Alternator test ... results confusion

I am certainly no expert but it looks like you need a new alternator stator - Lucas part no 47204.

However, if your equipment is original I think that you will need to get a new rotor as well since the bore of the 100W three wire alternator (all you can get nowadays) is about 4 mm bigger on diameter than the 1960's stator.

All the parts are available from Norvil (min £157.25 plus VAT/post); RGM (£113 plus VAT/post).

Regards,

Previously john_baker2 wrote:

I have read and followed the tests outlined by Alan Osborne and have results that are 'incomplete'(ish)....help in understanding appreciated.

model 88 slimline 6v positive earth. Fails to charge. Alternator wires are green, green/yellow and white/green.

STATIC results.

green/yellow and white/green = 1.3

green and white/green = 1.7

green and green/yellow = 2.0

Each wire separately and earth = no reading

DYNAMIC results engine revved with bulb

green/yellow and white/green OK

green and white/green OK

green and green/yellow NO light

What is this telling me please? New alt or rotor ?

thanks John.

Hi John, did you remember to set your meter to volts on alternating current when doing the check. If you have the meter set on DC it will give a false low reading as the alternator produces raw alternating current before it gets rectified to DC.

Cheers Alan, Shenstone branch sec.

Right here we go.....The alternator test above is correct, this alternator should work. I assume the 1.3 1.7 etc are resistance readings and are about right. When testing Lucas alternators you do not bother with measuring volts or amps, you will not get any result you can trust. The lamps test is perfectly good for all functions and saves misunderstanding meters and rubbish results. The colours mentioned above appear 'near enough' just think of the GREEN as the GREEN and BLACK. As this alternator is good then non charging is only the rectifier and wiring/connectors. As it is a 6V machine.

Some other points-the rotor will not 'stop' the system charging, the rotor may have very week magnetism but this is only a quantity issue. Std rotor RM21 or RM19 will give up to 9 amps at 3K revs but if very week then perhpas reduced to a few amps, perhpas not enought to cover ignition drain in the very worst case but there will always be some output. (not that I have seen rotors this week) but I have seen rotors that cannot cover lights with ignition ie 6amps.

Al Osborn.

Previously john_baker2 wrote:

Yes, I can buy replacements, maybe upgrade to 12v...BUT I was hoping someone might explain what is wrong!!!

All the magnets on Rotor seem OK , Stator wires check out for continuity, readings at coils are same as for cables.

Anyone got ideas?? Thanks

Also in the event of 12v upgrade has anyone got a wiring diag for the Mercury...which appears to be a 12v single coil, single points, dist version...and presumably without the Lucas PRS8 switch unit.

All help appreciated.

regards John

The Mercury was 12V and had twin points, your 88 would have had 6V RM19 and the PRS8, both of which can be reconnected for 12V. As there is nothing wrong with your alternator your charging problem must be elsewhere, I suggest you get in touch.

Al Osborn.