Alternator identification & fitment

Check the wiring diagrams. There are now 3-phase stators on the market - I've not encountered one but they are advertised - and they presumably have 3 wires.

The Dommie had 3-wires (usually?). One leads via one coil to the return wire (plain green) and the other leads via two colis also the common green. If both these wires are joined then all three coils are used. The light switch does this when headlight is on. It sounds like the Commando is the same but I have no experience.

If you have a modern regulator you can join these permanently. Then you have a 2-wire alternator. So Q4 is yes provided the wiring is altered. I have a Boyer Power Box and have joined by three wire stator to make it into a 2-wire one.

Watch out there are 2 sizes. Earlier magnet rotors had smaller diameter. If used with standard stator the gap is too large and the generator won't charge the battery. As far as I know that is the possible mismatch - unless you encounter a 3-phase alternator.

No idea about numbers.

The rotor magnets should be central with the stator coils. I thing the rotor is flat on one side - that goes towards the engine.

DON'T forget the spring washer under the rotor nut. Or the rotor will come loose and wear the woodruff key slot and you'll have to file your own specially matched key. Don't ask how I found that out...

Previously wrote:

Q1. I have a number of alternators off various nortons. (either Commando, P11 orN15CS)Some have 2 wires and some have 3 wires. some of the stators are green and some are black.Can the rotors and statorsbe mismatched?

Q2. Doesthe number system identification on the rotor have any meaning to the untrained person?

Q3. Does the rotor have to be fitted the correct way round? i.e. LUCAS facing outwards?

Q4. Can you fit a 3 wire unit in place of a 2 wire unit and vice versa?

Any advice welcome.

Regards, Paul.

Paul,

All alternator rotors and stators (factory) fitted since the mid 60s have 74mm rotors the earlier ones were 70mm (mostly open wire) Obviously fitting the smaller rotor will give a lower output (might still trickle charge the battery though, you will 'get away with it' if you have a magneto ignition) The Green and Black (and even Brown encapsulation means nothing.

Apart from the 70/74mm all rotors are the same, these are NOT matched (despite what is written else where on here.)

The numbers on the later rotors are not significant as far as electricity produced and any electrical point-they are all the same. The number can mean the construction method. The earlier ones often fell apart! 54212006 was notorious for this. 54202298 was Hot Riveted and hence did not fall apart quite so often. There are several more numbers. Electrically/magnetically no difference. As they get older 10 years? then the magnetism reduces, hence electrical output reduces. If you are checking/replacing an older unit then check its mechanical soundness ie is that central boss coming loose?? There is NO front or back when fitting. 8thou is the minimum clearance rotor/stator gap turn the engine over while checking.

2 or 3 wire??? All early ones (70mm rotors, RM18 and earlier) where 3 wire and intended for 6V. Although they an be connected for 12V usage. (GRN/BLK connnects to GRN/YLW. With WHT/GRN becomes a 2 wire 12V)

From 74mm-RM19 (still 3 wire-6V) there are many types and 2 or 3 wire does not mean any thing! There is always a 47*** number somewhere on these stators which tells you what it is. RM19-47204 is the only (3 wire)6V stator you can buy new. RM 21-47205(2 wire) is the 12v standard output 120W.

3 wires MIGHT be 3 phase , there is high and medium output, High output single phase (RM23) (as fitted to MkIII and JP Special) MIGHT can come in 2 or 3 wire versions.

If you mix the wrong stator to its rectifier-regulation then you can have a 'melt down' if you are unlucky, but certainly you will not get a proper result. It is the usual result-casual action with fitting parts gets casual results.

So there

Al Osborn.