BMW iX Xdrive40 75kWh battery teardown

[pie314isi]

I posted this over at AEVA, but I thought it'd be interesting here too.

I was fortunate enough to get hold of a dismantled BMW iX Xdrive40 battery.

It's 330-350V in ten modules connected in series.
75kWh total.



Each module has a connector with 18+ wires, exposing all the individual cell voltages and temperature sensing.



They are all bussed together in a loom to a CSC module:



the CSC might be on a CANBus, but we couldn’t see any useful output directly. It turns out it’s transformer isolated, but didn’t investigate whether it can talk yet.



Inside the CSC is a bunch of microcontrollers and some isolation:



And some surface mount power resistors. It seems it does some balancing, but obviously the balance current is pretty low - small wire gauge and small resistors:



I’ve done some basic capacity testing of the batteries. At 75kWh and 330V quoted capacity they should be around 220Ah.

The top cover is just plastic and comes off easily. I didn’t need to cut the main power cables, I made some threaded connectors that mate to the orange screw terminals pretty well.





- 18 cells in a series/parallel arrangement  in each module. 9S2P arrangement.
- one module weight about 40kg.
- Just bare cells with a connector that exposes each cell voltage and three temperature sensors
- no BMS or balancing circuit - because it’s in the CSC module
- initial voltages as I received it all 3.936V, all within about 1mV of each other - very good matching.
- charged them all to 4.05V (max nominal might be 4.1 or 4.2, depending on chemistry)
- discharged with an approx 60A load. Discharged to approx 3.05V, which is a common endpoint for lithium cells.
- main current carrying terminals are a TE connectivity thing with a conductive ring and an internal M4 thread.

Curve below:



Shows we got just about 200Ah between 4.05 and 3.05V at a ~4 hour discharge. That’s 27V to 36V for a module.

I think this is pretty typical, and we’d expect about 10% more capacity if we pushed it to the limits, so it seems bang on spec.

Internal resistance measured at about 3.5milliOhms(?) for the pack. Seems high, maybe - should check again.

For what it’s worth I bought one of these:

https://www.ebay.com.au/itm/353853522667?epid=1642437107&hash=item52635042eb:g:aVgAAOSwCk1h3omb:sc:AU_ExpressDelivery!3055!AU!-1&amdata=enc%3AAQAIAAAA8EZnobqGKNqnkJ914G4U6tiBcP509q%2FivcWanY4ljCYBuY%2Bo2luoMhC7T6UNFbwLUDIk6wNj9YFYzht5j8o%2BQUydeYeyNV5nW16R1BwF00dPe9hAZ4rVAuH51dMOzs90f2vODp6KJG72DEC%2BgnXBepAH3fnnx8jgijZvTZQ5wv9hOsRtmZsKypTIuMJUcAECYM92CU4GKE7y7nZEz3H%2BhoJrMQTRrfk13SQiQwJWkvU8WrzMwNhEqslwmYBJmZwK2b6QyEE2cahpBOtHi1AhBcVNbZblXQI0mL6pHQnIRnDhNy17RGfIhOjzaVpw%2B9vgZQ%3D%3D%7Ctkp%3ABFBMnPrIiLti

Which happily runs off the pack and feeds a good 1200W into the grid.

I can supply more photos or measurements on request if anyone is interested.  There's other parts that I didn't get good photos of; the parts that interface to the rest of the car and the charging subsystem and the safety cutout and so on. This is what I had, for what it's worth.


cheers, hope someone finds it entertaining,
cms

[hojnikb]

How are these cooled?

[nctnico]

It is nice to see this is a serviceable battery pack (you can replace modules) which should give the car a better resale value / lower depreciation.

How are these cooled?

The top picture shows two black tubes and tubing between the batteries so I guess it is liquid cooled. AFAIK no sensible car manufacturer uses passively cooled batteries in a BEV nowadays.

[pie314isi]

How are these cooled?

there's an aluminium plate "sandwich" on the bottom with coolant channels stamped into it.

https://imgur.com/gallery/yvZPd3E

[tom66]

I'm surprised how much volume is not used by battery cells - I guess they use the same casing for the 105kWh models.

330V is quite a low nominal voltage for an EV.  Normally it is closer to 400V.  But if they want to maintain a similar architecture, that means they stay within 450V by adding 4x extra modules.  I would guess rapid charging and performance is more limited for 330V model.

Looks like overall a good design of pack, as nctnico points out looks very serviceable, it'll all ultimately come down to whether these are good quality cells or not.

I would guess these are CATL or Samsung prismatic cells.

[pie314isi]

I had wondered if some of the unused volume was for side intrusion crumple zone.

I can't photograph it, but looking very closely down some gaps with a torch I can make out CATL on the cells.

[Siwastaja]

Having a large crumble zone makes sense - problem is not volumetric energy density, it's the weight, but that empty space does not weigh much but adds impact protection plus can be filled with thermal insulation which is helpful in winter time (but then the need for active water cooling for summer time is even bigger, but it seems most manufacturers are finally getting there).