Auxiliary Battery Charging - an Observation

[KiwiME]

That's clearly gone through a significant re-design for cost reduction with the 14-year old Texas Instruments microcontroller replaced with a RISC-V Chinese equivalent. I'd imagine the manufacturer of the BM2 couldn't believe their good fortune when EVs came along.

It's entirely possible that an accurate calibration has fallen by the wayside or there's a laser-trimmed resistor in place. I'd be surprised if that's done using the JTAG pins at the top of the PCB but that's also possible.

 

[Tim94549]

Update on my observations -- (I just replaced my 12V battery over the weekend. Took 5 mins. Purchased the INTERSTATE, higher cranking one)

- When SOC is over 40%, my BLUELINK "wakes up" and reports "DOORS UNLOCKED" on a fairly regular basis -- about every 4 hours when I'm Parked in our garage. My BM2 reports these as the times the 12V battery is getting charged/topped. And again after driving & turning off the vehicle.

- When SOC is under 40%, I receive that BLUELINK msg 1 time per day. So it appears the 12V is getting charged once per day at that SOC. This was apparently insufficient for my old battery. It was draining fast, even after driving. Presumably because I allowed SOC to get to 20% or so on a regular basis since purchasing the car. (I only drive it 2-3 times per week, and usually short trips.

- When Driving, my BM2 is showing that the 12V is "CHARGING". So my assumption is that is another point when the 12V is actually getting topped off.

So I guess my lesson learned after having this for 5 years (18,500 miles) is that I never want the SOC to get below 40% if I expect the 12V to be maintained/topped. This flies in the face of what I've read/heard before about maintaining a 20%-80% SOC so the traction battery isn't degraded.

Shoutout to everyone (esp. KiwiME) who has been involved in this thread. I've learned a lot.

 

[KiwiME]

As a note the 20-80% doesn't mean you need to drop as far as 20. More so it suggests to avoid being outside that range if practical. The time-based component of battery degradation is lowest the closer you are to around 40-50%. But there's no need to obsess over it, just stating the facts.

As I've probably mentioned I have to stay over 50% for my Kona to apply a 4-hourly schedule, a change that I think was in the Oct 2023 BMS update that was intended to address DC charging issues. I don't know if that update applied to J1772 markets.

But I don't see any problem with the once-a-day charge, noting that I don't have Blue Link overheads. I was experimenting to see if the daily-charge schedule ever returned to the 4-hour on its own, but it seems not. 12.7 V as a settled voltage is a fully charged battery.

The "door" problem you have is not easy to diagnose. Myself, I would first check to see if the hood switch can trigger this first because I've heard one report of it being less than reliable. The easy way to test that is to unplug the connector located at the your passenger side of the car. When unplugged it indicates 'hood closed' to the car.

If that doesn't help perhaps try to trigger the fault by pushing on each door in turn in case one of the switches is flakey.