A320 Electrical Logic
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Joined: Dec 2025
Aviation Qualifications: Non-Aircrew
Posts: 1
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From: Portugal
A320 Electrical Logic
Hi everyone,
I’m diving deep into the A320 electrical system and I’ve run into a logic puzzle I can’t quite solve.
The Scenario:
Total AC loss (Dual Engine Failure).
RAT has deployed and is successfully powering the AC ESS Bus, which in turn powers the DC ESS Bus via the ESS TR.
Crucial factor: In this hypothetical, the Main Batteries have completely failed or depleted (0% charge).
The Question: What happens to the Hot Battery Bus (1 & 2) and the vital services connected to them (like fire extinguishing squibs, engine clocks, etc.), if the battery eventually runs out?
In my mind, it doesn't make sense for the ESS Busbars to be powered by the RAT while the Hot Busbars go dark. If the RAT is supplying the DC ESS Bus, is there a "back-feed" or a charging circuit that keeps the Hot Battery Bus energized even if the physical battery is dead?
Or, are the Hot Battery Buses strictly "battery-only," meaning we'd lose fire protection even with the RAT spinning?
Would love to hear from any A320 pilots or maintenance tech who can explain the internal "bridge" between the DC ESS and the Hot Battery Bus in this specific emergency config. Thanks.
I’m diving deep into the A320 electrical system and I’ve run into a logic puzzle I can’t quite solve.
The Scenario:
Total AC loss (Dual Engine Failure).
RAT has deployed and is successfully powering the AC ESS Bus, which in turn powers the DC ESS Bus via the ESS TR.
Crucial factor: In this hypothetical, the Main Batteries have completely failed or depleted (0% charge).
The Question: What happens to the Hot Battery Bus (1 & 2) and the vital services connected to them (like fire extinguishing squibs, engine clocks, etc.), if the battery eventually runs out?
In my mind, it doesn't make sense for the ESS Busbars to be powered by the RAT while the Hot Busbars go dark. If the RAT is supplying the DC ESS Bus, is there a "back-feed" or a charging circuit that keeps the Hot Battery Bus energized even if the physical battery is dead?
Or, are the Hot Battery Buses strictly "battery-only," meaning we'd lose fire protection even with the RAT spinning?
Would love to hear from any A320 pilots or maintenance tech who can explain the internal "bridge" between the DC ESS and the Hot Battery Bus in this specific emergency config. Thanks.
Joined: Jun 2007
Posts: 3,443
Likes: 39
From: Wanderlust
RAT doesn't charge batteries. That's why while starting a flight you check battery condition. Also with both AC buses failing in air repeated starting attempts of APU is not recommended as it knocks off 3 mts battery charge out of the 30mts total charge available.
