That is a standard Showman's lighting set of the 1950s-1990s, producing 220A at 110V DC. It started life as a WW2-era searchlight generator used to power the carbon-arcs in 90 & 150cm AA projectors. About 15,000 were built between the early thirties and the end of the war, consisting of a Lister 40/4 4-cyl indirect-injection diesel driving a Mawdsleys 4-pole compound dynamo at 1100 RPM, all mounted on a Taskers single-axle trailer. WD searchlight sets were basic and robust, not particularly economical, rather maintenance intensive and hard work to start in the cold (hand start only... Lister's patented variable compression system ensured they would always fire first time, if only you had the oomph to turn the bl**dy thing fast enough to get over the first compression!)
When many of them were sold off after the war, they were ideal replacements for powering Showmens' machines, as they had similar ratings to the traction engine-mounted generators of earlier decades. They were adequate to power a number of small rides outright or either the lighting or the drive of a really big one.
NFA Link:
Billy Smart's pair of original searchlight sets
NFA Link:
Harris Bros 'crossed pair' with the working sides facing out
They gave good service but eventually by the 1960s / 70s the original engines wore out, or the owners got tired of oiling and cranking the heavy old Listers, yet the dynamos were usually still in their prime. So, many were converted with a Gardner 5LW or 6LW direct-injection engine, one of the standard engines found in commercial vehicle fleets at the time. By the 1980s, most searchlight sets, by then the most common source of 110V DC on the showground, had been fitted with a Gardner engine, either by showland mechanics or professional genset builders. They were usually taken off their trailers and mounted two-abreast on a ballast tractor, with a pair of old lorry rads facing out of the back.
In the meantime, the last few Listers soldiered on. John & Anna Carter and their sons ran nine of them at one time, both the 4-cyl 110V DC sets and the similar WD 3-cyl 15kVA AC units. They looked after them carefully and kept some of them going up through the 90s, including a couple on the original trailers still only with hand start. One had a centre bearing seize and bent a rod, eventually the others reached the end of their practical service life, and in the time-honoured fashion some rather nice Gardners took their place (If you visit, look for the 6L3.)
Although both the Lister JP and the Gardner LW debuted in the early 1930s, the crucial difference was that the Lister was purely an industrial engine, but the Gardner was designed from the outset as a high performance road vehicle engine. Much more sophisticated than the Lister, and more economical due to its direct injection and other refinements, the LW and its derivatives and relatives (L2, L3, LX... LCXT etc) were one of the great British diesels that powered Scammells, ERFs etc for many decades, plus trains, boats and industrial plant too. Their endurance is legendary but that's another story.
Back to the one in the picture. The switchboard is original WD spec, although the voltmeter has been replaced. The dynamo looks like a standard Mawdsleys searchlight unit but an additional AC generator has been piggybacked and belt-driven. This was a popular mod in the 1970s as rides started to need AC power too, for the sound system and other electronics, while the lighting and drive remained 110V DC. The engine is a 6LW but I am not sure of its provenance. It seems to have an industrial flywheel with barring holes, but might still have been a vehicle engine. The bedframe and rad are not original searchlight set items either.
And now the inevitable puzzle: Below the knife switch, just to the left of the Niphan socket for the worklight, there is an additional switch contact. What was its function?
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Oops the picture links didn't all work out, try again:
National Fairground archive pics of original searchlight sets on the gaff:
Searchlight set still on its original trailer
Billy Smart's pair of original searchlight sets
Harris Bros 'crossed pair' with the working sides facing out
National Fairground archive pics of sets converted to Gardner:
Typical pair of Gardnerised searchlight sets, W. Nichols
4LW version, Chipperfields
Typical multi-set truck, Stanley Thurston
