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Those who have toured Europe behind a 6v ‘Prince of Darkness headlight and longed for a 12v illumination may have well converted their machines. For the rest of us it is an action worth considering even if then you decide total originality is your bag and don’t proceed. On the grounds of simplicity, the alternator wins hands down over dynamo charging systems. As they are crankshaft/mainshaft mounted, drive chains or gear trains aren’t required and device itself is devoid of brushes and a commutator. But during their early evolution, control became a problem – a problem which continued for decades. The alternator can be regarded as nothing more than a progression of the direct lighting coil set-up common to many flywheel magnetos systems. But unlike to many flywheel magneto/lighting coil set-up, the magnets are carried by the crankshaft mounted rotor, which rotates within the coils carried on the static stator, whereas often with the flywheel magneto/generator set-up the flywheel carries the magnets, which revolve around the coils, again stator plate mounted. The output of both systems is identical in that it’s in the form of alternating current (AC)—fine for powering light bulbs but unable to charge batteries. The solution was/is to convert AC to direct current (DC) by a process known as rectification. Some markers around the world of flywheel magneto/generators, including Villiers, solved the problem by using a simple two-segment commutator. Towards the end of the vintage period markers began making what we today regard as alternators. And in the UK rectification was usually by the Westinghouse all metal plate rectifier. This system was an advance, but power output was low and Westinghouse rectifiers were fragile –even vigorous removal of lea connections could wreck them as rough handling could twist the plates about their central mount and break the bridges. After the Second World War, electrical firms began making higher (not high, just higher!) output alternators. For example Lucas introduced a two coil (stator mounted) six pole rotor alternator and small coated metal rectifier to suit. While the output from these units was far from impressive, when the motorcycle’s lights were switched off it was sufficient to overcharge the battery –a problem which was to cause much head scratching over the next 20 years. Lucas overcame this problem in 1946 by incorporating a relay into the wiring circuit to run excess current into a resistor for dissipation. Progress over the next years was of the ‘hiccup’ variety. As more coils—in the case of Lucas four and then six –were added to the stator, more output was created; great when more powerful headlights were used, but when the lights were switched off there was more output to control which in turn could boil batteries and troubled rectifiers as the all coated metal plate rectifier could only handle low alternator outputs. Rectifiers were developed from the all coated metal design through selenium then silicon to the so-called ‘solid blocks’ we buy today. Actually regardless of origin these comprise the rectifying solid state diode type design encapsulated in resin. Taking Lucas as an example. In 1954 the company launched what can be regarded as a new generation of alternators, the RM14. These were in effect a progression of the earlier RM12 but had the option of three stator thicknesses (thick, intermediate and thin). The design comprised six coils mounted to the stator with three cables – see following table for colours. Because this alternator delivered a decent output, current control became more complex with the six-volt electrical system commonly in use in the period. In the next few years, the Lucas alternator range was further developed to give the following main designs of which there were from time to time detail variations: · RM13; intended for low geared higher speed engines · RM13/15; wider rotor to give increased output at low engine speeds · RM 15; deeper alternator than RM 13 series · 5AF: variant of RM13/15 with cooling fins cast/moulded to rotor for fan cooled engines such as scooters. Gearing available for electric start. 1962 launches: · RM18, RM19 and RM20; have progressively more stator and rotor laminations · 9AF; for scooter applications Later came: · RM21; encapsulated stator windings (coils) · RM23; high output · RM 24: three phase While final examples mentioned were primarily intended for 12v applications, the rest, including those launched in 1962, were usually employed with six volt systems and as outputs became higher, control became more troublesome. Lucas, in common with other markets, worked on a staged output delivery system. Regarding the six coils of the exampled 1954 on and 1962 launched Lucas alternators indended primarily for six volt applications as three pairs: · Each pair of coils is in series · The three pairs of coils share one lead as a common cable out from the stator · From the other end of the coils one lead serves one pair and another lead serves the remaining two pairs Motorcycle electrical component makes and motorcycle factories then evolved a series of seemingly ever more complex wiring concepts, switchgear and some resister systems to control the alternator’s output to prevent overcharging of battery. For example, if the machine was running without lights, just one pair of alternator coils was in play charging the battery. When the lights were switched on the remaining two pairs of coils were linked into circuit to enable full output from the alternator to compensation for the large load on the battery. This in itself is bad enough, but some machines with coil ignition might need the output of more than one set of coils to maintain the battery under normal riding conditions with the horn and brake light being used from time to time, but the output of two sets of coils may be too much! Then there may be other considerations such as an emergency start switch position to permit full alternator output into the electrical system to provide a spark with coil ignition if the battery is flat— and so it goes on with considerations such as battery less energy transfer systems, booster coils… The conversion: Why convert? Simplicity of voltage control, better lights, allied with more efficient battery charging and simpler wiring. Why not convert? Originality and a desire to stick with the machine’s 6v system. When converting an alternator charging system from a 6v to 12v Zenor Diode control, a number of the machine’s individual electrical components need either replacing or considering as detailed in alphabetical order. Battery: Most will choose a 12v battery which will fir the battery tray, though it’s worth remembering some small 12v batteries may have insufficient capacity for the load of lights and other equipment carried by the motorcycle. An alternative may be to use two six-volt dry cell batteries connecting in series to in effect create 12v battery pack which is then packed side by side in a old style six volt battery case (available from many trade sources) to fit on the machine’s original battery tray. Yet other choose to use two 6v wet batteries also connected in series (see diagram). Whatever route one chooses, and ideal is to use or create a 12v battery or battery pack with at least a 7Ah capacity, although a larger capacity battery would be even better but accommodation may be difficult for many motorcycles. Horn: Much literature recommends replacing the original 6v horn with an appropriate 12v item but it’s known some don’t bother and claim the horns survive. Obviously this column cannot recommend this action but can mention the fact… Ignition No alterations are required to ignition system for magneto ignition machines. Models with battery and coil ignition require the coil and condensers have been spotted which claim on the box they are suitable for both 6v and 12v applications. Being old fashioned souls we’ve yet to try these! Energy transfer ignitions systems with six volts components will also need upgrading. But having stated my views on the subject in the past, which solicited a few angry responses from fans of the concept, despite their thoughts this scribe remains adamant of ‘never going there again’ –views gained after working with so-equipped scrambles machines in period. Light bulbs All will know these need uprating and of course appropriate LED or halogen bulb replacements will be suitable too. Rectifier None of the early type coated metal plate or selenium rectifiers are suitable for this conversion to 12v system. But using Lucas as an example, the black silicon bridge units (part number 49072) introduced in April 1962 will be fine if one wishes period equipment or the modern units available from specialist classic electric suppliers are small and easily hidden on the motorcycle. Zenor Diode In principle the Zenor Diode simplified the system alone and is connected between the supply side direct current terminal of the rectifier and earth. In practice, the system initially had complications as the first Zenor Diodes couldn’t cope with the full output from the three pairs (six) of coils of the alternator when at maximum output and the lights off. This makers still relied on a staged switch system where two coils were in play for lights off with magneto ignition machine and four coils were used for coil ignition models with lights off, all six coils (three pairs) were switched into the system when the lights were turned on. But Zenor Diodes rapidly improved and the need for this complication ended as the Zenor could handle the power they were asked to absorb—with exceptions. Again, these exceptions apply to existing 12v systems to more ‘modern’ classic such as Norton Commandos and late Triumphs with high output (RM23) alternators, where a matched pair of Zenor Diodes wired into the circuit with appropriate wire of precise lengths. Details can be found in wiring diagrams of such equipped machines. FINAL NOTE: On conversion, other electrical accessories (heated waistcoats, kettle, multi-track music centres, etc…only joking) must be suitable for the 12v system you now have. -Richard Rosenthal When riding, don't forget to wear a custom painted helmets or a carbon fiber helmets
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