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Please help me understand my 100W x 2 panels.

gingerboy

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Aug 13, 2020
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17
Hello, everyone:
I have 100W X2 Renogy panels(RNG-100D, used), I use them to charge my 12V LiFePo4 (100A) for Aux pump (12V). I use MakeSkyBlue MPPT V118 for test them. (Battery type, Li, charge Voltage 14.40)
With single panel, shows Voltage 20.31, Watts 46.16, it is ok. (here in New York, and Winter) I tested 2nd panel, about the same. So I go ahead set them up in Series, then I noticed the Voltage from Pv is 40.98, and Watts is 45.78. The Voltage is double as connect in Series, but output like single panel(100W). Then I change the connection to Paralell, they are 20.12V and 45.91W. I disconnect and connect each panel individually to test again, seems ok, each panel output about 44W. But when I put them back to Series, Voltage rise and Watts output same as single panel.
First I thought maybe my battery almost full charged. So, I discharge LiFePo4 down to 12.9V, and test again. Samethings happened, 2 panels connected together, but output just like single panel. I am really not sure what I did wrong. Both PV and Battery wires are #10AWG.

Anyone, any ideas?
 
Here's a reference to good vs. counterfeit product:


When two panels in series had same performance as single, I expected two in parallel to deliver double (if your SCC was PWM). But you always got the same output. I'm puzzled unless it is a 4A charge controller (or battery is full, but you tested for that.)
 
I am discharging my other 100A AGM battery, will test again other day.
The "MakeSkyBlue" is good 60A, cause I have a bigger array for 60V battery bank, 335W x 6, as today the best output is 1635W, so MPPT is not the problem.
 
Interesting to see how this turns out. I have the V119 version of the same controller. I'll be putting it into service in a couple of weeks. The only thing that comes to mind is did you give the MPPT part enough time to adjust? I have two EPEver 50a in service at the moment and when I turn one or the other off, it takes time for the other to adjust to being the only one. It also takes the off one time when it is turned on again.
 
Wow, finally make it work. Still not sure about what part did I make right.
The battery drain down to 11.5V, adjust the setting of MPPT controller, save the setting. And disconnect the battery (POWER OFF the MPPT controller), wait a few seconds to reconnect the MPPT.
(I believe the POWER OFF then POWER ON the MPPT Controller, that is make the new setting save and function.)
2 100W panel connects in series, output 92W - 127W. It is working.
So, I believe that is about the MPPT charge controller. Somehow, after adjusts the setting and save, still need to power off and power on to make it functioning. But seems only happen when I charge 12V battery, it was working good with my 48V battery bank and 60V battery bank (no power off and power on need.)
 
I found out more. The problem is the MakeSkyBlue charge controller. 100A LiFePo4 battery, voltage is 12.1V, connect to controller. The setting from MakeSkyBlue is Li, 14.4V. then with 100W x2 panels, out put 93W, but if I change the charge Voltage to 14.8V, the output is 119W. Today is nice sunny, even in winter single 100W panel output 73W - 82W.
So, when I increase the charge voltage, the controller output more. Seems the charge method for Li battery has a bug or something.
 
I found out more. The problem is the MakeSkyBlue charge controller. 100A LiFePo4 battery, voltage is 12.1V, connect to controller. The setting from MakeSkyBlue is Li, 14.4V. then with 100W x2 panels, out put 93W, but if I change the charge Voltage to 14.8V, the output is 119W. Today is nice sunny, even in winter single 100W panel output 73W - 82W.
So, when I increase the charge voltage, the controller output more. Seems the charge method for Li battery has a bug or something.

14.8/4 = 3.7V per cell

That sounds too high. What is the cut-out voltage of BMS?
Could it be Li current is supposed to taper off at this point?
Is there voltage drop from charge controller to battery, due to resistance in wire, fuse, connections between cells, etc?
 
14.8/4 = 3.7V per cell

That sounds too high. What is the cut-out voltage of BMS?
Could it be Li current is supposed to taper off at this point?
Is there voltage drop from charge controller to battery, due to resistance in wire, fuse, connections between cells, etc?
Hi, I am sure the problem is the "MakeSkyBlue". Seems it does not work or charge so well with 12V small watts system.
Yeap, 14.4V is correct charge voltage for LiFePo4 battery. I increase the charge volt setting just for test. There isn't voltage drop during my test, both PV and battery are AWG #10 copper wire about 8 feet.
Right now under full sun, 100W x2 panel shall be product around 140W - 150W, but if the controller setting is "14.4V", all I got was about 90W, 6A, but I get 73W with single 100W panel. I believe the controller's charge method is weir, it seems to increase output watts by increase charge voltage. I try to get other 100W panel, I need it anyway, going to make 3 of 100W in series, want to see if increase PV voltage will make any different.
I am confused, this "MakeSkyBlue" works so well with my 2000W PV and 48V or 60V battery bank. Maybe need other MPPT controller of 12V batteries?
 
earlier today I was using my Renogy Wanderer to charge a 100ah LFP from two 100w HQST panels in full Sun and got 140 watts in. I am located in Maryland, so similar angles to you in New York. I have been happy with the performance of this relatively cheap pwm controller for a two or three 100w panels in parallel.
 
Hi, I am sure the problem is the "MakeSkyBlue". Seems it does not work or charge so well with 12V small watts system.
Yeap, 14.4V is correct charge voltage for LiFePo4 battery. I increase the charge volt setting just for test. There isn't voltage drop during my test, both PV and battery are AWG #10 copper wire about 8 feet.
Right now under full sun, 100W x2 panel shall be product around 140W - 150W, but if the controller setting is "14.4V", all I got was about 90W, 6A, but I get 73W with single 100W panel. I believe the controller's charge method is weir, it seems to increase output watts by increase charge voltage. I try to get other 100W panel, I need it anyway, going to make 3 of 100W in series, want to see if increase PV voltage will make any different.
I am confused, this "MakeSkyBlue" works so well with my 2000W PV and 48V or 60V battery bank. Maybe need other MPPT controller of 12V batteries?

Hi, new member here, solar tyro, and my first post. I'm not sure this helps your situation but here's what I know.

I have a system much like yours, with two 100Ah AGM Deep cycle 12v batteries in parallel (200w and 2x 100w panels in parallel) running exterior Malibu type lighting around the perimeter of my house as well as water feature pumps. In no way do I get a DOD close to where I won't charge even on a cloudy day.

I was in contact with the tech support at makeskyblue about using their CC with my system and LiFePo4 batteries as my batteries are getting on in age and I am thinking of adding a gable attic fan and a couple more pumps and possibly another panel .

Anyway, they said that their CC doesn't support the LiFePo4 battery charge profile (support lacking in their specs) and to really optimize the charge with my existing AGM batteries, putting my panels in series/parallel and running the system at 24 volts would be more efficient.

So I'm keeping the PWM controller for the time being.

I hope this helps.
 
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