How efficient are the on board chargers in the smart #1 and #3?

I had already addressed the topic at the beginning of 2019, when the 22 kW charger in the smart EQ was new and the 22 kW charger in the smart ED was very expensive. You can find the article from back then here, I will continue to refer to it later when I compare the efficiency of the new #-smarties with the old ones.


In general, such an efficiency measurement is not only interesting for people with a solar systems, but also for everyone else. Load management is particularly popular in large parking garages with many charging points. Then your own car is sometimes turned down and no longer gets the full 11 kW or 22 kW. In these cases too, it is of course practical if the charger is as efficient as possible.



What is efficiency and how we measured it


Basically, the HV battery is operated with direct current (DC). Since our power grid works with alternating current (AC), the car has to convert the charging current from AC to DC on the type 2 charging station. To put it very simple, the charger also has to adjust the voltage from 230 V to 400 V to the 370 V to 465 V of the HV battery.

There are losses in this so-called conversion. These are reflected in waste heat and do not end up in the battery. This is where the issue of efficiency comes into play: The more efficient the charger, the less waste heat there is and the more power ends up in the battery, where I can actually be used.


At CCS charging stations, this conversion already happens outside the car, so these charging stations must have the necessary technology themselves. That's why they are more expensive and can only be found in locations where they can be used by many. In the future, they could also become standard at home and I'll go into that in more detail in this comment. But that shouldn't be an issue here.


To measure the efficiency of the charger, we measured how much power comes in on the AC side and how much of it comes out on the DC side. For this purpose we used an NRGkick as a charging station. This can measure the current and voltage of the individual phases and tell me exactly how much power is going through. In order to see how much comes out of the charger on the DC side, we accessed current and voltage values from the charger output using a smart workshop diagnostic tool.

These two values, when offset against each other, result in the efficiency. With an efficiency of 100%, no waste heat is generated and everything goes into the battery. At an efficiency of 0%, only waste heat is generated and the HV battery is not being charged at all.


My smart BRABUS #1 was tested with its 22 kW charger in ampere increments from 6 A to 32 A, both 1-phase and 3-phase. A smart #1 pro+ with a 7.2 kW charger and a smart #3 Premium with a 22 kW charger were also measured. The #1 pro+ and #3 Premium were measured in larger steps because it turned out that they behave exactly the same as the BRABUS #1.

In addition, random measurements were taken to determine how much electricity was arriving in the HV battery. In addition to the losses from the charger itself, there are of course also minor losses from additional consumers such as cooling pumps and control devices that have to run during the charging process.


At this point a big thank you to the smart center Esslingen (Russ Jesinger Automobile GmbH & Co. KG). Without their support, I would not have been able to measure how much power the charger delivers on the DC side and how much of it reaches the battery. On top of that, the selection of additional test vehicles was very helpful as well.

It was nice to see that there are still true smart centers with smart towers and a focus on smart.



General information about the chargers in smart #1 and #3


It was interesting to see what I had already suspected: The chargers in the smart #1 and #3 are identical. Their values do not differ at all in terms of efficiency and the 22 kW charger and 7.2 kW charger are practically the same in the diagnostic device. The 22 kW charger and the 7.2 kW charger are equipped with the same 7.2 kW power modules.

While the 7.2 kW charger simply has one 7.2 kW power module on L1, the 22 kW charger has three such 7.2 kW power modules. One for each phase. In the diagnosis, these power modules are even listed individually in the charger. Strangely enough, they say “Module A”, “Module B” and “Module C”. For reasons I don't understand, "Module C" is responsible for L1.


This also explains why the #1 pro and #3 pro can only charge in 1 phase. Although it would of course be more practical for customers if the 7.2 kW chargers were 2-phase and could therefore charge the full 7.2 kW at 11 kW charging stations. They simply saved two power modules in the 7.2 kW equipment variant and did not have to develop any additional hardware for them.

I wouldn't even be surprised if the existing 7.2 kW charger in the pro could be expanded by two additional 7.2 kW power units and then the pro could also charge 22 kW. You would then also have to replace the wiring harness in the vehicle. Being able to retrofit 22 kW is just speculation on my part. But I now know for now that the charger and the DCDC converter are one unit, because they appear in the smart diagnostic device as one control device.


7,2 kW an 11 kW



The only strange thing was that vehicles with 7.2 kW chargers do not show what is happening on the DC output side in the diagnosis in the actual values. These values are missing there. So we had to take the measurements and see what was going into the battery.



Efficiency in 3-phase charging


The efficiency of chargers is usually best at their rated power and if they are limited to low power, the efficiency suffers noticeably. But the 22 kW charger in the smart #1 and #3 runs at 93% to 95% across the entire range. An extremely respectable value, which 10 years ago only the expensive 22 kW charger of the smart ED, which was subject to a surcharge, was able to achieve. The cheaper 22 kW charger in the smart EQ could only dream of such values, it ranged between 50% and 93%.


smart #1 & #3 efficiency 3 phase



With these charging powers, the additional consumers play practically no role, so that in everyday life you could easily reduce the 22 kW charger to 6 A (4.1 kW) without having to accept any significant losses. Perfect for PV-controlled charging.



Efficiency in 1-phase charging


As already mentioned above, the 7.2 kW charger and the 22 kW charger are most likely equipped with the same power electronics. So that the efficiency is practically the same even with 1-phase charging. Here in the graphic we can now see my smart BRABUS #1 with a 22 kW charger being supplied with 7.2 kW on just one phase.

The efficiency of the chargers is so good and consistent across the entire range that our measurement method, which is actually very precise, still has its limitations.


smart #1 & #3 efficiency 1 phase



With such limited power, the additional consumers are now becoming more relevant. If you charge with 22,000 W, 150 W for cooling pumps, control devices and the like are irrelevant. If you reduce the power to 1,400 W, they become noticeable. So that the charger itself still has 93% to 95% efficiency, but by the time the power reaches the battery, the efficiency drops to 84% to almost 90%.

But ultimately, this is still a great value. The smart EQ with a 22 kW charger achieved less than 50% efficiency.



Conclusion


Personally, I'm really excited about the results. It was foreseeable that the chargers would be significantly better than the smart EQ. But the fact that they are so good and that you don't have to worry about efficiency at all with solar controlled charging is a great result.

In fact, the efficiency was so surprisingly good that in the future I will make sure to reduce the cars SoC to 0% if possible. So the DC voltage is lower, the current is higher and the measuring method is even more precise than it was here.


In this article, some of the technology has been explained in a very simplified manner. You are welcome to go into more detail in the comments or ask questions. :)


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This article was supported by Russ Jesinger Automobile GmbH & Co. KG. The client has no influence on the content or statements I make.

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