In my last article I mentioned the advantages of electrified motor vehicles, including hybrid electric vehicles (HEVs), that have become the go-to vehicles in Zimbabwe.,
Hybrid electric vehicles (HEVs), plug-in hybrids (PHEVs) and battery electric vehicles (BEVs) have high voltage batteries/rechargeable energy storage system (RESS) as one of the propulsion power sources.
These high voltage batteries are made of different chemistry architectures in the form of lithium battery family and nickel metal hydride, just mention a few.
Electric Bus
Lithium battery family – lithium manganese oxide (LMO), lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC), lithium nickel cobalt aluminum oxide (LiNiCoAlO2 or NCA), lithium iron phosphate (LiFePO4 or LFP), etcetera, are all used in different BEVs at one point or the other.
Lithium types of batteries are similar to other batteries that have an anode, cathode and electrolyte.
In other cases, the anode is made of carbon(C) or graphite carbon, and the cathode is made of lithium metal oxide (Li2O), and the most common electrolyte in lithium batteries is lithium hexafluorophosphate (LiPF6), also known as lithium salt, in an organic solvent.
Lithium battery releases power through the transfer of ions from the anode to cathode.
Electric Bus Batteries and other Components
This movement of electrons allows electromotive force (EMF)/voltage to operate a motor/e-machine or other electrical device.
When ions transfer within, battery heat is generated.
The heat must be monitored by the battery controller, so that it can adjust the charging or discharging event to minimise the possibility of thermal runaway.
When thermal runaway begins, the battery controller will systematically adjust the cells within the pack/RESS to quickly control the event.
If the event is left to operate without controls in place, the lithium-ion cells will quickly heat up as the ion exchange happens.
Burning Electric Bus
This unmetered temperature change will quickly get to a point where the battery will catch fire.
The 2020 Nissan Leaf we have in Zimbabwe has a 300kg, 40 kWh, 350 volts lithium nickel manganese cobalt oxide (NMC) battery pack/RESS.
When a cell or cells fails within the pack, there is possibility of it or them to cause other cells to short, thus increasing the battery pack temperature.
When lithium battery packs on vehicles or buses are involved in an accident, and the cell structure is compromised by impact, cell temperature can significantly escalate.
The escalation of temperature will release oxygen in the electrolyte and provide it as the catalyst for a fire to start.
Because the electrolyte is organic with the oxygen that has been released, a fire can be produced that cannot be extinguished externally.
Because the lithium battery packs release the oxygen internally and providing it as catalyst for the fire, these batteries can explode or catch fire days or weeks after the accident.
For the above reason, Zimbabwe needs trained first and second responders that are going to attend accident scenes involving these vehicles and buses that use lithium family battery.
The buses utilise bigger high voltage battery packs, which makes it even more dangerous, as they carry more passengers onboard.
The fires and explosions caused by electric buses when they are involved in a collision and compromises the battery packs will be extensive, and it will be impossible to extinguish externally.
Electric Bus On Fire
The only procedure the first responders and fire fighters will do is to try and cool down more than one high voltage battery pack modules/stacks found in these heavy-duty vehicles.
The first responders should be trained to depower the electrified vehicles like BEV, electric buses, etcetera, before the medical technicians can attend to injured occupants.
Because we currently do not have hybrids and electric vehicles high voltage standardisation in Zimbabwe, no one is monitoring the buses and electric vehicles being imported into the country to see if they meet the regulation standards.
High voltage applications have the ability to incapacitate technicians, if they are operating on these systems and touch the wrong location.
To help ensure the safety of technicians, multiple standards have to be developed by governmental or standards organisations that have no federal affiliations.
Through federal and third-party regulatory and compliance requirements, there should be a multitude of standards that govern how the high voltage system on HEVs and BEVs are controlled; how equipment used to work on them must be constructed, and how failures within these systems should be diagnosed.
Knowledge of standards will allow technicians to maintain a high level of safety.
In the USA, National Highway Traffic Safety Administration (NHTSA) governs the rules and regulations that vehicles must adhere to when operating on highways across that country.
NHTSA provides safety guidance and specifications through the Federal Motor Vehicles Safety Standards (FMVSS), which, when followed, allow vehicles to operate in the safest possible manner.
For example, the standard FMVSS 305 requires the following of OEMs (original equipment manufacturers) and their vehicles; that any propulsion battery system located outside the passenger compartment never enter the passenger compartment; and that there be no less than 500 ohms (units of electrical resistance) per volt (or 100 ohms per volt) of electrical isolation between the battery propulsion system and vehicle’s electricity-conducting structure.
For example, a 300-volt system requires a system-to-chassis isolation barrier of 150 000 ohms per volt.
*Taurayi Raymond Sewera is ASE & AUTOCATE ASSOCIATION certified World Class Master Technician with 39ASEs, ASE Advanced Level Specialist L1, L2, L3 and L4, AMI Accredited Master Electric Vehicles and Master Automotive Manager, ACDC certified Master Hybrid and Electric Vehicles Technician. Taurayi is the founder and CEO of TauRay Automotive. He can be contacted on +263 77 234 1193, +263 77 235 7296 or [email protected]
