Hello all,

I want to discharge a 6 cell, 20.4 volt (3.4 volts/cell), 3000mAh Lithium-Ion battery. I want to discharge it either at 6A or 3A so it will take either a half hour or hour to discharge, respectively. But I also want to hook it up to some timing mechanism to see how long it actually took to discharge. Any ideas on how to incorporate the timing mechanism? Thank you for any help.

 

Put a clock in parallel to the load.

 

You might consider using three #1154 automotive 6v turn/brake/parking lamps in series; if you connect both filaments you'll be drawing about 3.2 Amperes. The advantage of using incandescent lamps is that their resistance is dependent upon the temperature of the filament; it increases as the temp goes up. So, as the battery becomes more discharged, the voltage across the lamps decreases, which causes the resistance to decrease, and the current flow stays more constant than it would through a simple resistor. It's pretty inexpensive, too - around a buck per bulb.

 

Connect both ampmeter & voltage meter;record measurments every 10 min or so, closer as 18 V approaches & terminate at 18V to avoid battery damage- from Battery University.