Sorry I don’t have an answer for the difference. Heard lots of theories over the years but non have made the numbers tally.
My guess is both are cheap measuring devices aren’t accurate so don’t tally.
The leaf app I was once told is power used by drive motor excluding lights heating lights etc.
I once charge my car at home for four hours drove round until car was at pre charge %. Smart meter less background was 29 kw, smart charger 25kw and ar app 22 kw. Think they are just a guide like using a pine cone to predict when it’s going to rain.
Charger boxes measure amount Kw purchased including 10% or some other number plucked out of fantasy land for losses during process.
Smart meter numbers don’t come out the same as either of above.
If you find an answer please share as no one really knows but everyone has a theory.

 

Welcome to the murky world of losses. The reason I say "murky" is because they are very real, cost real money and yet they are rarely mentioned. During the charging process, you will note that cables and plugs are warm and the charger is warm, but, if you lift the bonnet, you will find that the radiator is hot! The 12% that you are losing from invoice meter to battery is fairly typical and measuring accuracy is probably quite good. Unfortunately, you will also get a similar loss from battery to road wheels. So, when calculating power cost per mile, the real cost is not what car or App tells you as much of the losses are ignored.

 

Wow, so it is literally down to losses. I hadnt realised it'd be so much.

So another question then. Using November as the example again. The cost to charge car in total was £75 (give or take a few pence) according to the charger app whilst the car app states £66. So essentially due to these losses and given the same mileage I will lose the energy and cost of a full top up each month?. which would be around 2600 miles each year or £110(ish)

Am I right in saying that whilst the charger records £75 worth of energy given to the car, the car will see only £66 worth because of these losses? - Im just checking that my 6am brain has woken up!

 

You are correct its losses during adding or taking power out of a battery. Please don’t take the smart charger as being accurate they aren’t tested and calibrated by an independent body like petrol and diesel pumps. It’s the amount used and recorded on your electricity meter that is the actual figure used to calculate pence per mile. That is a lot more expensive than car manufactures dash board or app are telling you.

The lost electricity isn’t a constant figure for each month as temperature of battery pack varies day to day due to air temp and how car has been driven. I guess the two extremes are air temp around 22 degrees C and plugging in to charge as soon as arriving home from over 100 miles of driving in one hour of charging the car battery % increases a lot more than when air temp minus 5 degrees C with car left parked for a few days before starting charging battery.

A friend of mine often keeps his car in a heated workshop in winter when at work at around 18:degrees C for forty hours a week and he claims when he gets home in winter his battery charging is as efficient as it is in summer .


Claims of miles per kilowatt or pence per mile are just a guide and if you multiply a weeks figures by 52 or a months figures by 12 you end up with a very misleading figure. Our old transport manager used to say his estimated fuel uses for the fleet of vehicles was a pure guess and the finance guy had to take medication for his blood pressure when trying to predict next years costs and blamed any inaccuracy on the poor transport manager.

 

Sunstoner, I'm afraid that it is all about losses. From my own observations, your 12% loss is actually a bit on the low side and if you do the measure a few times with closer attention, you will probably get a higher number. Troy's advice re battery temperature is spot on though he is perhaps overly negative on the measuring accuracy of the charger; sure, it doesn't have official calibration but measuring electronics are cheap and very good. As a matter of interest, your losses with the Granny Charger will be even higher as the ancillary and parasitic losses such as running circulation pumps and fans represents a higher percentage of total power. Its not just battery in/out that creates losses, of course. Across the wires, breaker, charger and connectors you will lose over 2% and the rectifier that converts AC to DC is quietly chucking out 3% or more and who ever mentions that? Your financial brain was in gear at 6am though don't worry about what the battery sees as key is miles travelled for the £75. After all, the road wheels will see less than the battery. However, think about when you bought hydrocarbon; you happily drove along throwing over half of the energy away!

 

Sorry to go off topic but wonder how many people on here know what a trolleybus was. My father drove these electric double decker buses in the 1950s and said its best feature was that you could follow the overhead cables in heavy fog and find your way. He was driving electric vehicles seventy years ago never thought of him as a trend setter!

 

Bradford, like many cities, had trolleybuses. The city is in a great depression with steep hills out from the centre. The electric buses went up the hills as if they were barely there but the diesel buses that replaced them used to crawl up in low gear. Of course, in those days, diesel buses didn't come with 20 or 30 hp/tonne.