What is the Best Volts/Amps arrangement for Solar Panel Output to Controller

The_Dreamer · 09-15-14, 07:06 PM

I am brand new to this forum, having joined in hopes that someone with more knowledge and experience of solar design can help me move forward on my project. I am a full-time RVer, living in a converted school bus going on four years. I am doing an upgrade and redesign of my solar auxiliary battery system.

I have four solar panels, 140 watts each. Their specs are as follows:

Voc 20.6V
Vop 17.3V
Short circuit current (Isc) 9.63A
Working current (Iop) 8.1A

I have purchased a Morningstar Tristar 60 Amp PWM controller. I have two Concorde Sun Xtender AGM batteries (153 AH each). I have a Go Power 3000 HD inverter to feed power from my batteries back into my RV's main power controller using a 30 Amp switch from Go Power.

My question relates to how best to wire my solar panels to provide the maximum power to my Morningstar Charge Controller while experiencing a minimum of voltage drop. I should mention I have about a 40 foot run from my panels to my charge controller and I currently have 6 AWG wire to run between them.

My battery bank is arranged as a 12 volt system. I will be using the Morningstar controller to keep the batteries charged at a maximum manufacturer voltage of 14.4 volts. Does it matter what voltage I run from the panels to the charge controller? I am assuming that whatever voltage and amps come into the charge controller are converted to the proper voltage and amps to charge a 12 volt battery since there is a jumper switch in the controller to choose a 12 volt battery system.

I had been reading what others say about setting up a solar system, and I am finding that if I hook all four panels in parallel that my voltage remains steady at a maximum power output of 17.3 volts, while my current quadruples to approximately 32 Amps. From what I am reading, this will cause a tremendous amount of resistance in the wiring. What I am reading is that it is better to have higher voltage and lower amperage to alleviate resistance.

Should I connect all four panels in series to have approximately 68 volts and 8 amps, or do them half parallel and half serial to have 34 volts and 16 amps? What would be the best configuration, and would the Morningstar properly handle the input and deliver it to the batteries without damaging anything?

As you can tell, electrical theory is not my strong suit. I did all the AC and DC wiring in my bus, and I haven't fried anything yet. I want to keep it that way. Any help would be appreciated. If you need the specs on the Morningstar charge controller, it says that it is rated for 12, 24, or 48 volt systems and 60 amps current. It will handle solar overloads of up to 130%, tapering them down.

The manual says "Do not connect a solar input greater than a nominal 48V array for battery charging. Never exceed a Voc of 125V."

I am unclear on the statement above as I am not sure what is meant by "a nominal 48V array for battery charging." Are they referring to the voltage Vop coming from the panels?

Any help to sort out my confusion will be appreciated. Thanks!

09-15-14, 07:06 PM	#1
The_Dreamer Joseph Herrin Join Date: Sep 2014 Location: Georgia Posts: 7 Thanks: 4 Thanked 0 Times in 0 Posts	What is the Best Volts/Amps arrangement for Solar Panel Output to Controller I am brand new to this forum, having joined in hopes that someone with more knowledge and experience of solar design can help me move forward on my project. I am a full-time RVer, living in a converted school bus going on four years. I am doing an upgrade and redesign of my solar auxiliary battery system. I have four solar panels, 140 watts each. Their specs are as follows: Voc 20.6V Vop 17.3V Short circuit current (Isc) 9.63A Working current (Iop) 8.1A I have purchased a Morningstar Tristar 60 Amp PWM controller. I have two Concorde Sun Xtender AGM batteries (153 AH each). I have a Go Power 3000 HD inverter to feed power from my batteries back into my RV's main power controller using a 30 Amp switch from Go Power. My question relates to how best to wire my solar panels to provide the maximum power to my Morningstar Charge Controller while experiencing a minimum of voltage drop. I should mention I have about a 40 foot run from my panels to my charge controller and I currently have 6 AWG wire to run between them. My battery bank is arranged as a 12 volt system. I will be using the Morningstar controller to keep the batteries charged at a maximum manufacturer voltage of 14.4 volts. Does it matter what voltage I run from the panels to the charge controller? I am assuming that whatever voltage and amps come into the charge controller are converted to the proper voltage and amps to charge a 12 volt battery since there is a jumper switch in the controller to choose a 12 volt battery system. I had been reading what others say about setting up a solar system, and I am finding that if I hook all four panels in parallel that my voltage remains steady at a maximum power output of 17.3 volts, while my current quadruples to approximately 32 Amps. From what I am reading, this will cause a tremendous amount of resistance in the wiring. What I am reading is that it is better to have higher voltage and lower amperage to alleviate resistance. Should I connect all four panels in series to have approximately 68 volts and 8 amps, or do them half parallel and half serial to have 34 volts and 16 amps? What would be the best configuration, and would the Morningstar properly handle the input and deliver it to the batteries without damaging anything? As you can tell, electrical theory is not my strong suit. I did all the AC and DC wiring in my bus, and I haven't fried anything yet. I want to keep it that way. Any help would be appreciated. If you need the specs on the Morningstar charge controller, it says that it is rated for 12, 24, or 48 volt systems and 60 amps current. It will handle solar overloads of up to 130%, tapering them down. The manual says "Do not connect a solar input greater than a nominal 48V array for battery charging. Never exceed a Voc of 125V." I am unclear on the statement above as I am not sure what is meant by "a nominal 48V array for battery charging." Are they referring to the voltage Vop coming from the panels? Any help to sort out my confusion will be appreciated. Thanks!