Michael,
It may indeed be possible to build such a BMS but that is not the way most of them work. The device generally referred to as a BMS for Lithium batteries monitors the cell voltage on each cell in the serial string, either using analog or digital electronics looking for an overvoltage or undervoltage condition. An output of the BMS can be connected to the charger itself, a relay on the AC side of the charger, and/or to an alarm. If any of the cells exceeds a predetermined voltage the BMS shuts down the charger and/or rings an alarm. It can also balance the pack by shunting some of the current around the higher voltage cells. While the pack is under load, the BMS monitors each cell for an undervoltage condition and can shut the system down, reduce the throttle, and/or sound an alarm.
Available BMS systems for lithium batteries can be more or less sophisticated, from a mini-bms which performs the above functions for a few hundred dollars to very complex systems with computer outputs, CAN bus, etc.
I have a mini-bms on my 16 cell 160 Ah traction battery and an Elcon charger. I have tested it extensively and use it on my boat. It is very satisfactory.
Best wishes,
Ned
On Apr 15, 2012, at 4:38 PM, Michael Mccomb wrote:
Hello all,
A new question. I am interested in a 48v 200ah LiFePO4 battery (bank) and BMS but I am very fuzzy on exactly how the BMS functions. I know that there is both a maximum charge rate and a maximum discharge rate that should not be exceeded with the battery pack. I assume that the BMS regulates and prevents such problematic usage of the battery pack.
Can someone tell me if there is a required min or max to the voltage and amperage fed to a BMS for charging purposes. I assume that the BMS can regulate discharge and charge at the same time and that in effect it is only the net difference between the two functions that can adversely impact the battery.
I'd love to be able to feed the BMS 48v (or 52v or whatever) and 50amps and then have the BMS completely manage the pack. Does anyone think this completely feasible?
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