Help me understand my BMS

[Dukhudo]

I'm having a bit of a hard time understanding my charging. I have car scanner so I've taken a few screen grabs to try to help me explain a bit better.

Starting out based on another thread asking the SOH, I'm at 96% according to car scanner. The truck is about 3-4 weeks old and it's been this way since I first got car scanner back at 1,300kms. I now have 2,100 km on the truck and it's still the same. As part of that thread, someone suggested that I drain the battery and then charge it to 100%.

So I did that, I got it down to 15% and charged it today. But something weird happened (or at least I think so) and the truck stayed at 99% for 2 hours while continuing to pull 6kw (mobile charger). In the end, it got charged to 130.7 as shown below, and 100% HVB SOC, while the dHVB SOC Display stayed at 99%. I unplugged and plugged back in, and the truck displayed 100%.

After this, I took it for a drive immediately to burn off some of the battery. What I got was below. Now the truck was at 100% displayed SOC, while the HVB SOC was 94.3 and energy was 122.16

I kept driving and this was where the display SCO finally dipped below 100%

So now I have questions what 100% in my truck is or if there's a way to correct the BMS so it's a bit more accurate. I did try to take this to the dealer, but unless there's an error code, they wouldn't do look at it.

Any help is appreciated.

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[Heliian]

Once you understand battery capacity and the factors that affect it then you'll be fine. First thing I see is voltage.

 

[VTbuckeye]

Why is it that when charged to 100 percent (indicated) the math works out to 131kWh for the whole pack, but at lower charge levels the math works out to a lower pack capacity?

125.45/0.9586= 131
89.37/0.7409 = 121

Do I have a problem? Is the bms wrong/inaccurate? I'll check again, I am currently at 45 percent indicated.

 

[Dukhudo]

Once you understand battery capacity and the factors that affect it then you'll be fine. First thing I see is voltage.

I’m not sure I understand here. My battery is 131kwh usable. What’s weird is that my HVB SOC shouldn’t be at 100% when it’s charged to 131kwh as the battery is actually 143.4 kWh as per the sticker on the battery.
And what do you mean by Volts?

 

[bmwhitetx]

So I did that, I got it down to 15% and charged it today. But something weird happened (or at least I think so) and the truck stayed at 99% for 2 hours while continuing to pull 6kw (mobile charger). In the end, it got charged to 130.7 as shown below, and 100% HVB SOC, while the dHVB SOC Display stayed at 99%. I unplugged and plugged back in, and the truck displayed 100%.

I thought I remembered someone saying that last bit can take a long time. Maybe balancing cells, etc. The few times I charged to 100% I did it overnight.
When you unplugged did the truck say it was done? If it was still pulling 6 kW maybe it was still charging. Just a thought.

 

[Dukhudo]

I thought I remembered someone saying that last bit can take a long time. Maybe balancing cells, etc. The few times I charged to 100% I did it overnight.
When you unplugged did the truck say it was done? If it was still pulling 6 kW maybe it was still charging. Just a thought.

It dropped down to 1kw when it reached 130.7 kWh and wouldn’t go beyond that. I say in the car waiting and it would just hover at 130.7 - 130.71. I unplugged it and plugged it back in and it then said it was done.

Something just doesn’t seem right. While it won’t affect me most of the time, it definitely does with when the charging drops after 80% at fast chargers.

80% of 121 and 80% of 131 are quite a bit different when travelling with this brick.

 

[bmwhitetx]

Something just doesn’t seem right. While it won’t affect me most of the time, it definitely does with when the charging drops after 80% at fast chargers.

The charge curve on the truck slows DCFC significantly at 80%, and then slows even more between 85-100%.

If you truly want 100% on your home charger, let it go overnight.

Here's a charge curve Tom posted: suggest reading his article.

 

[Heliian]

I’m not sure I understand here. My battery is 131kwh usable. What’s weird is that my HVB SOC shouldn’t be at 100% when it’s charged to 131kwh as the battery is actually 143.4 kWh as per the sticker on the battery.
And what do you mean by Volts?

How is it measured and since it's not reporting it fully then how is it calculated?

Voltage, current and time are used to give you basic capacity for ex.

I'm not familiar with the battery software of the lightning so I can't give you any further details but there is a little pfm happening.

 

[Dukhudo]

The charge curve on the truck slows DCFC significantly at 80%, and then slows even more between 85-100%.

If you truly want 100% on your home charger, let it go overnight.

Here's a charge curve Tom posted: suggest reading his article.

Yea, I know this.

Just saying that 80% of 121kwh is only 96.8kwh where it would start to taper off vs 80% of 131kwh 104.8kwh. That extra 8kwh would be nice when travelling. Next time I DCFC I’ll check which level I hit.

 

[Dukhudo]

How is it measured and since it's not reporting it fully then how is it calculated?

Voltage, current and time are used to give you basic capacity for ex.

I'm not familiar with the battery software of the lightning so I can't give you any further details but there is a little pfm happening.

It did report as 100%. But it required me to unplug and plug back in.
Though it would stop accepting charge once it hit 131kwh.
It’s weird because other people’s percentage reading show the 144.3kwh for a full battery.

 

[VTbuckeye]

Why is it that when charged to 100 percent (indicated) the math works out to 131kWh for the whole pack, but at lower charge levels the math works out to a lower pack capacity?

125.45/0.9586= 131
89.37/0.7409 = 121

Do I have a problem? Is the bms wrong/inaccurate? I'll check again, I am currently at 45 percent indicated.

Adding 45 percent screenshot

52.88/0.4498 = 117... Why the different values for kWh capacity? I've only had the truck down to the upper 30s and will not discharge further just to see what happens. I have only charged to 100 percent a couple times. Could it simply be that the information that we see with carscanner is not accurate?

 

[Dukhudo]

Adding 45 percent screenshot

52.88/0.4498 = 117... Why the different values for kWh capacity? I've only had the truck down to the upper 30s and will not discharge further just to see what happens. I have only charged to 100 percent a couple times. Could it simply be that the information that we see with carscanner is not accurate?

It’s a thought I had as well. I may change odb readers to double check that as well.
I’m going to charge it overnight this weekend and let it sit at 100 for a few hours to see if that helps.

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