Power Module Calibration

Hi. I’m running the latest emlid-raspbian image on my Navio2 - powered quad. I am using the emlid power module, but am finding it not to be very dependable. The defaults proposed here:

https://docs.emlid.com/navio2/ardupilot/tips/

Give me a terrible current estimate (in that the battery always claims to be >95% full even when depleted), and a very poor voltage estimate. I don’t have another current meter so I can’t gauge precisely what values I should be using for the parameters governing current estimation - to obtain semi-accurate voltage readings I’ve had to set the following:

BATT_VOLT_MULT 11.05

To get any sort of depletion on the battery % I’ve set this

BATT_AMP_PERVOLT 170 Amps/Volt (!)

Does the sensor have an official calibration somewhere? Is mine faulty - in that it should work with the defaults?

On the battery voltage reading - I also notice signficant voltage sag when under load. (e.g. it will read 9 volt when I’m full throttle and then go back to 11v when I stop) Is that expected for a LiPo cell?

Thanks!

Luca

Hi, first of all no you are not doing anything wrong and ist not faulty, just this current sensor is rather useless. if only gives reading of some kind if the copter draws at least 3-4 Amps, and you would need to measure the output value of the sensor and the current to do a proper calibration. i invested a significant amount of time in this and also bought a current clamp to do the calibration. All waste of time and money i must say.
At the end i bought a calibrated current and voltage sensor from Jeti, since im anyway using a Jeti DC-16, so that was the obvious choice for me. But for you it depends what RC remote you are using and if there is a sensor for that too.

On the other hand voltage readings from the power module is quite accurate and you can use a simple voltmeter to calibrate it.

The voltage drop you are reading seems to be a little low. i assume its a 3S LiPo ? so that means each cell has only 3V. thats rather low. If you discharge the lipo lower that 3V/cell it might get damaged (or in your case it might be damaged already) or the LiPo cant take the current which the copter needs, dont know
If you are not familiar with LiPos and how to take care of them you might want to read about them fist.
e.g. https://rogershobbycenter.com/lipoguide/

from the voltage under load you can estimate how “empty” you LiPo is, but this is just a rule of thumb, not accurate
measurements.
hope that helps a bit