Solar Panel Voltage at Charge Controller

System

I am hooking up a Solar Boost 2000E and a 100 watt solar panel to two 12v. lead/acid batteries. (I have the temp sensor and the dip switches on the controller are set in accordance with the manual)

I checked the voltage at the panel and it's 20.xx. When I hook the system up, the voltage at the solar panel terminals on the controller is 15.xx. Is that normal?

Other than the 5v. drop when I hook the panel up, the charge controller seems to be working fine.

RW

BB.

Re: Solar Panel Voltage at Charge Controller

If everything is connected correctly, and the batteries are pretty much fully charged... Then the controller is probably working fine.

The "MPPT" part of the controller (Maximum Power Point Tracking) occurs when the controller is charging a severely discharged battery (below ~85% or so state of charge)... The controller is trying to pump as much energy (current) into the battery as it can.

It does this by monitoring the Panel Voltage and Current... And maximizing the equation Power=Voltage*Current (adjust the current until Power is maximized). The controller then takes that Power and (at the panel's Vmp and Imp) and converts it to Pbatt=Vbat*Ibat (with a few percent loss of power in the controller). This is the "Bulk Charging" stage.

Once the battery is above ~85% State of Charge--the controller cuts the controller uses less than maxim current from the solar panels--which allows the solar panel voltage to creep up towards Voc (Voltage Open Circuit)--called "Absorb Stage". If you are reading 15 volts on the battery--it sounds like you are in this mode.

As the battery approaches full capacity, the charger will cut back on the battery voltage to around ~13.8 volts. "Float" stage. At this point, there is very little current flowing into the battery and the controller is just providing enough voltage and current to keep the battery fully charged. The PV panel voltage will approach Voc (open circuit) and the panel current will be very low (probably well under 1 amp).

-Bill