House vs Starter Battery: Isolation, LVD & Storage Mode

Rule #1: your smart lock never touches the starter battery. Ever.

1) Isolation: Keep Systems in Their Lanes

• Alternator → DC-DC charger → House bank. Do not tee into OEM starter circuits for "just a little 5V."
• Benefits: correct charging profile, surge control, and no starter-battery parasitic nibble.

2) Source of Truth for the Lock

• Feed the lock from the house battery bus on a fused branch (0.5–1 A).
• Place the buck converter near the door; verify 5.0–5.2 V during actuation.

3) LVD (Low-Voltage Disconnect)

• Add an LVD module on the lock branch or upstream on the 12 V house bus.
• Set cut-off ~11.4–11.8 V (lead-acid) or ~10–11 V (LiFePO₄ vendor spec). The lock remains operable with a mechanical key.

4) Storage Mode (Weeks or Months)

• Master kill switch for electronics (lock remains mechanically usable).
• Rotate to a mechanical-only routine if stored indoors; leave a service card inside with re-enable steps.

5) Health Checks

• Log idle draw (mA) and actuation peak (A). If idle creeps, find the phantom load.
• Torque-mark fasteners and note LVD set-point on the service card.

Related Reading

• 12 V Integration for Vanlife Smart Locks — Fusing and buck converters.
• Cold-Start Behavior in Vans — Battery chemistry and performance.