smart ED3 17.6kWh Battery - Accumotive E18-1 Teardown & Analysis

The Deutsche Accumotive GmbH & Co. KG has set a major milestone with the E18-1. With the first made in Germany battery cells that where used in a series production vehicle, they build a battery pack, that's truly developed and made in Germany. For 2012, it's performance date is impressive:

  • Continuous output: 42 kW (2.4 C)
  • Peak power: 63 kW (3.5 C)
  • Energy content: 17.6 kWh
  • Nominal voltage: 400 V
  • Weight: 175 kg

The battery pack can be cooled and also heated via a fluid based thermal management. It consists of 3 modules each with 31 pouch cells and thus has a total of 93 pouch cells. When discharged, it has a total voltage of about 310V and fully charged at a total voltage of about 390V.

In addition to the smart, this pack was also originally made for the electric Mercedes Benz B class, they wanted to use two in parallel. The high standard of Mercedes is also wha the battery pack is so reliable, even after up to 8 years. My own smart ED3 now has that cracked 200,000 km, that corresponds approximately 2,000 cycles and still hast got 90% of its original capacity.

In the following I would like to show what's inside the smart ED3 battery pack and how it works.

EQpassion would be nothing without its community and supporters:

I would particularly like to mention Thomas Rebele from Tom’s Garage. As a motor vehicle master with high voltage certificate, Thomas is a great help. His workshop in Stuttgart (Germany) has helped EQpassion readers by repairing smaller and larger defects. In his private life, he is fully electric, with a smart ED3 convertible and a Tesla Model 3.

I would also like to thank the ElectrifyBW trio around the Spanish car2go. They bring almost 100 decommissioned car2go smarties back into shape. The exchange with them is beneficial for both sides and has also helped a lot for this post.

Marcus Zacher from Blog was very helpful GenerationStrom. During his studies, he had worked at Accumotive and therefor is a big help at understanding how the battery works.

Step 1 - Orientation and expansion of the E18-1 from the smart ED3

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

For orientation. This is how the battery sits in the smart and its connections.

  • battery pack
  • canbus
  • Water cooling inlet and outlet
  • HV connection

The battery is screwed into the car from below and is additionally secured by two strong parts on the right and left. This ensures that it stays in place.

Nevertheless, its removal is extremely easy and can be completed in about 30 minutes.

Step 2 - Open the battery

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

Accumotive GmbH & Co. KG designed this part for us somewhat hard. First the screws have to be removed, then the rivets need to be drilled out and then the adhesive has to be removed. Before you can lift the lid, you have to unscrew the canbus Interface and the HV connection from the cover.

The background to this complex fuse is to keep the battery water tight.

Thankfully, everything else is simply screwed into the battery and nicely modular.

Step 3 - The water cooling

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

Here we see three things

  • Water cooling inlet
  • Water cooling outlet
  • CSE connection

The water cooling is hosed so that each module is cooled in parallel to the others. This means that cooling is equally effective for all modules.

There is also the so-called CSE (Cell Supervision Electronics) on the individual modules. I will go into this later.

Step 4 - The dry cartridge

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

Every smart ED driver has heard of it: The dry cartridge*, this is what it looks like when installed in the battery.

Should some moisture get inside the battery, the dry cartridge will bind it. It is exchanged during the inspection and is even free of charge if the battery is rented.

*A 789 340 33 00

Step 5 - Battery management and series resistor

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

Here is the heart of every battery, it's BMS (Battery management system). The CSE draws its power directly from the cells and is only optically coupled to the BMS. The BMS gives instructions on how to handle the battery. It also informs the rest of the car about the condition of the battery. You will find out how it works in mine basics of electric cars.

There's also a resistor, which can be set in series with the relay.

Also important is the current sensor, for example, with its help, the BMS can determine the remaining capacity of the battery. To our right we also find two HV contactors. You hear them every time you turn the smart on and off. Also when the charging process begins or ends. They ensure that high voltage is applied only when driving and when charging to the outside the battery. As the battery is now on the pallet, there is no voltage at the HV connection. Above from the HC connection is also a HV fuse. (450VDC; 225A)

Side note:

Here's how you can reset the P18051C

Step 6 - cooling

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

Now seen here:

  • Cooling plate
  • Cooling pad
  • Cell connector / contacts

On the top of each modul we've got two cooling plates, which are then connected to the cell connector / contacts via the cooling pads.

Cooling the contacts of the cells seems strange at first, but is actually the most effective way to cool a cell, since the contacts have the best thermal connection right into the cell.

Step 7 - CSE and overview of a module

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

Now there is a lot to see:

  • Battery cell
  • module
  • CSE
  • Cell connector / contacts
  • Connection to the next module

The black parts that you see here are not the cells. These are the frames, in which there are the cells. This ensures that the cells are never subjected to mechanical loads. The cells are always rotated by 180 ° to each other, so that the minus pole of the first cell lines up to the plus pole of the next cell. The cells are then connected via metal bridges. The metal bridges are incorporated into the pouch cells themselves and cannot be removed.

The metal bridges are also connected to the CSE. The CSE is the green board in the middle of the module. It monitors the cell voltages and adjusts them if necessary. It also has an eye on the temperature sensors, each module has a total of three. One on each side and one in the middle.

All three modules are identical and connected in series with each other via rails. Overall, the smart ED3 battery is a 1p93s circuit.

Step 8 - Remove module

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

After the first module has been removed, two remain. The cooling tubing has also been removed, as well as the BMS and all other cable sets.

The modules are screwed onto the lower part of the housing. This has welded cast parts with matching threads. The underside of the case is much more stable than the lid, so it is also significantly heavier.

Step 8 - One of 93 cells

smart ED3 17,6kWh Akku - Accumotive E18-1 Teardown & Analyse

If you take the module further apart, you get to the individual cell. At the least now everyone understands why they are called pouch cells. Around it is the already mentioned frame.

In fact, it says on the cell that it only has 50 Ah, not the 52 Ah specified by the manufacturer. Still, it has 52 Ah. From a legal point of view, the 50 Ah understatement makes sense here, but is otherwise of no concern.

Schematische Draufsicht E18-1

Here you can see schematically everything that happens in the battery. The cooling is hidden. I also noted here which cell number can be found where. This is helpful if, for example, you are using the DIY battery tool and detect a weak cell, but don't know where it is now.

It is also worth following EQpassion on its social media platforms. The next project is now to show you what can be repaired or exchanged and what things have to be considered.

Current sensor (for E18-1)

Current sensor (for E18-1)

Current sensor (for E18-1)