Editing Rectifier (section)

=== Electromechanical ===
Before about 1905 when tube-type rectifiers were developed, power conversion devices were purely electro-mechanical in design. [[Mechanical rectifier]]s used some form of rotation or resonant vibration driven by electromagnets, which operated a switch or commutator to reverse the current.

These mechanical rectifiers were noisy and had high maintenance requirements, including lubrication and replacement of moving parts due to wear. Opening mechanical contacts under load resulted in electrical arcs and sparks that heated and eroded the contacts. They also were not able to handle AC [[frequencies]] above several thousand cycles per second.

==== Synchronous rectifier ====
{{main|Synchronous rectification}}
To convert alternating into direct current in [[electric locomotive]]s, a synchronous rectifier may be used.{{Citation needed|date=October 2009}} It consists of a synchronous motor driving a set of heavy-duty electrical contacts. The motor spins in time with the AC frequency and periodically reverses the connections to the load at an instant when the sinusoidal current goes through a zero-crossing. The contacts do not have to ''switch'' a large current, but they must be able to ''carry'' a large current to supply the locomotive's DC [[traction motor]]s.

==== {{anchor|Vibrator}}Vibrating rectifier ====
{{Main|Mechanical rectifier}}
[[File:Vibrator rectifier battery charger.jpg|thumb|A [[vibrator (electronic)|vibrator]] battery charger from 1922.  It produced 6 A DC at 6 V to charge automobile batteries.]]
These consisted of a resonant [[reed switch|reed]], vibrated by an alternating magnetic field created by an AC [[electromagnet]], with contacts that reversed the direction of the current on the negative half cycles. They were used in low power devices, such as [[battery charger]]s, to rectify the low voltage produced by a step-down transformer. Another use was in battery power supplies for portable vacuum tube radios, to provide the high DC voltage for the tubes.  These operated as a mechanical version of modern solid state switching [[inverter]]s, with a transformer to step the battery voltage up, and a set of vibrator contacts on the transformer core, operated by its [[magnetic field]], to repeatedly break the DC battery current to create a pulsing AC to power the transformer. Then a second set of [[mechanical rectifier|rectifier contacts]] on the [[vibrator (electronic)|vibrator]] rectified the high AC voltage from the transformer secondary to DC.
{{clear}}

==== Motor-generator set ====
{{Main|Motor-generator|Rotary converter}}
[[File:Rotierender Umformer.jpg|thumb|A small motor-generator set]]
A ''motor-generator set'', or the similar ''rotary converter'', is not strictly a rectifier as it does not actually ''rectify'' current, but rather ''generates'' DC from an AC source. In an "M-G set", the shaft of an AC motor is mechanically coupled to that of a DC [[Electrical generator|generator]]. The DC generator produces multiphase alternating currents in its [[armature (electrical engineering)|armature]] windings, which a [[commutator (electric)|commutator]] on the armature shaft converts into a direct current output; or a [[homopolar generator]] produces a direct current without the need for a commutator. M-G sets are useful for producing DC for railway traction motors, industrial motors and other high-current applications, and were common in many high-power DC uses (for example, carbon-arc lamp projectors for outdoor theaters) before high-power semiconductors became widely available.
{{clear}}