Hello MIA-explorers,
Recently i have serviced with a little luck successfully 2 MIA’s with a BMS shut down. The thought is that BMS will shut down the traction battery after noticing 10 times an excessive low voltage state of the 12V 18 Ah service battery.
How can the 12V 18Ah service battery become too low?
When the car is switched off EGV checks the 12V voltage every hour. Driving is not necessary at all. MIA charges automatically the 12V service battery as long as the traction battery contains 20% or more energy AND ALL THE THREE DOOR ARE CLOSED in the eyes of the BVS.
I imagine the last condition is neglected in most of the cases by the owners and the severe consequences initially by the software engineers from the different companies The new E4V 6 kWH battery’s are after all free from such a BMS counter.
Because there was a BMS shut down I checked this automatic charging cycle and I like to share some results.
When the MIA is in rest the 12V 18 Ah service battery is discharged by 0.085A. So in 24 hours it will drain (24 x 0,085=) 2 Ah. Theoretically after (18 Ah/ 2Ah =) 9 days the battery will be completely dead if it is not charged by the system.
A datalogger was connected on the CAN bus connector by fig.1 and collected data is shown in fig.2
To speed up the discharge cycle a little the ceiling light was switched on. At minute 518 EGV wakes up and sense the service battery voltage is below threshold and EGV activates the DC mode. RP076 is switched on. Two DC/DC converters are therefore connected with the traction battery and a strong 13,7V/100A power supply is available to charge the 12V service battery for the next 55 minutes. At minute 700 the ceiling light is switched off and the discharge rate is slowed down. Conclusion: EGV seems to take care of the 12V service battery well.
Greetings,
Miactief