C15 stator wires

[Alan1]

Hi Everyone
Just got a C15 in loads of boxes and the stator has 3 wires Red Black and pink the loom wires are green/yellow   White / green.  Green/ black
What goes to what ?
Alan

[Spaceman]

Normally, the resistance between the 3 stator wires is as follows:

GB To WG:  R (ohms)

GY to WG:   0.5 x R

GB to GY:  1.5 x R

where R is the resistance of each pair of coils (3-4 Ohms) with the stator.

If you measure the resistance between the red, black and pink values in pairs they should show the pattern of values given above allowing you to work out which corresponds to the normal GB, WG and GY coloured wires.

[Spaceman]

The resistance of 3-4 Ohms given above is wrong - I think R should be nearer 0.7 Ohms. So you should measure typically:

GB To WG:  0.7 Ohm

GY to WG:   0.35 Ohm

GB to GY:    1.05 Ohm

[Alan1]

Thank you I will try it tomorrow

[Spaceman]

Sometimes people replace the wires coming from the stator because the PVC can harden and disintegrate over time and not everyone has access to the correct colour coded cable and use whatever they have at hand. Hopefully, the resistance measurements will confirm it's a pukka Lucas C15 stator.

[Alan1]

Red/ black 1.4
Red/ pink. 1.9
Pink /black 1.4
These are the readings ?

[Spaceman]

Unfortunately, those readings don't correspond to a 3-wire Lucas alternator as used on a C15 - two of the reading should not be identical. It would be worth measuring the ID of the stator to see if is about 75 mm. It would also be useful to see a picture of the stator.

[Spaceman]

Sorry - I meant to type that the stator ID for the C15 alternator should be about 71 mm (70 mm rotor) - the more powerful alternators fitted to later bikes had a 75 mm stator ID.

[Alan1]

It is 71 ID

[Alan1]

Photo

[Spaceman]

I thought the stator was just lying in one of the boxes! Since it is fitted to the engine, it should be ok despite the resistance measurements.

It should be possible to see the wiring connections between the coils (yellow sheathed wires?). Of the 3 wires coming out of the stator, the common connection (normally WG) should connect directly to 3 of the coils (every other coil). The high power output (normally GY) wire should connect directly to 2 of the remaining coils. The low power output (normally GB) should connect directly to the final coil.

If this is not the arrangement, it would be useful to know which coils each output wire connects to, perhaps numbering them coils 1 - 6.

[Alan1]

I have been building it up over the last few weeks and got to the stage of the new loom fitting . I will look tomorrow
Thanks for your time

[Spaceman]

It's difficult to see why this alternator stator should not be ok for your C15. I wasn't able to find any other stator with those coloured wires and so they must have been replaced at some point after the original wires perished.

Measuring resistance values of the order of 1 Ohm can be inaccurate sometimes depending on the quality of the DVM used and the state of its internal battery. Hopefully, checking the internal wiring will show you which output wire is which as indicated above.

[JulianS]

A check of the metal part of the stator will probably reveal a Lucas part number which will start with 47.....

From the 1962 season the C15 Star used RM18 with stator number 47161.

Triumph issued a service bulletin in 1965 giving rwsistance figures. 47161 is the last on the list. Unfortunately it does not give the test procedure use for these figures. The caveat on measurement mention by Spacemen is most important.

Cold resisatnce figures in no way guarantee it will function when hot.

[Spaceman]

The official resistances show the 0.5 x R, R and 1.5 x R pattern of values as expected. The concern in this case is that two of the measurements were identical and that is difficult to explain by an inaccurate DVM.

At face value, the only way I can explain the results is by assuming the DVM is not very accurate and that one pair of coils has gone open circuit?