[Steve Macfarlane]

I purchased a second hand first gen Ioniq a few months ago and I love the car - it's so easy and relaxed a drive and, of course, finally doing zero-emissions driving puts a smile on my face

However, I've noticed that the car's reported m/kWh consumption figures are always lower than my calculations. Has anyone else had this issue and any idea why?

For example, I recently did a round-trip of exactly 400 miles with four rapid charges on the journey plus a slow charge at home before and after. The car reported a trip consumption of 4.4 m/kWh, but my calculations (I use the FuelIO app to log my charges) give a figure of 4.1 m/kWh. Why does the car report so much better a figure?

My calculations are below (and attached) if you want to check the details...

FuelIO data

FuelIO calculations

My calculations

Date

Odometer

Charged kWh

End %age charge

mi/kWh

Mileage since last charge

Cumulative mileage

End capacity kWh

Start capacity kWh

Capacity used for this trip kWh

mi/kWh

Time stopped mins

Est. Time Charging hours

Charging speed kW

10-Jun​

84726​

17.12​

74%​

4.38​

20.72​

3.6​

26-Jun​

84759​

15.85​

100%​

3.88​

33​

33​

28​

12.15​

8.57​

3.85​

Ubitricity @home

27-Jun​

84850​

17​

86%​

4.34​

91​

124​

24.08​

7.08​

20.92​

4.35​

38​

0.47​

36.4​

Rapid - Polar

27-Jun​

84946​

24.1​

92%​

4.3​

96​

220​

25.76​

1.66​

22.42​

4.28​

46​

0.68​

35.3​

Rapid - Ecotricity

27-Jun​

85031​

18.1​

81%​

3.98​

85​

305​

22.68​

4.58​

21.18​

4.01​

37​

0.53​

33.9​

Rapid - Polar

27-Jun​

85083​

15.127​

88%​

3.97​

52​

357​

24.64​

9.513​

13.167​

3.95​

27​

0.28​

53.4​

Ultra - Polar

30-Jun​

85159​

18.84​

85%​

3.85​

76​

433​

23.8​

4.96​

19.68​

3.86​

3.38​

5.6​

Ubitricity @home

Total journey 27-June (no mileage since):

400​

97.367​

4.11​

Car reports

4.4​

 

[Hitstirrer]

Perhaps it's about the losses in wall to car charging. The house and Rapid meters will record the kWh's dispensed but not all of that arrives in the battery due to resistance and heat losses. Your own calcs are based on the house meters but the car bases it on the number of kWh's that it receives. So that your own calcs of miles divided by the house meter kWhs will show a lower figure than the car because that manages to travel 400 miles using the lesser amount of kWh's that actually arrive there.

A guess. But sounds plausible to me.

 

[Derekosb]

The only suggestion I have is that your consumption calculation is based on amount of energy to recharge, which will include any charging losses.

The car is calculating on energy used.

Charging losses can be as high as 10% which might explain your discrepancy.

HTH,

Derek

 

[IoniqHugh]

Like Derek & Hitstirrer, I believe there are some charging losses that might account for a proportion of this. Out of interest, what is the data source for End and Start Capacity? I note that they some are to three decimal places, and I can't work out what will give you such accurate figures. Also the one entry of exactly 28 kWh I presume is just taken from the nominal capacity of the battery. I'm wondering whether the data sources in total add up to an additional proportion of variation against actual. I should add that I have admitted elsewhere on this forum, that I am a bit thick when it comes to numbers so I would trust more enlightened responses over mine
I have just completed an almost identical distance (124 +88 + 88 + 124 if my memory serves me) with all necessary data so I will try and replicate and see what mine calculates to when the better half comes back with the car.

 

[DBMandrake]

Yes, calculating miles/kWh based on power use measured from the chargers will give a different, lower figure than the cars own figure. But both are valid in different ways.

As mentioned above there are some losses in charging. In the case of AC charging the onboard charger in the car may only be 80-90% efficient tops. At 80% efficiency that means for every 10kWh that goes into the battery, 12kWh is drawn from the wall, the rest went up in heat in the on board charger, running cooling fans / AC to cool the battery during charging, or into fixed overheads in the cars electronics systems, which could be a few hundred watts during a charge session. Battery charging losses in the actual battery itself at charge rates 7kW and below are negligible (less than 1% in one of my calculations) so can be ignored especially if the onboard charger has an unknown efficiency somewhere in the 80-90% range.

These losses makes the miles/kWh figure look worse when calculated based on power use from the wall. 80% is actually typical of many EV onboard chargers, but the Ioniq might be a bit better than this in which case the figures would be closer.

For DC rapid charging we presume that the kWh dispensed is measured at the output of the rapid charger, which is after the AC/DC conversion losses in the charger. So the losses in the rapid charger itself are not counted against the car, (unlike AC charging) however due to the high charge rate there will be resistance losses in the battery itself, the cables, connectors etc... on a 43kW rapid charge this could amount to approx 3% in some rough calculations I did on my Ion.

So which figure is valid ? Both, as long as you understand the difference.

The figure the car calculates is based on how far it can drive for a given kWh being discharged from the battery. This figure does not include charging losses, and losses in the battery itself during charge or discharge, which are highest at high charge/discharge rates. It's simply a measure of energy coming out of the battery propelling you a certain distance. This figure is useful to calculate anticipated range based on a known usable battery size and miles/kWh consumption, and is the figure most people will quote when they compare miles/kWh between different cars and driving styles.

The figure you're getting by monitoring the kWh dispensed at the wall or rapid charger is an indication of how much you will pay for your electricity per mile, with all efficiency losses that you would be charged for included. This is the figure you would use if you were calculating running costs.

 

[Steve Macfarlane]

Like Derek & Hitstirrer, I believe there are some charging losses that might account for a proportion of this. Out of interest, what is the data source for End and Start Capacity? I note that they some are to three decimal places, and I can't work out what will give you such accurate figures. Also the one entry of exactly 28 kWh I presume is just taken from the nominal capacity of the battery. I'm wondering whether the data sources in total add up to an additional proportion of variation against actual. I should add that I have admitted elsewhere on this forum, that I am a bit thick when it comes to numbers so I would trust more enlightened responses over mine
I have just completed an almost identical distance (124 +88 + 88 + 124 if my memory serves me) with all necessary data so I will try and replicate and see what mine calculates to when the better half comes back with the car.

Yes, you could be right about those variations, since the end capacity is what the car reports as a %age and the start capacity is calculated from that minus the charge that the charger reports it has delivered, all based on the nominal 28kWh = 100%. The charging losses will certainly introduce some significant differences here that I hadn't thought about. I'll be interested to see how your own values compare!

 

[Steve Macfarlane]

Thank you, everyone, for detailed and speedy responses

Yes, your thoughts about losses in charging make total sense and I had not even thought about that, I must confess. I understand that both sets of figures have value, but for different reasons. Apart from using my comparative figures, is there any easy way to find out the efficiency of the onboard charger or do I just need to track two sets of figures, recording the car's reported figures after each journey or charge as well as the input figures from the chargers? I ask because I like to keep track of my consumption rates and with an ICE it was easy to enter fill-up figures into an app or spreadsheet and get accurate fuel consumption mpg values, but now I see that the same cannot be done for an EV because of the losses in charging. Any suggestions?

 

[Hitstirrer]

....... I like to keep track of my consumption rates..........

All depends on your motive for this tracking. If it's just for interest then using either metric consistently will give valid comparisons. Just don't mix the two.

However, if you are trying to calculate to three decimal places the pence per mile that raises problems if charges are a mix of home and away. Rapid costs are clear and visible but not many people have independent meters to log the kWh's dispensed from the home mains. And using the cars' information gives an inaccurate and low figure.

Your present spreadsheet would seem to be sufficiently detailed to give a good indication of consumption rates for most purposes and I would suggest that no further action is required to refine it just to gain academic accuracy.

 

[Steve Macfarlane]

All depends on your motive for this tracking. If it's just for interest then using either metric consistently will give valid comparisons. Just don't mix the two.

However, if you are trying to calculate to three decimal places the pence per mile that raises problems if charges are a mix of home and away. Rapid costs are clear and visible but not many people have independent meters to log the kWh's dispensed from the home mains. And using the cars' information gives an inaccurate and low figure.

Your present spreadsheet would seem to be sufficiently detailed to give a good indication of consumption rates for most purposes and I would suggest that no further action is required to refine it just to gain academic accuracy.

Actually Hitstirrer, I can track kwH dispensed "at home" because my "at home" charging is from an Ubitricity lamp-post charger in the street outside my house, since I don't have off-road parking, so I can track the actual costs very accurately!
I'd love to be able to use the figures for re-fuelling to give me accurate m/kWh consumption figures, but without knowing the losses in the onboard charger, which I suspect will vary with temperature and maybe other parameters, I suppose I will just have to note down the car's reported consumption figures separately (unless anyone knows the efficiency/loss figures for the Ioniq charging?).
And, yes, both are for academic interest, as I like to track such things and seeing how efficiently I can drive the car is a day-to-day challenge I enjoy Thanks.

 

[Lutek1000]

Hi @Steve Macfarlane

I am after first gen Ioniq and hopefully you can give some advice.
I can see your car has covered nearly 90000 miles. Personally I am sceptical about buying a high mileage car.
Would you say it is safe and fine to go for higher mileage Ioniq?
If you could share your point of view from your own experience.
Was the mileage during your trip the maximum, or close to maximum, what car could achieve?
I'd appreciate your opinion.

 

[GMat]

The only thing I will mention, nobody seems to have considered what the car put back into the battery through regeneration. But don't ask me what the calculations would be because I wouldn't know where to start.

 

[Hitstirrer]

I suppose I will just have to note down the car's reported consumption figures...........

In my classic 28 kWh Ioniq I have always found the cars predictions and actual results to be pretty much spot on. The other day was the first time that I doubted it when it predicted 153 miles available after a full overnight charge. The car has only been used for misc 20 mile local trips during this period and had built up a good history of 5.3 to 6.1 miles per kWh journeys operating from no more than 50% SOC. No way will it go 153 miles said I as I planned an 84 miles round trip with 80% motorway driving. However, I got back with 70 miles left. OK, I was on adaptive cruise only set at 66mph indicated that sometimes slowed down to match traffic. Also, it was a warm dry day but that was unexpected and at well over 5 miles per kWh over 84 miles mixed driving that was impressive. And I then believed the car when it said I could have gone another 70 miles.

 

[Steven4]

You might avail yourself of very detailed charging and driving statistics available through diagnostic port, using Car Scanner ElmObd2 app Android / iOS.

If you compare stats from Car Scanner and Ubitricity, you could probably calculate the charging losses or other data discrepancies.

 

[Steve Macfarlane]

Hi @Steve Macfarlane

I am after first gen Ioniq and hopefully you can give some advice.
I can see your car has covered nearly 90000 miles. Personally I am sceptical about buying a high mileage car.
Would you say it is safe and fine to go for higher mileage Ioniq?
If you could share your point of view from your own experience.
Was the mileage during your trip the maximum, or close to maximum, what car could achieve?
I'd appreciate your opinion.

HI Lutek1000. All I can tell you about my car is that I have had no problems with it. Range predictions are accurate and 80-90 miles between charges at motorway speeds is about right - it's not worth the risk of running the battery down too low - I've done it once and ended up in 'turtle' mode just before coming off the motorway - that is not a safe thing to do! I have learnt from that error! And, of course, rapid charging slows down quite a bit after 80% and will only top up to 94% max, so you can't really use the full 100% range of the car on a long journey. As others have said though, the predicted range is very accurate on the Ioniq - only in the last ten miles does it run down more quickly than you'd expect.
For me, I purchased this car as it was the cheapest 1st gen Ioniq I had ever seen - because of the high mileage. But it had only one previous owner and is in excellent condition. Most importantly, I could afford it

 

[Steve Macfarlane]

In my classic 28 kWh Ioniq I have always found the cars predictions and actual results to be pretty much spot on. The other day was the first time that I doubted it when it predicted 153 miles available after a full overnight charge. The car has only been used for misc 20 mile local trips during this period and had built up a good history of 5.3 to 6.1 miles per kWh journeys operating from no more than 50% SOC. No way will it go 153 miles said I as I planned an 84 miles round trip with 80% motorway driving. However, I got back with 70 miles left. OK, I was on adaptive cruise only set at 66mph indicated that sometimes slowed down to match traffic. Also, it was a warm dry day but that was unexpected and at well over 5 miles per kWh over 84 miles mixed driving that was impressive. And I then believed the car when it said I could have gone another 70 miles.

Yes, I agree the GOM is accurate, apart from the very last ten miles, when it runs down quickly. I will be trying to avoid that in future...!

 

[Steve Macfarlane]

You might avail yourself of very detailed charging and driving statistics available through diagnostic port, using Car Scanner ElmObd2 app Android / iOS.

If you compare stats from Car Scanner and Ubitricity, you could probably calculate the charging losses or other data discrepancies.

View attachment 132445

Thanks, Steven4. I do have an OBD2 connector, but I have only once managed to connect it to an app on my phone - it was canIoniq. I shall take a look and see what figures it gives me. Good idea.

 

[DBMandrake]

The only thing I will mention, nobody seems to have considered what the car put back into the battery through regeneration. But don't ask me what the calculations would be because I wouldn't know where to start.

Regeneration doesn't need to be separately considered.

Miles/kWh reported by the car already includes the effects of regeneration. For example if the total kWh discharged from the battery is 30kWh and 5kWh of regeneration goes back into the battery during the same driving session, the net discharge (ignoring losses) is 25kWh and this is the figure that goes towards calculating the miles/kWh.

In essence, power regenerated goes into increasing the overall miles/kWh attained. Regeneration itself has a round trip efficiency as well from wheel to battery back to wheel, (something like 70%) but that's really getting into the weeds.