SR to ER battery swap DIY project

[bmwhitetx]

The smaller pack in the ER battery is the same as the regular packs in the the SR, and in the case of a failure, out of warranty - better to have any pack then none at all...

They are the same size kWh wise (40 cells), but not the same configuration or part. All SR modules are 4P10S - 333V nominal. The ER small module is 5P8s - 355V nominal.

There would be a voltage mismatch - so not compatible.

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[kdkool]

They are the same size kWh wise (40 cells), but not the same configuration or part. All SR modules are 4P10S - 333V nominal. The ER small module is 5P8s - 355V nominal.

There would be a voltage mismatch - so not compatible.

Yes to expand on this, the ER large modules are 5P11S. Essentially the ER and SR modules do not share the same internal battery modules, but the ER and flash do.

The SR is 98 kWh with (9) 4P10S modules. 333V nominal as a battery pack. 360 cells total.
The ER is 131 kWh with (8) 5P11S and (1) 5P8S. 355.2V nominal as a battery pack. 480 cells total.
The Flash is 123 kWh with (6) 5P11S and (3) 5P8S. 333V nominal as a battery pack. 450 cells total.

The modules themselves are just placed in series with one another so it isn't really a voltage mismatch issue but more of a BMS mismatch issue. The BMS would for sure flip out with the incorrect module in place.

 

[NW Ontario Ford Lightning]

yes, all the packs need the same number of cells in parallel groups - for balancing reasons, so it makes sense. The ER small pack needs sets of 5 to match the other modules in the battery. Quite Right.

So the OP swaped out the SR to ER battery - but the BMS is exterior to the battery isn't it?
So the BMS 'sees' the larger number of cell groups via the connector and doesn't flip out?
OP said the truck recognized the larger battery immediately - this may be how it does.

 

[kdkool]

yes, all the packs need the same number of cells in parallel groups - for balancing reasons, so it makes sense. The ER small pack needs sets of 5 to match the other modules in the battery. Quite Right.

So the OP swaped out the SR to ER battery - but the BMS is exterior to the battery isn't it?
So the BMS 'sees' the larger number of cell groups via the connector and doesn't flip out?
OP said the truck recognized the larger battery immediately - this may be how it does.

BMS is internal to the battery pack. That's essentially why its plug and play because the truck just gathers and reports the battery status from the pack's internal BMS. The BMS communicates via a serial communication bus so it consolidates all the thermal sensing, contactors, voltage sense, and current balancing wires.

All the battery packs have 9 modules that are in series with one another. For the ER, there are (8) modules of (5P11S) and (1) module of 5P8S. The last single module being a lower overall voltage than the other 8. Cell balancing is done by the BMS for each of the (9) modules down to the cluster of 5 parallel cells. These battery cells are typically very well matched (very close in ESR) so minimal balancing should be required.

Each cell is roughly 81A.

5P11S => 55 total cells. This means there are 11 sets of 5 cells that are in parallel. The 11 set of 5 paralleled cells are then placed in series. Each cell is ~3.7V. Paralleled cells combine for more current. Cells in series increase voltage. So for the 5P11S module, the overall voltage of this module is 40.7V or about 16.5kW overall.

The small module is 5P8S which means it has an overall voltage of 29.6V and about 12kW overall.

This gives us the ER total voltage of 40.7V x (8 modules) + 29.6V x (1 module) = 355.2V.

Each cell is 3.7V x 81A = 300W. Since there are 480 cells in the ER, this gives us 300W x 480 = 144kW. Ford derates the battery capacity by roughly 9% to avoid the extreme conditions of fully charged and completely drained for maximum battery life. After the additional derating, this gives us the advertised 131kWh rating.

 

[SMMD]

You are unbelievably amazing! I assume you probably lack some of the fear/survival based circuitry that most of us carry around in our heads, which I guess sometimes can be a good thing.

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