Reading SOH

EVentropy said:

I guess it’s rediculous chasing <0.5%
Anyway. Sheesh, I think I will dial back the 3.6V HV cut off on boat LFP’s. They do start balancing with continued charging, at 3.4V though, but at minuscule current.

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In terms of the extra capacity I'd agree. But you will need to work out the best balance of high-voltage cut-out vs. how much time you are giving your BMS to do its balancing. This will depend on many factors, but in particular at what rate you are charging at when the reported SOC is > 99%, how often your LFP's reach that capacity and whether your BMS is an active or passive one. It's not recommended practice to start balancing LFP's below 3.4V, but as the cells reach 3.6V, the voltages will rise extremely quickly, giving less time for balancing to take place.

A lower cut off will help longevity, though it's likely that calendar ageing will be a bigger factor than number of cycles for most home type battery systems.

FWIW, on my home battery (16-cell, 280Ah LFP's) I normally keep the cut-off at 3.45V, with a very reduced trickle charge (just 4A) when the cells are above 98%. A few times a year I will adjust that to 3.5V or even 3.55V to give some more balancing time, but then I only have a passive balancer.

As you say you are charging at minuscule current, I'd be inclined to try 3.5V for the cell cut-off, but keep monitoring the max cell delta when your first cell hits 3.5V. I'd be very happy with anything less than 50mV at those voltages.

My LFP SE SRs SoH got bumped from 94.8 (measured the other day at 16 months old and 15k miles) to 95.7 this morning. This was due to a 6% to 100% slow charge. Before charging I left the car at 6% for about an hour. Balancing took way longer than usual, possibly an hour.

Moreover, the State of Charge reported by the OBD2 port now matches the one on screen. Previously it was always a bit skewed by 1 to 2 per cent points.
Now the car shows 94%, OBD2 says 94.4%.

(The SoC displayed OBD2 value is still out, reporting 97.2% but I maybe it’s referring to something else)

fnegroni said:

Moreover, the State of Charge reported by the OBD2 port now matches the one on screen. Previously it was always a bit skewed by 1 to 2 per cent points.

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I think that there is always a point where the "display" ("usable") SoC is the same as the "real" ("actual") SoC. They are effectively two straight lines with slightly different slopes that cross at some point.

But I have seen posts that suggests that there may be a third SoC value. Si it's all rather murky at this stage.

fnegroni said:

My LFP SE SRs SoH got bumped from 94.8 (measured the other day at 16 months old and 15k miles) to 95.7 this morning. This was due to a 6% to 100% slow charge. Before charging I left the car at 6% for about an hour. Balancing took way longer than usual, possibly an hour.

Moreover, the State of Charge reported by the OBD2 port now matches the one on screen. Previously it was always a bit skewed by 1 to 2 per cent points.
Now the car shows 94%, OBD2 says 94.4%.

(The SoC displayed OBD2 value is still out, reporting 97.2% but I maybe it’s referring to something else)

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What does the info centre relate transitioning from charging to balancing?
Does it go to "trickle charge" at 99% then click over to 100% within minutes?
On termination of balancing does "balancing" mode just disappear with no other message?
Are you using the car scanner app on info centre or OBD2 Bluetooth to phone and "all sensors"?
Sorry for the 1000 questions, but this would help me up the curve.
I tried to couple up getting the car to 5% yesterday with jobs around town- bad idea.
Got caught too low, in the pouring rain, so had to do partial fast charge. Best laid plans of mice an .............
Cheers.

EVentropy said:

What does the info center relate transitioning from charging to balancing?
Does it go to "trickle charge" at 99% then click over to 100% within minutes?
On termination of balancing does "balancing" mode just disappear with no other message?
Are you using the car scanner app on info center or OBD2 bt to phone and "all sensors"?
Sorry for the 1000 questions, but this would help me up the curve.
I tried to couple up getting the car to 5% yesterday with jobs around town- bad idea.
Got caught too low, in the pouring rain, so had to do partial fast charge. Best laid plans of mice an .............
Cheers.

Click to expand...

Mine does not say anything when balancing. Just keeps going past 100% for some time (normally 20minutes) and keeps updating the projected time to finish and that’s it. It balances once it has reached 100%.

I use CarScanner with a VeePeak Bluetooth dongle and be careful you have to use the latest MG4 profile which has just been updated to use a custom connection string which does what I mentioned in other posts wrt a particular setting.

There are indeed 3 different state of charge values and I use the one called HV battery state of charge which does not show decimals and now matches the one on the drivers display. The other two show decimal places, but the one called ‘SoC displayed’ is always out by quite some margin and it might refer to a mix between full capacity including buffer and usable capacity, while the other now matches what I see in the car.

fnegroni said:

Mine does not say anything when balancing.

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On mine it says balancing on one display and trickle charging on the other.

fnegroni said:

Just keeps going past 100% for some time (normally 20minutes)

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I had previously assumed this was rounding up for the display since it takes roughly 20 minutes for 1 percent on a granny that i use. So 98.1 through 99.0 would show as 99, and 99.1 through 100 would show as 100.

If someone with wallbox finds it typically lasts closer to 10 minutes on 100% that would back up that theory, otherwise .

fnegroni said:

while the other now matches what I see in the car.

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If this value has a decimal place, that could show what (if any) rounding is going on perhaps?

DixieTGS said:

On mine it says balancing on one display and trickle charging on the other.

I had previously assumed this was rounding up for the display since it takes roughly 20 minutes for 1 percent on a granny that i use. So 98.1 through 99.0 would show as 99, and 99.1 through 100 would show as 100.

If someone with wallbox finds it typically lasts closer to 10 minutes on 100% that would back up that theory, otherwise .

If this value has a decimal place, that could show what (if any) rounding is going on perhaps?

Click to expand...

Next time I’ll connect the dongle and check, now that the numbers seem to make more sense.

Did another SOH check today as the car has now done 30k miles in a tad under 2 years. 97.2 % so happy with that , it was 97.6 % last time I checked so looking good. Trophy LR.

fnegroni said:

Mine does not say anything when balancing. Just keeps going past 100% for some time (normally 20minutes) and keeps updating the projected time to finish and that’s it. It balances once it has reached 100%.

I use CarScanner with a VeePeak Bluetooth dongle and be careful you have to use the latest MG4 profile which has just been updated to use a custom connection string which does what I mentioned in other posts wrt a particular setting.

There are indeed 3 different state of charge values and I use the one called HV battery state of charge which does not show decimals and now matches the one on the drivers display. The other two show decimal places, but the one called ‘SoC displayed’ is always out by quite some margin and it might refer to a mix between full capacity including buffer and usable capacity, while the other now matches what I see in the car.

Click to expand...

Hi @fnegroni

I've got the same Veepeak / car scanner approach as you (I'm android) and I can connect using Bluetooth just fine. When I try Bluetooth LE it doesn't connect to the ECU.

The main challenge I'm having is with ABRP and I wondered if you use that? When I try to connect that to my Veepeak it just connects to the adapter but not the car. If car scanner is running I can't even see the adapter but I wasn't sure if ABRP needs Car scanner to read / interpret the data?

Hopefully that makes sense and if you or anyone can make any suggestions I'm all ears

I was hoping to get live data for ABRP but so far no joy.

The good news is that I can see my SOH is 99.1% which sounds ok for an 18 month old car.