MG4 51kWh LFP Battery Health

[Everest]

From the supply - the energy has to come from somewhere (first law of thermodynamics) and there is only one supply source - the charge port. If balancing was using a lot of energy it would show up in the charging energy consumption.

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Judging by that, it seems the charger doesn't actually continue charging the battery during the balancing stage and the 80 W is used to power the monitoring side of the BMS.

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In fact, when one cell has the bleed resistor turned on,

All of which are assuming passive balancing, though. Do we know that for sure, or could the BMS be doing active balancing?

 

[gdog]

when I turn on the battery heater it doesn't change the estimated range

When you turn it on I wouldn't expect GOM to change if there's no power draw. It would be a total wild wild wild guess to adjust GOM for battery heater as there are so many variables that would come into play and they are all in the future.

But if there is a power draw surely the GOM is adjusted?

Or maybe it's just considered as a running mil/kWh inefficiency? After all it may be on for 10mins or 120min.

 

[T1 Terry]

All of which are assuming passive balancing, though. Do we know that for sure, or could the BMS be doing active balancing?

Does any manufacturer use active balancing?

T1 Terry

My schoolgirl maths suggests that would depend on how many miles he is doing a year

Following the plot, how many yrs would that be?

Judging by the cut and paste bits, the vehicle has done 30,000km at the moment .... in about 16mths? So maybe another 2 yrs or so ....

T1 Terry

 

[Everest]

Does any manufacturer use active balancing?

I've no idea

 

[siteguru]

The battery packs in the MG4 are supplied by CATL, in case that helps.

 

[hojnikb]

I'm surprised nobody tore down this pack already..

 

[gdog]

I'm surprised nobody tore down this pack already..

Im waiting patiently. but suppose its a good sign. right

 

[WXman]

I'm not sure I'm any the wiser about battery health and capacity! I did a charge from 4 miles left on GOM last night and put in 50.8kWh of energy to get to 100% according to Ohme charger. My car's done 41k miles and I may have lost an odd mile or two of range in 2yrs of ownership, but nothing particularly noticeable so far - long may it continue...

 

[fnegroni]

I'm not sure I'm any the wiser about battery health and capacity! I did a charge from 4 miles left on GOM last night and put in 50.8kw/h of charge to get to 100% according to Ohme charger.

a home charger is 90~95% efficient. You put 47kwh in there. Given you maybe had 1 to 2 kwh in the battery already, you have lost around 5% capacity or so.

 

[Tomg4]

The SOH dro

a home charger is 90~95% efficient. You put 47kwh in there. Given you maybe had 1 to 2 kwh in the battery already, you have lost around 5% capacity or so.

Could you explain that please? The charger itself is located in the car essentially

 

[Coulomb]

The charger itself is located in the car essentially

Exactly. The Ohme EVSE ("charger") is measuring power from the wall. The on-board charger will lose some 7%, and there will be some 12V loads and DC-DC losses. So of the 50.8 kWh that the Ohme measured, only very roughly 90% if that ended up in the HV battery. Call it 0.8 x 50.8 ~= 46 kWh, plus the ~2 kWh it started with, comes to some 48kWh. I note that if it was summer there it might have taken more energy, I'm hazy on how that works. Given that the usable nominal capacity when new is 50.8kWh, your SoH is very roughly 100% x 48 / 51.8 = 93%, or 7% degradation. Give or take several percent, because there are so many guesses in this calculation. Also it will likely look better in summer.

 

[T1 Terry]

I'm not sure I'm any the wiser about battery health and capacity! I did a charge from 4 miles left on GOM last night and put in 50.8kWh of energy to get to 100% according to Ohme charger. My car's done 41k miles and I may have lost an odd mile or two of range in 2yrs of ownership, but nothing particularly noticeable so far - long may it continue...

View attachment 33958

Hmmmm...... so if battery health is declining, yet range remains close to the same over 41,000 mile .... as the nasally red head would say "Please explain?"

T1 Terry

 

[Tig170]

I'm not sure I'm any the wiser about battery health and capacity! I did a charge from 4 miles left on GOM last night and put in 50.8kWh of energy to get to 100% according to Ohme charger. My car's done 41k miles and I may have lost an odd mile or two of range in 2yrs of ownership, but nothing particularly noticeable so far - long may it continue...

View attachment 33958

Knock the charge rate down to 3.44Kw - it has many benefits - incl. cheap charging as soon as one plugs in??

 

[hojnikb]

Hmmmm...... so if battery health is declining, yet range remains close to the same over 41,000 mile .... as the nasally red head would say "Please explain?"

T1 Terry

Doesn't range estimation vary depending on consumption, so looking this way at degradation is kinda.. pointless?

 

[fnegroni]

The SOH dro

Could you explain that please? The charger itself is located in the car essentially

I stand corrected: I meant the on board charger or ‘when charging from home’ - there are additional losses if you use something like a granny charger I think.

 

[gdog]

"Please explain

Car is getting broken in improving efficiency

additional losses if you use something like a granny charger

Regardless of AC power source whether wall charger or granny charger, the cars onboard inverter converts AC to DC is where the losses occur. So it's always about 10% loss. I believe about 7-8% in inverter and about 2-3% ancillary draws like cooling pump etc

 

[siteguru]

When charging there are fixed losses (those always there, which are the same amount irrespective of charging rate), and variable losses which are proportional to the charging rate. Therefore the higher the charging rate, the better the charging efficiency. That's because the fixed losses are a higher percentage of the overall losses at a lower charging rate.

A made up example for demonstration:

Fixed losses 100W
Variable losses 5% of charging rate

7kW charging rate = 0.1kW + (5% of 7kW) = 0.1 + 0.35 = 0.45kW. Efficiency = (7 - 0.45) / 7 = 93.6%

2kW charging rate = 0.1kW + (5% of 2kW) = 0.1 + 0.1 = 0.2kW. Efficiency = (2 - 0.2) / 2 = 90%

 

[gdog]

Fixed losses 100W
Variable losses 5% of charging rate

My understanding is that the inverter consumes more energy with higher the power, from observing my home battery. this is not fixed but proportional.

however you have highlighted a very good point and i do agree that the lower charging rate like with a granny charger is less efficient overall as the ancillary devices losses are always there like the cooling pump. Therefore if you charge at the higher power these ancillary losses are a smaller ratio of the losses.

reading that again i think I am reading your explanation wrong and we are saying the same thing

 

[T1 Terry]

Sounds much like my inverter explanation, the efficiency % is when the unit is working at its designed peak performance. The loses are constant, reversing the system to generate DC at a higher voltage than the AC input, the loses through rectifying the AC to DC are proportional to the current passing through them, and so is the cooling required.
It would require a Hall Effect sensor around the battery cable to measure current flow in each direction as well as the voltage to calculate the third reading of watts and linked to a device to plot the lines in conjunction with a similar set up to measure the AC input at the plug end. A true comparison could then be made between each charging system and charging speed.
DC is obviously the most efficient because it is what the battery accepts straight out of the plug, but how much does the fast charging cost as far as loses running the cooling system .... it is efficiency and not $$ cost we are looking at here ....

T1 Terry

 

[wattmatters]

DC is obviously the most efficient because it is what the battery accepts straight out of the plug, but how much does the fast charging cost as far as loses running the cooling system .... it is efficiency and not $$ cost we are looking at here ....

The point of DC charging is speed. Cost and efficiency are subsidiary. If time was not the primary concern then you would AC charge every time, in which case cost trumps efficiency.

Since DC charging is fast, then any sub-system will only be operating for a short time.

But we have to also ask, at which point are we measuring efficiency? DC chargers use an AC power supply.