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Hawk - Connecting a solar panel

The Hawk is fitted with a 3500mAh LiPo rechargeable battery. This is designed to allow for a 'full season' deployment, to be later recharged and then redeployed for the next season. 

For permanent installations, aggressive sampling/upload rates, or when using power-hungry sensors - a solar panel can be connected to the Hawk. 


Without proper protective circuitry in place to protect the external battery and the solar panel, current WILL flow in the wrong direction and could cause a fire or damage to components. 

Panel Requirements

  • 6V+ (Hawk min operating voltage)
    • For continuous operation at high temperatures and high output load currents, we recommend an input voltage of 12V or higher.  
  • 5W+


  • Hawk build in July 2023 will include a switch to change between high and low charge rates.
  • This will enable lower-wattage panels to be used with the Hawk (down to 1W)


Connect the panel to the external power terminals on the Hawk base-board (Vin + GND)


Charging Internal Battery

In order to charge the internal battery, the input voltage must be switched to 5V to work correctly with the charging circuit.


  • V_in -> switcher -> 5V ->charger
  • The switcher is ~90% efficient when converting an input voltage to 5V.
  • The Hawk internal battery is charged at a maximum current of 400mA.
  • Therefore, 400mA at 5V = 2W.
  • Accounting for ~10% conversion loss, the power required is ~2.2W.
  • Therefore, a 5W panel is recommended to ensure 2.2W can be met even when the panel isn't in strong sunlight.

The internal battery is charged at a maximum current of 400mA. This means it will take 8hrs 45 min to fully charge the battery from empty. 

Charging in Extreme Temperatures

It is important to note that the back up battery will not be charged if the temperature is <-10°C, or >45°C. This means that if the device is left exposed in the sun on a hot day, a solar panel will not charge the battery. 
Ensure you take measures to reduce the internal temperature of the unit as much as possible (i.e. mount device under the panel in the shade).

Monitoring Panel Output/Hawk Charging

  • The Voltage output by the panel will simply be the input to the Hawk, which is reported in Analogue 2
  • The battery is fully charged at ~4.1V
  • The battery is empty at approximately 3.6-3.7V

Vext Digital Input

The Vext Parameter tab can be configured to map the external power status (Good/Not Good) to Digital Input 3

In general, it is best to leave this on defaults (no active or inactive action) - since a solar panel voltage may fluctuate during the day leading to a large number of unnecessary logs. 

This is more typically used when connected to mains power and we desire an instant alert on the server when this is disconnected.

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