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gmaijoe avatar image
gmaijoe asked

Low Watts Compared to Expected

Hi all,

I bought a 150V 45A 48V victron charge controller.

I have 8 245W YL245P-29b solar panels (stats attached)

1719353362570.png

At 3pm, I'm measuring around 120 W total (around 57V and 2.1A) total via the Victron iOS app.

My solar panels are 4 pairs of 2. The pairs are connected in series, and then 4 pairs are in parallel. Using the Pmax values, I should be getting around 29.6V X 2 = 59.2V and 8.28 * 4 = 33.12A at Pmax. So Pmax should be maxed out around 1960W for my 9 panels in total.


When I measured one of my pairs (out of 4 pairs), I read on the multimeter 62V and 2.2A, which is 136.4 W. But someone my total input is 120 W according to Victron.


When I disconnect all my panels except the pair I measured earlier (62V and 2.2A), Victron smart controller drops my W to around 30W, which is 25% of the total.


My battery system is 48V so with 45A max, this system should be able to handle 2160W, just around the Pmax value of my solar system.


My victron is on bulk charging also, so it's not an issue with float or absorption. Battery percent is around 87% according to Victron shunt. I'm at a loss for what is wrong.


FWIW, my wiring from the batteries (4x 12V 200AH wired in series to be 48V) connects to a bus bar, which connects the victron battery shunt, the charge controller, and the inverter. My solar charger is connected to the PV wires from the roof. I've attached a picture for better visibility.


Thanks so much - looking to figure out what's wrong so I can make my system more efficient

screenshot-2024-06-25-at-61717pm.png

MPPT Controllersbattery chargingMPPT SmartSolar
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2 Answers
klim8skeptic avatar image
klim8skeptic answered ·

@Gmaijoe The Vmp of 59.2v for 2 series panels is too low to charge a 48v battery.

Try rewiring the panels as 2 strings of 3 series panels.

Look at the Victron mppt calculator.

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gmaijoe avatar image gmaijoe commented ·

thanks - can you help me understand why 2 series is too low? I manually measured the V from the panels in series (2) and it was around 62V on the multimeter.


Does the MPPT charge controller change something to affect this? Why is there such a discrepancy between the multimeter's measurement of V/A and W, and the reported Watts on the charge controller?


Just trying to learn.

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klim8skeptic avatar image
klim8skeptic answered ·

@Gmaijoe I manually measured the V from the panels in series (2) and it was around 62V on the multimeter.

If you measure the panel voltage without a load, (mppt charging the batt) it will be higher than the panels rated Vmp (Voltage at (panel) Max Power).

Your 2 panels Vmp of 58.2v (even lower at panel temps above 25c) is not high enough to reliably charge your 48v battery.

Your mppt requires battery voltage, plus 5 volts before it will start charging. After it starts charging the panel voltage can be batt voltage plus 1v.

You running the panels way above their Vmp, output current will be reduced, therefore low power output.

Run the array config through the calculator.

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