Hopefully this is an easy design question to answer. I'll start with some background information.
The case is with lithium iron phosphate or LFP batteries that are "48 volts" used for household photovoltaic battery backup.
There are many brands and there are different lithium chemistries, but we will be talking about the 16 S configuration using the 3.2 volt (nominal) LFP batteries. This creates a battery pack that is 51.2 volts nominal. (LFP 51.2V systems have a maximum operating range of 40V to 60V with 43.2V and 58.4 more typical for longevity.)
These battery systems typically use a balancing BMS to provide safety to the cells. However most of these BMS systems cannot be connected in parallel if you want to add battery storage. Additionally, the ones that can be connected in parallel must be connected to the same brand of BMS. The main reason for this is that if one battery pack has a higher state of charge than another battery pack, then when they are connected in parallel they will produce very high amounts of current causing the BMS units to disconnect then reconnect over and over rapidly which damages the BMS (in cheaper commodity type BMS, not Mil-spec).
Now the challenge. How would you design a bi-directional current limiter that could be placed on the common port terminals of the BMS output allowing no more than 50A, 100A, 150A, or 200A to be continuously delivered to/from the battery pack without the BMS shutting down? This added device would enable any brand battery to be placed in parallel with another without harming the cells or the BMS (given the same chemistry and voltage).
The system example is simply adding a second 10kWh battery pack capable of 100A to an existing one of the same specification, but 5 years older, and a different BMS. These will be connected to the same solar inverter with built-in MPPT charger.
The case is with lithium iron phosphate or LFP batteries that are "48 volts" used for household photovoltaic battery backup.
There are many brands and there are different lithium chemistries, but we will be talking about the 16 S configuration using the 3.2 volt (nominal) LFP batteries. This creates a battery pack that is 51.2 volts nominal. (LFP 51.2V systems have a maximum operating range of 40V to 60V with 43.2V and 58.4 more typical for longevity.)
These battery systems typically use a balancing BMS to provide safety to the cells. However most of these BMS systems cannot be connected in parallel if you want to add battery storage. Additionally, the ones that can be connected in parallel must be connected to the same brand of BMS. The main reason for this is that if one battery pack has a higher state of charge than another battery pack, then when they are connected in parallel they will produce very high amounts of current causing the BMS units to disconnect then reconnect over and over rapidly which damages the BMS (in cheaper commodity type BMS, not Mil-spec).
Now the challenge. How would you design a bi-directional current limiter that could be placed on the common port terminals of the BMS output allowing no more than 50A, 100A, 150A, or 200A to be continuously delivered to/from the battery pack without the BMS shutting down? This added device would enable any brand battery to be placed in parallel with another without harming the cells or the BMS (given the same chemistry and voltage).
The system example is simply adding a second 10kWh battery pack capable of 100A to an existing one of the same specification, but 5 years older, and a different BMS. These will be connected to the same solar inverter with built-in MPPT charger.