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!

Xringer · 09-15-14, 07:58 PM

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

That doesn't sound right. How would you charge a 48V bank?
My four 125w panels are connected in series (about 70vdc).
Small gauge wire* is what I use to feed my TS-45 charger for my 48v bank.

Since the total current in my system never over 7 or 8 amps, the losses are minimal.

I have also used the TS-45 with with Four 200W panels (abt 120vdc) 9A max and it worked fine..

The wire I'm using for this test is RG-8 type coax cable.. It works pretty good.

Currently, my 800w array is feeding directly into a hotwater heater..

My 48v bank is only for back-up, so my solar mostly goes to making hotwater..

Our A7 hotwater heat pump ran about 6 hours since April..

The_Dreamer · 09-15-14, 08:45 PM

Quote:

Originally Posted by Xringer

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

That doesn't sound right. How would you charge a 48V bank?
My four 125w panels are connected in series (about 70vdc).
Small gauge wire* is what I use to feed my TS-45 charger for my 48v bank.

Since the total current in my system never over 7 or 8 amps, the losses are minimal.

I have also used the TS-45 with with Four 200W panels (abt 120vdc) 9A max and it worked fine..

The wire I'm using for this test is RG-8 type coax cable.. It works pretty good.

I think I read somewhere that the Tristar Charge Controllers can handle an input voltage up to 150 volts. Your experience with your two configurations seems to validate this. I do appreciate your feedback. It leads me to think that I should connect all four of my panels in serial. My own set-up would not be much different than your four 125 watt panels hooked in serial.

Thanks for sharing what has worked for you.

Xringer · 09-15-14, 09:08 PM

That sounds like something I've read somewhere.
It might even be in my manual. Not sure but it's got to be at least 150v..

When you are charging a 48v bank, your voltage has to be well over 50v.
Otherwise it will take too long to charge and the sun will be gone.
70volts seems to work pretty well for my needs.

A lot of people put their panels in parallel and just charge at 12v..
12v inverters are a lot more common than 48v inverters, is the main reason..
They have to buy a lot of thick copper wire. Big bucks.

But the other reason is the high voltage.. Be VERY careful with high DC voltage!
If you make a mistake, it's worse than being shocked by the AC mains..
It can kill you.. That's why firemen hate solar panels.. Even at night..
I heard one guy say the fire truck lights could make the panels live and shock the firemen.. Crazy..

Use a 10A fuse at the panels and it should never pop, even with a dead short..
It's just for looks mostly.. It will last forever.

A good solar forum is at Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun

The_Dreamer · 09-15-14, 09:15 PM

What you are saying about the voltage needed to charge a 48 Volt battery bank is certainly true. That is why I was confused by the quote in the TS-60 manual, "Do not connect a solar input greater than a nominal 48V array for battery charging." Not sure what that means.

I am sure I will have more questions as I put my system together. Thanks for the recommendation on the Northern Arizona forum.

OffGridKindaGuy · 09-16-14, 05:17 AM

The manual says the max. input voltage can be up to 125 volts. your panels are 20.6 Voc (Volts Open Circuit) each. Connected in series is less than 125 volts. (84.4 volts) This would be fine if you were charging a 48 volt battery. Not a concern with charging a 12 volt battery..

The charge voltage can be selected via programming (Settings) in the controller. You can choose to charge at any of the three voltages. (12, 24, 48 volts)

In your case, you plan to charge at 12 volts, your panels should be connected in parallel. If you want to connect your panels in series to reduce the wire gauge between the controller and the panels to charge at 12 volts, you need a different type of controller. (MPPT)

What is Maximum Power Point Tracking (MPPT)

The_Dreamer · 09-16-14, 07:24 AM

Quote:

Originally Posted by OffGridKindaGuy

The manual says the max. input voltage can be up to 125 volts. your panels are 20.6 Voc (Volts Open Circuit) each. Connected in series is less than 125 volts. (84.4 volts) This would be fine if you were charging a 48 volt battery. Not a concern with charging a 12 volt battery..

In your case, you plan to charge at 12 volts, your panels should be connected in parallel. If you want to connect your panels in series to reduce the wire gauge between the controller and the panels to charge at 12 volts, you need a different type of controller. (MPPT)

Hello OffGridKindaGuy. I appreciate the info on the 125 volts limit for this charge controller. I am not following your reasoning, however. If my charge controller will handle the 84.4 volts my panels could produce, why would I need to wire them in parallel and limit them to 20 volts? This would cause the amperage to balloon to 32 amps, causing a lot of resistance in the line, with very little voltage to push it along.

I have read that MPPT controllers are best for very large voltages, especially when one gets above 150 volts, but I am not clear on why you say I would need a MPPT controller if my volts are only half of that.

You wrote:

"In your case, you plan to charge at 12 volts, your panels should be connected in parallel."

I am not disagreeing with you. I am simply trying to understand the concepts involved as having an understanding of what is going on in electrical theory seems to be prudent when tackling a job like this. Why do you say I need to connect in parallel if I am charging a 12 volt battery bank? Would not a higher voltage, low amperage input do the job just as well, if not better? Doesn't the charge controller regulate the volts and amps being fed into the battery bank?

If you could explain your conclusions I would appreciate it.

Thanks in advance!

OffGridKindaGuy · 09-16-14, 08:07 PM

Quote:

Originally Posted by The_Dreamer

Hello OffGridKindaGuy. I appreciate the info on the 125 volts limit for this charge controller. I am not following your reasoning, however. If my charge controller will handle the 84.4 volts my panels could produce, why would I need to wire them in parallel and limit them to 20 volts? This would cause the amperage to balloon to 32 amps, causing a lot of resistance in the line, with very little voltage to push it along.

I have read that MPPT controllers are best for very large voltages, especially when one gets above 150 volts, but I am not clear on why you say I would need a MPPT controller if my volts are only half of that.

You wrote:

"In your case, you plan to charge at 12 volts, your panels should be connected in parallel."

I am not disagreeing with you. I am simply trying to understand the concepts involved as having an understanding of what is going on in electrical theory seems to be prudent when tackling a job like this. Why do you say I need to connect in parallel if I am charging a 12 volt battery bank? Would not a higher voltage, low amperage input do the job just as well, if not better? Doesn't the charge controller regulate the volts and amps being fed into the battery bank?

If you could explain your conclusions I would appreciate it.

Thanks in advance!

Your Morningstar controller is limited to 60 amps. This is the maximum amount of current that it can manage, with regard to the desired charge voltage setting. It will only handle "X" amount of wattage in panel per the desired charge voltage setting. The "Working" voltages per setting is 15 for 12 volt charging, 30 for 24 volt charging, and 60 for 48 volt charging.. (With a small window for error)

Each charge voltage setting limits the amount of panel that can be controlled. It's in the math.. (^ being the controller current limit and * being the desired working voltage from the panel array)

^60 X *15 = ~900 watts (For 12 volt charging)
^60 X *30 = ~1800 watts (For 24 volt charging)
^60 X *60 = ~3600 watts (For 48 volt charging)

In your situation, you are charging a 12 volt battery. The controller will shunt the voltage from the panels to ~ 15 volts maximum. The charge to the battery only needs to be ~ 14.2 to 14.8 volts maximum for bulk charging. After the bulk voltage is achieved, the controller will then knock the voltage down to the float level voltage, which is ~ 13.2 to 13.6 volts. There is no need for the voltage from the panels to the controller to be any higher than ~ 15 volts. If it goes higher, the controller will shunt the power from the panels to regulate the voltage to ~ 15 volts and dissipate the extra power in heat, not to charge the battery..

The 125 voltage rating for the controller is the maximum amount of voltage "Spike" the controller will withstand. This voltage level would only be a concern while using the controller to charge a 48 volt battery, in the event of an open circuit condition. (Battery disconnect with no load on the controller, panels connected to the controller)

Your panels.. Connected in parallel..
Voc - 20.6 volts (Open Circuit Voltage)
Vop - 17.3 volts (Working Voltage)
Iop - 8.1 Amps (Working Current)

The working voltage is already at 17.3 volts. The controller will hold that down to ~ 15 volts or below, depending on the load of the battery. (Charge Condition/Mode of Charge)

In an open circuit voltage condition, the voltage will never go above ~ 22 volts max. That level will never hurt the controller..

4 panels @ 8.1 working amps is ~ 33 amps. Only around half of the maximum current rating of the controller..

Hope this helps..

The_Dreamer · 09-16-14, 08:27 PM

Thanks to OffGridKindaGuy. That was a great explanation. I appreciate your patience in explaining this matter in the depth you have done. I found it very helpful. It certainly leaves me no doubt that wiring my panels in parallel and keeping the voltage low is the only way to go as long as I have a pwm controller and a 12 volt battery bank.

I am truly getting an education here, and I appreciate the help. Someone could have just said, "Wire the panels in parallel," and given no explanation, but knowledge is power. I am reminded of the saying, "Give a man a fish and feed him for a day. Teach a man to fish and feed him for a lifetime."

Thanks!

Xringer · 09-16-14, 11:26 AM

The losses due to heating up the wire increase with current.
Watts of loss= Current Squared x Resistance.

(Notice that voltage isn't in the formula).

~~~

I've never even looked at using a 4 panel series array to charge at 12V..
But, it seems like it would put more demands on the charge controller.
Even with PWM, controlling how hard you hit a 12V battery when starting off with 100vdc, isn't real simple. Something to research there..

~~~~
In addition to (12, 24, 48 volts) battery packs, I believe my CC can be configured for Golf Karts.. 36volts! LOL!!

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!

09-15-14, 07:58 PM	#2
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	"Do not connect a solar input greater than a nominal 48V array for battery charging. Never exceed a Voc of 125V." That doesn't sound right. How would you charge a 48V bank? My four 125w panels are connected in series (about 70vdc). Small gauge wire* is what I use to feed my TS-45 charger for my 48v bank. Since the total current in my system never over 7 or 8 amps, the losses are minimal. I have also used the TS-45 with with Four 200W panels (abt 120vdc) 9A max and it worked fine.. The wire I'm using for this test is RG-8 type coax cable.. It works pretty good. Currently, my 800w array is feeding directly into a hotwater heater.. My 48v bank is only for back-up, so my solar mostly goes to making hotwater.. Our A7 hotwater heat pump ran about 6 hours since April.. __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less..

09-15-14, 09:08 PM	#4
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	That sounds like something I've read somewhere. It might even be in my manual. Not sure but it's got to be at least 150v.. When you are charging a 48v bank, your voltage has to be well over 50v. Otherwise it will take too long to charge and the sun will be gone. 70volts seems to work pretty well for my needs. A lot of people put their panels in parallel and just charge at 12v.. 12v inverters are a lot more common than 48v inverters, is the main reason.. They have to buy a lot of thick copper wire. Big bucks. But the other reason is the high voltage.. Be VERY careful with high DC voltage! If you make a mistake, it's worse than being shocked by the AC mains.. It can kill you.. That's why firemen hate solar panels.. Even at night.. I heard one guy say the fire truck lights could make the panels live and shock the firemen.. Crazy.. Use a 10A fuse at the panels and it should never pop, even with a dead short.. It's just for looks mostly.. It will last forever. A good solar forum is at Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less..

09-16-14, 05:17 AM	#6
OffGridKindaGuy Hi-Tech Hillbilly Join Date: Mar 2010 Location: Ohio Posts: 97 Thanks: 1 Thanked 16 Times in 15 Posts	The manual says the max. input voltage can be up to 125 volts. your panels are 20.6 Voc (Volts Open Circuit) each. Connected in series is less than 125 volts. (84.4 volts) This would be fine if you were charging a 48 volt battery. Not a concern with charging a 12 volt battery.. The charge voltage can be selected via programming (Settings) in the controller. You can choose to charge at any of the three voltages. (12, 24, 48 volts) In your case, you plan to charge at 12 volts, your panels should be connected in parallel. If you want to connect your panels in series to reduce the wire gauge between the controller and the panels to charge at 12 volts, you need a different type of controller. (MPPT) What is Maximum Power Point Tracking (MPPT) __________________ If it don't, I'll always think it shoulda.. Last edited by OffGridKindaGuy; 09-16-14 at 05:22 AM..

09-16-14, 11:26 AM	#10
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	The losses due to heating up the wire increase with current. Watts of loss= Current Squared x Resistance. (Notice that voltage isn't in the formula). ~~~ I've never even looked at using a 4 panel series array to charge at 12V.. But, it seems like it would put more demands on the charge controller. Even with PWM, controlling how hard you hit a 12V battery when starting off with 100vdc, isn't real simple. Something to research there.. ~~~~ In addition to (12, 24, 48 volts) battery packs, I believe my CC can be configured for Golf Karts.. 36volts! LOL!! __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less..

09-15-14, 09:15 PM	#5
The_Dreamer Joseph Herrin Join Date: Sep 2014 Location: Georgia Posts: 7 Thanks: 4 Thanked 0 Times in 0 Posts	What you are saying about the voltage needed to charge a 48 Volt battery bank is certainly true. That is why I was confused by the quote in the TS-60 manual, "Do not connect a solar input greater than a nominal 48V array for battery charging." Not sure what that means. I am sure I will have more questions as I put my system together. Thanks for the recommendation on the Northern Arizona forum.

09-16-14, 08:27 PM	#9
The_Dreamer Joseph Herrin Join Date: Sep 2014 Location: Georgia Posts: 7 Thanks: 4 Thanked 0 Times in 0 Posts	Thanks to OffGridKindaGuy. That was a great explanation. I appreciate your patience in explaining this matter in the depth you have done. I found it very helpful. It certainly leaves me no doubt that wiring my panels in parallel and keeping the voltage low is the only way to go as long as I have a pwm controller and a 12 volt battery bank. I am truly getting an education here, and I appreciate the help. Someone could have just said, "Wire the panels in parallel," and given no explanation, but knowledge is power. I am reminded of the saying, "Give a man a fish and feed him for a day. Teach a man to fish and feed him for a lifetime." Thanks!