[Peter Cittern]

So after all the shenanigans with my 12v/water in doors issue, which I hope is now sorted, I’ve been looking at the Battery saver (BS) logic. I've had my new BM2 up and working for over a week now, and I'm trying to work out exactly what triggers the BS to kick in. Somewhere, I saw some info that it comes on every 72 hours unless you've been on a >30 min trip in the meantime. So that is one thing I’ve been keeping track of, plus obviously voltage trends.

My thoughts so far:-

• The car is mostly in the garage so I wouldn’t generally see a dash/blue light indication from the car that the BS is working, it likely does work but but I haven’t proved to myself yet that that it does. Also I have never seen a message popping up on the dash display telling me it has worked even when I could plainly see from the BM2 data that it had.
• So far the BS has kicked in as much as nearly every day, but there doesn't seem to be any exact time pattern in terms of exact hours since last time/ignoring >30 min drives.
• Over ~24 hours when the car is unused, the voltage drops ~0.1v every 12 hours.
• When it kicks in, the BS lifts the voltage from ~12.6 to ~12.9 over about 20 mins.
• The BS seems to kick in when the voltage gets to or has been at ~12.6v for a few hours. Bearing in mind that the voltage the BM2 is reading out could/probably is subtly different from that which the car reads and is using.

 

[Peter Cittern]

deleted

 

[Peter Cittern]

Having got over 2 weeks more data, I was wrong on some of my earlier post, mainly that there is most definitely a strong time element. So if for instance the car is just parked up and not driven, then the BS will kick in exactly 24 hours after the end of the last BS cycle to the minute. Typically on mine the voltage will be lifted from 12.5 or 12.6 to 12.9 over 20 minutes. If the car has been unlocked and locked a few times whilst parked and the battery depleted slightly then the BS may come on for longer (I saw 60 minutes once). If the car has been driven, typically I would say for less than 30 or even 40 minutes this wouldn’t be quite enough to return the 12v battery to the pre-drive voltage and also won’t affect that 24 hour BS cycle.
I would say a journey of more than 40 mins is required to maintain the pre drive voltage so lots of short trips will slowly deplete the 12v battery, similar to an ICE, however the BS should mitigate this in theory. I haven't yet been brave enough to deliberately deplete the 12v battery significantly so to as to see if the 24 hr BS cycle is ever shortened.

 

[Peter Cittern]

Further update.

The first 2 graphs show that the BS kicks in at exactly 24 hrs after the end of the previous BS event. It also shows that simply opening the doors once at C causes a significant drop in voltage, although in terms of the overall voltage profile, one such event isn’t particularly significant. Several such openings and closings would be interesting to investigate as this could lead to failure if the BS is too time oriented and not voltage triggered.

However, the event at E is also interesting, as it shows that 2 x 50 min drives with a 2 hour stop in between led to an overall drop in voltage. Contrast that with the 2 x 10 minute drives at point F after which the voltage had increased. So I am guessing that this was triggered due to the lower starting voltage of 12.5 prior to F vs 12.6/7 prior to E. Or is some kind of glitch!

Quite tricky to sort out the exact logic?

Finally the BS stopped working at point H, I thought oh no here we go again, my previous BS failed never to come back to life, however this one did revive after being disconnected/reconnected.