AndyH
Well-known member
Now is the time on Sprockets when we analyze the battery. :lol:
We have access to the owners and service manuals now - and some of the mysteries are running away.
Some scattered observations in no particular order...
- We don't yet know the actual capacity of a single cell or the entire pack.
- We don't yet know the limiting voltages for [Nissan/NEC (AESC)]'s variant of LiMn2O4 cells
But we have some new 'knowns' courtesy of the service manual:
- The pack is constructed in one series string - not broken into two parallel strings like the US Electricar/Hughes cars and trucks from the 1990s/2000s.
- Inside each of the 48 'sardine can' modules is four cells arranged 2P2S - two cells connected in parallel to make a 'higher capacity cell' then two of these 2P groups in series.
- The entire pack uses 192 cells in a 2P96S configuration.
- When a maintenance tech replaces cells and/or modules, (s)he uses a purpose-built charger/discharger/balancer to work with the module.
- Module voltage can be between 5.0 and 8.5V
- When replacing cells in a module, the tech discharges the module to 5.0V
A 5.0V voltage level for a 2P2S module shows us that Nissan is fine with cells being discharged to 2.5V. In normal use, cell voltage can be up to 4.25V.
The battery management system is quite capable. In addition to monitoring high and low cell voltage, pack charge and discharge current, pack temperature, and cell internal resistance, the computer knows fairly accurately the state of charge (SOC) from both the actual cell voltage and indirectly by counting charge into and out of the pack.
The service manual lists a cell voltage between 3.2V and 3.4V for an approximately 5% SOC, and 4.0-4.2V for approximately 95% SOC. I don't know for sure, but suspect this is 'ultimate' or 'pack-limit-referenced' capacity rather than 'consumer capacity'.
-----
Expanding a bit to look at the system...
All of the systems and controllers are connected by CAN bus. The liquid cooled on-board charger receives pack info from the pack's computer - so it has all the info it needs to completely protect the pack during charging. The Level 3 quick charger port does send the DC charge electrons directly to the pack's high voltage DC wiring, but there are separate relays and current sensors in the DC quick charge circuit that are controlled and/or monitored by the on-board charger. Swapping the existing 3.3kW charger for a future 6.6kW unit will be plug and play, but because of the level of integration we likely won't be swapping off the shelf chargers anytime soon.
There is no fan inside the battery box.
The charge control wiring diagrams and troubleshooting documents do include the PTC connections and processes. PTC energy use is/can be/will be monitored and reported on the energy use display. There is no sign of the PTC devices or heating elements in the battery pack diagrams though. Maybe they're not yet fully published as it's still a future option, or maybe the pack heater is documented in another manual section. edit...the PTC connection is for the 5kW cabin heater - not the pack heater. Sorry. /edit
Nissan's done their homework - this is a nice improvement over the 1990s/2000s Hughes/Solectria/Ford Ranger EV/Chevy S10EV battery/monitoring/management systems!
We have access to the owners and service manuals now - and some of the mysteries are running away.
Some scattered observations in no particular order...
- We don't yet know the actual capacity of a single cell or the entire pack.
- We don't yet know the limiting voltages for [Nissan/NEC (AESC)]'s variant of LiMn2O4 cells
But we have some new 'knowns' courtesy of the service manual:
- The pack is constructed in one series string - not broken into two parallel strings like the US Electricar/Hughes cars and trucks from the 1990s/2000s.
- Inside each of the 48 'sardine can' modules is four cells arranged 2P2S - two cells connected in parallel to make a 'higher capacity cell' then two of these 2P groups in series.
- The entire pack uses 192 cells in a 2P96S configuration.
- When a maintenance tech replaces cells and/or modules, (s)he uses a purpose-built charger/discharger/balancer to work with the module.
- Module voltage can be between 5.0 and 8.5V
- When replacing cells in a module, the tech discharges the module to 5.0V
A 5.0V voltage level for a 2P2S module shows us that Nissan is fine with cells being discharged to 2.5V. In normal use, cell voltage can be up to 4.25V.
The battery management system is quite capable. In addition to monitoring high and low cell voltage, pack charge and discharge current, pack temperature, and cell internal resistance, the computer knows fairly accurately the state of charge (SOC) from both the actual cell voltage and indirectly by counting charge into and out of the pack.
The service manual lists a cell voltage between 3.2V and 3.4V for an approximately 5% SOC, and 4.0-4.2V for approximately 95% SOC. I don't know for sure, but suspect this is 'ultimate' or 'pack-limit-referenced' capacity rather than 'consumer capacity'.
-----
Expanding a bit to look at the system...
All of the systems and controllers are connected by CAN bus. The liquid cooled on-board charger receives pack info from the pack's computer - so it has all the info it needs to completely protect the pack during charging. The Level 3 quick charger port does send the DC charge electrons directly to the pack's high voltage DC wiring, but there are separate relays and current sensors in the DC quick charge circuit that are controlled and/or monitored by the on-board charger. Swapping the existing 3.3kW charger for a future 6.6kW unit will be plug and play, but because of the level of integration we likely won't be swapping off the shelf chargers anytime soon.
There is no fan inside the battery box.
The charge control wiring diagrams and troubleshooting documents do include the PTC connections and processes. PTC energy use is/can be/will be monitored and reported on the energy use display. There is no sign of the PTC devices or heating elements in the battery pack diagrams though. Maybe they're not yet fully published as it's still a future option, or maybe the pack heater is documented in another manual section. edit...the PTC connection is for the 5kW cabin heater - not the pack heater. Sorry. /edit
Nissan's done their homework - this is a nice improvement over the 1990s/2000s Hughes/Solectria/Ford Ranger EV/Chevy S10EV battery/monitoring/management systems!
