Victron Bluesolar LCD & USB PWM solar controller:

Victron Bluesolar Duo is a PWM two battery controller for RVs, caravans, boats and cottages. Designed for 20 amps at 12 volts DC. Victron's range of  PWM and MPPT charge controllers are both widely used to charge batteries with solar power. The PWM controller is in essence a switch that connects a solar array to the battery. The result is that the voltage of the array will be pulled down to near that of the battery.

A PWM controller is not a DC to DC transformer. The PWM controller is a switch which connects the solar panel to the battery. When the switch is closed, the panel and the battery will be at nearly the same voltage. Assuming a discharged battery the initial charge voltage will be around 13 V, and assuming a voltage loss of 0,5 V over the cabling plus controller, the panel will be at Vpwm = 13,5 V.

The voltage will slowly increase with increasing state of charge of the battery. When absorption voltage is reached the PWM controller will start to disconnect and reconnect the panel to prevent overcharge (hence the name: Pulse Width Modulated controller).
 

Features:

Liquid crystal display- For status monitoring and set-up

External temperature sensor- Included

2 separate battery outputs- Charges two separate batteries. For example, the starter battery and the service battery of a boat or mobile home. 

Protections- Protected against reverse polarity connection of the solar panels and/or battery. 

Programmable battery charge algorithm- Algorithms for AGM, GEL or Flooded lead-acid batteries and LiFePO4 batteries (with internal BMS). 

Two 5 Volt USB outputs- Maximum current of the two outputs combined: 2A