Strix PSU

The Strix PSU is a test board created to test both the new PSU chips (required due to the chip shortage) and test the process of creating a board from scratch, post-COVID. Project files can be found on GitHub.

Background

The Strix PSU is a prototype for the proposed Project Strix (Martlet IV) power supply, and as such is required to be compact, rechargeable, and store a high energy density.

The core architecture is a 2S Li-Ion battery pack, connected to a balancer, charger, and two voltage regulators. The regulators create 3.3V and 1.8V voltage outputs at up to 300mA, to accomodate a large safety factor over the power budget of the proposed Strix subsystems. The system is designed to be recharged by a 12V lead-acid battery - so that the avionics system can be recharged on the pad.

Li-Ion Battery Charging

There are two key phases to Li-Ion battery charging: the constant current and constant voltage regimes.

Experimental Testing Log

Day 1: 22/11/21

Initial Testing

• Cheap DuPont jumper wires were soldered up to the underside of the right-angle headers to make connections easily in lieu of actually buying receptables and crimps.
  • Male to male connectors were attached to the battery, 3v3, and 1v8 connectors on the board.
  • Male to female connectors were attached to the cells themselves.
• Regulator outputs were tested with multimeter, correct voltages measured.
• VBatt measured at 7.9V, within spec.
• Regulators and board temp were measured with fingers, warm to the touch but no burning.

Charger Testing

• Male to male DuPont jumpers were soldered to the charger input of the board. These jumpers were connected to a benchtop PSU at variable voltage from 8.9 (8.4 + 0.5) - 22V to simulate charger input.
  • Output voltage over both cells ranged from approx 8.2-8.4V, as per specification.
  • Slight anomalous voltage measured over the pack at 8.6V, noted but no adverse affects observed.
  • After a short period of charging, the pack voltage was measured to be 9V - this is above the expected 8.4V and a cause for concern.
    • Cells were noticeably warm after charging.
    • Board was hot to the touch during charging, especially the inductor.
• Charging needs to be investigated in further detail tomorrow - some weird behaviour seen from benchtop PSU, and charging from lead-acid battery needs testing.

Day 3: 24/11/21

Henry gives up.