Charging Algorithm for 12V Battery?

[STS134]

Has anyone figured out what the charging algorithm is for the 12V auxiliary battery? What I've been able to figure out so far:

- When connected to EVSE, voltage starts at 14.40V, then drops to 14.30V. Not sure if it drops farther or will eventually float at 13.8V, or if the charger is simply disabled when the main drive battery reaches full capacity (didn't keep my vehicle connected that long)

- When put into READY mode, the 12V auxiliary battery is charged using the main drive battery. Voltage starts off at 14.70V, and later drops to 14.40V and then 14.30V. The length of time before the voltage drops from 14.70V to 14.40V seems to depend on the SoC (likely the current taken) by the auxiliary battery, since I've seen it drop to 14.40V as little as 4 minutes and as many as 10 minutes after putting the vehicle into READY mode.

- There does not appear to be a threshold at which the system will charge the 12V auxiliary battery from the main drive battery (at least if you don't use the WiFi) or if there is, I have never let the vehicle sit long enough to reach it.

 

[Katmandu]

I can't answer your question but I can ask another.
Why given the size of the dc battery and that it is never allowed to discharge much below 30% is the auxilary battery ever allowed to go flat? Surely there is some form of converter/inverter/transformer that could keep it charged.

 

[greendwarf]

I can't answer your question but I can ask another.
Why given the size of the dc battery and that it is never allowed to discharge much below 30% is the auxilary battery ever allowed to go flat? Surely there is some form of converter/inverter/transformer that could keep it charged.

There is - in normal use when driving and when parked up but only if you have wifi. However, this is insufficient if you switch on but don't go to "ready". Users have found things like radio & lights etc. which work in "Aux." mode will rapidly drain the 12v to below the level it can then "boot up" the car's systems. :shock:

 

[Katmandu]

What do you mean "only have wifi" why should that make a difference?

 

[STS134]

What do you mean "only have wifi" why should that make a difference?

If the WiFi is enabled, the car apparently charges the 12V battery daily (from the main drive battery) even if it's just parked and unplugged, but if WiFi is disabled, it won't ever charge the 12V battery unless you connect it to a EVSE or put it in READY mode.

BUT, without WiFi, it only loses about 15% SoC per week. So whatever amount of power the WiFi consumes compared to the rest of the vehicle must be significant. It's likely not just the WiFi but an entire computer that's kept running 24/7 when the vehicle is switched off.

 

[Katmandu]

What a great idea, thanks Mitsubishi TIC.

 

[STS134]

Well I just found out that the 12V battery charges during CHAdeMO charging. This was very interesting because I didn't expect the vehicle to be running the onboard charging equipment since CHAdeMO bypasses the OBC. But the vehicle was applying 14.10V to the 12V battery during CHAdeMO charging! Maybe it's because the vehicle is sort of in a special type of READY mode to run the cooling system during CHAdeMO. I suspect that the actual voltage put in depends on the SoC of the 12V battery, just as it does when you're driving.

 

[Craigy]

Well I just found out that the 12V battery charges during CHAdeMO charging. This was very interesting because I didn't expect the vehicle to be running the onboard charging equipment since CHAdeMO bypasses the OBC. But the vehicle was applying 14.10V to the 12V battery during CHAdeMO charging! Maybe it's because the vehicle is sort of in a special type of READY mode to run the cooling system during CHAdeMO. I suspect that the actual voltage put in depends on the SoC of the 12V battery, just as it does when you're driving.

When a car is charging using a DC rapid the Car is certainly not off and the on board charger is in control of the rapid charger. It’s how it works, so it wouldn’t be great if the 12V battery ran out while charging......

 

[STS134]

When a car is charging using a DC rapid the Car is certainly not off and the on board charger is in control of the rapid charger. It’s how it works, so it wouldn’t be great if the 12V battery ran out while charging......

OBC should not be used during rapid charging. OBC is what converts AC to DC when doing Level 2 or Level 1 charging. I suspect that the system is simply powered ON and is using the main drive battery to run, and since it's powered ON, the 12V battery also charges.