Shutdown on low SOC doesn't shutdown

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aphexer asked Oct 5, '22

Shutdown on low SOC doesn't shutdown

I've got the following off-grid setup:

- 1 BlueSolar 75/15 MPPT on PV string 1
- 1 BlueSolar 100/30 MPPT on PV string 2
- Venus running on a raspberry pi
- Phoenix Inverter
- 12V AGM battery bank
- Smartshunt

The MPPTs & smartshunt are connected to the Venus using a VE.direct-USB cable. The inverter is connected to the Venus using a MK3-USB cable.

I'm trying to get the Phoenix inverter to shutdown based on the State of Charge (SoC) value reported by the Smartshunt. I've configured it as you can see below in the screenshot with a SOC low shut-down at 80%. The smartshunt reports SOC at 75%, however the inverter is still active... You can also see in the last screenshot synchronizing VE.bus SOC with battery is active.

The low battery LED is flashing on the Phoenix inverter, but it's not shutting down. Also there's a discrepancy between SOC reported through VE Config and what the smartshunt reports.

Does anyone know why the discrepancy in SOC and why the inverter doesn't shut down?

Update: during the night the inverter shutdown and the "low battery" LED was solid on while the "inverter on" LED was off. That happened when the battery voltage went down to 11.82V. I checked this morning in VE Config and the state of charge reported by the inverter was still at 85% (the battery shunt showed 45%). This specific error condition (low battery LED solid on; inverter on LED off) is not even in the Phoenix inverter manual.

SOC shutdown

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Answer 1 · 2022-10-05T20:00:13Z

aphexer answered · Oct 05, 2022 at 08:00 PM

I checked again, the battery shunt now reports SOC only at 65%, but VE config tool still reports 85%. Anyone any idea why the Phoenix inverter's SOC isn't going further down?

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klim8skeptic ♦ commented · Oct 05, 2022 at 08:20 PM

You have 2 battery monitors. the Smart Shunt, and the 1 in the inverter charger.

The monitor in the phoenix is not particularly accurate, and is harder to set up.

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aphexer klim8skeptic ♦ commented · Oct 06, 2022 at 11:30 AM

Isn't the "synchronize VE.bus SOC with battery" supposed to synchronize both?

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klim8skeptic ♦ aphexer commented · Oct 06, 2022 at 01:47 PM

"synchronize VE.bus SOC with battery"

Once you add in the solar mppt chargers DC currents, the simple voltage based soc figures of the inverter charger, go out of whack.

The inverter charger knows how much current it is feeding into a battery. But the inverter charger has to rely on calculations from the GX device to aggregate additional battery charging currents from the mppts.

The smartshunt actually measures current going into / out of the battery.

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