Danu

the Sub · system

Power

About 3.7 kWh across three battery banks, plus an independent survival battery, watched cell by cell — fused at every source, with a supervisor-driven master cut.

Power one-line

Bank A · 4S16P + BMSBank B · 4S16P + BMSBank C · 4S16P + BMS60 A fuse60 A fuse60 A fuseORing diodeORing diodeORing diodeMain fuse · 80–100 AContactor — master cutPropulsion bus + bulk caps6× ESC → 6× T2005 V rail → fuse block12 V rail → lights, coilJetson · Pixhawk · sensorsSurvival 12 V → SupervisorMagnet → reed → SupervisorCharge port (surface) → BMSSupervisor opens the contactor on fault / leak / low-batt / disarm.Hull floats — DC isolated from water · magnesium anode · a fuse at every source.

Decisions & notes

Power & energy

  • ~3.7 kWh across three 4S16P banks (Daly 4S 100 A smart BMS each) + an independent 12 V survival battery.
  • Protection: a fuse at every source — ~60 A per bank (before the ORing diode), ~80–100 A main, ~10 A survival + electronics; high-interrupt ANL/MIDI for lithium.
  • Master cut: supervisor-driven continuous-duty contactor + an external magnetic/reed arm switch (arm with a magnet — no penetrator).
  • Anti-spark XT90-S on the pack; bus bulk caps near the ESCs.
  • Corrosion: DC floats from the hull/water; magnesium sacrificial anode (freshwater).
  • Charging: surface charge port through a penetrator (or open the endcap).

Path to 14-day missions

14 *active* days ≈ ~9–10 kWh (~2.5–3× the current pack); a *dormant/monitor* profile (sleep ~3–6 W, brief daily tasks) fits in far less. The 4″ hull is modular, so more energy = add a 4th bank / longer 400 mm tubes later — a bolt-on upgrade, not a redesign. Build v1 at 3.7 kWh, size the bus/charger/structure for +1–2 banks now, measure real draw in the reservoir, then scale. Hibernation + DVL nav are the enablers.

Parts (23)

Power moduleHolybro PM08-CAN (DroneCAN, 2-14S / 200A, dual 5.2V BEC)Arrived
Pressure tubes ×6WTE Locking Tube 4in aluminum - 1x 300mm (electronics) + 3x 400mm (battery banks)Arrived
Power switch ×2M10 switch 5AArrived
Battery cells ×198Samsung INR21700-58E — 5330 mAh min, 10.7 A cont, flat top. 4S16P per bank x3 = 192 cells + 6 spares; ~3.7 kWh total. See docs/POWER-BUDGET.md.Arrived
BMS ×24S 60/80A Li-ion BMS, 61x42mm (Create idea, 2-pack)Ordered
Survival batteryBioenno BLF-1206A 12V 6Ah LiFePO4Arrived
Spot welderGlitter 801D capacitiveArrived
Nickel stripPure nickel strip 0.15mm x 8mm (~15m needed)Ordered
Pack materialsPack materials — fish/barley paper, Kapton tape, cell-top insulator rings (cell holders are 3D-PRINTED, not purchased)Arrived
Connectors/wireXT90-S anti-spark (pack/bus trunk) + XT60 (thruster & accessory branches); silicone 10 AWG trunk + 12-14 AWG branches + 16-22 AWG signal; JST-GHArrived
5V regulators ×2Pololu D24V50F5Arrived
12V regulators ×2Pololu D36V50F12Arrived
Ideal diodes ×4LTC4357/LTC4359 modules (bank ORing)Planned
Fuses & holdersFuse kit — 4x ANL/MIDI holders (3 banks + main bus) + 6-8 way blade fuse block (low-current branches) + assorted ANL (60A, 80-100A) & blade (10A) fuses + sparesArrived
Thruster-cut (solid state)Solid-state high-side thruster disconnect — 4x IRFB7430 (40V ~1.3 mOhm) paralleled + high-side charge-pump gate driver (LTC7000/LTC7001 class) + TVSArrived
Magnetic arm switchWaterproof magnetic reed switch (NO/NC, 2-pack) — external magnet arms/disarms through the hullArrived
Bus capacitors ×235V 1000uF low-ESR filter capacitor (XT-lead) — mount on the ESC busArrived
Charge portCNLINKO LP20 IP68 2-pin panel connector (20A) — surface charge interfaceArrived
3.3V regulator (LDO) ×23.3 V LDO, 250-500 mA, fed from the 5 V rail — supplies the RM3100 compass (VDD + I2CEN) and any future 3.3 V logicArrived
Pack collectors0.5mm (24ga) C110 copper sheet, 300 x 600mmOrdered
Cell checker ×21-8S LiPo/Li-ion balance-lead voltage checkerOrdered
Timer releaseDIY: ATtiny + coin cells, pottedPlanned
Pack/joint temp ×12DS18B20 1-Wire sensors (TO-92) + 4.7k pull-upPlanned