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How to avoid a fire in the battery system? Here the cause of fire in the battery system is analyzed.

January 8, 2021

How to avoid a fire in the battery system? Here the cause of fire in the battery system is analyzed.

 

HOPPT BATTERY conducts matching analysis based on battery fire accidents, from assumptions to extended experimental dimensions.

 

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Because the entire analysis is only to match the extreme event of battery system fire, we distinguish the content caused by mechanical abuse. The battery system's design basis focuses on placing the vehicle in a safer location to prevent. There are problems with the use of vehicles. Although the entire mechanical design is currently a large number of experimental safety content such as acupuncture and extrusion, in fact, problems caused by mechanical abuse have become easy to solve.

 

Take Tesla as an example:

 

T3: A fire broke out in Smyrna, Tennessee, USA. This electric car rushed to the trailer hitch that fell on the road, and a fire broke out after the chassis collided.

 

T2: The driver hit and crossed a concrete wall while turning, and finally hit a tree and stopped and caught fire.

 

T1: In Seattle, the owner said he hit a metal fragment in the road, so he left the highway. After the car failed, he smelled burning again, and the car caught fire.

 

This kind of mechanical design is also simple. Considering more protection on the periphery of the structure and the bottom cover, you can achieve immediate results: the struck objects penetrated the aluminum pan at the forward area of ​​the battery, damaging the lithium-ion cells of the HVB.

Remarks: We can remove the manufacturer from what happened this year, and we can think about it again. Is the car fire a battery or something other than a battery?

 

A large part is a load outside the battery.

 

The cable is overheated, => the peripheral part is ignited more.

 

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Here we can divide the basic three levels, the essential cause of the fire.

 

1) The release of heat energy in the battery that is not by the design intent + internal and external combustion.

 

2) Release of combustible gas + ignition point in the battery.

 

3) Flammable liquid release + ignition point in the battery: This includes electrolyte leakage and coolant leakage.

 

We can consider the heat release of the battery system:

 

1.1 Overcharge of the battery pack or battery cell

 

Generally speaking, overcharging is indeed the more common cause of heat release. Battery pack-level thermal runaway events can be subdivided into multiple batteries (modules, single overcharge) = "Battery overcharge and electrolyte evaporation = "Heat event.

 

Overcharge caused by SOC calculation error

 

In the high SOC state, it is caused by energy recovery, not by the protection.

 

Overcharge caused by the stuck charging control program

 

1.2 Thermal energy released by people with short circuit and overcurrent

 

Battery pack/high voltage circuit failure causes short circuit => heat.

 

Here, it is mainly caused by the internal short circuit and external short circuit of the battery pack, causing the conductor & connector to overheat and the monomer overheating to cause subsequent thermal events. Further subdivision can also be broken down into component overheating caused by the short circuit of the module.

Module-level short circuit

 

A short circuit in the battery pack

 

A short circuit caused by external corrosive/conductive liquid

 

1.3 Heating of high connection impedance

 

The battery pack/high voltage circuit's failure leads to a high resistance position in the charging and discharging circuit. The current temperature rise at this high resistance point may cause adjacent materials and subsequent heat transmission.

 

Poor contact of dry road connection points, corrosion caused by heat

 

The internal resistance of the battery increases, and internal overheating occurs.

 

1.4 The exhaust of the single-cell produces flammable gas, and the subsequent heat source (arc, the thermal runaway of the single-cell) causes excess heat in the battery system

 

Remarks: In this, the single-point failure thermal runaway of a single cell is defined as an experiment. It can be considered that a single cell can be extended to the overall aspect. Under the established conditions, the filing of each battery pack will be disclosed. Some reference functions, but the experimental conditions It is unlikely to coincide completely with the occurrence of the fault.

 

Part Two Case Review

 

In fact, fire incidents are all intertwined, and the part and the third part are often deeply integrated:

 

2.1 Leakage and short circuit

 

Case 1: Car A caught fire

 

Phenomenon 1: More than two packs of battery cells leak in the battery box

 

Phenomenon 2: The insulation between the battery cell and the aluminum case of the battery box is damaged

 

Operating vibration=》Intermittent short-circuit of local battery in the battery box=》The insulation damage point forms a strong voltage short circuit loop through the ground of the battery box and the support=》Thermal energy release, electrolyte + heating of the battery body=》Initiated

The fire spreads, lighting up the interior.

 

Case 2: Car B caught fire

 

Phenomenon 1: After a violent collision of the vehicle, the battery structure is damaged, and the cooling pipe ruptures causing coolant leakage

Phenomenon 2: Slow chemical action caused by coolant immersed in BMU circuit

 

After the sampling point was immersed, the board level did not have a thorough waterproof design, which caused the slow heating to trigger the coolant ignition point=》The parking lot caught fire after a few weeks.

 

summary:

 

1) Fire is a very extreme thing, but the exposure is very high. Everyone's reaction is the battery system. From various analyses, there must be a failure and heat accumulation from the battery system on fire.

 

2) If more public information is put together, then disassembled and compared, and the system analysis process is improved, some consensus can still be reached to avoid many future fire accidents.

 

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