question

geomz avatar image
geomz asked

Why does my MPPT system continually stop charging?

I have 2 100/30 Smartsolar MPPTs integrated with a Quattro 5000 into an ESS, running on 24V lithium batteries. That system consists of 4 panels in 2x2 in parallel.

Can someone please explain to me the reasons for the attached pic?

It's a snapshot of the last 48 hours worth of charging. Both were equally sunny days (actually day 2 was sunnier). The batteries reached a nice good charge of around 95% (possibly reaching absorption voltage) on day 1. Then through the day's consumption, day 2 started out in the low 70s% SOC. But as you can see from day 2, hardly anything came in. The day finished up slightly higher @~75%. Why?

There was plenty of sun. The batteries clearly needed the charge. Yet?

It's obvious the system tried to hold some voltage on the batteries and I'm confused why. This is not the first time this has happened and I'd like to understand how to stop this unproductive behavior from reoccurring.

Thanks in advance,

George

MPPT ControllersESSchargersolar
annotation-2020-02-09-033358.png (153.9 KiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Hi Goemez,

You have not mentioned the firmware version of your GX device, or mppt.

Please include "Mppt state" [288] & [256]

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geomz avatar image geomz commented ·

GX Device: v2.42

Mppt: v1.46

State: External Control


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wkirby avatar image wkirby ♦♦ geomz commented ·

It would still be useful to see a MPPT or VE.Bus state chart for this period.

It seems like the system is still in Float for day 2 so the lower target Voltage is limiting charge current.

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1 Answer
JohnC avatar image
JohnC answered ·

Hi @Geomz. Analyzing your graphs..

Day 1. Targetting an Abs of 28.2V (which it reached for a while), most of the energy pushed to the batts occurred at ~27.1-27.2 V. Charge backed off heavily in Abs, then further when Float was reached for a short while at 26.8V.

Day2. Abs wasn't targetted (for some reason), just the 26.8V Float. Being below what appears to be your batt optimum charge level (~27.2V), it didn't charge so much. It did a good job holding that though, and the unsynched mppts actually 'traded places' with their priority (an interesting side-effect).

Conclusions? Your Abs doesn't need to be that high, and Float is too low to give full charge.

I don't know why Abs was skipped, but 'External Control' means ESS or a BMS is having a say to at least some extent.


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