Joe Perez wrote:I saw that, along with his note that "If you are running LiFePO4 just ignore the fuel gauge until the Ah accumulation is integrated in the beta software here."
Since I am running a LiFePO4 battery, I understand that it's not up to par yet, this particular behavior just struck me as exceedingly odd. I'll try calibrating Rbatt and see if that makes it behave more logically- based on Justin's post on page 14 (where RBatt = (V1 - V2) / A) it looks like I should configure it as 066 (it's at the default 199 right now)
Hi Joe, indeed this behaviour is coming from an incorrect (too high) battery resistance value. When you are drawing current, the CA tries to extrapolate what the actual pack voltage would be with no current before it references the lookup table. So suppose you are drawing 10A, and reading 47V from the pack. If RBatt was set to 200 mOhm, then the CA would assume your actual battery voltage is:
47 +10A*0.2 Ohm = 49V
If your actual RBatt is only say 100mOhm, then the actual open circuit voltage of the pack is more like 48V
47 +10A*0.1 Ohm =48V
If you then increase the current draw to 20A, the voltage on the pack would fall down from 47V to 46V, but the CA would overcompensate even further when extrapolating the open circuit pack voltage, now to:
46 + 20A * 0.2 Ohm = 50V.
So this is why with RBatt too high, you have an effect where drawing more current causes the battery indicator to go up. Once you play around with it you can find a value that causes the graph to neither go up or down with increased load.
This is however somewhat moot as the Beta15 code no longer lets you input the RBatt value. Instead, it computes it in real time, and this allows it to track your changing battery resistance both as it ages and as it varies with temperature and state of charge. So there is now a new screen which lets you see the instantaneous RBatt value that the CA has deduced from watching the recent voltage/current history, and you as a user no longer need to worry about setting this up:
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