Battery Failsafe

The battery failsafe can be configured to automatically switch the vehicle into SURFACE mode or disarm if the vehicle battery voltage drops below a specified voltage for 10 seconds or the estimated remaining capacity has dropped below a configurable threshold.

Note

This failsafe requires the vehicle have a working Power Module.

Note

ArduPilot supports up to 9 batteries/power monitors. The discussion below applies to those optional batteries also. Each can trigger a failsafe and each can have different actions and setup values. In addition, a group of batteries can be treated as a single unit, see BATTx_MONITOR = 10.

When the failsafe will trigger

If enabled and set-up correctly the battery failsafe will trigger if the main battery’s:

  • voltage drops below the voltage held in the BATT_LOW_VOLT parameter (or FS_BATT_VOLTAGE in older versions) for more than 10 seconds. The default voltage is 10.5 volts. If set to zero, the voltage based trigger will be disabled.

  • remaining capacity falls below the BATT_LOW_MAH parameter (or FS_BATT_MAH in older versions) 20% of the battery’s full capacity is a good choice (i.e. “1000” for a 5000mAh battery). If set to zero, the capacity based trigger will be disabled (i.e. only voltage will be used)

What will happen

When the failsafe is triggered:

  • Buzzer will play a loud low-battery alarm

  • LEDs will flash yellow

  • “Low Battery!” will be displayed on the ground station’s HUD (if telemetry is connected)

Then one of the following will happen, depending on BATT_FS_LOW_ACT:

  • Nothing (value 0)

  • Disarm motors (value 1)

  • Enter SURFACE mode (value 2)item has been programmed (see Using DO_LAND_START).

As with all failsafes, the user can re-take control of the vehicle by changing the flight mode switch to another mode. The battery failsafe will not trigger again unless the two-layer failsafe is setup (see below)

Note

Once a battery failsafe has triggered, it cannot be reset until the autopilot is rebooted.

Setting up using Mission Planner

  • On the INITIAL SETUP | Mandatory Hardware | Failsafe page:

    • If the Battery section parameters are greyed out follow instructions to setup the Power Module

    • Set the “Low Battery” threshold voltage (i.e. 10.5 volts)

    • Set the “Reserved MAH” or leave as “0” if the failsafe should never trigger based on estimated current consumed.

    • Select the desired behavior (Land, RTL, SmartRTL, etc) from the drop-down list

../_images/Failsafe_Battery_Setup.png

Two-Layer failsafe

ArduPilot includes a two-layer battery failsafe. This allows setting up a follow-up action if the battery voltage or remaining capacity falls below an even lower threshold.

  • BATT_CRT_VOLT - holds the secondary (lower) voltage threshold. Set to zero to disable.

  • BATT_CRT_MAH - holds the secondary (lower) capacity threshold. Set to zero to disable.

  • BATT_FS_CRT_ACT - holds the secondary action to take.

Advanced Settings

  • BATT_FS_VOLTSRC allows configuring whether the raw battery voltage or a sag corrected voltage is used

  • BATT_LOW_TIMER can configure how long the voltage must be below the threshold for the failsafe to trigger

  • BATTx_ parameters can be setup to trigger the failsafe on other battery monitors.