Battery Isolation and Pre-Charge
High-Voltage DC Contactor Bank with Pre-Charge and Pyro Backup
High-voltage DC contactor assembly with pre-charge resistor, normally-closed pyrotechnic backup disconnect, and arc-suppression that electrically isolates each battery rack from the main bus during fault, maintenance, or scheduled disconnect.
Purpose
Provide the last-line electrical safety feature for the battery system — break high-voltage DC fault currents before they propagate, allow safe robotic module replacement, and avoid inrush damage when racks reconnect.
Context
Sits at the rack output of each L3-ESS-LITH-RACK, between the rack bus bar and the main DC bus in L1-PDM. Commanded by L3-ESS-LITH-BMS for normal operations and by L2-ESS-MGMT for system-level events; can also be tripped by hardware safety interlocks.
Principles
- ▸DC arc extinction is harder than AC — DC contactors require sealed magnetic-blowout arc chambers, hydrogen gas-filled chambers, or vacuum interrupters
- ▸Pre-charge resistor (typically 50–100 Ω, several seconds) limits inrush when reconnecting a capacitor-rich bus
- ▸Pyrotechnic disconnects (e.g., Eaton SDR) sever bus bars in milliseconds for catastrophic events — single-use
- ▸Contactor coil-hold currents minimized via PWM economizer to reduce continuous power
- ▸Latching contactors hold state without continuous current — preferred for long-life applications
- ▸Voltage ratings: 800 V DC, 200 A continuous for the rack — main consideration
Typical implementations
- ▸Gigavac GX series HVDC contactors (terrestrial automotive, used on spacecraft via space-grade variants)
- ▸Eaton Pyrofuze pyrotechnic disconnects on spacecraft
- ▸TE Connectivity Hartman contactors (legacy aerospace)
- ▸Custom NASA Glenn HVDC contactors for lunar applications
- ▸Tesla high-voltage main contactors (terrestrial, with vacuum-arc-suppression heritage)
Lunar considerations
- ▸Long-duration sealed-magnetic contactors require hermetic enclosures to maintain dielectric integrity over 25 years
- ▸Pre-charge resistor must dissipate 0.5–2 kJ per reconnect cycle without damage — high-power ceramic resistors
- ▸Pyrotechnic backup disconnect is single-use and must survive 100-year storage without misfire — NASA-grade NSI initiators
- ▸Lunar dust ingress into mechanical contactor mechanism mitigated by sealed housing
- ▸Latching mechanisms preferred to minimize continuous coil power during long lunar nights
- ▸Hardware safety trip path bypasses software — direct from BMS comparator outputs
Specifications
Functional
| primary function | Connect/disconnect battery rack from main DC bus under normal and fault conditions |
| inputs | Control commands from L3-ESS-LITH-BMS, Hardware safety-trip signal (over-current, over-temperature), Pyrotechnic fire command (catastrophic shutdown only) |
| outputs | Mechanically closed or open contacts in main bus, Auxiliary contacts for state confirmation, Telemetry: coil current, contact temperature, position |
| contactor voltage v dc | 800 |
| contactor current continuous a | 200 |
| contactor current breaking a | 1000 |
| operating cycles min | 10000 |
| pre charge resistor ohms | 75 |
| pre charge duration s | 3 |
| pyrotechnic disconnect time ms | 5 |
| coil hold power w | 2 |
| latching design | True |
Physical
| mass kg | 5 |
| dimensions | 200 × 150 × 100 mm sealed enclosure |
| materials | Cadmium-bronze contact surfaces, Hermetic gas-filled (H2) arc chamber, Ceramic high-voltage standoffs, Pyrotechnic device with NSI standard initiator, Wirewound ceramic pre-charge resistors, Anodized aluminum housing |
| operating temperature c | -40, 80 |
| radiation tid krad | 100 |
| ultimate load g | 12 |
Operational
| power consumption w holding | 2 |
| power consumption w transition | 30 |
| thermal range c | -40, 80 |
| lifetime years | 25 |
| mtbf hours | 500000 |
Interfaces
Provides
- Switched connection between rack and main DC bus
- Contactor position and health telemetry
Requires
- Open/close commands and safety-trip signals
- Rack bus bar input
- Coil power supply (~30 W transient)
Cite this entry
Lunar Ark Codex. "Battery Isolation and Pre-Charge" (L3-ESS-LITH-ISOL). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-ESS-LITH-ISOL
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.