Display Of Early Dynamos


Replica made by Rex Redding of DalbyThis replica is of Thomas Edison’s first practical design of dynamo. Edison used larger dynamos of this type to generate electricity for his Pearl Street scheme in the Wall Street financial district of New York. This major scheme gave the first public supply in the USA. Switch-on was in September 1882.

​These dynamos were nicknamed ‘Long-legged Mary Ann’ because of their long field magnets. The electric current in the field windings on the long legs produced a strong magnetic field across the armature windings on the rotating shaft.Electricity is generated in the coils rotating with the shaft. Dynamo output is direct current, commonly referred to as DC. The current generated is collected from the dynamo via the two brushes that rub against the commutator as the shaft rotates.


Nameplate details: “EDISWAN” DYNAMO, No. 190, VOLTS 100. AMPS 60, REVS 1500
This Edison-Hopkinson generator is possibly from about 1885. It is a commercial machine made by the Edison&Swan United Light Company Limited of England.
With the objective of improving the efficiency of his early long-legged dynamos, Edison sought advice from Professor John Hopkinson, Professor of Electrical Engineering at King’s College in London. Hopkinson advised that shorter field magnets would be more efficient. The shorter, more compact field magnets of this machine are a result of Professor Hopkinson’s recommendation.
The output of the generator is 6000 watts or 6 kW. (100 volts by 60 amps) Six kilowatts is about 8 horsepower.
Thomas Edison of the USA and Joseph Swan of England each independently invented the incandescent electric lamp. Following a legal battle, they agreed to combine their business activities in England. The result, the Edison&Swan United Lighting Company, founded in October 1883. From then, the company had a virtual monopoly on electric lamps in the UK for a number of years. These lamps were made to Swan’s design rather than to Edison’s.
The business name Ediswan existed in the UK until about 1964.


A DC motor driving a DC generator. 

A motor generator set or m-g set, was used to convert one form of supply to another form. Many m-g sets converted AC supply to DC; others DC to AC; others one voltage supply to another. 
This machine was used to convert 220 volts DC supply to 6 volts DC. A likely use was for battery charging. 220 volts was a common DC supply voltage. Early cars had 6 volt batteries.
In this example the motor is on the left and the generator is on the right.
Nameplate details


  • Motor: VOLTS 220, B.H.P. 2, R.P.M. 1250, No. 35953
  • Generator: VOLTS 6, R.P.M. 1250, AMPS 230, No. 39199
  • Both machines made by Crompton & Co. Ltd. (an English firm).

B.H.P. is brake horsepower; R.P.M. is revolutions per minute
To handle its high current, the 6 volt generator, on the right, has a longer commutator with a larger set of brush gear. The carbon ‘brushes’ of the brush gear rest on the commutator to switch and collect the current generated by the shaft-mounted armature windings.
The handle projecting from the box mounted between the two machines operates the motor starter.

A separate, oval, nameplate shows that the set was the property of the City Electric Light Co Ltd, which supplied electricity to the central area of Brisbane in the first half of the 20th century. For a time, the CEL encouraged new load by offering to hire out electric motors to its customers. It appears that this set is an example of this. From this fact, the estimated date of manufacture is in the 1910s, which is supported by the machine nameplates indicating that the machines are covered by patents dated 1910.

The CEL nameplate states ‘This motor is the property of The CEL Co Ltd Brisbane, motor no. 1327’.