Hello,
I 'm experimenting running capacity test on my new Chins 100AHr LFP battery, but have come up with a few questions. Pls let me know best practices on these:
(BTW, using an Electronic Load, but verifying with DMM voltage measurements and Hall-effect DC current probe)
1. Low Voltage disconnect- As the battery might have 50milli-ohms (.05ohms) internal impedance, a 0.2C (20Amp) test will cause the battery terminal voltage to drop 20A * .05ohms=1.0 volt immediately. Recommended LVDisconnect voltage varies, but lets say 10.6 volts. So under 20Amp load, eventually the terminal voltage will drop to 10.6volts, execute disconnect. But then, with the load removed, the terminal voltage will recover to something > 10.6volts, e.g 10.6volts + 1.0v=11.6v with internal drop now removed, right??? Is this a valid 100% State of Discharge criteria, as no load battery terminal voltage is > 10.6V??
2. Watt-hours vs. Amp-hours-As the battery voltage starts ~ 14.0volts, and disconnects at ~ 10.6volt, seems Watt-hour would be more useful figure than Amp-hours. But I typically see Amp-hour specs but rarely Watt-hour specs but always equaling 12.8v * Amp-hours. Which is better?
3. Wire and connector resistance in test set-up- If wires + Connectors resistance is say 0.02ohms (~ 6ft of #6 copper wire and wild guess ~ .016hm for minimum 4 connections). The battery will see the load of heating the wires (I^2*R), but the Electronic Load will not. So I'm guessing the Electronic Load Watt-hour reading will be lower than actual battery load by (20A)^2 * 0.02ohms= 8 watts then *5 hours= 40watt-hours seen by the battery, but not by the Electronic Load. So Battery capacity in Watt-hours is measured less than actual, right? Not sure how the Amp-hour measurement might be effected, but perhaps goes back to question #1, depending on how LVDisconnect is implemented.
Appreciate your feedback and insights!
I 'm experimenting running capacity test on my new Chins 100AHr LFP battery, but have come up with a few questions. Pls let me know best practices on these:
(BTW, using an Electronic Load, but verifying with DMM voltage measurements and Hall-effect DC current probe)
1. Low Voltage disconnect- As the battery might have 50milli-ohms (.05ohms) internal impedance, a 0.2C (20Amp) test will cause the battery terminal voltage to drop 20A * .05ohms=1.0 volt immediately. Recommended LVDisconnect voltage varies, but lets say 10.6 volts. So under 20Amp load, eventually the terminal voltage will drop to 10.6volts, execute disconnect. But then, with the load removed, the terminal voltage will recover to something > 10.6volts, e.g 10.6volts + 1.0v=11.6v with internal drop now removed, right??? Is this a valid 100% State of Discharge criteria, as no load battery terminal voltage is > 10.6V??
2. Watt-hours vs. Amp-hours-As the battery voltage starts ~ 14.0volts, and disconnects at ~ 10.6volt, seems Watt-hour would be more useful figure than Amp-hours. But I typically see Amp-hour specs but rarely Watt-hour specs but always equaling 12.8v * Amp-hours. Which is better?
3. Wire and connector resistance in test set-up- If wires + Connectors resistance is say 0.02ohms (~ 6ft of #6 copper wire and wild guess ~ .016hm for minimum 4 connections). The battery will see the load of heating the wires (I^2*R), but the Electronic Load will not. So I'm guessing the Electronic Load Watt-hour reading will be lower than actual battery load by (20A)^2 * 0.02ohms= 8 watts then *5 hours= 40watt-hours seen by the battery, but not by the Electronic Load. So Battery capacity in Watt-hours is measured less than actual, right? Not sure how the Amp-hour measurement might be effected, but perhaps goes back to question #1, depending on how LVDisconnect is implemented.
Appreciate your feedback and insights!
