Testing alternator

[Jimbo550]

I have an electrical problem which I think could lead to the alternator but electrics isn't my strong point so I,m looking for some help.  I've checked across the battery terminals with the bike running and I can only get 11.5 volts max at 4000rpm.  I then disconnected the plug which come from the alternator into the left side casing with the 3 yellow wires.  I put the multimeter on ac voltage and while the bike was running I tested each yellow wire with + terminal while - terminal was to earth. I don't get any readings. Am I testing this correctly? If so does this mean my alternator is duff.

[Jimbo550]

Correction. I wasn't testing it correctly. I've tested pairs of yellow wires and only seem to be getting 1.5v ac when revving it to 4000rpm. I'm thinking this is duff and need to be rewound. What voltages should I expect?

[Bryanj]

You will only get AC out if DC is going into the field coil on the green and white wires

[Jimbo550]

Ok thanks Bryan. Electrics I really have problems understanding. I have tested again with a dc supply going in and seem to be getting different figures. 10v, 15v, 2vac. What should I expect to get?

[Bryanj]

From memory 40-50Vac between each pair, I would remove the  cover and check the connections

[Jimbo550]

I've gone through all the connections and everything seems in very good condition. I've taken the stator to a specialist who has looked at it and put a meter on it and he thinks there is nothing wrong with the stator at all.   Where can I go from here and what should I test next?

[ka-ja]

Hi,
    It is a good chance that if the alternating coils are OK, the culprit could be the regulator working incorrectly, as previously stated, if the voltage to the exciter (inner) coil isn't correct, the ac output will be wrong, the only other thing that effects the output is the rectifier, but this only changes ac current into dc for the system and usually works or doesn't-no inbetween, the regulator is prime suspect, but hard to test correctly without the right gear, do you know anyone who can lend you one for a trial-Ken
   PS If you haven't got the test methods for testing out PM me
   

[Jimbo550]

I took the whole casing with inner coil (Magnetic bit) and ouuter ac coils to a guy who rewinds these things for a living so sure knows more then me.  He put an ohm meter all over it and said all the figures came back as what he would expect and there was no problem with it.  I have put it back together and still have only 11.5 v max at 4000rpm.  i've tried getting some readings in ac from the three yellow wires but not with much success but i may be doing this wrong.  Can someone point me in the right direction to test the ac output correctly? 

i'm also thinking i should check the dc supply to the inner coil(magnetic bit)?

Thanks for your help.

[Jimbo550]

I think I,ve sorted it!! Turns out to be the rectifier. Bolted a new one on and getting over 14v going into the battery which is better than what I had previously. Thanks or all the advice given:-))

[Bryanj]

OK now make sure all the green earth leads make good contact along with the big one from the battery to the LH rear motor mount

[Jimbo550]

I've been through all my earth connections previously and all seem good. The rectifier could of been down for a while.  Thanks for advice.