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kshilanski avatar image
kshilanski asked

Why SmartSolar MPPT continuing to charge beyond 'Charged Voltage'?

Hi, We recently got a SmartSolarMPPT 85/150 and a BMV-712 in our motorhome. We have 5 x 160w panels on our roof, and run 4 AGM batteries in a 12v system with a total of 440AH.

I have noticed that sometimes the SmartSolar continues to be putting in power to the batteries even after they have exceeded the 'charged voltage'. Why is this? The setting for 'charged voltage' in the BMV-712 is set at 13.4 (per LifeLine AGM manual). The settings in the SmartSolar MPPT are custom set to Absorption 14.4v, Float 13.4, Equalization 15.5v. I have the SmartSolar and BMV linked via Bluetooth.

I'm attaching screenshots from the App on a day when it was really sunny and the battery voltage was up to 14.17/14.19v. Do I have a setting wrong? Thanks so much!




MPPT ControllersBMV Battery MonitorSOCVE.Smart Network
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1 Answer
Mark avatar image
Mark answered ·

The MPPT solar charge controller acts independently and is in full control of the charge cycle and charge voltages.

The BMV-712 only provides the MPPT with accurate battery voltage and battery temperature data to work with via the VE.Smart Network (via Bluetooth).

The absorption voltage set in the MPPT is 14.40V and the screen image shows that the MPPT is in absorption phase.

However, the configured voltage set-point is subject to temperature compensation (unless its deactivated) - at a battery temperature of 29°C and with a temperature compensation coefficient of 16.2mV/°C the corrected absorption voltage set-point would be 14.40V + (29-25)*-0.0162 = 14.33V. So ~14.3V is the TARGET that the MPPT is trying to maintain during the absorption phase.

The measured/actual voltage shown is ~14.2V which is very close, but I can also see in the BMV data that there must be a large load active at the same time, as the MPPT charge current is not enough to cover the load and charge the battery - there is a current draw of -34.9A from the battery and this would be pulling the battery voltage down a little.

The BMV 'charged voltage' setting is only one of the criteria required to 'synchronize' the BMV SOC reading to 100%. It does NOT change the charge state of the MPPT or communicate this information to it.

In solar applications it is generally better to set the BMV 'charged voltage' to the MPPT absorption voltage -0.2 to -0.4V. This helps to prevent false/premature synchronizations to 100% SOC due to fluctuating solar conditions/charge current.

14.4V is a typical absorption voltage for lead acid based batteries, but if your battery manufacturer recommends something different then you need to adjust this set-point in the MPPT configuration.

I would also recommend to check the battery manufacturers recommend temperature compensation coefficient, for most lead acid based batteries it's typically a little higher than the default ~24mV/°C to 30mV/°C (for a 12V battery/bank).

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