Smart Car of America Forum banner

41 - 42 of 42 Posts

·
Registered
Joined
·
170 Posts
The SOC gauge is just a voltmeter. Where is this watt-hours counting coming from?

My disconnecting the 12v battery is the whole point. The "working hypothesis" hereabouts makes no sense to me, although the fear of a self-destructive hv battery is very real. Best to find out by doing experiments but not with the 12v battery; this will always be disconnected and kept on a float charger when I'm away on a trip.

My concern with the Smart HV battery is that the BMS has direct access to the module voltage at all times and through mis-design or component failure the BMS might somehow deplete the high voltage.
--
 

·
Registered
Joined
·
1,193 Posts
Discussion Starter #42
The SOC gauge is just a voltmeter. Where is this watt-hours counting coming from?

My disconnecting the 12v battery is the whole point. The "working hypothesis" hereabouts makes no sense to me, although the fear of a self-destructive hv battery is very real. Best to find out by doing experiments but not with the 12v battery; this will always be disconnected and kept on a float charger when I'm away on a trip.

My concern with the Smart HV battery is that the BMS has direct access to the module voltage at all times and through mis-design or component failure the BMS might somehow deplete the high voltage.
--
No, resting voltage in lithium cells is only a rough SOC indication - and when under a discharge load like driving, and under varying ambient temperature, the voltage is a useless indication of SOC. SOC meters are Coulomb counters - measuring watt hours in and out of the battery pack and comparing it to the total allowable capacity of the battery pack. There are also probably "calibration points" to keep the gauge accurate - for example, resetting to 100 percent when the battery pack reached a complete full condition when charging.

The hypothesis comes from at least one case here where hte 12v battery was removed from the car for the winter, and the HV pack was foiund to be totally dischargs in the spring. But yes, a malfunction of the BMS might have been the cause and the 12V battery removal had nothing to do with it. If I leave my smart in storage, I'll keep the 12V battery connected, but I will put a maintenance charger on it.
 
41 - 42 of 42 Posts
Top