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.
The battery as collected.
Warning tags.
First there were a lot of bolts to remove from the cover and later on the base of the battery enclosure.
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.
Cutting the bonded rubber (polyurethane based?) seal.
Battery with the top cover removed.
Main power connectors are on easily removable connector pins.
Balance connectors to BMS module below the white and blue power connectors for 2 x 22 cell banks.
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);
}
}