question

chris2 avatar image

Multiplus II discharging battery under min. SOC

Hi !

My Multiplus II sometimes discharges the battery with 4W or 9W when min. SOC has been reached. It switches between 0W, 4W and 9W in undefinable minutes, or even hours. I´ve set the min. SOC to 15 % .

As I looked into the system after about 12 hours later, the battery has been discharged to 11 %.
I don´t know if it would go under 10 %, because system started to charge at 11% at morning.

I´ve installed the system just a few days ago, so I don´t have much experience with it so far.

Does anyone face the same issue ? Did I set somehing wrong in the setup ?

System is running in ESS optimized mode without battery life, no scheduled charging.

1xMultiplus-II 3000
Venus GX
2x Pylontech US2000 4,8kWh
AC coupled PV-Inverter Fronius IGTL 4.0 connected to AC-in



Thanks in advance for your help !

Regards,

Chris

Multiplus-II
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3 Answers
DeVo Tyler avatar image
DeVo Tyler answered ·

Youre devices are always drawing energy day and night to stay powered on. draw less energy from the battery of get a bigger battery bank to compensate.

hopefully I understood you're question.

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jdoern avatar image
jdoern answered ·

We have exactly the same problem right now!

Is there a solution?

3 comments
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jdoern avatar image jdoern Daniël Boekel (Victron Energy Staff) ♦♦ ·

yes but can you explain me in detail why this is the normal behavior?

All DC powered devices (inverter, GX device, etc.) you have are discharging the battery. If you have a BMS, that also draws some energy from the battery. Over time, it all adds up.

Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @chris2

When the SOC reaches 5% below the set minimum SOC, it will recharge the battery back to the set SOC.

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yes but why is the system going under the minumum soc limit?

we do not want the system to recharge the battery at night!

Pylontech 2000 batteries can go as low as 10 percent this is in the pylontech manual so i assume the pylontech bms is controling this

"yes but why is the system going under the minumum soc limit?"


The inverter will no longer supply energy to AC loads when the battery reaches minimum SOC you set, but it (and devices like Venus GX, Cerbo GX, SmartShunt, BMV, MPPTs - powered from the DC bus, so only from the battery at night) still draw some energy from the batteries.

Is your GX-device powered by the DC-bus directly? In that case min 0,3kWh per day might be absorbed by GX directly, right? If you have no PV-supported charging during the day, the battery level gets reduced continously.