I’m not all surprised by that.
In one of the Wiki’s I found a report that most current sensors are designed for larger currents as drones usually use currents in excess of 40A. So whilst you can measure something in regards to low current it is not reliable unless you have at least a current of 20A or more.
Also whilst the current advice is for at least 10A for any calibration, (https://ardupilot.org/copter/docs/common-power-module-configuration-in-mission-planner.html)
in other documents I’ve found clear advice of using at least 20A for any calibration and reliable readings.
Yes, roughly ten times sounds about right in MP settings. If remember correctly I’ve got around 158 set as Amps per Volt for my 3S battery setup. In my 6S drone I’ve got 208 Amps per Volt and a voltage divider of 10.9
In my case I have the advantage of having a laboratory power supply available and can dial in something like 12V and a current of 25A for calibration. Which means I have a precise comparison between actual current to indicated current in MP. - But the more basic way works as well providing you can achieve a higher current for initial configuration.
Another thing I’ve noticed over time is that setting the current divider in QGroundControl was not successful in some earlier versions - haven’t tried a recent version. Also had that problem using earlier versions of MP running on Linux. ( I believe MP 1.3.74 on Linux works as it uses Mono )
Yet running MP on Windows worked fine.
See also this:
CodeChiefTony WallPro user
Current sense at low amps is not accurate, take the props off and run it up to about 10 amps then take measurements again to calculate the amps per volt. That is documented on the APM Web site. I don’t think Navio is any better at this (the original Pixhawk and APM compatible PDB I use both have the same limitation and the Navio power cable appears to be identical to the Pixhawk cable).
Hmm, yes the accuracy improves as the Amp goes up.
Because the code (in addition to voltage monitoring) monitors the current usage and triggers the failsafe on low battery, I found the the current calculations may be tripping things up much earlier than expected. I am going to change it to monitor just the voltage for failsafe, until I test a bit more on the current side of things.