Avionics Power System (APS) Requirements

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Requirement Semantics

There are three levels of requirements: - MUST = The requirement must be met. - SHOULD = We really, really want it, but don't have to have it. - MAY = "Wow wouldn't be great if"

Requirements

General requirements
- Parts SHOULD cost <150$ in small quantities (does not include battery)
- APS sleep current under (,100,750)uA
Umbilical
- MUST seamlessly shift between shore power and battery power
- MUST be able to detect the presence of shore power
- MUST wake up APS microcontroller if shore power turned on
- MUST be able to sense if connector is inserted or removed (launch detect)
Battery pack
- SHOULD be a 4-series cell Li battery
- Battery SHOULD cost <500$
- Overall Battery SHOULD have energy-mass density (100,,) W.hr/kg
- Overall Battery energy-volume density SHOULD be (200,,) W.hr/l
- Battery capacity SHOULD be (4,8,) Ahr (TODO: TBD on new power budget)
- SHOULD have dimensions less than (,3.0,3.5) inches in the cross sectional plane of the airframe, length (,,10)inches
- MUST have a fuse in the pack before the lead
- Total battery "unplugged" leakage MUST be < C/(1,5,) year rate (e.g. ~ 100 uA for 4 Ahr)
Battery charger
- MUST meet standard lithium charge/discharge safety requirements (thermal, voltage, current, time, fuse)
- MUST be able to charge at (,1C,C/2) rates at internal air temperature of 50 deg C.
- MAY equalize cells up to some small bypass power (e.g., .5W)
- MUST indicate charging status (on/off)
- MAY indicate some kind of charge % (blink rate, color, LED bar graph, etc)
Battery Sensors
- MUST monitor charge ("coulomb counter")
- MUST measure pack voltage
- SHOULD: monitor the voltage on each cell
- MUST monitor battery pack temperature (MUST be compatible with charging chip)
- SHOULD separate high current connector from sensing connector
Power Switches
- MUST have (8,,) independent resettable electronic circuit breakers with adjustable current trip and trip delay. Setting can be via resistor strap, EEPROM, etc. Current trip should be latch-off or selectable.
- MUST have Soft on/off feature
- MUST have no mechanical switches in main power path.
- MUST indicate power switch on/off state (LED for human, and electrical signal for APS node)
- MAY indicate power switch fault state
- MUST operate continuously within 20% of the over-current set point
- MUST allow set currents in the range (0.1, 5)A
- MUST allow over current transients of 100% for minimum 100 ms without fault to the load
USB hub
- SHOULD be USB 2.0 compliant High Speed (480 Mbps)
- MUST handle (8,,) downstream devices (devices may be further hubs)
- SHOULD have hub status LEDs
Backchannel
- MUST handle (8,,) downstream devices
- MUST listen to the Pyro node by default
- SHOULD wake on Pyro backchannel message (via Pyro radio)
Firmware
- SHOULD power up the FC and ? when umbilical connector insertion/extraction sequence is detected
- MUST be able to pipe UART umbilical to FC serial terminal
- MUST execute power switch and battery charging commands from FC over USB
- MUST execute power switch and battery charging commands from external PC over umbilical UART
- MUST check power switches and reset as necessary
- MUST have modes of operation: unarmed, armed (more TBD)
- MUST check battery status and set battery charger AND power switches as appropriate to mode
- SHOULD execute power switch and battery charging commands from backchannel
- TODO: More?

Misc Notes

Umbilical should have a power indicator light, RX and TX lights, at the connector, or probably better within a few feet of the connector.