Lithium Battery Monitor 48 cell
Posted: Thu Jun 07, 2012 7:31 pm
I have been thinking a lot about the pros and cons of cell balancing. I have also been pondering the ramifications of a BMS fault scenario (fire?).
There has also been mention on the web of the BMS current draw contributing to imbalancing of the cells.
I will be buying a lithium pack soon and here is the monitoring approach I propose to take.
I will charge each cell individually to 3.9v for the first time using a lab power supply. Thereafter I propose to balance manually at two month intervals and see
how far the cells drift over that period.
For charging and discharging I propose to use a cell monitoring (not balancing) solution whereby the charger cuts off when the first cell reaches 3.7v and when discharging set an alarm when the lowest cell hits 2.9v. I plan to use the Maxim part MAX11080 which is a 12 channel battery pack fault monitor. The datasheet for this part looks good and the part is about £2.30. I think this will be a robust and EMI tolerant system and as it is daisy chainable I should be able to make a 48 way board. Power consumption is neglegible compared to a picaxe and the system only needs two isolated ports for communication with a simple picaxe based master. For the isolator I propose to use the Analog Devices ADuM1201 for its miniscule power consumption and ability to shift logic levels. The parts will be surface mount and the project another leap into the unknown
Derek
There has also been mention on the web of the BMS current draw contributing to imbalancing of the cells.
I will be buying a lithium pack soon and here is the monitoring approach I propose to take.
I will charge each cell individually to 3.9v for the first time using a lab power supply. Thereafter I propose to balance manually at two month intervals and see
how far the cells drift over that period.
For charging and discharging I propose to use a cell monitoring (not balancing) solution whereby the charger cuts off when the first cell reaches 3.7v and when discharging set an alarm when the lowest cell hits 2.9v. I plan to use the Maxim part MAX11080 which is a 12 channel battery pack fault monitor. The datasheet for this part looks good and the part is about £2.30. I think this will be a robust and EMI tolerant system and as it is daisy chainable I should be able to make a 48 way board. Power consumption is neglegible compared to a picaxe and the system only needs two isolated ports for communication with a simple picaxe based master. For the isolator I propose to use the Analog Devices ADuM1201 for its miniscule power consumption and ability to shift logic levels. The parts will be surface mount and the project another leap into the unknown
Derek