Cuav nora battery remaining indicator (using can pm) is wrong, but current is correct, how to solve?

I have built two same quad copters with same configuration using CUAV NORA, and 6S battery. Both have same problem: Wrong battery remaining indicator. Nora supplied CAN Power module in the package (lite version), so I followed all the instruction, that this CAN PM should be installed on the C power port of NORA.

Battery monitoring parameter is set to 8 , so Battery Voltage and Current are correctly displayed as expected without any adjustment/calibration. Both Quad copters fly well, however something strange occurred, the Remaining battery as displayed by Nora is not consistent with battery consumption. Nora displays remaining battery (in percentage) is much lower than it should be. I mean if we calculate the remaining battery manually, it should be : Total battery capacity deducted by battery consumed. Even though, Nora displays the battery consumed correctly, but the battery remaining is much lower. This is very weird. I have checked, there is no explanation about how is the calculation based. I tried to increase battery capacity become double than actual, but problem is still exist.

As Nora displayed battery remaining much lower than actual, then in a short time, the indicator become very low. This is very dangerous as it can cause Battery Fail Safe.
I attached screen capture of this battery display problem.

As example in this display, I set the total battery capacity is 40000 mah (= 40A), after hovering about 2 minutes, it consumed about 764 mah, BUT the battery remaining indicator is 75%, which is wrong.
Firmware is Arducopter 4.1, battery is 6S.

Until today I can not solve this problem. Anybody can help? Any advice is highly appreciated. Log file is here :

Thank you.

In that log you’ve got the battery set to 30000. If you are going to set that and expect the percentage to be correct then also set
BATT_LOW_MAH = battery rated capacity x 0.2 (80% used)
BATT_CRT_MAH = battery rated capacity x 0.1 (90% used)

For 6S lipo you should have these values:
and always these:

Set the correct/real BATT_CAPACITY and the other params then lets see a new .bin log.

It may be that we need to figure out more yet, or it could be as simple as setting BATT_FS_VOLTSRC,1

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Hi @xfacta ,
Thank you for your response. I will test again according to your advice… So do you think this error occured because of my wrong parameter setting?? I don’t think so… Why? The logic is like this:

  1. Why this error never happened on my other drones with similar battery oarameter setting??? ( But using analog PMU with previous Firmware (4.0xxx)…
  2. I have built several Ardupilot drone with similar setting, and never have this battery indicator issue.
  3. I believe this error is related to the CAN PMU, because only occur when I use Cuav Can PMU lite with Nora.

For your info, I use LiOn battery…
Thank you…

When I checked the (full sized) CAN PMU circuit diagram it looks good and the voltage is measured from the battery input side of the current sensor. The CAN PMU Lite might be different, where the voltage is measured from the drain side of the current sense resistor - this would explain what you are seeing.
I found exactly the same issue with the CUAV HV PM and I made a simple voltage divider and connected it to the battery input side and output to the voltage sense wire (obviously breaking into the voltage sense wire so it’s not getting the CUAV voltage reading too).
This could be much harder to “fix” with the CAN PMU, as you’d need to do a bit of circuit board surgery.
It might be easier to just set up a voltage divider and feed it into the analog voltage sense port and set up BATT2 with a suitable voltage divider value and battery failsafe parameters.
Take the battery voltage failsafe parameters out of the 1st BATT group and just leave the current measurement in place.

This is disappointing and CUAV should really fix those PMUs to read the voltage accurately under load. To fix it ourselves makes a mess of the wiring and we fiddle with the parameters, when it should be neat and “plug and play”

For 6s Li Ion use:

Hi @xfacta ,
Excellent, this is what I suspect… Any idea how to solve this problem without doing any hardware modification (the Can lite version PMU ? ) I mean, just changing the battery parameter setting? The weird part is, : BATTERY VOLTAGE AND CURRENT ARE CORRECT, BUT THE PERCENTAGE (Battery remaining) is WRONG… So my key question is HOW Mission Planner DOES THIS CALCULATION (percentage of the remaining battery)???
Thank you…

Hello gentlemen,
Any updated on this CUAV Nora CAN Power Module Lite problem??
If CUAV can not solve this problem, my question is how to modify parameter is Mission Planner to “Recalculate” Battery remaining (in percent)??
Maybe @Michael_Oborne can help??
Any comments or advise is highly apprecited.
Thank you.

You may want to do a manual calibration of the current. The CUAV PM Lite was off by 10% leading to wrong capacity calculations for @hwurzburg .

He created this PR to have have a CAN battery scaler to adjust for the error here,

On 4.2Dev it is called BATT_CURR_MULT