Editing Motor–generator (section)

{{Short description|Device for converting electrical power to another form}}
{{Distinguish|text = [[engine-generator]], a device that uses an internal combustion engine to drive an electric generator}}

[[Image:Umformer.jpg|thumb|222px|Aircraft radio modulator unit from the Second World War, showing a dynamotor (the black cylinder) which converts the aircraft's 24–28 V DC to 500 V DC for the transmitter. [[Dübendorf]] Museum of Military Aviation]]

A '''motor–generator''' (an '''MG set''') is a device for converting [[electricity|electrical power]] to another form. Motor–generator sets are used to convert [[frequency]], [[voltage]], or [[Phase (waves)|phase]] of power.  They may also be used to isolate electrical loads from the electrical power supply line. Large motor–generators were widely used to convert industrial amounts of power while smaller motor–generators (such as the one shown in the picture) were used to convert [[battery (electricity)|battery]] power to higher DC voltages.

While a motor–generator set may consist of distinct motor and generator machines coupled together, a single unit '''dynamotor''' (for [[dynamo]]–motor) has the motor coils and the generator coils wound around a single rotor; both the motor and generator therefore share the same outer field coils or magnets.<ref name=arrl1976>[https://archive.org/details/RadioAmateurHandbook1976 Radio Amateur's Handbook], 1976, pub. [[ARRL]], p331–332</ref> Typically the motor coils are driven from a commutator on one end of the shaft, while the generator coils provide output to another commutator on the other end of the shaft. The entire rotor and shaft assembly is smaller, lighter, and cheaper than a pair of machines, and does not require exposed drive shafts.

Low-powered consumer devices built before 1933, such as [[vacuum tube]] vehicle radio receivers, did not use expensive, noisy and bulky motor–generators. Instead, they used an [[Inverter (electrical)|inverter]] circuit consisting of a [[vibrator (electronic)|vibrator]] (a self-exciting relay) and a [[transformer]] to produce the higher voltages required for the vacuum tubes from the vehicle's 6 or 12 V battery.<ref name=vib>{{cite web |url=http://www.radioremembered.org/vpwrsup.htm |title=Vibrator Power Supplies |newspaper=Radioremembered.org |access-date= 18 January 2016}}</ref>