Voltage from 36v to18 in the day

jweslock

I have my 4-100w panels in two series sets. I find my mppt controller initially recognizes 18 v but i have it wired in 2 panel series and as i understand it the voltage should be double. How can it be detecting only 18volts. In the middle of the day the voltage ramps up to +30 volts and then when the pvs start to become shaded it goes back to 18volts. Any idea whats happening?

vtmaps

Welcome to the forum. 

What controller do you have?  What voltage battery are you using?

--vtMaps

jweslock

I have a 60 amp mppt (rock mars) and 12volt 

vtmaps

I do not know anything about that controller.  My best guess is that when you have shading your controller loads down the panels until their voltage drops to 18 volts.  The panels will make full voltage in the shade, but without any significant power.  As soon as the controller tries to draw power, the voltage drops. 

--vtmaps

zoneblue

Sounds like a PWM controller to me. People wonder why these off brand controllers dont do what they say on the box. Moral of the story? stick with name brand stuff.

westbranch

agree with shade being the issue and possibly the PWM CC....  Check the Vmp of those panels, it sounds to me like the shade is killing 1/2 of your PV output, and it only ''sees'' the voltage of one PV...