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12 V low-voltage battery cutoff

Bench build · Batteries and solar · Intermediate · about 40 minutes

Disconnects the load before the battery is damaged. Lead-acid and lithium batteries are damaged by deep discharge. A comparator watches a fraction of the battery voltage against a TL431 reference and switches the load’s MOSFET off below about 10.9 V. Positive feedback (R_h) adds hysteresis, so the load only comes back above about 12 V instead of chattering on and off.

12 V low-voltage battery cutoff: the finished build running on the simulator's bench

Build it in the labGuided build, test sheet and fault finding, free in your browser.

Parts list

Test procedure

Each test has an expected value and a pass range, like a factory test sheet:

  1. 12.6 V: load on
  2. 10.6 V: load off
  3. Back up to 11.85 V: stays off (hysteresis)
  4. Recharged to 12.3 V: back on

How it works

What it does: Disconnects the load before the battery is damaged.

Build it (guided or ready-made), then run its test procedure below. Every test has an expected value and a pass range, just like a factory test sheet.

Background

Built into every solar charge controller’s load output and car fridge.

More builds: batteries and solar