Blog - Tests and diagnosis

TEST: The Winston LiFePO4 cell 160AH short-circuit at 1000Amp for 13 minutes

This test proves the safety of the LiFePO4 technology: no fire, no uncontrolled explosion into in fire, no sparking, no burning, no fire smoke (black).

The short circuit on an over-charged cell.  This video shows the extremely high speed discharge (nearing the short circuit) of the Winston 160AH cell. To intensify the abuse conditions, the Winston cell was overcharged and become swollen before the short circuit discharge.

The over charged cell has already damaged internal structure (higher internal resistance). Thus the cell will release more heat than a healthy, regular cell with no overcharge. 

• After 3 minutes of short circuit the temperature of the terminal connectors increases. Due to the high temperature of the terminals, there is a small smoke coming from the plastics case around the terminals.
   
• After 10 minutes the internal temperature of the cell has increased too high. The high temperature causes the gassing of the chemical substances inside the cell and as a result the cell has become severely swollen. More and more gasses start to be released from the safety valve on the top of the cell.
    
• After 12:30 minutes the internal gassing is so high that the gasses start to be released from the safety valve. At this moment the temperature of the cells is around 180 *C and the internal structure if the cell is collapsing. The cell is no more releasing any energy, but most of the energy is burnt inside as a heat.
    
• At  12:40 the release of the gasses from the cell is so high than the cell makes a „trumpet like sound“. At this moment the internal pressure increases to the maximum.
    
• At 12:56 plastic case will no longer withstand the internal pressure and the plastic case breaks out making an „explosion like sound“, with a lot of smoke. At this moment all gasses inside the cell are released at one moment.  The cell continues to generate the smoke.
   

During the short circuit test there was not any smoke with heat and fire (black color smoke). The cell did not set itself on fire, the cell did not burn, the cell did not explode because of fire.

The „explosion“, or rather burst opening, of the cell was because the case (outside shell) of the cell did not withstand the internal pressure. If the cell was in a battery pack, or tightly located in a proper battery case, the cell would keep the shape, as the neighboring cell would not allow the cell to become swollen.  In a battery case, the cell would not most likely „burst open“: it would continue to resale the gasses thru the safety vent much longer.

The regular capacity of the cell is 160 Ah at 3.2V.  The charging capacity is 160AH at 4V. This makes 640Wh of energy. With some overcharge, it can be estimated that the cell was holding of 700Wh of energy.  This energy was released at some 13 minutes of short-circuit discharge. This corresponds of 3250W of immediate power. At 3.2V the short circuit current was about 1000Amp.