Spring 2018

Gloucestershire Heritage Hub

Discovery down under


A recent enquiry to the local Dursley & Cam Historical Society was referred to me by their Chairman, Andy Barton. He had received a photograph of an AC/DC motor generator set mounted on a cast iron bedplate clearly bearing the name Mawdsley’s Ltd. Dursley, Glos.


Shows AC/DC MG set as found.                                               Detail showing field coil clamp.                                            

Detail of brush gear and rocker with coiled collector lead to allow rocker adjustment

The machine had been discovered in the Hawkes Bay, New Zealand  Opera House when work was started to reinforce the foundations against future earthquakes. Many tons of concrete have been pumped into these basement areas and the motor generator set was one of the many old artefacts found in a sealed room before the pumping operation commenced. The Opera House was built in 1915 and the enquiry was whether the set dated from then or a later period.

Mr Mawdsley began manufacturing his machines at Dursley in 1907 and his earliest designs employed yokes of cast iron with the poles cast in as one piece and no Inter/Commutating poles.  With the nameplate carrying patent No’s 6666/02; 9604/03 and 19174/07 and the yoke and poles clearly of solid cast iron I realised it must be one of these very early designs and so could date the set from the very early years of the Opera House where it may have been used to supply DC power for arc lighting or scenery hoists motors.


            Generator(Dynamo) nameplate

The nameplate data  of 80 volts and 80 amperes gives an output of 6.4kW at 900 rpm and, from the  information I had found from this period and included in my book, “The Mawdsley Story”, I deduced it should be in the M6 frame size and subsequent measurements taken in New Zealand confirm that this is the model,  with its 10 inch diameter armature.

The AC  induction driving motor, an early model of a type invented in 1888, was made by General Electric, Schenectady, USA. With a nameplate output of 20HP at 960 rpm it may have been the nearest stock size machine that was then available.  Mawdsley’s, themselves, did not manufacture AC motors until the late 1920’s 

This is a very rare find of one of Mr Mawdsley’s original design machines and could well be the only one still in existence.  In 1957, to celebrate the Firm’s fiftieth anniversary, an exhibition of old machines was held and, despite enquiries made at the time, no “M” type machines were found.

I understand that the Opera House people intend to make a museum space for the various artifacts found so, hopefully, these very old machines will be preserved .

L H Jones CEng. MIET.      





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