48V Vehicle Architecture Explained: Why Ford and Leapmotor Are Ditching 12V (Wiring, Arcing, No Aux Battery)

 

Bottom line: After 70 years of 12 V, two automakers just put dates on replacing it. Ford's Universal EV (UEV) and Leapmotor's LEAP 5.0 both go 48 V and zonal, and Leapmotor also deletes the auxiliary battery. Here's where 48 V really saves copper, what it breaks, and what losing the 12 V battery costs.

What happened

• Ford (reported Oct 9): After camera-fault finger-pointing between suppliers and OEM, Farley said Ford "purposely decided the UEV had to be a zonal electric architecture with 48 volts designed all in house." Ford says the platform uses five main modules where a conventional vehicle has more than 30 scattered ECUs, and that the midsize truck's harness is 1.3 km (4,000 ft) shorter and 10 kg (22 lb) lighter than in its first-gen electric SUV.
• Ford e-box: the 48 V DC-DC converter, DC fast-charge hardware and AC onboard charger share one box mounted inside the battery pack (GreenCars lab tour).
• Leapmotor (Sept 30 Tech Day): 48 V brings total wiring under 500 m and harness weight down by up to 50%. CTC 3.0 drops the standalone 12 V battery; the main pack keeps a small reserve below 0% displayed SoC for power-up and central locking. Models arrive from 2027.

Two separate levers: shorter and fewer wires come mostly from zonal topology (ECUs wired to the nearest zone controller, with an Ethernet backbone linking the zones). Thinner wires come from 48 V. The headline weight savings combine both.

Point 1: 16x is the textbook number; expect 5 to 8x

Take a 1 kW load on a 3 m feed with a 3% voltage-drop budget (copper at 0.0172 Ω·mm²/m, chassis return). At 12 V the feed carries 83 A. A 0.36 V budget calls for about 12 mm², or roughly 320 g of copper. At 48 V the current is 21 A and the budget is 1.44 V, which gives 0.75 mm² and about 20 g. That is exactly 1/16. But 21 A in 0.75 mm² dissipates about 10 W/m, too hot for a bundled harness, so thermal limits push you back to 1.5 to 2.5 mm²: a realistic 5 to 8x copper saving on power feeds. Signal wiring (CAN, Ethernet, sensors) doesn't shrink with voltage, which is why whole-harness savings top out near 50%. These are my estimates.

Point 2: arcs that don't go out, and only about 8 V of headroom

Per Aptiv's design guidance, 12 V break arcs usually self-extinguish, while 48 V arcs can persist long enough to destroy terminals, so hot disconnects and fretting corrosion become thermal events. The window is tight too: LV 148 defines 36 to 52 V for unrestricted operation and 52 to 54 V with restricted function, and protection is designed to 60 V. Above 60 V DC it's high voltage (orange cable, HV rules), leaving about 8 V of room for load-dump and regen transients. Hence 80 to 100 V MOSFETs, IEC 60664-1 creepage, and semiconductor eFuses in place of fuses and relays; NXP's CoreRide Z248 reference design integrates exactly that.

Point 3: with no 12 V battery, what keeps the car alive?

The aux battery wakes the car with HV contactors open, backs up brakes and steering if the DC-DC fails, and buffers spikes. Leapmotor uses a main-pack reserve instead, and on energy alone that's better. A 2 W parked load over 30 days uses 1.44 kWh, or 2.4% of a 60 kWh pack. A 60 Ah lead-acid battery holds 0.72 kWh nominal, and at about half usable it is flat in 7 to 8 days. The harder questions: which part of the stack feeds the LV rail with contactors open, how a kilowatt-class converter stays efficient at 2 W, and where by-wire brakes and steering get their second independent supply. Leapmotor hasn't said (my inference on the risks).

Point 4: why Ford brought the DC-DC in-house

Ford says HV-to-48 V conversion "can account for a surprising amount of wasted energy," so it took power-electronics design in-house in 2023. At a 400 W average LV load, 94% versus 97% efficiency is about 13 W, roughly 0.15% of traction energy at 60 km/h. The real waste is likely long light-load periods (charging, OTA, connected parking) where converters are least efficient (my inference). Mounting it in the pack also deletes a heavy LV feed. Ford's claim of similar range from a battery up to one-third smaller is a whole-vehicle claim, not a 48 V one.

Open questions

• Does the Ford UEV keep a small 48 V lithium battery or supercapacitor buffer? Ford hasn't said.
• After a crash or HV disconnect, what powers Leapmotor's redundant brake supply, hazard lights and eCall? Not disclosed.
• Will 12 V accessories (dashcams, power outlets) run from small 48-to-12 V islands? No OEM detail yet.
• Gauge, thermal and standby figures are illustrative; real values depend on bundling, ambient and ECU sleep design.

Related videos

• Why Automakers Refuse to Build Cheap, Non-Smart EVs?
• From 400V to 800V: The Silicon Carbide Revolution

Quick poll: would you buy an EV with no 12 V battery? A) Yes, the main pack outlasts lead-acid. B) No, I want a physical backup. C) It depends on the warranty. Tell me in the comments.

Sources: Ford Authority: Farley on the UEV 48 V zonal architecture (Oct 9, 2026), Stellantis Media: Leapmotor LEAP 5.0 and CTC 3.0 (Sept 30, 2026), Ford: UEV electrical architecture and power conversion, Ford: UEV harness 1.3 km shorter, 10 kg lighter, GreenCars: Inside the UEV Program, Aptiv: How to Make the Leap to 48V, NXP CoreRide Z248 48 V zonal reference system, testxchange: LV 148 voltage ranges.
Published on The Automation Core | Video: The Engineering Core YouTube channel