Two-cell Ni-Cd charger study

How it works

The LM311 compares the battery voltage with an adjustable reference. In the original design, the transistor supplies charging current until the comparator changes state, while an LED indicates charging. The historical notes target two series-connected 350 mAh Ni-Cd cells.

A fixed pack-voltage threshold is not a complete charge-termination strategy. Temperature, charge current, cell mismatch, and elapsed time all matter, so the original 2.81 V cutoff must not be interpreted as a generally safe setting.

On the bench

Reference only pending charger review. Do not use this circuit for lithium cells or substitute battery chemistries. Use a charger designed for the exact cell chemistry and capacity.

Resources & provenance

Rewritten from the original circuits/chi/ud5n9vz_chi002.php page. Component values and historical performance claims have not been independently bench-tested. The circuit figures have had their watermarks removed.