Re: Switch to LiFePO4

Brent Cameron

I asked that exact question of the BB guys and they assured us that the second battery would refuse any charge as a result of being wired in series (I gather because the first one is taken completely out of the circuit by its internal BMS). That said, it’s relying on an internal solid state relay to switch off 100A so I personally am still not totally convinced it’s totally kosher but I guess if they stand behind that architecture with a 10 year warranty you aren't out much (except the inconvenience somewhere in the South Pacific). I think it is one more reason to go for the 50A 24VDC batteries instead of wiring two 100A 12VDC batteries in series. 


On Aug 15, 2020, 4:59 PM -0400, Scott SV Tengah <Scott.nguyen@...>, wrote:
One last thought:

If BB batteries have internal BMS that can disconnect charging and load on a battery level, some questions come up.  For example, if battery 1, consisting of 4 cells, has a high voltage condition, the BMS in that battery stops charging in Battery1 only. 

At first glance, that seems ideal. You may not need an external charge or load disconnect circuit because the battery experiencing a fault just stops accepting charge or stops driving load if there's a high cell voltage or low cell voltage condition, respectively.

My question is what happens then? I only ask this because I don't know but it could cause problems. Say you have 12 batteries = 6 pairs of 12v batteries. Each 12v battery pair is in serial to create 24v and each pair of batteries connected in parallel to the other 5 pairs to create your AH total. Say Battery1 has a high cell voltage condition and the internal BMS cuts off charging to this battery, but still allows load. That means that Battery 1 is still connected to its Battery2 serial pair and hence connected to the entire bank. The charger is still outputting 26+ volts. But for this battery1-battery2 pair, only one of them is accepting charge. Is that ok?

2007 A54 #69
SV Tengah

Brent Cameron

Future Amel Owner & Amel Owner Registry Moderator

Oro-Medonte, Ontario, Canada

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