Battery capacity not match with consumption figures

[gary333]

Empty the car to close to zero and fill it up to 100%. Pointless looking at the software as it's shite. You then have your answer what the loss is.

 

[dam92]

I just don't understand what you mean.

I thought the issue was the car isn't accurately reporting where the power is going.

Now you are claiming that this has something to do with the battery capacity.

Or are you claiming that the car is misrepresenting the efficiency of the motor?

I don't think you are being consistent with your complaint here, but are trying to make out that something is outrageous.

If you want to get more accurate figures on the uses get an OBD device and measure it all accurately.

Im sorry for the confusion.

If you see the 1st message, you can see i was telling about used power and efficiency figures doesn't match the advertised battery capacity. That's the primary problem.


Then if you carefully follow the conversation, you can see few other also reporting similar figures. Calculated capacity is about 51kwh, which is similar to my case.

But the chargers seems to be putting fairly acceptable amount of energy in to the car (about 61-62kwh).
People also provided their own charging data.

Then came new questions, where did that 10kwh go?.
Does it have to do with poor efficiency of the charger?. Poor efficiency of the inverter?.
What is the actual output we get?.

 

[dam92]

Empty the car to close to zero and fill it up to 100%. Pointless looking at the software as it's shite. You then have your answer what the loss is.

Yes. Thats what im planning to do.
I will update this once its done..

 

[Martinonline]

I believe, @dam92, that you are right to question the information you have been given based on the data the car provides.

However, it would be interesting for you to state, exactly, what concerns you have and what the implications are for you.

For example, I bought my Trophy for its range and upgraded specifications, eg rear view camera etc. I did not know about NMC and LFP batteries nor charging/discharging efficiency.

If the range had been substantially lower than I was told then I would have been mightily put-out. But it is not. The car takes ~67kWh for a 100% balanced charge and that meets what I was told the battery size was. It would be nice to have a higher charging efficiency but that probably, but not certainly, with a more expensive car.

Back to your figures: if you assume that the miles/kWh value is correct and the mileage is correct then the usage data is correct. However, by doubling the value you assume the usage is linear over the 100%, which may not be true. Certainly the GOM does not believe that because it shows a remaining mileage of 124 miles for the last 50%.

The 'WhatCar Range and Efficiency Test' video (winter) with a Trophy ER came to the conclusion that the usage efficiency was accurate over their 100% usage test.

If that is correct for your 50% usage then a 50kWh battery would give you 195 miles, a 60kWh 234 miles with the (assumed linear) GOM 248 miles.

You can test these figures by running down your battery and then let us know the results and then follow with a metered charge to check the efficiency.

Good luck.

 

[dam92]

I believe, @dam92, that you are right to question the information you have been given based on the data the car provides.

However, it would be interesting for you to state, exactly, what concerns you have and what the implications are for you.

For example, I bought my Trophy for its range and upgraded specifications, eg rear view camera etc. I did not know about NMC and LFP batteries nor charging/discharging efficiency.

If the range had been substantially lower than I was told then I would have been mightily put-out. But it is not. The car takes ~67kWh for a 100% balanced charge and that meets what I was told the battery size was. It would be nice to have a higher charging efficiency but that probably, but not certainly, with a more expensive car.

Back to your figures: if you assume that the miles/kWh value is correct and the mileage is correct then the usage data is correct. However, by doubling the value you assume the usage is linear over the 100%, which may not be true. Certainly the GOM does not believe that because it shows a remaining mileage of 124 miles for the last 50%.

The 'WhatCar Range and Efficiency Test' video (winter) with a Trophy ER came to the conclusion that the usage efficiency was accurate over their 100% usage test.

If that is correct for your 50% usage then a 50kWh battery would give you 195 miles, a 60kWh 234 miles with the (assumed linear) GOM 248 miles.

You can test these figures by running down your battery and then let us know the results and then follow with a metered charge to check the efficiency.

Good luck.

Thank you. I'm not complaining about the estimated range — I understand that estimates can vary.

My concern is with the usable capacity of the battery. Based on my own observations and data from others, it appears to be around 51 kWh, including auxiliary loads. That suggests around 10 kWh of capacity is effectively lost or unavailable, which is a significant discrepancy.

As a power electronics engineer, I design power converters and chargers for a living, so I tend to be especially sensitive to these kinds of figures.

These values are typically calculated using current and voltage sensor readings. If the reported usable capacity is this far off, it suggests there may be an issue — either in measurement accuracy, calibration, or system design.

It's not about cost. In fact, I’ve seen far better accuracy and efficiency from even low-cost Chinese power converters.

 

[Martinonline]

Thank you for your explanation and as you say there may be an issue with measurement factors et al.

And MG may not have the best designed system but unless you look at all EVs you cannot say this is not typical of the market at this price point.

Will you be running down your battery to sub 5% to see if the usage figure exceeds 50kWh? And to see how many miles you covered? (For the miles/kWh figure.)

Finally, have you checked to see if the (not so) intelligent battery heating is on?

 

[dam92]

Thank you for your explanation and as you say there may be an issue with measurement factors et al.

And MG may not have the best designed system but unless you look at all EVs you cannot say this is not typical of the market at this price point.

Will you be running down your battery to sub 5% to see if the usage figure exceeds 50kWh? And to see how many miles you covered? (For the miles/kWh figure.)

Finally, have you checked to see if the (not so) intelligent battery heating is on?

Yes. That's the plan. At least wait until it goes below 10%. I need to do an equalise charge as well to get it to the optimal capacity.
No battery heating enabled.
Yes I agree. Its not the best and I wouldn't expect it to be at this price tag. Let's see what happens.
From my experience on designing these type of converters, I know it's not too much to ask for reasonably accurate calculations. On the other hand, it's much much more complex to design the power electronics and its controller firmware. MG seems to have designed the motor controller well. No sudden jerks and it's pretty smooth.

That's why I am surprised to see this discrepancy in the figures.

 

[Coulomb]

That's why I am surprised to see this discrepancy in the figures

The firmware in the motor controller must be written by different engineers than the display firmware. Possibly a different section within SAIC, or possibly by a different company altogether.

 

[Martinonline]

@dam92, I hope you are ok with your car's battery capacity now. The following may help.

Over the last 4 days I had to charge my Trophy to 90% and balance twice as I needed to make a longer journey than my pootling about the town. The journey would be a mixture of A and B roads with speed limit variations.

After the first charge I covered the same ~22 miles 3 times. The discharge figures showed I'd used 23% of the battery using 14kWh (+ 3kWh regen). Multiplying that 14kWh would give a battery capacity of ~61kWh.

I then charged for free to 90% again and covered, essentially, the same route with a detour to avoid roadworks. This time the journey used 10% of the battery using 6kWh (+ 1kWh regen). Multiplying that 6kWh would give a battery capacity of 60kWh.

Thus I would guess that the car's calculations aren't good when covering multiple short journeys.

 

[gary333]

How can you balance if you didn’t charge to 100%

 

[dam92]

@dam92, I hope you are ok with your car's battery capacity now. The following may help.

Over the last 4 days I had to charge my Trophy to 90% and balance twice as I needed to make a longer journey than my pootling about the town. The journey would be a mixture of A and B roads with speed limit variations.

After the first charge I covered the same ~22 miles 3 times. The discharge figures showed I'd used 23% of the battery using 14kWh (+ 3kWh regen). Multiplying that 14kWh would give a battery capacity of ~61kWh.

I then charged for free to 90% again and covered, essentially, the same route with a detour to avoid roadworks. This time the journey used 10% of the battery using 6kWh (+ 1kWh regen). Multiplying that 6kWh would give a battery capacity of 60kWh.

Thus I would guess that the car's calculations aren't good when covering multiple short journeys.

Thank you for the input. Dealership has updated the software to the latest and all the figures has been reset. I have to do a full charge discharge cycle to see what happens.

 

[EvTek23]

@gary333, the battery will balance when it achieves the target charge level selected. You can move the slider on the battery bar in the charging tab of the infotainment screen to a target level between 40% to 100% in 10% increments. This is certainly true of the Trophy/ SE LR with NMC batteries, I can't say this is true for SE SR with LFP batteries.

 

[hojnikb]

You can't set a charge limit on LFP cars. And they only balance at 100%

 

[EvTek23]

Thank you @hojnikb for clearing that point up. @Martinonline profile says he has a Trophy, but I guess @gary333 has an SE SR, so I can now understand his query about only balancing at 100%

 

[Ian Key]

@gary333, the battery will balance when it achieves the target charge level selected. You can move the slider on the battery bar in the charging tab of the infotainment screen to a target level between 40% to 100% in 10% increments. This is certainly true of the Trophy/ SE LR with NMC batteries, I can't say this is true for SE SR with LFP batteries. View attachment 38980

You are correct that the battery will balance at the set target level but the idea of balancing is to get any under-performing cells to perform at 100%. If you only ever balance at 80% for example any cells that under-perform by 20% won't improve and you run the risk of prematurely lowering the SOH.

 

[EvTek23]

Yes agreed @Ian Key, mine gets balanced to both. On the more regular 80% recommended charge health mode, and 100% long range mode.

 

[Evergreen]

You can drive yourself crazy doing all the mathematical permutations involved in getting an "accurate" or even sensible answer . The two figures above and under the power graph are more illuminating and along with the regen figure and the photos you have provided it can be done to jiggle the figures that makes sense. Also if you have just got the car some of those averaged out numbers will be from a previous owner . Just doing one balance charge to reset the system most likely won't be enough ,you will need to put your miles on the car and again a balance charge to reset and calibrate it to your style of driving. Sadly , just taking a snapshot view of a couple of numbers does not make a sensible result . After two years of ownership I think I'm starting to understand the maths , then it sends out some curve ball numbers to again confuse the issue. Most have given up trying to understand the algorithms and are happy to drive on just the m/kwh figure. Also the usage is not perfectly linear from 100% down to lower limits so that will confuse the issue when trying to calculate what should be , on the face of it , simple into as you have discovered , not!
If you find a formula that consistently works you would gain instant hero worship status on this forum.

You are correct that the battery will balance at the set target level but the idea of balancing is to get any under-performing cells to perform at 100%. If you only ever balance at 80% for example any cells that under-perform by 20% won't improve and you run the risk of prematurely lowering the SOH.

I have done an exhaustive test on my MG 4 77 and find the usable battery capacity between a fully balanced full charge and an indication of 0% is consistently about 68 kWh which goes someway to explain the disappointing range compared with the claim figure. I have tried to claim under warranty and have been told the car is behaving normally. There are only two interpretations
1 the advertising is fraudulent and MG know that the actual battery capacity usable is 10% less than the claim or
2 my car has suffered premature battery degradation and they are trying to escape warranty responsibility

 

[EVentropy]

You can't set a charge limit on LFP cars. And they only balance at 100%

Yep. No point as there is no delta until 98%+ unless you got badly matched cells. Very flat charging plot.
Btw, hojnikb , I have a comparison on top charge/ balance plot from PeterWA for LiFePO4,
Exactly the same as mine!

 

[hojnikb]

I have done an exhaustive test on my MG 4 77 and find the usable battery capacity between a fully balanced full charge and an indication of 0% is consistently about 68 kWh which goes someway to explain the disappointing range compared with the claim figure. I have tried to claim under warranty and have been told the car is behaving normally. There are only two interpretations
1 the advertising is fraudulent and MG know that the actual battery capacity usable is 10% less than the claim or
2 my car has suffered premature battery degradation and they are trying to escape warranty responsibility

How did you came with that value?

 

[siteguru]

The ER has a nominal 77kWh battery pack, with about 74kWh usable (per the specs). As per above I'd be interested in how you calculated 68kWh.