In the first of a series, Bryce Gaton looks at the core part of the EV, its battery pack, and how to give it the longest possible life. In later articles, he will explain the options for testing and monitoring the battery pack in your EV.
WE ARE all familiar with the ways to prolong the life of an internal combustion engine (ICE) vehicle—regular service, monitor the oil, etc—but EVs are a whole new ball game. What do they need to maintain them in tip-top working order? And how can we test them to know if things are going wrong?
While in general EVs need less maintenance than conventional cars, there are some considerations which will help keep the car performing well for longer and reduce maintenance costs. The battery pack is the component that is both the costliest to replace and the most within our control to keep healthy.
For example, for an ICE vehicle converted to battery electric, replacing the battery pack can cost from $110 to $300 per lithium cell with the battery pack size ranging from 30 to 100 cells—at a cost of $3300 to $33,000. For a Nissan Leaf, replacing the 24 kWh battery is around $6500 fitted (AU$ equivalent to US$ replacement cost—Leaf replacement batteries are not necessarily available here).
What is an EV battery pack made of?
All the pure EVs and hybrids on the market now use variations of a lithium ion chemistry. A common one is lithium iron phosphate, commonly written as LiFePO4. Lithium offers many advantages over previous battery technologies. In particular, it allows for much lighter batteries than lead-acid, which is what EV batteries used to be made from.
Lithium batteries can also be more deeply discharged, down to 20% capacity, giving more available energy to take you further; they hold a stable voltage through most of their discharge range (see graph); they can take high charge and discharge rates, allowing for hard acceleration and fast charging; and they are largely maintenance-free.
They should also have a long life, if looked after, with 70% to 80% capacity remaining in the battery after eight to ten years. And even after that, lithium EV battery packs are still usable in less demanding applications, such as home storage
Lithium cells have some features that need to be taken into account in the design of the car and charging systems. If they are overcharged or discharged (below 2.5V or above 4V), they will likely be destroyed (although LiFePO4 are more abuse resistant and may be recoverable). And, in some formulations, they can catch fire. This is particularly a problem for the super light, very energy dense ones in phones and the like: think Samsung Note 7. EV batteries are now made with formulations that are more resistant to starting or maintaining a fire.
To allow for these issues, modern EVs and hybrids include a battery management system (BMS). The BMS is a complex set of electronics that manages the charging of each cell, as well as controlling the current available to drive as the battery discharges.
Read the full article in ReNew 139.
This entry was posted on Wednesday, March 22nd, 2017 at 2:00 am