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Josep morancho avatar image
Josep morancho asked

Charge/discharge current limit in pylontech

Hi, i am planning to install an off-grid installation with 4 strings of 1000w each, multiplus II 5KVA, smartsolar 250/85, cergo gx and 4 x us3000c pylontech batteries.

I see that pylontech batteries have a charge/discharge current of 37A and a peak current limit of 74A being the inverter cable of 120A. On the other hand, the multiplus II 5KVA has a power peak of 9000w that represents a current pesk of almost 200A.

who/how limit the discharge current peak to avoid damage in the batteries?

If pylontech allows up to 16 units of the batteries in parallel that represents more than 48kw, bigger inverters will request currents higher than the nominal current and cable sizes. For instance, a Quattro 15kVA inverter will have a nominal current much higher than max current of batteries and inverter cable.

Thanks


MultiPlus Quattro Inverter Charger
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2 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

If your inverter has a peak current demand of 120A, then you need a minimum of 2 battery strings in parallel to avoid battery over-current. The current sharing between the batteries is managed by equal lengths of correctly sized cable. Both strings must have equal lengths. If you can connect the data from the BMS to the inverter through a Venus OS device with dynamic voltage & current control (DVCC) enabled, then this will be used to control the inverter current.

Larger inverters will, as you point out, require more battery strings in parallel to service the peak current.

Alternative is to use a different make of battery that can supply 2 or 3 times the Ah rated current. (i.e. 2C or 3C).

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Matthias Fuchs avatar image
Matthias Fuchs answered ·

Ok I finally tried to set the VEConfig setting for the battery to 35A. I initially used 25A because I only had one battery.

It seems this overrides the DVCC and CCL settings from the BMS. It doesn't matter how much batteries you have, it seems to be a fixed value.

The only problem I see here is that it might override the BMS settings as well, when only connected to one battery and therefore might damage it.


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