Battery Monitoring
Drones are often flown using Lithium Polymer (LiPo) batteries. Depending on the size of the drone and the current drawn by the components, different kinds of LiPo batteries are used. Their variation often comes in regards with the number of cells used in the battery as well as its capacity.
However, there are characteristics of a battery cell which can be taken as constant as well as the thresholds depending on when failsafes, warnings or stops must be triggered. The commonly used values for these are given in the table below. These are the recommended values and any changes made to them would be at a user's discretion.
| Setting | Value (V) |
|---|---|
| Max Cell Voltage | 4.2 |
| Low Cell Voltage | 3.7 |
| Critical Cell Voltage | 3.55 |
| Emergency Cell Voltage | 3.2 |
These values must be filled out under the appropriate settings by navigating to Battery as given below.
Web Interface: Settings > System Monitor > Battery
Under these settings, the user can also fill out the number of cells used in the battery to power the drone.
Calibration
The voltage and current multipliers are necessary for converting the analog inputs from the power module to actual measurements. These multipliers are usually provided in the specification sheet of the power module as voltage and current dividers. However, if they are not specified, they can be calculated as follows.
\[ V_{multiplier} = \frac{Max\ voltage\ of\ power\ module}{power\ module\ analog\ signal\ range} \]
For example, if a power module has a maximum voltage rating of 60V and sends an analog signal in the range of 0-3.3V. The voltage multiplier would be 18.18. The resulting \( V_{multiplier }\) should be filled in the Settings.
Since correct battery voltage monitoring is essential for battery failsafe modes, it is advised that the voltage multiplier is calibrated by hand using a multimeter:
Measure the battery voltage using a multimeter. This value is called \( V_{measured}\). Check the battery voltage in the web interface. This value is called \( V\). If \( V_{measured}\) is not equal to \( V\), update the \( V_{multiplier }\) value with the following formula:
\[ V_{multiplier} = \frac{ V_{measured}}{V} * V_{multiplier_{prev}} \]
The procedure for the \( I_{muliplier} \) computation is similar and is an optional value.