athlonfx avatar image
athlonfx asked

Multiplus-II GX not obeying Discharge Current Limit

Hello everybody,

my Multiplus-II GX, combined with 2 Pylontech US2000 (new) and an EM24 is configured as a grid tied ESS system (AC IN connected only). There's also a grid tied PV micro inverter (Hoymiles). The Multiplus II GX detected the batteries correctly. The Discharge Current Limit (Pylontech battery -> Parameters) is 50.0A.

The batteries are connected to the Multiplus-II GX via the supplied wires, there's a DC circuit breaker (80V 63A, CBI Electric QYD18U263B0) in the positive connection.

Today there was a higher load (baking oven), the Multiplus-II GX supplied power. The circuit breaker tripped, what surprised me. The Multiplus-II GX does not seem to obey the Discharge Current Limit. Is that the normal behavior?

If that's the case, why is there no Limit discharge current setting?

What's the maximum power the Multiplus-II GX will deliver (if there's demand) in a grid tied ESS configuration (AC IN connected only)? The peak power of 5500W?

So the workaround seems to be activate Limit inverter power and set the Maximum inverter power to 2000W?

(expected dissipation of about 200-250W and a safety margin;

I read that Victron recommends a 125A circuit breaker, but I want the Multiplus-II GX not to exceed the Discharge Current Limit of 50A (recommended by Pylontech).

Thanks in advance for your answers.

Multiplus-IIPylontechcurrent limit
2 |3000

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Do you have any Dc coupled solar?
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No, there's no DC coupled pv, only AC coupled pv.
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2 Answers
raymiller avatar image
raymiller answered ·

The point of any protection device i.e. fuses and circuit breakers are to protect the cable from overheating causing fires etc. The Pylontech batteries have inbuilt overload protection from overload (as well as other conditions) which uses inbuilt Mosfet switches controlled by the BMS.

The recommended cable protection device ratings should always be used.

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I understand what you say and I had known the purpose of fuses/circuit breakers before I posted my question.

I thought that the Limit discharge current setting is obeyed by the Multiplus-II GX, so that the circuit breaker only trips when ether the Multiplus-II GX or one of the Pylontech US2000 malfunctions.

I read that those mosfet switches can get damaged if the current is way to high, that's something I really want to prevent.

I still hope someone can answer my questions.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Give us some more information about your system.

Components? Settings?

Make another test, turn on the oven and look into the remote console of the GX device to see how much current the MultiPlus is taking from the battery.

Maybe the breaker you are using is just bad and trips to early. I recommend to use a fuse instead.

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What kind of information regarding the components are missing?

I installed the ESS assistant and set the settings mentioned in the official documentation regarding the Pylontech batteries.

The current logged in the VRM portal before the circuit breaker tripped was 44.7A at 49.0V, but I doubt that this was the max value, it was just a spike.

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