Author Topic: Question on series/parallel strings for most output..  (Read 356 times)

mickhill

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Question on series/parallel strings for most output..
« on: June 04, 2019, 01:47:53 PM »
Just a quick question... I have 8 - 100 watt Renogy panels, a Midnite Classic 150 and 4 - 125Ahr Vmax AGM batteries. Right now I have them hooked up in 2 strings - 5 panels in Series, and 3 panels in Series, joined in a combiner box. The most watts Im seeing on the Midnite is 400~ Watts. (Usually 430-450).  I had hooked them up that way because I plan to add a couple more later on, for a total of 10 -  2 strings of 5. Would it be beneficial right now to do 2 strings of 4 instead? Im just not sure why Im seeing 400 watts out of 800 watts in panels.

Doug

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Re: Question on series/parallel strings for most output..
« Reply #1 on: June 04, 2019, 02:04:57 PM »
Hi Mickhill,

It would be good to start with the stringsizer at http://www.midnitesolar.com/sizingTool/index.php

It sounds like you have 3 panels in parallel with five. This is not good.
Combined strings should be of similar voltage so strings of the same number of series panels should work better.
Be sure to not overvoltage the Classic.
The stringsizer will help with cold temperature voltages as well.

Doug
« Last Edit: June 04, 2019, 02:08:13 PM by Doug »

mickhill

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Re: Question on series/parallel strings for most output..
« Reply #2 on: June 04, 2019, 02:14:04 PM »
I have used the string sizer and Im well under max input voltage. The problem is the string sizer wont let you enter an odd amount of panels per string, so it really doesnt tell me anything. And I have the 2 separate strings in Series. 5 panels in series and 3 panels in series.

Doug

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Re: Question on series/parallel strings for most output..
« Reply #3 on: June 04, 2019, 02:21:57 PM »
The string sizer will allow an odd number of strings but does require that all strings have the same number of panels.
The problem is once the voltage of the five panels goes above the voltage of the three panels they essentially stop contributing.
What is the VOC of your panels? Five in series will likely be above 150 Volts.

mickhill

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Re: Question on series/parallel strings for most output..
« Reply #4 on: June 04, 2019, 02:32:18 PM »
Right, I have an odd number of panels on my strings. I'll probably just do 2 strings of 4 today after the sun goes down. Open circuit voltage is 22.5 x 5 = 112.5 @ 5.29 Amps Plus 3 panels 67.5 @ 5.29 Amps.  But I would have thought the wattage reading would still total ~700+watts instead of 400+. I'll re-wire them and see how they read tomorrow.
« Last Edit: June 04, 2019, 02:37:34 PM by mickhill »

Doug

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Re: Question on series/parallel strings for most output..
« Reply #5 on: June 04, 2019, 03:07:08 PM »
That should work better for you.
Let us know how it goes.

Doug

mickhill

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Re: Question on series/parallel strings for most output..
« Reply #6 on: June 04, 2019, 03:25:05 PM »
I just went ahead and re-wired them into 2 strings of 4. Batteries are in absorb mode right now but it still wouldnt show over 490 watts when I first connected it. Now its back down to 200+ watts. I still dont understand why I dont see more watts. Does the wattage half in parallel like the Volts do? I understand I'll get the same amount of Volts and double the amps with 2 strings, but I would think the wattage would be true (700-800 watts). I guess I'll learn/figure this thing out one day. Thanks for your help.

Doug

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Re: Question on series/parallel strings for most output..
« Reply #7 on: June 04, 2019, 03:34:54 PM »
The wattage will reduce when you are in absorb.
If you still have good sun and can put a load on it it should come up.

Westbranch

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Re: Question on series/parallel strings for most output..
« Reply #8 on: June 05, 2019, 12:26:07 AM »
If you are not using your batteries, and drawing about 40% of their potential you will NOT see the full potential,of your panels.  The full potential at this time of year , June (summer) will be in the range of 70  - 75% of the rated wattage.... Why?  because the panels are 'rated' in a laboratory like factory at 25* C, etc etc... conditions that you seldom get in the normal outside conditions.....
« Last Edit: June 05, 2019, 12:28:37 AM by Westbranch »
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mickhill

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Re: Question on series/parallel strings for most output..
« Reply #9 on: June 05, 2019, 09:50:57 AM »
Right now there isnt a really big load on the batteries. I have a small chest freezer and that is all. Its averaging about 40 watts per hour. In the mornings my 500Ah battery bank is at about 80-85% or around 400Ah remaining.

ClassicCrazy

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Re: Question on series/parallel strings for most output..
« Reply #10 on: June 05, 2019, 08:28:20 PM »
Are you using a Whizbang ? You must be otherwise you wouldn't have SOC percentage for batteries.
What battery voltage are you running ?
As others have said - depending on your settings and the batteries - once it is in absorb it will cut back the amount of current going into the batteries and hold the voltage at absorb voltage until it either gets to absorb time - or ending amps if  you have that set up -- which ever of those comes first . Then it will go to Float. 
« Last Edit: June 05, 2019, 08:30:58 PM by ClassicCrazy »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie