Everything Wrong With This Acorn Stairlift Transformer

Everything Wrong With This Acorn Stairlift Transformer

- Certified for 15VAC output (±10% per NEC Class 2 limits).
- Internally, a standard doorbell transformer with no isolation or regulation.
- Measured output: 18.2VAC RMS with a fluctuating DC offset from +7V to -12V, indicating internal failure (e.g., shorted winding or contamination).
- This AC+DC signal fed the Acorn 120’s unregulated bridge rectifier, charging two 12V/7Ah SLA batteries in series (24V system).
- The distorted input tricked the control board into suppressing error codes (H7/F7), falsely indicating normal operation.
- Chronic overvoltage and ripple current forced batteries into thermal runaway, causing one SLA unit to vent toxic sulfuric acid mist and lead oxide particulates (visible as white crust).
- All components were enclosed in a sealed chassis—no visual access, no gas venting, no alarms.
- The user, dependent on the stairlift and unaware of the silent hazard, is now deceased.
- Root cause: A non-failsafe transformer combined with a charging system lacking overvoltage or ripple protection—a known but unaddressed risk in Acorn’s design.