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Discussion Starter #1
Has anyone else calculated the charging efficiency of their car's charger?

I have CT clamps and voltage sensor monitoring 3 home electricity feeds: Grid, Solar and Consumer unit. Using those, I can calculate Pod-point charger actual usage. I understand my CT clamps can be inaccurate, but it should still give us a guideline figure.
Car usage stat comes from Nissan CarWings telemetric. I've been sure to click "OK" everytime start up the car. All trips are recorded as far as I can see.
For calculation, I took 13th morning at 80% to 22nd morning at 80%. So sum of 14th to 22nd kWh-per-day; whereas driving data is sum of 13th to 21st.


75.4 kWh car telemetric vs 93.75 power delivered from the meter => 80% charging efficiency?
For the 281.4 miles driven, that means I only got 3 mi/kWh from grid to wheels. :(
Is that right?


Car manufacturers must know their AC-DC charger efficiency, why none of the published figures and testing method take that into account?
You go buy petrol, the calculated MPG from fuel vs mileage is usually very close to the car computer calculation. Should we expect the same from EV's?

It feels like it's an area that should be included in the car's efficiency figure, an area that should be visible to consumer and any improvement is celebrated.
 

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Discussion Starter #4 (Edited)
I'd thought the efficiency reading provided by the car would include power losses in traction battery to inverter to motor, heating and aux power consumptions, etc?

Good way to test is to turn on max heating for significant amount of time and see what the car telemetrics record.

Either way, point is, the efficiency reading should include EVERYTHING. Similar to how petrol MPG includes everything, from the pump.




Power factor is close to 1 when charging, because charging is a resistive load. The kit I'm running will also calculate power factor by measuring phase difference between voltage and current. I've calibrated the voltage sensor. I've got the system running for over 2 weeks now, so far, looking at the total consumption, its accuracy when compared to consumption meter is over 95%.

The inaccuracy I talked about is due to the solar production used in calculation is on 100 amp CT sensor range, but peak production for my system is only 12 amp. Due to calculation is sum of 3 CT readings, it usually reports outdoor -5 to -10w when no load is outside.

==== Edit:
Checked last night, I had a photo of the meters when I initially set up the CT sensor system. Where its cumulative all-time readings are all 0.
  • Electricity grid reading is over 98% accurate, less than 2% lower than meter reading.
  • Solar generation reading is 95% accurate, 5% less than generation meter reading.
 

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Don't they include this in all the major efficiency tests now? I'm sure the American MPGe number is based on energy only measured at the wall with an AC charger.
 

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Discussion Starter #6
Don't they include this in all the major efficiency tests now? I'm sure the American MPGe number is based on energy only measured at the wall with an AC charger.
Another reason to use the EPA rating rather than the totally useless NEDC and useless WLTP.


The 2014 Leaf said to have 3.33 mi/kWh, which is plausable. My lifetime efficiency is a hair over 4 mi/kWh according to car telemetrics. 80% of that is 3.2 mi/kWh.
 

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Discussion Starter #8
Is it? I assumed the ac-dc coils would make it an inductive load.
The article posted above agrees with you. This has gotten me to question this. Having added power factor to logging, I shall get back to you with power factor graph of my car charging over tonight.

The real power comes out of my CT sensor unit is very close to apparent power by simply multiplying amp and voltage. So I thought charging a battery will give close to 1 power factor.
 

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Has anyone else calculated the charging efficiency of their car's charger?
Yes, I've measured the efficiency of the on board charger in my Ion at 2kW. (granny charger speeds...)
I have CT clamps and voltage sensor monitoring 3 home electricity feeds: Grid, Solar and Consumer unit. Using those, I can calculate Pod-point charger actual usage. I understand my CT clamps can be inaccurate, but it should still give us a guideline figure.
Car usage stat comes from Nissan CarWings telemetric. I've been sure to click "OK" everytime start up the car. All trips are recorded as far as I can see.
For calculation, I took 13th morning at 80% to 22nd morning at 80%. So sum of 14th to 22nd kWh-per-day; whereas driving data is sum of 13th to 21st.


75.4 kWh car telemetric vs 93.75 power delivered from the meter => 80% charging efficiency?
For the 281.4 miles driven, that means I only got 3 mi/kWh from grid to wheels. :(
Is that right?
Unfortunately that's probably about right. The figure I got for my Ion was about 80% as well, based on measuring the power drawn from the wall with a digital kW meter vs the reported DC charge current and voltage at the battery from the car's own BMS retrieved using an ODB-II diagnostic tool. There is some uncertainty in the measurement of course but I reckon it'll be 80% +/- 5%.

My figure does not include losses in the battery itself either, (since I was measuring current going into the battery) however I've calculated those based on cell resistance to be only a small fraction of a percent at 2kW - cell resistance losses only start to become a factor at rapid charging speeds, or during discharge while driving.

@andrew*debbie 's 95% figure is theoretically achievable, however I doubt that many if any EV's achieve this in practice.
Car manufacturers must know their AC-DC charger efficiency, why none of the published figures and testing method take that into account?
You go buy petrol, the calculated MPG from fuel vs mileage is usually very close to the car computer calculation. Should we expect the same from EV's?

It feels like it's an area that should be included in the car's efficiency figure, an area that should be visible to consumer and any improvement is celebrated.
I think it simply comes down to the fact that improving the efficiency of the onboard charger of an EV past the 80% which is easily achievable does nothing to increase the all important figure - range. Sure it means you draw slightly less power from the wall so electricity costs you less, but EV's are so ridiculously cheap to "fuel" already using a residential tariff that I don't really care whether my 1000 miles of driving per month cost me £30 in charging or £27. In short people care a lot about the range of their EV but not much about the exact cost of charging it, except that it is already very cheap compared to Petrol/Diesel so a few percent here or there makes no odds.

Would you buy a car with a 95% efficient onboard charger instead of 80% if it would cost you £1000 more and not have any additional range ? Better engineering doesn't come free. Would you buy a car with a 95% efficient onboard charger that cost the same but had 10% less range because they had to skimp on the batteries to meet the same target price with the more expensive charger ?

These are the kind of decisions manufacturers have to make and at this point in time range is king and getting costs as low as possible is king. A few years from now when EV's are at price parity or cheaper than ICE and batteries are large and have lots of range, manufacturers may turn their eye towards the charger efficiency and start to optimise that, and that also helps by reducing power dissipation while charging. But for now I think it's low on their priority list and range and price reduction are at the top of their priority list.
 

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Discussion Starter #11
Thank you. So 80% is all that can be expected from first generation EV :(


True that range is king at the current moment in time, but it shouldn't be. Part of the movement into EV is about getting more out of energy, so I think efficiency should be king.

If the shorter range, but better engineered car will meet my daily range needs or my usual long journey hop length, whichever longest. If there's sufficient charging infrastructure and it recovers the hop length in sufficient time. I would actually choose the shorter range car.

But I understand my way of thinking is minority. Perhaps this is why people buy stupidly big "tractors" for local trips to the school.
 

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If the shorter range, but better engineered car will meet my daily range needs or my usual long journey hop length, whichever longest. If there's sufficient charging infrastructure and it recovers the hop length in sufficient time. I would actually choose the shorter range car.

But I understand my way of thinking is minority. Perhaps this is why people buy stupidly big "tractors" for local trips to the school.
I agree, and hope that the maximum spacing between Rapids reduces faster than the range of my 13 reg Leaf.
 

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Thank you. So 80% is all that can be expected from first generation EV :(
I don't think there are many figures around for different models so only by measuring it ourselves would we know. Both cars are what I'd call first generation so the situation may have improved recently.
True that range is king at the current moment in time, but it shouldn't be. Part of the movement into EV is about getting more out of energy, so I think efficiency should be king.
Don't get me wrong, from an engineering perspective I agree chargers should be at least 90% efficient and it's certainly doable because the drive inverters are usually 90-95% efficient despite being much higher power more complicated devices than an onboard charger...

But I think that only serves to illustrate my point - optimising the efficiency of the drive inverter (and motor for that matter) improves range and performance, and manufacturers are trying to squeeze every drop of range out of the "small" batteries currently available, so a lot of effort has been expended on optimising the drive inverter. Spending the same engineering effort on onboard charger efficiency doesn't improve range or driving performance, so there is less incentive to do it.

It's a simple matter of priorities and engineering return on investment. I think that will eventually change though.
 

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Given that some car systems are on during charging, and thus using power, I'd expect 2kW charging to be somewhat inefficient. The charging circuits themselves may have fixed losses too.
At 7kW they will likely be better, possibly the 90% mooted as being more acceptable.
 

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Discussion Starter #18
Given that some car systems are on during charging, and thus using power, I'd expect 2kW charging to be somewhat inefficient. The charging circuits themselves may have fixed losses too.
At 7kW they will likely be better, possibly the 90% mooted as being more acceptable.
That's an excellent point. The faster the charger, the smaller percentage any other electronic drain will be.

At my Leaf's 3.3kW, the difference between 80% and 90% is 330w, entirely possible for the car aux computers to be using.
 

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Given that some car systems are on during charging, and thus using power, I'd expect 2kW charging to be somewhat inefficient. The charging circuits themselves may have fixed losses too.
At 7kW they will likely be better, possibly the 90% mooted as being more acceptable.
Good point, there will be some overhead due to other systems like heating/cooling of the battery (although not in the case of the Ion as it doesn't do this on an AC charge) and the coolant pump for the onboard charger - which does run during AC charging on the Ion, albeit very intermittently, about 30 seconds every few minutes. Also large contactors have to be held closed while the battery is charging, this uses some power too.

When the car is in ready to drive mode sitting in neutral with heating etc off "parasitic" power drain is around 300 watts so it may be similar during charging.

Ultimately though this all counts towards "charging efficiency" even if the onboard charger itself isn't responsible for all of the losses.
 

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Discussion Starter #20
Is it? I assumed the ac-dc coils would make it an inductive load.
Here is the power factor plot for overnight charge of my Leaf. There are 2 charging sessions: first is timed to 80%, second starts at 3:30 to charge to 100%. You can see when charging, the recorded power factor is 1.
35ACBEA9-8A6A-4BF7-95AD-4413BD25DA69.png
 
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