Hello
In the early stages of tuning a large HEXA X multi-copter using T-motor P80-100KV motors, Alpha 80A ESC and T-motor MF 3218 props.
When doing hover tests the system is experiencing battery failsafe because of voltage sag (attached is a log from a hover test). The batteries used in this log are two Tattu 6S 32 amp 10C connected in series by the power distribution board. Because this is a new build, I’m somewhat paranoid regarding setup / design.
I’m using two Mauch PL-250 sensor boards connected to a Mauch Sensor hub which is then connected to a Mauch power cube. In MP the Voltage Divider is 19 volts and the Amps/Volt = 153 (which is the sum of A/V data from Mauch for two sensor boards). With no load the voltage I’m seeing in MP correct (when comparing to a battery tester / multimeter).
Of course, I can set the critical voltage failsafe lower but wanted to confirm if this level of voltage sag is ‘normal’? I’m guessing the battery monitoring set-up is correct and working properly, but maybe an issue there?
@SLangton Have you figured it out? I am also experiencing a voltage sag on my 13Ah Foxtech 6s semisolid state battery. The failsafe is triggering early due to voltage sag reducing the flight time.
Sorry, but have not learned much beyond my posted question (no one replied!).
This was an experimental build with limited flights - but the sag was large - even though some sag during flight is expected.
I was questioning the power monitoring system setup - but the resting voltage seems correct.
I ended up lowering the failsafe just to facilitate the test flights.
Interesting I have used the same battery type you mention on other builds – with those I also see fairly large voltage sag (but not as large as the build I mention above).
The C rating on some of these batteries is somewhat low, not sure if that could be an issue? Overall though these batteries have performed very well for me.
Have you looked into using sag-compensated voltage for the failsafe and pid scaling? Check out BATT_OPTIONS for the former, not sure where the latter is, (maybe MOT_?)
The real answer to your question of “is this sag appropriate for the batteries” is to get the voltage curves from the battery manufacturer. From there ideally you can pick a resting voltage that represents a charge level that you’d like to failsafe at, and then set your failsafe voltage to the “sag-compensated” voltage that ardupilot computes. After flights, compare the resting and instantaneous voltage to make sure that you are staying above the manufacturers limits for the battery.