Electrokinetica The Electro-mechanical Museum

Air Ministry Mark II 20kVA Mobile Generating Set - Progress

Minor works

Various small jobs were completed in odd moments. Being parked up in a convenient spot near the workshop, it was easy to pop into the trailer for a quick tinker.

Lister spanners

Lister spanners

March

July

Panel meters

Panel meters

Ammeter and voltmeter repaired. Both had fatigued and disintegrated internal parts, due to the heavy vibration the set imposes on the switchboard. They had also been crudely repaired before, and both will require new pivots to achieve proper accuracy, but are working for indication purposes. The bakelite cases are repaired and the peeling paint on the voltmeter dial treated with fixative. Voltmeter approximately calibrated as far as the stiff pivots permit, and damaged ammeter vane repaired. Faulty battery charger investigated. Temporarily replaced shorted selenium rectifier with silicon bridge.

November

New spare gaskets

New spare gaskets

June

In anticipation of running the set at full load, the fuel system was thoroughly cleaned out and new filters fitted. The engine governor was set carefully to 1000 rpm, the correct speed for generating 50Hz AC with a 6-pole alternator. All loose items were removed from the trailer and heavy tools brought on board.

The set comes to life!

July

The essential tool for replacing the coupling was a 2 inch Whitworth spanner, with which to remove the flywheel nut. Flywheels (particularly Lister diesel engine flywheels) tend to be securely attached as the forces acting on them are substantial and they must not be allowed to shake loose. We did not want to mess about. A very high quality spanner over 3 feet (1 metre) long was offered up and Lucien’s weight plus Edward’s clout with a 12lb (5.5kg) sledge hammer were applied to it. The nut was not apparently in the mood to argue for more than a minute or two! The alternator and switchboard were unbolted from the bed and moved out of the way, and a puller attached to the flywheel. This was tightened up good and hard and tickled with the hammer, and the flywheel went ‘clunk’ and came free. It was off for about half a minute, just long enough to slip the bolts in.

July 8th - startup day

Coupling bolts fitted

Coupling bolts fitted

First, a simple reassembly job. The shims that had previously been missing from the alternator were found wedged under part of the frame, and allied with the shims found in one of the lockers the correct thicknesses were made up and the alternator was set up true on the bed, doweled and bolted. The coupling was assembled and all the bolts either lockwired or split-pinned. Some of the new parts fitted to the coupling assembly had been in their wrappers for over half a century.

Preparations in progress as the machine is re-installed on the genset bed. Watch video: Fitting the generator

The wiring was lashed up with a few quick repairs just to make it functional, then a final check was made on the insulation to ensure that the generator was safe to power up. The Tonum regulator was visibly out of adjustment and required an overhaul, so the voltage regulation was switched to manual control. By this time Dave and Alex had arrived to join Edward and Lucien and watch the lights come on. After a false start (Lucien left the fuel rack locked in the stop position) the generator responded with volts as the exciter field was increased and at 220V Edward flipped the lightswitch on the trailer wall.

First run with the generator coupled up. Watch video: The lights blaze out

Planned works

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