Dynamo

Dynamo

In 1928, following closure of the Harford and Bristol Brass Company, the mill was bought by Eric Butler, a director of William Butler and Company, 'Tar, Rosin and Oil Distillers' of Crews Hole on the Avon between Saltford and Bristol.

Butler was a Freeman of the City of London, Liveryman of the Worshipful Company of Wheelwrights, and Special Commissioner for the Inland Revenue. He was also a keen sportsman who fished, piloted his own light aeroplane and played tennis and squash. Butler owned the Craig, opposite the mill, and purchasing the mill to use the building as a sports centre.

Butler converted a workshop occupied by a set of battery hammers into a squash court, installed electric light to illuminate the squash court and adapted one of the waterwheels to drive a dynamo to provide power for the lighting; noting that at this time the national grid did not exist and Saltford itself was not provided with electric power.

He laid concrete floors and provided a concrete plinth above the flood level on which he mounted an 'Ediswan' (Edison-Swan) dynamo. The dynamo produced direct current (modern domestic supplies are alternating current) and was capable of generating 11 kW at 210 volts when rotating at 1450 rpm. Power was distributed from a switchboard, provided with a volt meter, ammeter, voltage regulator and distribution switches.

A combination of chain and belt drives were used to connect the waterwheel to the dynamo, enabling the dynamo to be turned at 1450 rpm with the waterwheel revolving at just over 9 rpm. With such a gear ratio fine control of speed, and hence voltage, would have been difficult. A small increase in the waterwheel speed, say to 10 rpm, would have resulted in the voltage increasing to 225 Volts which would have probably 'blown' the electric lamps.

The dynamo still works but has been down rating in consideration of its age and the condition of the wiring. When first installed, the dynamo was self exciting, producing 210 volts DC with the voltage being regulated by a rheostat regulating the current through the field coils. Today we excite the machine using an external 12V supply which enables the machine to generate between 12V and 24V, sufficient to light a small bank of LED lamps for demonstration purposes.

Later Use

In 1956 the mill was sold to Charlie Sheppard, who operated as Bristol Boats Ltd. The Sheppards installed a bench saw adjacent to the dynamo, which rotated at 1600 rpm and was capable of cutting timbers up to 9ft long. The installation included three additional pulley wheels to connect the saw to the dynamo drive and a ‘belt shifter’, known as a 'fast and loose mechanism' to enable the saw to be stopped without stopping the waterwheel.