Hi,
I was wondering which mavlink message is used by QGC to draw battery info from Pixhawk. After searching the mavlink message definition, I found the message no: 147 to be handling the battery status from the autopilot. But it says that this message does not output the current from the battery. how does QGC read the current from the battery then?
Hi,
As you can see in the BATTERY_STATUS (#147) message:
| id | uint8_t | Battery ID |
|---|---|---|
| battery_function | uint8_t | Function of the battery |
| type | uint8_t | Type (chemistry) of the battery |
| temperature | int16_t | Temperature of the battery. INT16_MAX for unknown temperature. |
| voltages | uint16_t[10] | Battery voltage of cells. Cells above the valid cell count for this battery should have the UINT16_MAX value. |
| current_battery | int16_t | Battery current, -1: autopilot does not measure the current |
| current_consumed | int32_t | Consumed charge, -1: autopilot does not provide consumption estimate |
| energy_consumed | int32_t | Consumed energy, -1: autopilot does not provide energy consumption estimate |
| battery_remaining | int8_t | Remaining battery energy. Values: [0-100], -1: autopilot does not estimate the remaining battery. |
| time_remaining | int32_t | Remaining battery time, 0: autopilot does not provide remaining battery time estimate |
| charge_state | uint8_t | State for extent of discharge, provided by autopilot for warning or external reactions |
The “autopilot does not measure the current” is a reference for the return value of -1. All valid fields will return values different from -1 
Note that ArduSub does not use the current_consumed field. I’m not sure if we report 0 or -1. The current_battery field is updated, however.
How does QGC do current reporting? Some mavlink message involved?
With BATTERY_STATUS message, ArduSub will send it with all necessary data.
Thanks. 
My bad I didn’t read properly
Please let me know if you need any further help.
Patrick, we are trying to read batter voltage with pymavlink. We parse the BATTERY_STATUS message and receive the following:
BATTERY_STATUS {id : 0, battery_function : 0, type : 0, temperature : 32767, voltages : [65535, 65535, 65535, 65535, 65535, 65535, 65535, 65535, 65535, 65535], current_battery : 49, current_consumed : 4204, energy_consumed : -1, battery_remaining : 47}
The current measurement in centi-amps appears fairly accurate however, the array of voltage values doesn’t contain the measured voltage. We are using the latest version of the power monitor module.
Thanks in advance, Tim
You cannot read the individual cell voltages without a battery monitor that connects to each individual cell. We do not have any experience with this, if you do find one there may be some support issues with ArduSub.
@asjb Are you using ArduCopter or ArduPlane? If so, you will get some better help at discuss.ardupilot.org.
We simply want to read the battery voltage as it appears for example in qGroundControl, but using pymavlink. Please advise. Thanks.
Thanks Jacob!
The current being drawn from the battery, measured in centi-amperes (like cm is centimetres).
100 cA = 1 A, just like 100 cm = 1 m. Conversely, 1 cA = 0.01 A.
The value displayed in current_bettey in the BATTERY_STATUS item is 380. So how is it calculated?
With a suitable power sensor (e.g. our Power Sense Module) the relevant calculation parameters can be configured in the Power Setup Page. The calculation that occurs depends on the type of sensor that’s connected.
What is the meaning of the current_battery value among the BATTERY_STATUS items? The unit is cA. How many amperes (A) is 1 cA?
I am using a sensor sold by Blue Robotics.
The current is calculated from a measured voltage that’s proportional to the current. From the product page:
I wonder what 380cA means.
If 100cA = 1A, is 380cA = 3.8A?
If 1cA is a discharge rate of 1 centimeter, assuming that the length of the power cable is 1m, is it 100cA?