Mercedes C350e Battery Tear Down.

Tell us about the project you do with the open inverter
Post Reply
User avatar
Mouse
Posts: 138
Joined: Wed Sep 25, 2019 8:17 am
Location: Wales
Been thanked: 7 times
Contact:

Mercedes C350e Battery Tear Down.

Post by Mouse »

I managed to snag a Mercedes C350e Battery for £100 last month described as Spares or Repairs with internal fault but the cells are OK and a £100 starting bid. :D

I've seen a lot of these for sale and thought a detailed tare down would help anyone thinking of getting involved with them.

According to the bloke selling it there is a known fault with one of the internal 'modules' which might explain some of them being sold on the used market as 'untested' I believe this is some sort of communication fault problem or maybe some parameter measured internally that causes the main car brain to flag an error. It's something Merc know about but of course you cant fix it and need a complete new battery pack.
When I opened mine the cell voltages were all within 0.003V Max to Min so there is no obvious major obvious problem with the cells.

Battery Specs:
Capacity: 6.38 kWh
Power Output*: 60 kW (* as per specs of the Mercedes)
Voltage: 290 V
Capacity: 22Ah
Weight: 100 kg (approx 10kg enclosure)
Cell arrangement: 88s1p
Width: 106 cm
Height: 12 cm / 17 cm (there is a chunky reinforcement beam near the back hence increased height)
Depth: 61 cm

Important notes.
These things are not made for opening or worked on. You will destroy the top cover removing it as it's bonded in position and you will not be able to split the cells.
The cells are bonded to water jackets on the base in groups of 22s, These are joined in turn as 2 banks of 44s cells that can be separated without cutting the joining aluminum battery strap between the pair of 22s banks.
The water jackets are not removable as a hard and very strong resin of some sort has been used.
The BMS module appears to be a text book implementation string of LTC6804G-1 chips with no support microprocessor.
PC040217.JPG
The battery as collected.
tags.jpg
Warning tags.
PC040227.JPG
First there were a lot of bolts to remove from the cover and later on the base of the battery enclosure.
PC040234.JPG
To get the cover off you need to pry the edge of the lid open so the bonded rubber (polyurethane based?) with embedded copper mesh can be cut.
PC040237.JPG
Cutting the bonded rubber (polyurethane based?) seal.
PC040247.JPG
Battery with the top cover removed.
PC090282.JPG
Main power connectors are on easily removable connector pins.
PC090280.JPG
Balance connectors to BMS module below the white and blue power connectors for 2 x 22 cell banks.
C350cover.png
I made some covers for those battery pins as they are so close together and I don't want a 160V dropped spanner incident.

Code: Select all

//Code for OpenSCAD
//Merc C350 battery covers

pin_dia = 6.3; //With clearance
taper_dia = 6.95; //Pin hole tapers towards the end to hold it on
pin_length = 33;
wall_thickness = 1.5;
knob_dia = pin_dia + wall_thickness * 2 + 6;
knob_width = 3;

$fn = 100;

C350cover();
translate([17,0,0])
    C350cover();

module C350cover(){
    cylinder(h = knob_width, d = knob_dia);
    difference(){
        cylinder(h = pin_length + wall_thickness, d = pin_dia + wall_thickness * 2);
        translate([0, 0, wall_thickness])
            cylinder(h = pin_length, d2 = pin_dia, d1 = taper_dia);
    }
}
PC090293.JPG
There is a lockout / anti tamper switch on the fuse cover
User avatar
Mouse
Posts: 138
Joined: Wed Sep 25, 2019 8:17 am
Location: Wales
Been thanked: 7 times
Contact:

Re: Mercedes C350e Battery Tear Down.

Post by Mouse »

The next task was getting the main battery module out from the enclosure.
PC090302.JPG
After removing all the base bolts the main power cables and the BMS module (which was a bit tricky) the main battery block was removed.
PC090303.JPG
The cells are bonded to heat exchanges in banks of 22s with rubber tubes connecting the heat exchangers.
The glue is hard and very strong I cant see anyone ever breaking them in into smaller banks
These modules are joined with rubber hoses and support bracketery.
PC120307.JPG
There are two strong brackets on each length of the battery. The one on the terminal end of the pack is entrapped by the heatsink and battery terminals so can not be removed.
PC120315.JPG
To cut this bracket without damaging the battery cell I placed a metal shield under the bracket. I used two craft knife blades as they were handy and thin enough to go in the gap and a grinder slitting disc to make the cut.
This allowed me to separate the battery into two 44s packs which was about what I was after for a potential motorbike conversion.

The photos don't show it but the two 22s modules are joined by a single aluminum battery strap at the opposite end of the main connectors. To split the packs further this strap will need to be cut and joined.

I also replaced the cut end brackets to the 2 x 22s battery modules to give them some support when moving them about.
cube2.JPG
The rectangular pack format I was trying to achieve.
cube3.JPG
I may be able to reappropiate some of the original mounting holes and bits to hold them togeather in this format.
cube4.JPG
The water feed and BMS connectors are all at one end of the pack.
PC120317.JPG
The BMS module is made from 4 internal PCBs connected in a chain with 2 wires.
PC120327.JPG
Each BMS module has two isolated LTC6804G-1 chips making this a string of 8 x 11s balancing and control chips.
It also appears to be a text book implementation string of LTC6804G-1 chips with no support microprocessor But more experimentation is needed to test this idea.
PC120329.JPG
Hopefully they can be used with some sort of existing system
User avatar
Mouse
Posts: 138
Joined: Wed Sep 25, 2019 8:17 am
Location: Wales
Been thanked: 7 times
Contact:

Re: Mercedes C350e Battery Tear Down.

Post by Mouse »

Lastly it was removing the other auxiliary parts and stuff from the battery case.
PC210466.JPG
The Main contactor and bits.

PC220483.JPG
All the useful bits removed and ready to be re used.

2 x Panasonic AEV14012 M17 relays
AEC51012 Relay for the heater
450V 360A Fuse
450V 30A Fuse
850V 1.5uF Capacitor
2x 2000V 270nF Capacitor with discharge resistor.
Ceramic precharge resistor
2 x Large ferrite torrids
Unidentified gizmo - Current measurement?

PC210445.JPG
The control module at the other end of the battery.
PC210452.JPG
The case like the rest of the module is not ever meant to be opened and is carefully riveted shut.
PC210453.JPG
Main control board. Covered in a very hard conformal coating. None of the main components are common parts however there appears to not be a LTC6820 for communicating with the LTC6804G-1 BMS chips so I guess they've worked something else out.
PC210459.JPG
Just a couple of closeups of the main board.
PC210458.JPG
Just a couple of closeups of the main board.
Post Reply