Problem with the rectifier?
What should I do if the regulator rectifier is not charging properly? (13.9 – 14.6V charging is ideal)
If the charge is too much (charge level is above 14.8-15V), there is probably a problem with the regulator rectifier.
However, before you can state this immediately, make sure that the voltmeter (multimeter) is not discharged. If the battery is discharged in the multimeter (which in most cases is also indicated by the sign „LOBAT” or its icon), it can deviate a value up to 2-3V higher!
If the overcharge level measured by the multimeter is stable (eg. continuously shows a charging level 15.8V, regardless of RPM, with lamp, without lamp), it can also give rise to suspicion, that the batteries have already started to discharge (just not yet indicated by the multimeter) and therefore the measurement is inaccurate (and regulator rectifier doesn’t actually overcharge at all).
If the charge is too low (charge level is below 13.8-13.9V), it is likely that the problem is not with the regulator rectifier. In this case, the following control measures should have done:
Disconnect the regulator rectifier from the motorcycle and check the diodes with a voltmeter (multimeter). Click on this link to find a video showing how to measure the diodes of the voltage regulator: https://www.youtube.com/watch?v=NTjumDgixkQ&t=215s
Make sure that the voltage is not “lost” in the in the wiring of the motorcycle:
Oxidized or loose plugs can cause improper (low) voltage.
Check the plugs for any dirt that is causing the voltage fluctuation.
It is also a good idea to replace the molten plug.
Check the fuse (located next to the starter relay on most motorcycles) to see if the plastic in its area is not melted.
If the diodes are found to be OK, a generator check may follow:
Perform a generator short to ground. Place one end of the multimeter on the metallic body of the motorcycle (not on the paint !!) and the other on the generator terminals. For all three generator terminals, the multimeter should read “OL” or “1”.
If the magnets on the generator are glued (this may occur on some type of motorcycle, not all of them), check these magnets for slippage. The gap between the magnets must be the same width.
Check the battery:
Fully charge the battery with an automatic charger, then measure your voltage after waiting 10-15 minutes: you need to measure a voltage around 12.5-12.6V. If the measurement is below 12V, there may be a short circuit in the cell, it may be necessary to replace the battery.
If the above measurements have been made and the error has not been discovered, it is probably that the regulator rectifier is the problem.