# Calculating on-board chargers efficiency

In this article I’ll show you how easy it’s to estimate the on-board charger efficiency of an electric car by using WLTP ratings.

I’ll use WLTP ratings in this article, but you can also use EPA or NEDC ratings, since they also measure plug-to-wheels consumption, this means that they include charging losses.

It’s important to notice that for measuring the consumption the charging was made by using a domestic socket at low current (10 A) and some on-board chargers are not very efficient at low currents.

Let’s start with some of Europe’s most popular electric cars.

**Renault ZOE**

**Range**: 395 km**Consumption**: 17,2 kWh/100 km (with charging loses)**Usable battery capacity**: 52 kWh

First we start by calculating the consumption without charging loses.

395 km – 52 kWh

100 km – X

X = 52 x 100 รท 395 = 13,164556962 kWh/100 km

Now if we divide that number with 17,2 kWh/100 km we’ll get the on-board charger efficiency.

Y = 13,164556962 รท 17,2 = 0,765381218722 = 77 %

It’s no secret that Renault’s Chameleon on-board charger is not very efficient at low currents. However, Renault does seem to have made its on-board charger more efficient in the new generation of the ZOE. Previously, the charging efficiency of the R90 models at 10 A was estimated at 71 %.

Now that you know the steps required to calculate the efficiency of an on-board charger, in next examples I’ll just show you the final results.

**Renault Twingo ZE**

**Range**: 190 km**Consumption**: 16 kWh/100 km (with charging loses) –ย 11,2 kWh/100 km (without charging loses)**Usable battery capacity**: 21,3 kWh**On-board charger efficiency**: 70 %

**Dacia Spring Electric**

**Range**: 225 km**Consumption**: 14 kWh/100 km (with charging loses) – 11,9 kWh/100 km (without charging loses)**Usable battery capacity**: 26,8 kWh**On-board charger efficiency**: 85 %

**Volkswagen ID.3 Pro S**

**Range**: 549 km**Consumption**: 15,9 kWh/100 km (with charging loses) – 14 kWh/100 km (without charging loses)**Usable battery capacity**: 77 kWh**On-board charger efficiency**: 88 %

**Volkswagen e-up**

**Range**: 260 km**Consumption**: 14,4 kWh/100 km (with charging loses)ย – 12,4 kWh/100 km (without charging loses)**Usable battery capacity**: 32,3 kWh**On-board charger efficiency**: 86 %

**Peugeot e-208**

**Range**: 340 km**Consumption**: 17,6 kWh/100 km (with charging loses)ย – 13,5 kWh/100 km (without charging loses)**Usable battery capacity**: 46 kWh**On-board charger efficiency**: 77 %

**Nissan LEAF**

**Range**: 270 km**Consumption**: 17,1 kWh/100 km (with charging loses)ย – 13,3 kWh/100 km (without charging loses)**Usable battery capacity**: 36 kWh**On-board charger efficiency**: 78 %

**Kia e-Soul**

**Range**: 452 km**Consumption**: 15,7 kWh/100 km (with charging loses)ย – 14,2 kWh/100 km (without charging loses)**Usable battery capacity**: 64 kWh**On-board charger efficiency**: 90 %

**Kia e-Niro**

**Range**: 455 km**Consumption**: 15,9 kWh/100 km (with charging loses)ย – 14,1 kWh/100 km (without charging loses)**Usable battery capacity**: 64 kWh**On-board charger efficiency**: 88 %

Previously the Kia e-Niro was homologated with a WLTP range of 485 km, but Kia revised the rating in December 2018 and dropped it to 455 km. This change makes the on-charger efficiency estimation less reliable, because the e-Soul and e-Niro should have the same on-board charger, but we get different estimations.

**Hyundai Kona Electric**

**Range**: 482 km**Consumption**: 14,7 kWh/100 km (with charging loses)ย – 13,3 kWh/100 km (without charging loses)**Usable battery capacity**: 64 kWh**On-board charger efficiency**: 90 %

**Hyundai IONIQ Electric**

**Range**: 311 km**Consumption**: 13,8 kWh/100 km (with charging loses)ย – 12,3 kWh/100 km (without charging loses)**Usable battery capacity**: 38,3 kWh**On-board charger efficiency**: 89 %

**Tesla Model 3 LR**

**Range**: 580 km**Consumption**: 16 kWh/100 km (with charging loses)ย – 12,6 kWh/100 km (without charging loses)**Usable battery capacity**: 73 kWh**On-board charger efficiency**: 79 %

Summing up…

**On-board charger efficiency estimations**

**Hyundai Kona Electric**: 90 %**Kia e-Soul**: 90 %**Hyundai IONIQ Electric**: 89 %**Kia e-Niro**: 88 %**Volkswagen ID.3 Pro S**: 88 %**Volkswagen e-up**: 86 %**Dacia Spring Electric**: 85 %**Tesla Model 3 LR**: 79 %**Nissan LEAF**: 78 %**Peugeot e-208**: 77 %**Renault ZOE**: 77 %**Renault Twingo ZE**: 70 %

Anyway, remember that these estimations are for worst-case scenarios, by charging with domestic sockets at low current (10 A). If you charge at higher currents you can achieve better efficiency figures, especially if your electric car is a Renault.

If you can charge your electric car at 32 A, do it. Nowadays, a good portable EVSE with adjustable current is not that expensive.

Lastly, if you want to do your own calculations but can’t find some variables, let me know.

Dude, and where is invertor and motor efficiency and car electronics consumption coming from?

You just calculated drive and charging cycle efficiency, but not charger efficiency.

The only variable missing from the calculations is the efficiency of the battery itself but that is extremely high (close to 100 %) when batteries are new, it doesn’t mess with the estimations in this article.

Ok, let me try to explain a little better.

With the WLTP ratings we can’t calculate the efficiency of the drivetrain.

Let’s see the Renault ZOE’s example.

You get a 395 km range from 52 kWh, this represents a consumption of 13,16 kWh/100 km.

This consumption figure already contains the discharge loses of the drivetrain, but it doesn’t include the loses of the charging. It doesn’t consider how many kWh it took to charge those 52 kWh.

The official WLTP rating of 17,2 kWh/100 km does include both discharging and charging loses.

So when you divide 13,16 by 17,2 you get the charging efficiency. Considering that the battery efficiency is close to 100 %, we get a good estimation of the efficiency of the on-board charger.

We can also calculate that we had to use around 68 kWh from the grid to put 52 kWh in the battery.

X = 17,2 รท 13,16 x 52 = 68 kWh

Ok, I understand. This is clear, thanks.

It was weird to me, as my colleagues test charging Model 3 at 11 kW and it was extremely efficient, like almost 97 % or something like that. And they had pretty consistent results.

Charging at 11 kW should be much more efficiency than the figures I presented, but 97 % is very impressive.

The efficiency of LG Chem’s 11 kW on-board chargers can reach 95 %.

https://pushevs.com/2018/06/11/new-lg-chem-on-board-chargers-up-to-11-kw/

Yes, I was too very surprised by that high a number.

Those LG chargers are probably using SiC technology, right?

I don’t know, unfortunately LG Chem removed all information from its website.

Thanks.

Battery usable capacity is not always officialy published, when the usable capacity is estimated so is the charging efficiency.

That’s correct.

Hi Pedro,

EPA charge rating is done at 120V 10A or what they call L1 charging (at least used to).

At this very low rate, all chargers are less efficient than when charging at 230V 10A. So calculating charging efficiency by EPA rating will give lower number than calculating by WLTP one.

Thanks Giora, that’s useful information.

What happened to the 43 kW Continental 3-phase charger in the Zoe Q90? It is a technology that has disappeared when it seemed interesting for the massification of fast charging points in cities and towns, since a charging point in alternating current is much cheaper and easier to install than one in direct current.

I think that it was discontinued because of low efficiency at low currents.

https://pushevs.com/2016/12/17/renault-zoe-charging-time-efficiency/

Thanks for the info. Great Post

Thanks, this is very interesting. You forgot the Hyundai Ioniq. Here is what I found for the 38kWh version:

Can you check whether this is correct?

For the 28kWh Ioniq, there is no WLTP data I think, it was still in NEDC. Can we estimate it with NEDC ranges?

The WLTP range is actually 311 km, so the on-board charger efficiency is 89 %.

Yes, you can also use NEDC for your estimations since it measures plug-to-wheels consumption as well.

https://pushevs.com/electric-car-range-and-efficiency-wltp/

By the way, supercharging can also be inneficient due the need to cool the battery (down to 75%)

Here a charging point operator explaining it (in spanish)

https://youtu.be/YJ2euKDtAuw

That’s interesting, thanks for sharing.

DC fast charger: 44,2 kW

Tesla Model 3 battery: 36 kW

It seems that those 8 kW of difference were being used for heating the battery, not cooling it. This is temporary, isn’t active for the whole charging session.

This is one of the most important yet underated (or unknown) figure by people… They always say my car is spending ##kwh/100kms… but that is only car moving efficiency, not the charging efficiency.

Usually in the Leaf 40 I charge:

Weekdays at night @ 16amps;

weekend by day (taking advantage of photovoltaic energy) @ 6,2 amps;

I know I have higher losses at lower power, but like this i take all the photovoltaic energy i produce (otherwise I will “give it away” to the utility company).

One of the best Posts ever Pedro…and they are all very informative!

Thanks Freddy.

That’s great being able to charge your electric car with solar ๐

It’s a shame that Portugal still doesn’t have net metering and all the excess of solar production is given for free to the utility company.

Writing an article about net metering is something that I plan to do someday. I think that only corruption can explain why we still don’t have it here…

We have a “kind of” micro-netmeetering now in Portugal since February…for 15 minutes ๐ (so we have 15 minutes to spend any excess production before it is given away to the utility… It’s far from perfect, but better than nothing…

I would not necessarely speek of corruption, but more keeping the status quo of existing powers, lobying… whatever.

I for once, if had total netmeetering would have already invested much more heavily in PV has I have huge consumption in winter and residual in Summer. (exactly the opposite of PV production ๐ ).. I have now 1500w installed but could easily already have 4000w without much hassle…. and this would improove for sure Portuguese energy deficit, improove energy CO2 footprint, etc…

Not only that, but net-metering would also improve the efficiency and voltage stability of the grid.

With decentralized electricity production, electricity needs to travel a lot less distance from production to destination and we have less cable losses.

This is particularly important in remote areas where the grid voltage is very low.

Actually Pedro, small PVs have an issue with theirs variable production. For example, when PV is working as it should, inverter gives out 230V on 50Hz frequency (and whatever power its makes). This is predictable situation that can be easily managed by DSOs. The problem accures when there is a sudden fall in production and of course voltage with it. This is why sistem network needs to have primary-fourthiary back up (according to how fast it needs to react). With PVs, primal and secondar backup needs to fire up a lot of times and usually those are gas-based plants. Since even gas power plant cannot just turn on and off whenever we want managing systems has become a huge challange. Voltage varies too much for what the network was designed.

However, there are no good solutions for that kind of issues besides battery storages. This is why countries with a lot of PVs are investing big funds into storage units to mitigate this issue. Moreover, home storage units will become more and more important and network operators will need to find a way to incentives you to participate in to evening the system when sudden drops of production happens. Nothing impossible but it will affect into what DSOs will have to invest.

We have a year-based net metering here in Slovenia which is why most of Slovenians make PVs 11kWp or bigger. It gives you enough juice to power your home, heat pump and also EV (if your house is isolated and you have AA+ kitchen ware). Anyway, it looks as it is too good because some “officials” are doing everything they can to change it to monthly based metering which will discourange most to make PVs and once again kill PV industry in Slovenia and of course slower the transition to sustainables. Makes wind farms is imposible in our country and hydro is prohibitive because we cannot manage fish. So at the end, old boys still think coal (actually lignite) and nuclear is the way to go here. Sometimes it makes you wonder what kind of people make decisions on the world.

Sorry, but your calculations for the Zoe are totally wrong, as you ignore the power factor.

The chameleon charger has a low power factor at low power, so it takes many kVA, but not so much kW.

Hi Tom.

These estimations were made from WLTP ratings. Not measurements I made at home.

Are you saying that the WLTP ignores the power factor?

In the article : https://pushevs.com/2016/12/17/renault-zoe-charging-time-efficiency/, you calculated the efficiency with the formula : 0.8*battery capacity/(Charging time from 0 to 80% * current * 230), but this is false, the real formula is 0.8*battery capacity/(Charging time from 0 to 80% * current * 230 * power factor).

In this article you calculate the efficiency with the formula : battery capacity/(wltp range * power consumption) : this is not the efficiency of the charger alone, but the global efficiency of the car, which include efficiency of the charger, the battery, the inverter, the motor, the drag due to the Scx…

Oups, sorry, the second sentence of my comment is false : you are right, this is the efficiency of charging (charger+battery). However, does the WLTP specify the charging power ?

For consumer protection, NEDC, WLTP or EPA have to measure the charging efficiency in worst case scenarios with the portable EVSE that officially comes with the electric car.

In Europe this means charging at 10 A, 220 V, while in North America (as Giora pointed out) it means charging at 10 A, 120 V.

If automakers were allowed to sell their electric cars with a portable 16 A EVSE, efficiency ratings would improve. That however would be very risky, because not every domestic socket handles 16 A without overheating. My house is not that old and at least 2 sockets burned for using a simple heater… There are a lot of crappy electrical installations out there.

Maybe it’s time to replace type F (schuko) sockets with CEE, so we can move safely to higher currents.

Very interesting article, first time I see WLTP consumption explained.

BTW, can any one explain why volkswagen report its ID3 WLTP consumption through a range ?

” 15.4 – 16.9 kWh/100 km”

Hi Sam.

Usually when a model has different energy consumption ratings is due to different wheels. Smaller wheels are more efficient.

The ID.3 is available with 18, 19 and 20-inch wheels.

https://uploads.volkswagen-newsroom.com/system/production/uploaded_files/16185/file/0ecf6bebc8b7bd3398b559eb14951f54b1810840/The_new_ID_3_-_International_Media_Drive.pdf?1595402445

Thanks for the link. The first page lists Pro Performance as 15.4 – 16.9 kWh/100, while the Pro S is 15.9 – 17.7 : it seems you mistakenly labelled the best as Pro S.

About the wheels impact : good point. I didn’t think it could amount to 9% more consumption though, does wheel size usually makes such difference ?

Thanks Sam, I’ll revise the rating from 15,4 to 15,9 kWh/100 km.

There are other factors that can influence the consumption rating of a model, such as the weight of the standard equipment or having or not a heat pump.

Hello, there are two hypothesis that you didn’t take into account that in fact ruin all your calculation for an on-board charger efficiency:

1) Useable capacity is not an accurate value as the energy used for calculation in the WLTP regulation is the energy spend during a full deplete procedure (STP) and you can have really big variation between this number and the useable (or rated/nominal/announced) capacity of the car given by OEM. Examples I have in mind: BMW iX3 with 81kWh announced by OEM but only 76~77 are used during procedure or Tesla models in general.

2) While you are charging, the car is active and uses its cooling pumps and ECU’s. Because the charges are too long, these components cannot be active without the high voltage battery supplying current (with a DC ~400V to 12V~ converter). So you also loose the consumption of this DC/DC converter (can be as high as 2 to 5% of the total energy received from the plug).

The numbers you give are in fact Charge efficiencies (energy received by the battery divided by energy given by the AC plug) and not on-board chargers efficiency (energy at the output of the on-board charger divided by energy given by the AC plug).

The calculation for the Kona seems good for a 90% charge efficiency (but on-board charger efficiency can be between 94% to 96%)