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-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 13V, and assuming a voltage loss of 0.5 V over the cabling plus controller, the panel will be at V PWM = 13.5V.
