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Old 09-16-14, 05:24 PM   #11
The_Dreamer
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Originally Posted by Xringer View Post
For nerds, 1 amp is 1 coulomb flowing per second (a coulomb is approximately 6.241×10 to the +18th electrons
That is a whole lot of electrons. Makes me wonder who took the time to count them. I can envision some guy in front of an electron microscope going "1, 2, 3, 4..." He would be sitting there for a couple centuries counting up to 6.241 x 10 to the 18th electrons.

I do appreciate the assistance. This is a learning experience for me. I think I should have joined some forums a long time ago to get some input from people with more experience in this arena. I am having to backtrack and re-thing a lot of my system design choices. Better late than never.

The guys at the Northern Arizona Wind and Sun forum have been very helpful as well. Thanks again for the recommendation.

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Old 09-16-14, 08:07 PM   #12
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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..
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Old 09-16-14, 08:27 PM   #13
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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!

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