2017 M3 left for 2 years! what steps should I Take?

[Cosmacelf]

Side note:
I had to help my parents with a dead Automower (robot lawn mower) today.
Could not be started, did not take charge.

Most probably they forgot to shut it down and maybe even to get it fully charged before the winter. (Stowed away ~ 9 months ago). Battery did look “dead”.

Opened the robot, took out the battery (5 18650 in series). Each cell was 0.9-1.1V which is waaay below the 2.5V end of discharge for these cells.

I charged with one of my many hobby lithium chargers. Circumnavigated the BMS and charged right on the end if the cells. After filling up ~50% of the charge I put the robot together and started it, and charged in the charging station.
All good, filled up to 100% as as far as it looks it has not lost any capacity from last year.

Charging at a safe place, just in case it was anything wrong causing a fire.
View attachment 1052952

It’ll be interesting to see if the batteries last. I suspect they are damaged.

 

[AAKEE]

It’ll be interesting to see if the batteries last. I suspect they are damaged.

I have had quite a few similar things happening on the ~ 17-18 years I used lithium ion and lithium polymer batteries.
From my point pf view, the myths about the li ions are not correct at all.

I can not say for sure, but I suspect this battery is very fine.

It took charge without any problem.
Charging back 1100 mAmphs (out of 2000) did set the cell voltage on each cell to just what we would expect. All cells then was in good balance despite slight imbalance (200mV) when ”dead”.
I did put a little load on the battery (discharge with the charger) and the Voltage droop was not much, and consistent between the five cells.
(I have no data from 50-100% as I put the pack back and let the built in charging/balancer/BMS do the rest, but from charging time it looked correct)

I would say 90% that the pack is fines as new. I will get back if I see anything else.
I told my parents to time the running time on one charge, that will be a good indication of the capacity.

 

[Max Spaghetti]

For these and most other lithium batteries (not LFP) it is 4.200v/ cell.

Interestingly for LFP, it charges at a constant voltage of 3.426V (max cell) until the calibration phase at 99%. It then slowly ramps up the voltage (presumably while balancing) until the max cell voltage reaches 3.800V. It then keeps charging very slowly at this voltage (still balancing) for a few more minutes until declaring 100%.

It's not normal to charge LFP at 3.800V (most chargers won't go over 3.650V), but Tesla only does it for a few minutes.

 

[Zuikkis]

Naah, it doesnt.

There has been rumors about changed logarithms, but for my 23 Plaid I se around 10mV at 50-55% all the time. Charging higher reduces the imbalance, as it is balanced higher up in SOC. Also leaving the car for a while at higher SOC reduces the imbalance = balancing happening.

Its very possible that the BMS can balance at lower SOC when needed, but I see nothing of it.

No, you misunderstood me. Like you said, Tesla balances so that top voltage (4.2V) is equal on all cells. Balancing based on voltage would be pointless on lower SOC because it would ruin the top end.

But, after multiple charging cycles, it is possible to know that at 50% SOC a correctly balanced pack has 3.505V at one cell and 3.479V at some other cell (just examples). Now if cell #2 would have 3.500V it means it's "overcharged" and would reach 4.2V too soon if charging to 100%. I don't mean "overcharged" literally, just that cell has too much juice for that SOC.

This is why Tesla calculates the Ah values (CAC) for each cell.. if CAC differences are big, it means lower CAC cells voltage sinks faster when discharging. But still it's possible to know what is cell's "normal" voltage level for a given SOC and CAC.

So, cell voltages are not compared against each other, they are compared against same cell historical data!

Balancing probably only happens when charging, there's little sense in burning electricity on the bleed resistors if no external power is present.

So in conclusion; it is only top voltage (4.2V) that matters, but balancing starts at much lower voltages so cells would reach 4.2V at the same time.

 

[Ray Brown]

Good morning
30 minutes left to charge

 

[Ray Brown]

Good morning
30 minutes left to charge

292

 

[Ray Brown]

next project is the 2010 roadster

 

[Bouba]

Do

292

when it gets to 100% leave it a while still plugged in…the last time I did that I got an extra 3 miles

 

[tga]

Do

when it gets to 100% leave it a while still plugged in…the last time I did that I got an extra 3 miles

But then drive it down to <80% - don't store it at 100%

 

[brkaus]

And if you get the roadsters going, the best advice is to charge to 100%, then drive down to 20%. Then charge to 80% and drive down to 20%. Repeat 100 times.

Just kidding.

 

[brkaus]

You might want to post in the roadster section on those before you do anything. I don’t know what kind of low voltage protection they have.