Some cool battery graphs
I'm checking out the Costco GC2 batteries and Iota 55A converter as well as the new 16-bit a/d for Arduino. Prior to discharging the 208AH GC2 batteries, they were top charged with 16V for about ...
Forum Discussion
The battery was again discharged by 92.9 AH or down to 55.3% SOC. The battery was then charged with 4A constant current over the entire charge. The charge takes over 1800 minutes, or 30 hours. Data was taken every 5 seconds.
The charge is very linear until battery gets to about 87% SOC. That means battery resistance is constant below 87%. I previously measured it at 12 mohm. For some unknown reason, charging current increased from 4A to 4.5A at the 1600 minute mark. Some time later I discovered the issue and reduced current back to 4.0A It's actually good this happened as I can now calculate battery resistance when it's a 98% SOC.
R = delta V / delta I
R = 0.071V / 0.5A
R = 0.14 ohms
Battery resistance is over 10x greater at 98% than at 75%. The increase in voltage above 85% is due to increasing resistance. At the end of the charging test, a flattening of voltage to about 15.5V occurs. Flattening is an indicator of 100% SOC.
The second graph shows battery temperature. The probe was attached to the battery terminal and then covered with insulation. The probe has a granularity of 1 deg.C; programmable with software. Temperatures run from 6 C (43F) to 16 C (61F). The time 1800 min corresponds to about 3 pm.
The charge is very linear until battery gets to about 87% SOC. That means battery resistance is constant below 87%. I previously measured it at 12 mohm. For some unknown reason, charging current increased from 4A to 4.5A at the 1600 minute mark. Some time later I discovered the issue and reduced current back to 4.0A It's actually good this happened as I can now calculate battery resistance when it's a 98% SOC.
R = delta V / delta I
R = 0.071V / 0.5A
R = 0.14 ohms
Battery resistance is over 10x greater at 98% than at 75%. The increase in voltage above 85% is due to increasing resistance. At the end of the charging test, a flattening of voltage to about 15.5V occurs. Flattening is an indicator of 100% SOC.
The second graph shows battery temperature. The probe was attached to the battery terminal and then covered with insulation. The probe has a granularity of 1 deg.C; programmable with software. Temperatures run from 6 C (43F) to 16 C (61F). The time 1800 min corresponds to about 3 pm.
