Notes on alternators

How to order


Three phase stators have a higher output at low speeds than single phase, and must be used with a three phase regulator/rectifier (A Reg Three). (The 125W three phase stator as fitted to late Meridan Bonnies was originally used with Zener diodes, this was all that was available back in day & regulator/rectifiers are much more reliable).

They are sometimes confused with earlier 6V stators that also have three wires. To add even more confusion the colour coding of the wires is the same, but they are easy to identify. All single phase stators have 6 internal pole pieces whereas the three phase stators have 9.

The 6V stators will run a 12V system, the last 3 wire 6V stators were 120W & just the same as a 2 wire 120W with two wires joined together. If the stator is encapsulated, it will probably give at least 100W or so, most fitted to 500/650s were 120W. If it's not encapsulated throw it away.

All our single & three phase stators are compatable with the original Lucas rotor 74MM dia. There was an earlier 70MM rotor which isn't suitable and stators for this size are not available. In most cases both 74MM rotor & stator can be fitted with no problems. If when you fit a new stator you find a 0.060" or so airgap, you have a 70MM rotor. This combination will only give a miniscule output.

The 120W ALT10109 will start a bike without a battery when fitted with a capacitor, even with most electronic ign. systems. None of the other stators will, including 3 phase.

Used with an A Reg Six the 120W ALT10109 will reliably run a 6V system

When fitted & tightened there must be a minimum 8 thou. (0.008") clearance between the rotor & stator all the way round. Less than that & the rotor will touch the stator which will overheat & fail. Look for marks on the pole pieces & the rotor. It will say this in all the manuals & it is very important. The only adjustment is with a rubber mallet - be careful. On no account open the mounting holes in the stator.

A shot driveside mainbearing can also cause alternator/stator rubbing, but if this is the cause a failed stator is the least of your problems.

A loose rotor nut causing the rotor to rock back & forth against the woodruff key can sound like failed big-ends

Our alternators fit all Commandos, 650SS, Atlas. BSA C15/B40/B25/B50. A50/65. R3, All Unit 500 Triumphs, Unit T120/T140/T150/T160 and most other British alternator bikes 1959 - 1970s and earlier if the existing rotor is 74MM.


LUCAS alternator 3 wire colours for use on a 12V system

Common Link this To this
White/Green Green/Black Green/Yellow
Light Green/Dark Green Dark Green Mid Green
Light Green/Dark Green Dark Green Green/Yellow

WIPAC alternator 3 wire colours for use on a 12V system

Common Link this To this
White Light Green


Light Green Yellow Orange

MILLER alternator 3 wire colours for use on a 12V system

Common Link this To this
Red/Black Yellow Green or Yellow


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