Blog - Battery Monitoring

The CellLog8s has a bug in the firmware.  I’ve contacted the OEM via a radio-controlled model forum and he provided me with an updated firmware (v2.08).  The problem with the original firmware was that the alarm output from the cell / pack alarms did not trigger reliably when beyond the set points.

The CellLog8s also has a hardware bug in it that causes a cell load imbalance when used with more than 6 cells.  As delivered from the factory, it draws power from only cells 1-6 for the CPU and display.  So cells 7 and 8 would gradually go out of balance with cells 1-6.  The makers posted a picture of a hardware modification (adding a wire jumper) that cures this so that all 8 cells are drained equally. Unfortunately, it then does not work with 2 cells only after the mod (but I’m always going to be monitoring 8 cells so that’s ok).  They also posted an optional modification to replace one SMD resistor to reduce power consumption when using more than 6 cells. I’ve made both of these modifications.

http://www.rcgroups.com/forums/showpost.php?p=13452879&postcount=143

I’m using the CellLog8s alarm output with some external relay logic to provide an ENABLE/DISABLE input to the AC inverter load.  All AC inverters are designed for lead acid batteries and their Low Voltage Disconnect (LVD) settings are too low for lithium batteries (21V on a 24V battery inverter). So I use the CellLog8s to send a DISABLE signal to the inverter when the pack Voltage reaches either 24.0V or any one cell in the pack reaches 3.00V. That guarantees that the battery isn’t discharged by more than 90% in normal use.  The system then has to be manually reset by pressing a button on the relay logic controller, which provides an ENABLE signal to the inverter. This allows the normal remote control for the inverter to send a START command. The reset button cannot work until the CellLog8s alarm condition is cleared (by recharging the battery) so even if you try to force the load to restart, it cannot until the battery has been recharged enough.