Solar install on a Trailer, newbie questions

red31 wrote:
Controller to batt voltage drop limits batt charge voltage.

Current 'taper' during abs does not solve voltage drop, the panel is ether on or off, the taper comes from more off time and not reduced current from the panel.

Charge voltage is not limited below that required, since any reasonable combo of panel and wire will be able to draw the voltage at the battery up to its full absorption voltage. During bulk charging, voltage drop (both before and after a PWM controller) will result in a slight loss of efficiency, but it does not limit the ultimate charge voltage. As the battery nears a full state of charge, the current drops and so does the voltage drop.

Without remote voltage sensing, but with a significant voltage drop, the battery still gets charged, but the flat part of the battery voltage curve ("Stage 2" below) looks more like a ramp up to the final voltage.


After the controller goes into PWM regulation the voltage drop simply doesn't make any significant difference - it goes into regulation because there's energy in excess of that needed to hold the battery at the absorption voltage. There might be an early period of "99% on" PWM until the battery itself begins to hold at absorption voltage, but when PWM begins to taper the battery is being held at the required voltage.