Pro-Trak  
 

 
Interesting graphs using Li-Po Pro-Trak and graph software. 

All cars using Li-Po cells should have a voltage cut-off fitted to prevent  cells falling below the safety cut-off voltage recommended by the cell supplier.

The tests below would suggest that a car using 2 Li-Po cells should have a safety cut-off voltage of 3.4volts plus the recommended cut-off voltage of the cell supplier to prevent cell damage or even a hazardous situation.  Assuming the cells should not be discharged below 2.9 volts then a safe cut-off voltage would be 6.3 volts (3.4 volts + 2.9 volts)

 ie you have to assume 1 cell is at maximum voltage at the end of discharge to prevent poor cells being over discharged.


See below
     
CCCV charging
Constant current charge at 3 amps to 8.5 volts
Constant voltage charge until the charge current = 1 amp
Discharge current 20 Amps

D/CAP = Discharge capacity
TIME = Discharge time
PV1 = Pack or Cell volts at 5 minutes
AV1 = Average voltage over 5 minutes
AVE = Average over complete discharge
Match    The closer both cells are to 100% the better.
E/VOLTS = Voltage when discharge terminated
PEAK /V = Peak voltage of pack or cell.
CCAP = Charge capacity


The following report from Pro-Trak relates to the graph below.
 

D/CAP

TIME

PV1

AV1

AVE

MATCH%

E/VOLTS

PEAK/V

CCAP

2633

473

7.14

7.364

7.16

100

5.84

8.5

2781

2633

473

3.56

3.678

3.573

100

2.91

4.29

2781

2627

472

3.54

3.655

3.552

99

2.89

4.22

2781

 
   
  This is a well matched pack and discharging the pack to 6 volts would not be a problem.  
     
     
     
However the following pack is not well matched and discharging the pack to 6 volts would result in the worst cell discharging to  2.67 volts if the remote leads were not connected.   Please note that Pro-Trak  stopped the discharge on this pack when the cell was at 2.89. 
     
Constant current charge at 3 amps to 8.5 volts
Constant voltage charge until the charge current = 1 amp
Discharge current 20 Amps

The following report from Pro-Trak relates to the graph below.
 

 

D/CAP

TIME

PV1

AV1

AVE

MATCH%

E/VOLTS

PEAK/V

CCAP

PACK#04

2138

384

6.92

7.24

7.125

107

6.25

8.5

2464

CELL1/ 4

2127

382

3.4

3.582

3.514

99

2.89

4.33

2464

CELL2/ 4

2138

384

3.48

3.617

3.571

114

3.32

4.18

2464

 
     
   
  Equalising the cells to 3 volts made no difference to the performance of this pack..