Converting an Alternator system from 6 to 12V

 

If your bike has a Lucas 6V 3 wire alternator system, with a simple wiring change it will be able to power a 12V system.

Disconnect the Green/yellow alternator wire from the loom and join it to the Green/black alternator wire. That's it. The job's done.

The 3 wire alternator is only 100W max. so will be OK for points ignition but won't run a Boyer ignition with your lights on for long, the battery will go flat.

The existing 6V rectifier will be OK, but you need some form of Voltage control. Fit either a Zenor diode or remove the rectifier and fit a regulator/rectifier unit (Power module) (£29.95) These are more reliable, more efficient and easy to fit.

Fit 12V coils (£15.50) unless you're using electronic ign. then 2 x 6V coils or a 12V twin output coil £34.95

A 6V horn will be OK, but will sound louder.

Obviously you will need bulbs. If you've fitted a new alternator a 60/55W headlight bulb will be OK and give you a light as bright as a cars. If you're sticking with the old alternator a 60/55W will probably be OK, but a 45/40W is guaranteed. £8.25 for British Pre-Focus.

Tail light, standard 0.60P. Much Brighter Quartz Halogen £9.95. Brighter with low current LED £12.95

Speedo light 0.75P

For the battery, measure up for the largest battery that will fit.

Click here for the batteries page.

Earlier Lucas alternators used Light Green, Dark Green & Mid Green. Join DarkGreen & Mid Green for 12V

Wipac used White, Light Green & Orange. Join Light Green & Orange for 12V

 

This is a diagram of a basic 6V system converted to 12V using a Zenor diode for Voltage control. The wiring details of the more modern regulator/rectifier conversion are above.
Courtesy of the most marvellous old bike magazine in the whole wide world at www.RealClassic.co.uk They're modest as well.

 

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