I’m curious about the specs of the battery and how much “provisioning” is built into the design of the charging system.
I’ve seen from numerous sources that the battery is spec’d at 16kWh of capacity with 96 cells, but since there are no user settings for adjusting how low it can deplete or how full the system charges the battery, we have to assume that the engineers at Chrysler put sufficient cycle-life provisioning in place so that we get a lot of life out of the battery. That said, I’m still curious how the system works and where the set points really are.
I’ve noticed the system reports 100% and 1% for a lot longer than feasible so I’m convinced there is some kind of User eXperience curve applied to the actual reported capacity value. I’ve seen a few posts where people say that a reported 100% is closer to actual 80% and reported 0% is closer to actual 20%. While I’m convinced there is offset headroom provisioning at the high and low end I’m really curious about what the actual numbers are.
I have a Juice Box Pro 40 which has data logging of the charge current over time so this data is feeding my curiosity. I have a 2018 with about 500 miles on it so I have very little data and brand new batteries.
I have done a few electric only commutes to work now and when I get to 0 percent, the 240v charger puts a reported 13.2 kWh in to get back to “reported 100%”
2.8 out of 16kWh (at reported 0%) would mean there is actually 17.5% left for the hybrid system to manage electric only starts in city driving while keeping the battery from going fully depleted which is known to be hard on lithium Ion batteries.
The other bit of data I have is that the system doesn’t go into a slow roll off when it gets close to 100% (reported) charge. When you fully charge a 96 cell, battery managment systems often employ “load balancing” to keep any one of the 96 cells from getting over charged. To charge, the system applies a large DC voltage across all 96 cells in series and if one cell has less total capacity it will fill up before the others and get damaged. To deal with this the cells BMS will bleed off some of the extra which creates heat, also when batteries get near full capacity, charge systems apply a constant voltage and the the charge power starts ramping down at some rolloff dictated by the battery chemistry.
When my 2013 Nissan Leaf charges at 6.5kW to 100%, there is a knee around 92% where it rolls off and takes an hour to get the last ~2kWh of charge.
When the Pacifica is charged to 100% it stays pretty steady at 6.7kW and then for the last 8 minutes it first cuts immediately to half of that charge power, and then has a linear ramp to 0.
So my best guess is that the charge system is not putting the battery into Constant Voltage mode where it has to rely on load balancing, but it is cutting off the charge somewhere well before where a 6.7kW charge would normally roll-off if the battery was in Constant Voltage charge mode.
So I’m really curious what the actual design parameters are. Is the 16kWh battery really a 17.4 kWh where 92% is really 100% and 0% is really 17.5%? Or is it biased more towards the lower end? Or is 0% = 20% and 100% is 80% like I’ve read in some “hand wavy” posts..
Does anyone have the real spec numbers for the battery management system? Does the BMS do load balancing? Is the published capacity de-rated? Is any of this in the service manual?
They don't really give us this info, but there might be enough other info out there to put the picture together. The Battery total capacity quailifies it for rebates and grants and if it was 17.4kW i'm sure it would be advertised.
I would strat looking at the Lithium Ion battery Material first to understand the design requirements and characteristics as you pointed out, since it is dicated by the chemistry. Note, we are on the sencond gen EV Li-S batteries which have a higher power density by size and may have some other chemistry differences.
In actuality, the battery packs have layers of modules. I dont have the actual names of the internal control modules at the moment so I will refer to them by their general function. The battery pack control module (BCPM this ones a real name) is the interface to the vehicle and oversees the internal cell block manager and cell supervision modules. The cell supervision modules are essentially the basic Lithium Ion charge manager for a small group of cells very similar to the Lithium ion charge design guide IC's i linked. The cell block reads the charge status of the cell managers, voltages and temps and load balances the blocks of cells. And the BPCM recieves the statuses from the load balancing block modules and controls the regen charge acceptance and communicates to the on-board charge module(OBCM another real one) for J1772 charge.
You'll notice, or already know, at around 70-80% it switches to a voltage regulated phase to slow charge the remaining battery.
Since the Pacifica does not exhibit this as it completes its recharge process it must end at the beginning of the voltage regulated stage or is a difference 2nd Gen Lithium material.
The goal as you pointed out is to extend battery life. So understanding what ages Lithium ion batterys should be considered.
You'll note here that it mentions EV's use 85%-25% depth of charge/discharge but may be different for 2nd Gen lithium-air. It may be closer to 90%-15% since this spread is 75% of 16.6kW which is 12.5kW which is around whats needed to achieve 30mile range at EPA's rated 40kW/100mi.
It mathematically seems reasonable that around 4kW is not utilized from the battery. Note that charge losses are present in tour JuiceBox 13.2kW records so the difference I presume would be the charge loss. For those that are unfamiliar - Some of which is control module activity during charge, coolant pump and heater functions and on board charge module ECM consumption plus AC/DC converter loss and it all adds up. Longer it charges the more deviation will be recorded.
Here is the info I have on our batteries and charge process, heating cooling from Tech Authority.
Thermal efficiency of battery with heating and cooling management info.
Battery pack control module functions
HV Battery Functional description