Battery capacity not match with consumption figures

[decrep]

There's a difference between m/kWh from the Zappi and m/kWh from the battery.

If I'm drawing 1.9kW from the mains, the car says there's 1.6kW going into the battery.
That's quiet a big difference. Losses in the charger converting mains power to what the car needs, and losses in the car converting incoming AC into DC for the battery.

 

[dam92]

According to my SR last month it was doing 4.4 miles/kWh but my Zappi tells me that from the amount used to charge the car and the mileage I did it was doing 3.7 miles/kWh.

Great. Thanks for the input. More evidence that the calculations shown in the display are so wrong or the loss is pretty high.
Note that we are NOT talking about predictions. predictions can be off. That's totally fair.
These are calculations based on already available data, which shows 20%, 30% off from the real figures.
Please correct me if im wrong.

 

[Tight Git]

I know that 100% of the electricity does not get to the car and a 7kW charger is more efficient than a granny so probably about 10% loss on the Zappi which possibly means the car is 10% out as well.

 

[dam92]

I know that 100% of the electricity does not get to the car and a 7kW charger is more efficient than a granny so probably about 10% loss on the Zappi which possibly means the car is 10% out as well.

It shouldn't make any significant difference because all those 2kw, 7kw chargers are not actually doing anything other than taking care of communication. Its just 2 contactors with communication electronics.
All the power is handled by the car onboard charger. Those type 2 Chargers shouldnt have even 0.1% loss.

 

[decrep]

So the charger it self doesn't control the charge rate, just communicates the required level to the car?

 

[dam92]

So the charger it self doesn't control the charge rate, just communicates the required level to the car?

Charger will tell how much power that the car is allowed to draw from that particular charger. The car will limit the power it draws from that charger.
So for example, in case of the granny charger, it tells the car that it can only do 2kw. So car draws that amount. Any power loss is inside the car because power converter is inside.

DC charging is different. Power is controlled by the DC charger it self and car will tell how much it can take, so charger will take care of the power delivered. Now the power loss is inside the charger because power converter is inside the charger.

 

[Bam Bam]

Interestingly, the OBD reading still shows a State of Health (SOH) of 98.4%, which would be considered normal for a one-year-old car. This makes the situation even more confusing.

So you have an OBD scanner?

Doesn't that tell you the battery capacity?

 

[dam92]

So you have an OBD scanner?

Doesn't that tell you the battery capacity?

Not me. I have asked the technician to have a look at the SoH when my front radar being recalibrated.
Not the capacity, no. Just SoH.

 

[OriginalBigAl]

Not me. I have asked the technician to have a look at the SoH when my front radar being recalibrated.
Not the capacity, no. Just SoH.

As EvTek23 reported in post #16 , 22kw imported is around 33% capacity. Rough and ready figures but an answer to your original question which is easily repeatable with your own equipment. Beyond that there does not seem to be a consistent consensus on the maths ..... and its not even winter .

 

[dam92]

As EvTek23 reported in post #16 , 22kw imported is around 33% capacity. Rough and ready figures but an answer to your original question which is easily repeatable with your own equipment. Beyond that there does not seem to be a consistent consensus on the maths ..... and its not even winter .

Yes. I guess i will get the same readings. 5kwh loss from 22kw is huge isnt it?.

 

[Bam Bam]

I don't think I understand what the claim is here.

• Is it that the car battery isn't as big as claimed?
• Or that the car isn't as efficient as is claimed on the dashboard?

Tesla Bjorn does a great job of getting data on EVs by driving them from full to empty to see what happens. He also compares DC charging speeds so goes from low to full with the full stats.




You could prove your own battery size and efficiency by getting an ODB dongle and watching as you run the car from full to empty.

But Bjorn has already done that for the model.

 

[OriginalBigAl]

Yes. I guess i will get the same readings. 5kwh loss from 22kw is huge isnt it?.

Depends on which figures you give most credence to. 33% around 1kwh loss or the 17kwh used figure ? Of course neither could be accurate to the degree you are looking for , on another day it could be the other way around. Did I mention it would drive you crazy?

 

[dam92]

I don't think I understand what the claim is here.

• Is it that the car battery isn't as big as claimed?
• Or that the car isn't as efficient as is claimed on the dashboard?

Tesla Bjorn does a great job of getting data on EVs by driving them from full to empty to see what happens. He also compares DC charging speeds so goes from low to full with the full stats.




You could prove your own battery size and efficiency by getting an ODB dongle and watching as you run the car from full to empty.

But Bjorn has already done that for the model.

Thank you for the videos..
Here is the problem in simple terms.
You charge it by 22.8kwh. Mg says it only used 17kwh total (including auxiliary functions) . Where did the 5kwh go?.
17kwh at 33%, equal to 51kwh at 100%.
Where is the 61kwh capacity?.
This is not only me apparently. There are other people also getting the same figures.

So does this mean we loss 10kwh for something we dont know?. Actual usable capacity is 51kwh. ?

 

[siteguru]

When charging on my 7kW home EVSE I expect to get 90%+ efficiency, accounting for charging losses within the car. (The onboard AC-to-DC charger is not near 100% efficient - not at all. Plus there are other losses such as charging the 12V battery and powering other systems during charging). With my EVSE app I can see exactly how much kWh has been supplied to the car. Every time I've charged, if I multiply the supplied kWh by 0.9 the resulting kWh figure bears a close relation to the usable capacity of my SE SR (50.7kWh).

I rarely look at the battery tile screens as I don't think those figures make any real sense - I prefer to use real-world end-to-end figures as per above.

 

[dam92]

Depends on which figures you give most credence to. 33% around 1kwh loss or the 17kwh used figure ? Of course neither could be accurate to the degree you are looking for , on another day it could be the other way around. Did I mention it would drive you crazy?

Yes but chargers should be somewhat accurate isnt it. Obviously charger cannot be 5kwh off? If its this far off, that particular charger network is overcharging customers which should be llegal.
Either that, or MG calculations are wrong. We have to trust the charger figures.

 

[dam92]

When charging on my 7kW home EVSE I expect to get 90%+ efficiency, accounting for charging losses within the car. (The onboard AC-to-DC charger is not near 100% efficient - not at all. Plus there are other losses such as charging the 12V battery and powering other systems during charging). With my EVSE app I can see exactly how much kWh has been supplied to the car. Every time I've charged, if I multiply the supplied kWh by 0.9 the resulting kWh figure bears a close relation to the usable capacity of my SE SR (50.7kWh).

I rarely look at the battery tile screens as I don't think those figures make any real sense - I prefer to use real-world end-to-end figures as per above.

Yes. This makes much more sense.
Get the miles driven, gethe kwh figure from charger and use it to do our own estimates.

That being said, i still find 90% efficiency is quite poor for a modern power electronic equipment. Specially in automotive applications. I know this because i design those kind of converters.
We get 90% efficiency figures with very old IGBT based converters.
Modern SIC or Mosfet based ones should have more than 95%.
I dont know what MG has inside.

 

[Bam Bam]

MG4 has a maximum charging rate of 6.6kWh, so whatever your charger reports, the car itself will only be putting 6.6kWh into the battery.

As siteguru says, it will be somewhere between 89%-92% efficient.

I expect there are losses in the charger unit itself (don't they get hot?) and within the car itself converting from AC to DC.

I wouldn't put too much faith in what the car reports for its usage. It is quite possible it is not measuring everything accurately.

If you really want to get accurate figures then you could get an OBDB dongle like Tesla Bjorn does. Otherwise just accept it is an average EV in terms of efficiency and don't worry too much.

 

[dsr]

My experience is that, after a while, you come to understand how the GOM works, based on recent driving and other factors, and prefer to trust the computer in your brain. A recent example. I charged from 18% to 100% for a long run, with the GOM showing 348 miles (I wish!). After my long journey I charged from 18% to 80% - GOM at 224 miles.
Brain computer reckoning. My long journey was an airport run, largely dual carriageway with a need to drive at 70mph or thereabouts. I’m not going to get much more than 3 miles a kWh; I managed 3.2. Today I have done an 80 mile round trip, much of it on bendy B roads. I hoped to get 4 miles a kWh - 4.2 achieved.
Generally, I find that if I think distance, road type and busyness, car load, temperature and weather generally, I can plan confidently and ignore any GOM prediction.

 

[dam92]

MG4 has a maximum charging rate of 6.6kWh, so whatever your charger reports, the car itself will only be putting 6.6kWh into the battery.

As siteguru says, it will be somewhere between 89%-92% efficient.

I expect there are losses in the charger unit itself (don't they get hot?) and within the car itself converting from AC to DC.

I wouldn't put too much faith in what the car reports for its usage. It is quite possible it is not measuring everything accurately.

If you really want to get accurate figures then you could get an OBDB dongle like Tesla Bjorn does. Otherwise just accept it is an average EV in terms of efficiency and don't worry too much.

Im sorry but i find it hard to accept 10kwh loss from a 61kwh capacity as average.

My experience is that, after a while, you come to understand how the GOM works, based on recent driving and other factors, and prefer to trust the computer in your brain. A recent example. I charged from 18% to 100% for a long run, with the GOM showing 348 miles (I wish!). After my long journey I charged from 18% to 80% - GOM at 224 miles.
Brain computer reckoning. My long journey was an airport run, largely dual carriageway with a need to drive at 70mph or thereabouts. I’m not going to get much more than 3 miles a kWh; I managed 3.2. Today I have done an 80 mile round trip, much of it on bendy B roads. I hoped to get 4 miles a kWh - 4.2 achieved.
Generally, I find that if I think distance, road type and busyness, car load, temperature and weather generally, I can plan confidently and ignore any GOM prediction.

Thats pretty good milage. Can i please ask what kwh that charger was showing when you did that charge?.

 

[Bam Bam]

Im sorry but i find it hard to accept 10kwh loss from a 61kwh capacity as average.

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.