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Hi! Here's my doubt about the BYD BMU...
I'd like to use 1 or 2 B-Plus modules of my BYD B-Box Pro 7.5 system in another application, but I only have 1 BMU (the one that comes with the case). Is the use of a BMU mandatory, even if only 1 B-Pus module is used?
Can it be replaced by a shunt (ex. BMV 700 + shunt) or another BMS technology, like the VE.Bus BMS?
Thanks in advance!
The BMU is mandatory. It is how the battery communicates charge and discharge current limits with the rest of the power system.
@BYD_service may comment further, but I believe operating the BYD battery without the BMU will void the battery warranty.
It is possible to buy the BMU seperately.
Hi,
Sorry for digging out that very old post, but just to confirm ... That mandatory BMU is no more than a RS485 to CAN converter allowing communication with the 3 brands of inverters supported.
I do own a B-Box pro 10 IP55. 1st generation of BYD batteries, 4 x 50ah. BMU is out of service. I am living in Indonesia where BYD is not present, those batteries have been imported from Australia. I have been in contact with the Australian distributor (ALPS) where those batteries have been bought from but they would not deal with end user ... When the installer I bought the product from is now out of business. Ahah those pretended 10 years warranty ...
Anyway, to keep using the batteries I disconnected the BMU but wanted to be sure it would be safe. The BYD software (BYD BMS available from ALPS) clearly shows that each rack is equiped with its own BMS that limits all charge / discharge parameters as all BMS do. The only thing the BMU does is converting the RS485 signal of each BMS into CAN signal for communication between batteries & the inverters supported. Nothing more. It does not manage anything, BMS does ...
Hi @Zivva,
The BMU translates the battery information from the battery modules into the rest of the system.
The module level BMS can not limit the charge / discharge of the system, there is no method for it to do so without the BMU. It becomes a binary ON / OFF(Fault)
Limiting requires the BMU to communicate those battery parameters to the rest of the system (via the GX device) for them to be respected by the chargers and inverter.
I would not consider it safe to run a managed lithium battery without the management communications connected.
There is a lower level safety system where the individual modules can use a FET bridge to disconnect themselves, but unless the system receives the message that there is an error it may continue to try and charge. Also it may not be clear then an issue has occurred. Also there may be out of specification damage done that doesn't rise to the level of the FET disconnection, which I think might only be limited low cell voltage, high cell voltage and temperature, not current limits.
I can understand wanting to run the system in the mean time, but I would strongly recommend that you continue trying to source a replacement BMU.
Here you have the BMS parameters for each packs : BMS indeed controls individual cells & pack voltages, balancing start & stop, charge & discharge current limits and temperatures.
I am not sure to understand what additional protection offers the BMU ?
In both case and as for all BMS, protection is limited to OFF when 1 parameter gets off limit until that parameter gets back to recovery value.
Without the BMU there is no way for the charge & discharge current limits to be communicated from the battery modules to the GX device, so the charge and discharge sources (MPPT and inverter) will not be able to obey them.
The BYD system is not designed to use the FET bridge regularly as the primary control method, it is a last resort protection. The primary control method should be the pre-shutdown protection soft limits obeyed by the system.
There are electrical side effects of disconnecting a FET bridge under full load (e.g Voltage Transients, Overcurrent spikes)
Aside from system reliability (staying online) I am not sure what the consequences are for relying on the FET bridge to more regularly protect the battery, but it's not what BYD wants so I would expect there are some longer term issues with it that may be more difficult to resolve than using the battery as its designed with the BMU.
