Inside the ALDI Ferrex 20/40V battery charger with schematic

An internal exploration of the charger used for the dual voltage Activ Energy 20/40V power tool batteries.
The circuitry breaks down into two distinct sections. A fairly conventional power supply and a charge control system. The main oddity about the power supply section is that it has extra voltage regulation for its controller due to the variable output voltage range that is adjusted to maintain a constant charge current.

The low voltage control circuitry is based on a chip marked Lideal 1508 B9417001V89.
It has the facility for bidirectional communication with the battery pack, which has two sections with a common master control chip. It can also monitor the pack temperature during charging.
When the pack is charging the controller can adjust the power supply voltage to maintain a constant current via a sense resistor. Each section of the battery has its own MOSFET so it can be charged independently if needed, especially for basic balancing, although the batteries themselves don't seem to have individual cell balancing.

The tools that use the dual voltage batteries simply connect the two battery modules in series or parallel as needed. They are enabled by the detection of the battery thermistors, which are also used by the battery itself to signal that charge is low and stop the tool operating.


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