intermitant charging

so it appears that after about a month of carb cleaning and part replacemant my xj has come to life, very happy.
so now i move on to the next issue i appear to have an intermittent charging problem the old girl seems to charge from cold at 14v but stops charging when the bike starts to get warm, could it be the stator coil breaking down when it starts to warm up?

 

brushes may need to be replaced

this link contains info on testing
The Ultimate Relay, Switch, Sensor, and Diodes Guide
from above link there is more info on testing alternator at the link as well as fixes
Starting Load Test:

a) Adjust voltmeter to DC volts (20 volt range).
b) Place voltmeter leads to the battery terminals (positive to positive and negative to negative) .
c) Watch the voltmeter as you start your motorcycle, but before the engine is running.
d) If the voltage drops below 9.5 volts, the battery has very low capacity and should be replaced.



Charging System Tests:

a) Adjust voltmeter to DC volts (20 volt range).
b) Place voltmeter leads to the battery terminals (positive to positive and negative to negative).
c) Start the engine.
d) Bring engine up to approximately 2,500 rpm's.
e) Compare the voltage reading to the specification given below:

For all XJ-series models, the maximum available charging output VOLTAGE should be as follows (all values are approximate):

* approximately 500-2000 rpms: 1.8 volts gradually increasing to 14.2 volts
* 2000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts (all models except XJ700-X and XJ750-X)
* 3000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts (all XJ700-X and XJ750-X)

 

hi thanks for your reply its odd dont you think that it does charge from cold but then stops when engine starts to warm

 

could be your brushes are short and springs contract when heated up,
or your voltage reg is starting to fail, a complete test, inspection of components and connections is in order.
the charging system may also thing your battery if fully charged.
the true test is to hook up a meter and record the results of the charge when cold then when hot.
is it not reading this when hot but only when cold?
* approximately 500-2000 rpms: 1.8 volts gradually increasing to 14.2 volts
* 2000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts

is your battery full of acid if not add distilled water only

 

when cold its charging at or around 14.8v @2500 rpm, when she warms up at some point it stops charging, nothing at the battery.
i will have a look inside the alternator see if the brushes are good or clean up the rotor plate i have a multi meter but not sure if it works will have to borrow from a friend
otherwise.

 

Charging should stop when the battery is full (the regulator dumps excess current to ground so the battery doesn't get cooked). Could that be what is happening?

 

Does your model have a earth ground separate from the battery ground? If so make certain it has good connections to the frame (might need to remove a little paint) and engine.

Gary H.

 

umm UK bike head light is not always on is it
when it stops charging turn your headlight on with high beams see if it starts charging again

 

the battery when i checked was down to about 11.3 v so definitely no charging when bike warms up bit odd that it works for a while then stops

 

mines a japanese model so headlight not permenantly on, turning the lights off the other day meant i was able to get home just, bike was starting to splutter as the battery
was running down she got me home though

 

not sure exactly how mines wired will need to check terminals though, make sure there clean

 

also check for any joints that are not tightly connected. loose joints will sometime loose conduction when hot. even soldered ones.

 

so carried out a few tests tonight, getting 0 resistance across the stator wires so i guess thats the issue, and the brushes were well worn
one was at 10mm the other down to 8mm

 

The stator (three white) wires have a very low resistance (0.46 ohms ± 20%), but if you had your meter on the x 1 scale and it's properly zeroed then you have a bad stator.

 

i did try a few settings on my multi meter but got 0 on all so like you say looks like the stator is dead

 

i will double check with my meter, i did carry out a test on one of the coil/pickup wires too the tip of the brush just too see if my meter was working, there was a resistance reading so iam confident the meter works. i took the stator out to test an upon examination i noticed what appears to be oil on it, i have read on here somewhere that there is a seal behind the slip/rotor plate is this correct?

 

Yes, there is an oil seal and an o-ring on the bearing carrier that lies behind the alternator rotor.
If you have confidence that your meter is accurate then trust the reading and source a replacement stator.