about 0,4V across it dissipating about 1,6W of heat. This requires a heat sink and loses power to heat. The problem is that there is no way of reducing the volt drop, paralleling diodes may share current, but the 0,4V will still be there. The circuit uses a MOSFET in stead of the usual diode and the primary power loss is resistive.
For comparison, a 40W PV system using the circuit below with IRFZ48 mosfets has a loss of about 1/4W on Q2. This means less heat and more power for your battery. More importantly though, MOSFETS have a positive temperature coefficient and can be paralleled to reduce the ON resistance. Unlike the diode system, the total power loss can be reduced.
The project details including BOM and schematic, and information on kit availability can be found at Opend hardware.
Via the contact form.