AF motors & rectifiers

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How to wire an AF motor for DC Polarity reversing
and eliminate the reversing unit. by Chuck Smith cesmith@eznet.net

This is how an AF series wound motor is wired. The reversing unit wires are removed in this view for clarity. Power supplied is AC or DC.
This shows the full wave rectifier inserted between the armature and the field. Only DC power is supplied.

The rectifier has four leads, two marked as + and -. The + and - leads are the "output" and will serve to keep the polarity of the field constant when the input polarity is changed. This reverses the motor in exactly the same way as the reversing unit, by reversing the polarity between the armature and the field. The motor now can only run on DC. The direction of the motor should ideally be set to forward movement with the RH rail +. This can be accomplished by interchanging the output leads. The input for the 'rectifier' example above is directly from the tender pick up (for steam engines) or power leads (for diesels). The rectifier could alternatively be wired across the armature and the result would be the same.

Here is a picture of a rectifier installed in a tender.

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