EV Discussion thread

MeteredOut

I logged every charge individually, what was recorded as input to the car and what was recorded as use by the plug.  Overall, the kWh as shown on the Tesla app 516 kWh and shown by the power monitor plug 594 kWh.

That suggests the granny charger has a touch over 13% losses ((594-516)/594), which isn't too far away from the 15% your mileage based calculation provided.

I've recently got our first EV and still only using the granny charger (I can also charge for cheap at work so am still working out if its worth paying for a "proper" charge). I'm going to the same power monitor analysis with our next charge. I do wonder if different granny chargers have different losses, or if there will be different losses at different charge rates (the one I have can charge a 6A, 10A or 13A).

Grumpy_chap

JKenH said:

Hmmm! That would suggest that charging from the home charger was virtually 100% efficient. I kWh gives you 3.54 miles of range at the 85% efficiency of your granny charger. If your granny charger was 100% efficient you would get 4.16 miles. Your home charger, therefore based on this data has an efficiency of 99.5%. 

Yes, I did do that reverse calculation after I posted earlier and I was a bit unsure.
I have been keeping a spreadsheet, so will revisit it.
I also take screenshots and photos of mileage very regularly.
Need to pop off now as the MiL has just turned up

Grumpy_chap

@michaels
@JKenH
Thanks for your observations - I think there was an error in the split of granny charger versus home charger miles.

I have kept a detailed spreadsheet of charges using the granny charger but decided to only record monthly data in totals for the home charger.  Partly because the home charger allows that, partly because that is less effort and partly because aggregate is more useful than individual charges (where variables can have a proportionately larger impact).

The last entry for the spreadsheet on the granny charger was 23rd September at 2,108 miles. 
Total plug 594.44 kWh
Total car 516 kWh
15.2% charging loss on that occasion.

The home charger was installed on 27th September.
I have been through my screen shots and I did a charge on 27th September.  Car says 37 kWh.
In my photos for the same day, the home charger meter says 39.85 kWh.
That would be a charging loss of 7.7% (which is more akin to what I have read from other posters).
I also have mileage recorded from the evening of 26th September at 2,304 miles (recorded because it was a business journey).

This means my previous figures need correcting:

Grumpy_chap said:

Granny charger.  2,108 miles.  594 kWh.  3.54 miles / kWh
Home charger.   1,598 miles.  383 kWh.  4.14 miles / kWh

This should be:
Granny charger.  2,304 miles.  594 kWh.  3.87 miles / kWh
Home charger.  1,402 miles.  383 kWh.  3.66 miles / kWh
The car is currently (in that data set at 2nd November) "full" so I think I need to wait until the end of November to get a representative "home charger" figure which will be "full-to-full".

I could just do a charge to full now, but it is raining cats-n-dogs out there

MeteredOut said:

I do wonder if different granny chargers have different losses, or if there will be different losses at different charge rates (the one I have can charge a 6A, 10A or 13A).

I don't know how apparent any variance will be between one rate of "slow" and another rate of "slow", but the consensus of views that I have read suggest that charging faster is more efficient than charging slower.  

Martyn1981

GC, very interesting. So I'm sorry if this seems pedantic.  I'm only mentioning it so that comparisons can be made more broadly with others / other sources, but shouldn't you be dividing the lost energy by the gross energy figure to get the percentage loss?

Eg  594.44 - 516 = 78.44 / 594.44 = 0.13 x100% = 13% loss
and  39.85 - 37 = 2.85 / 39.85 = 0.07 x 100% = 7% loss

Grumpy_chap

Martyn1981 said:

GC, very interesting. So I'm sorry if this seems pedantic.  I'm only mentioning it so that comparisons can be made more broadly with others / other sources, but shouldn't you be dividing the lost energy by the gross energy figure to get the percentage loss?

Eg  594.44 - 516 = 78.44 / 594.44 = 0.13 x100% = 13% loss
and  39.85 - 37 = 2.85 / 39.85 = 0.07 x 100% = 7% loss

Possibly.
I just did the simple calculation:
594.44 / 516 = 1.152 so 15.2% of what was drawn from the plug did not make it to the car
39.85 / 37 = 1.077 so 7.7% of what was drawn from the plug did not make it to the car

Yours is the inverse calculation.  (516 / 594.44)

EDIT - I agree that my calculation was incorrect.  Thank you for the correction.

I am not sure how particular this needs to be, especially given that the car only reports in complete kWh.  That can have a massive difference in the loss that is recorded.
39.85 kWh from plug and 37.00 kWh into the car (7ish percent loss) is a lot worse than 39.85 kWh from the plug and 37.99 kWh into the car (5ish percent loss).

The important thing to know is that the home charger is more efficient than the granny charger.

It is also why I think longer term miles / kWh is more useful than individual charges.  Any variables (such as weather or vampire losses) are magnified in a single charge cycle but mitigated through the averaging of several cycles.

michaels

Grumpy_chap said:

Martyn1981 said:

GC, very interesting. So I'm sorry if this seems pedantic.  I'm only mentioning it so that comparisons can be made more broadly with others / other sources, but shouldn't you be dividing the lost energy by the gross energy figure to get the percentage loss?

Eg  594.44 - 516 = 78.44 / 594.44 = 0.13 x100% = 13% loss
and  39.85 - 37 = 2.85 / 39.85 = 0.07 x 100% = 7% loss

Possibly.
I just did the simple calculation:
594.44 / 516 = 1.152 so 15.2% of what was drawn from the plug did not make it to the car
39.85 / 37 = 1.077 so 7.7% of what was drawn from the plug did not make it to the car

Yours is the inverse calculation.  (516 / 594.44)

EDIT - I agree that my calculation was incorrect.  Thank you for the correction.

I am not sure how particular this needs to be, especially given that the car only reports in complete kWh.  That can have a massive difference in the loss that is recorded.
39.85 kWh from plug and 37.00 kWh into the car (7ish percent loss) is a lot worse than 39.85 kWh from the plug and 37.99 kWh into the car (5ish percent loss).

The important thing to know is that the home charger is more efficient than the granny charger.

It is also why I think longer term miles / kWh is more useful than individual charges.  Any variables (such as weather or vampire losses) are magnified in a single charge cycle but mitigated through the averaging of several cycles.

This is so useful having actual real world data, thank you - the manufacturers should supply data on charge efficiency of their own supplied granny chargers but of course they don't....

silvercar

I lose 10-15% between Podpoint charger and Tesla. I know this because the OVO measures the charge received from the car and the podpoint app the amount delivered by the charger. 

1961Nick

Grumpy_chap said:

Martyn1981 said:

GC, very interesting. So I'm sorry if this seems pedantic.  I'm only mentioning it so that comparisons can be made more broadly with others / other sources, but shouldn't you be dividing the lost energy by the gross energy figure to get the percentage loss?

Eg  594.44 - 516 = 78.44 / 594.44 = 0.13 x100% = 13% loss
and  39.85 - 37 = 2.85 / 39.85 = 0.07 x 100% = 7% loss

Possibly.
I just did the simple calculation:
594.44 / 516 = 1.152 so 15.2% of what was drawn from the plug did not make it to the car
39.85 / 37 = 1.077 so 7.7% of what was drawn from the plug did not make it to the car

Yours is the inverse calculation.  (516 / 594.44)

EDIT - I agree that my calculation was incorrect.  Thank you for the correction.

I am not sure how particular this needs to be, especially given that the car only reports in complete kWh.  That can have a massive difference in the loss that is recorded.
39.85 kWh from plug and 37.00 kWh into the car (7ish percent loss) is a lot worse than 39.85 kWh from the plug and 37.99 kWh into the car (5ish percent loss).

The important thing to know is that the home charger is more efficient than the granny charger.

It is also why I think longer term miles / kWh is more useful than individual charges.  Any variables (such as weather or vampire losses) are magnified in a single charge cycle but mitigated through the averaging of several cycles.

You'll find that the 'loss' increases with winter charging if you're charging it outside.

MY loss March - Oct is in the range 5.4% - 7.7%. Nov - Feb it's 9.8% - 10.4%.

I have one outlier which was July this year at 21.1% & I haven't a clue why. 

JKenH

michaels said:

Grumpy_chap said:

Martyn1981 said:

GC, very interesting. So I'm sorry if this seems pedantic.  I'm only mentioning it so that comparisons can be made more broadly with others / other sources, but shouldn't you be dividing the lost energy by the gross energy figure to get the percentage loss?

Eg  594.44 - 516 = 78.44 / 594.44 = 0.13 x100% = 13% loss
and  39.85 - 37 = 2.85 / 39.85 = 0.07 x 100% = 7% loss

Possibly.
I just did the simple calculation:
594.44 / 516 = 1.152 so 15.2% of what was drawn from the plug did not make it to the car
39.85 / 37 = 1.077 so 7.7% of what was drawn from the plug did not make it to the car

Yours is the inverse calculation.  (516 / 594.44)

EDIT - I agree that my calculation was incorrect.  Thank you for the correction.

I am not sure how particular this needs to be, especially given that the car only reports in complete kWh.  That can have a massive difference in the loss that is recorded.
39.85 kWh from plug and 37.00 kWh into the car (7ish percent loss) is a lot worse than 39.85 kWh from the plug and 37.99 kWh into the car (5ish percent loss).

The important thing to know is that the home charger is more efficient than the granny charger.

It is also why I think longer term miles / kWh is more useful than individual charges.  Any variables (such as weather or vampire losses) are magnified in a single charge cycle but mitigated through the averaging of several cycles.

This is so useful having actual real world data, thank you - the manufacturers should supply data on charge efficiency of their own supplied granny chargers but of course they don't....

I may be wrong but I was under the impression that the majority of the losses occur in the AC to DC conversion circuits onboard the car rather than in the “granny charger”. I would imagine it wouldn’t make much difference whether you used Tesla’s supplied charging cable or one from, say, Screwfix. 

MeteredOut

As another data point, when I charge at work, I get a bill showing kWh used/charged, and my car shows the % increase so I can work out the additional kWh stored in the battery. From that data, I've inferred a ~10% loss.

Now there is a margin of error in that because the car only shows in whole % points of battery charge, and what the car shows is not a 100% accurate representation of the actual kWh increase in the battery and it can actually go up or down 1% after charging has stopped and temperatures have change.