Sorry for the long post:
First - Thanks Mainsail for you excellent articles and posts on Battery Capacity Testing. I tried to follow them as best I could. You are understating that holding constant current for the duration of the test is "tedious" I tried my best but I'm afraid my ability to keep the current "constant" was somewhat limited and I didn't measure the temperature (oops). I think temperature was pretty constant in the range of 75 degrees but can't be certain so I know that effects the accuracy of the test. Next time I will make sure I measure Temperature and rig some method to better manually control current. (DC bulbs and a reostat) Below is the raw data from the test as well as a plot/graph of:
Voltage vs Time,
Discharge Rate vs time, and
Victron 702 measured AH discharged vs time.
The beginning was interrupted by a young man who fell off his boat trying to hook his mooring line and when I heard the splashing about I had to help with a quick recovery so I missed setting the current discharge rate and recording the exact starting time/voltage and current. Based on the Victron AH reading at 27 minutes (-3.4 AH) it looks like the avg current discharge was about -7.6 Amps for the first 27 minutes. (well below the target -10.75 Amps (215 AH Capacity / 20 hours) It reached 10.49 Volts at 21.58 hours!! My guess is that not being able to hold the discharge rate constant and some periods below 10.75 (the Peukert effect) impacted this. The Victron 702 read 203.5 AH discharged from the battery even though it took over 21 hours to do this.
So, my interpretation is that my battery is at or near 95% capacity (95% of 215 AH rated capacity). I am assigning a value of 205AH as Actual Capacity for the Battery Monitor (Like Mainsail said, "close enough" may be good enough). What do those who have done this, keeping in mind my limitations in holding constant current, not measuring temperature and missing the first 27 minutes of readings , think I should use as Capacity? Your thoughts are appreciated.
First - Thanks Mainsail for you excellent articles and posts on Battery Capacity Testing. I tried to follow them as best I could. You are understating that holding constant current for the duration of the test is "tedious" I tried my best but I'm afraid my ability to keep the current "constant" was somewhat limited and I didn't measure the temperature (oops). I think temperature was pretty constant in the range of 75 degrees but can't be certain so I know that effects the accuracy of the test. Next time I will make sure I measure Temperature and rig some method to better manually control current. (DC bulbs and a reostat) Below is the raw data from the test as well as a plot/graph of:
Voltage vs Time,
Discharge Rate vs time, and
Victron 702 measured AH discharged vs time.
The beginning was interrupted by a young man who fell off his boat trying to hook his mooring line and when I heard the splashing about I had to help with a quick recovery so I missed setting the current discharge rate and recording the exact starting time/voltage and current. Based on the Victron AH reading at 27 minutes (-3.4 AH) it looks like the avg current discharge was about -7.6 Amps for the first 27 minutes. (well below the target -10.75 Amps (215 AH Capacity / 20 hours) It reached 10.49 Volts at 21.58 hours!! My guess is that not being able to hold the discharge rate constant and some periods below 10.75 (the Peukert effect) impacted this. The Victron 702 read 203.5 AH discharged from the battery even though it took over 21 hours to do this.
So, my interpretation is that my battery is at or near 95% capacity (95% of 215 AH rated capacity). I am assigning a value of 205AH as Actual Capacity for the Battery Monitor (Like Mainsail said, "close enough" may be good enough). What do those who have done this, keeping in mind my limitations in holding constant current, not measuring temperature and missing the first 27 minutes of readings , think I should use as Capacity? Your thoughts are appreciated.