BMU Cell voltage smoothing

[TimPhev]

BMU Cell voltage smoothing

PROCEDURES FOR SMOOTHING CELL VOLTAGE
1.After the electric motor switch is "LOCK" (OFF) position, connect the M.U.T.-III to the diagnosis connector.
2.Turn the electric motor switch to the READY position.
3.Select "BMU" (№22) from System Select Screen of the M.U.T.-III.
4.Select "Special Function" from BMU Screen.
5.Select " Cell voltage smoothing" from Special Function Screen.
6.Press the OK button to smooth the cell voltage.
7.Check the "Execution status" displayed on the M.U.T.-III and check that the "Active" changes to the "Not Active".

Note: It may take a maximum of 2 hours until smoothing the battery cell voltage is completed.

A prerequisite! The laptop should not go into sleep mode!
It is best to connect it to the mains.
If go into sleep mode or save screen, will update error.

After the operation, while not shown, the temperature of the air after a while everything is restored.

 

[GreyBigFoot]

Now that's interesting.

Is this the cells balancing procedure done at the dealer that could increase a bit the total battery capacity?

 

[jaapv]

No, it is not quite the same but similar, but the dealer should be able to carry this out for you, it is an official service protocol by Mitsubishi. The factory procedure takes a bit longer than this and is usually carried out overnight.
The above might work, though, but carries the risk of being interrupted (if the laptop does go to sleep unexpectedly ot the connection gets lost, etc)

 

[elm70]

Does anybody has any issue on unbalanced battery pack on the PHEV ?

Per EvBatMon .. I never spot any difference bigger then 0.02v in my pack .. and normally is just 0.01v or less.

I have experience on keeping balanced the battery pack for my RC Hobby model aeroplanes, since over a decade ... and the only real need is to have all cell balanced when the pack is fully charged ... balance and charge on the same time will grant to have pack balanced once is fully charged .. so there is no need for additional slow balancing procedure

 

[Bert]

I had severe degradation down to 80% after 3.5yrs and 58.000km. The EV range dropped to only 35km in summertime.

After the cell smoothing procedure it got up to 99.7% and 37.9Ah. I'm currently documenting this all on my YT channel (https://www.youtube.com/channel/UCCwvk634ZX1R1_qhfRyczOg)
(not trying to harvest more viewers, it's all without monetisation )

Mitsi did this for free as they admitted the capacity was a bit down. Looks like it's a comBination of cell smoothing and recalibration of the MCU. I got over 60km on the GOM every morning and can easily do 50km now.

Cheers

 

[zzcoopej]

I had severe degradation down to 80% after 3.5yrs and 58.000km. The EV range dropped to only 35km in summertime.....
can easily do 50km now.

Interesting. Please post whether the "new" capacity holds after a month or 2, as other users who have had this procedure done say it is short-lived.

I'm very interested in what your charging style and EV driving style has been eg fast chargers, always charging to 100%, drive mostly EV or lots of ICE km?

 

[anko]

After the cell smoothing procedure it got up to 99.7% and 37.9Ah.

Quite impressive. Mine was / ius in a far worse shape. During the procedure 'I' went from 27.3 to 29.0. After 4 weeks I am already back at 27.9. Curious to learn what happens to your gain over time.

Will watch your videos shortly ....

 

[SolarBoy]

My capacity is 86.8% after 11,697 km.

I recharge between 2 and 5 times a day on a 16Amp charger.

Have I broken it?

 

[HHL]

I wonder if this "smoothing" is really just a way to re-synch what the BMU stored battery capacity is, by performing a more detailed measurement than the normal charge/discharge cycle can do, to try and establish the actual condition and set the BMU to that.
Cell balancing must be done quite often, I would think on just about every normal (not fast) charge cycle. From my observations using EVBATMON, there is rarely a difference between cells, and if there is, it shows 10mV, and that is even at the "empty" level, where it is most likely to show up any cell deviations.
My battery condition currently shows up as 88%, but I can't really say that the range has reduced noticeably.
One thing I find interesting is the charge level vs battery voltage seems to be quite pessimistic. I have just done a reading and EVBATMON says SOC 26% while the battery voltage is 304.8 (3.81V per cell). Unless the chemistry in these batteries is very different from other Li-Ion cells, this cell voltage would suggest a real charge level of close to 40%.
According to the manual, when the battery is depleted the engine will start at around 27% and stop again at 32%, thus cycling all the time in hybrid mode in slow driving. When I took this measurement, I had just returned from a 50km drive and the engine was cycling for the last few km. It had stopped just before I took the reading and it therefore should have been around 30% but showed 26%. So, somewhere along the line things don't quite add up. Happy to say though my car goes as good as when I bought it 2 years ago.

 

[anko]

I wonder if this "smoothing" is really just a way to re-synch what the BMU stored battery capacity is, by performing a more detailed measurement than the normal charge/discharge cycle can do, to try and establish the actual condition and set the BMU to that.

My car has undergone this procedure twice, and both times I have experienced an increased range and observed an increase amount of kWh going through the charge station during a full charge.

One thing I find interesting is the charge level vs battery voltage seems to be quite pessimistic. I have just done a reading and EVBATMON says SOC 26% while the battery voltage is 304.8 (3.81V per cell). Unless the chemistry in these batteries is very different from other Li-Ion cells, this cell voltage would suggest a real charge level of close to 40%.

Maybe there is a large chunk of unusable capacity 'at the top'. If the BMU takes that into account, the reported SOC could deviate from the actual SOC. Although, it would require a 18.5-ish kWh battery for these numbers to match up.

According to the manual, when the battery is depleted the engine will start at around 27% and stop again at 32%, thus cycling all the time in hybrid mode in slow driving.

The cycle is much shorter and depends on your speed (and whether the engine already had a chance to warm up). Typical, a high speed cycle is (from the top of my head) 30.5% - 32% and a low speed cycle is approx. 27% to 28.5%. But when driving really slow you can go as low as 25.5% (or even a bit lower when the last part of your trip is in reverse, I noticed yesterday). So, there are several different cycles, but to the best of my knowledge, 27% - 32% is not one of them. Unless you would speed up in the middle of a cycle. But I cannot imagine they would put that in the manual

 

[HHL]

"Maybe there is a large chunk of unusable capacity 'at the top'. If the BMU takes that into account, the reported SOC could deviate from the actual SOC. Although, it would require a 18.5-ish kWh battery for these numbers to match up."

Maybe they just enable a deeper discharge.....that would give you extra range before the engine starts and also lets you put more back into the battery

 

[anko]

"Maybe there is a large chunk of unusable capacity 'at the top'. If the BMU takes that into account, the reported SOC could deviate from the actual SOC. Although, it would require a 18.5-ish kWh battery for these numbers to match up."

Maybe they just enable a deeper discharge.....that would give you extra range before the engine starts and also lets you put more back into the battery

This particular comment was in response to your observation that reported SOC and actual cell voltage did not match up. How does this relate to 'allowing a deeper discharge'?

 

[HHL]

Well, I was more thinking about your comment that "smoothing" gave you an improved range and more kWh going into the battery.
From what I know is once a Li-Ion battery has degraded, nothing can restore lost capacity. But it is certainly possible to alter the behaviour of the battery management system to allow more usable capacity, especially since the our cars seem to be quite conservative in the maximum allowable discharge initially.

 

[anko]

I hope not. As the gain both times disappeared very quickly after the procedure was executed (within a matter of weeks), it would mean that I now had the same low capacity as before, but now with smaller safety butters. This would mean my battery had actually degraded in two big steps in the few weeks right after the procedures were executed.

Unless the reprogramming of the BMU was magically undone in those few weeks, of course. But to me, that does not seem very likely.

 

[maby]

My capacity is 86.8% after 11,697 km.

I recharge between 2 and 5 times a day on a 16Amp charger.

Have I broken it?

Unless you are doing a hundred miles per day, you must be doing a lot of small top-ups to be charging that many times per day - a pattern of usage that Mitsubishi warn against. You really should be in a pattern of full charges running down to more or less empty.

 

[anko]

Unless you are doing a hundred miles per day, you must be doing a lot of small top-ups to be charging that many times per day

Unless he recharges from (e.g.) 50% to 70% several times a day, during short stops. And then it would not be much different from what the ICE / generator does.

 

[Tipper]

Later cars have a longer range on battery...is this because they have better BMU software based on running experience since introduction or because there is a real difference in the battery/other hardware in the cars?

If the former, can early cars benefit from a simple BMU software upgrade? Perhaps this is what has been done to the cars identified here that had lower battery capacity and are now performing better?

 

[SolarBoy]

My capacity is 86.8% after 11,697 km.

I recharge between 2 and 5 times a day on a 16Amp charger.

Have I broken it?

Unless you are doing a hundred miles per day, you must be doing a lot of small top-ups to be charging that many times per day - a pattern of usage that Mitsubishi warn against. You really should be in a pattern of full charges running down to more or less empty.

We drive to the next town two or three times a day, the journey is too far to do twice on one charge and so have to top up between journeys.

I don't see there being a solution.

EDIT: We do a 20 min pre-heat in the morning's whilst plugged in during the winter and aircon in the summer which also uses a lot of juice.

 

[anko]

If the former, can early cars benefit from a simple BMU software upgrade? Perhaps this is what has been done to the cars identified here that had lower battery capacity and are now performing better?

Perhaps this can be done. But my car was treated twice and I gained a little range twice. So, IMHO not likely.

 

[elm70]

Well, I was more thinking about your comment that "smoothing" gave you an improved range and more kWh going into the battery.
From what I know is once a Li-Ion battery has degraded, nothing can restore lost capacity. But it is certainly possible to alter the behaviour of the battery management system to allow more usable capacity, especially since the our cars seem to be quite conservative in the maximum allowable discharge initially.

For me it is quite odd that the battery can be used only between 4.1 down to 3.8v

Especially with aging, and increase in IR .. 3.8V can be reached very fast

As far as I know it is totally safe to bring the Lithium battery to 3.7v ... and I'm quite sure that just reprogramming the car to allow to use battery down to 3.75v ... there will be no negative effect on battery life ... but still over 10% of extra range, even more for "old" battery with high IR

I'm also wondering what means the "target voltage" that is shown by the ODB2 tools for out PHEV .... I hope the BMW does not try to balance down the cell for align down the voltage ... BMU when balance cells, as far as I know .. it is always discharging the cells with the highest voltage ... BMW that can take power to high voltage and give to low voltage cells, I believe does not exist

PS: Something odd happen to my PHEV .. per the PHEV watchdog .. in the last month, I lost 0.5Ah of capacity ... from 35.3ah to 34.8ah ... before I was losing around 0.1Ah every 2 months ... first data I got from my car, that was already over 3y old and 120.000km .. was 36Ah ... around 1y ago