Aprilia RS125: Charging System & Stator Diagnostic Guide
If your battery is constantly draining or the bike dies mid-ride, the charging circuit has failed. This guide outlines how to test the Rotax 122/123 generator:
The Stator (The Generator): Located behind the flywheel on the left side. It produces AC (Alternating Current).
The Test: Unplug the three yellow wires from the regulator. Use a multimeter to check the resistance between the pins—it should be very low (approx. 0.1 to 1.0 ohms).
Voltage Check: With the engine running at 5,000 RPM, the AC output across the yellow wires should be roughly 60V AC or more. If it’s significantly lower, the stator is burnt out.
The Rectifier/Regulator: Converts the AC to DC to charge the battery.
Healthy Reading: At the battery terminals with the engine running, you should see 13.5V to 14.5V DC. If you see less than 13V or more than 15V, the regulator is faulty.
Common Failure: Metal shavings from a failing starter motor bendix often get stuck to the magnetic flywheel, "grinding" the stator coils until they short out.
Grounding: Always check the thick black earth wire on the engine casing; a loose ground will mimic a dead stator.
Alternator output tests
Start the engine and run to 6000 revs per minute as this is the speed at which the alternator starts working .
The attach voltmeter at to volts and test at the battery terminals reading should be 13,5-15v
if its less than this you have charging circuit problem if more than this a possible reg/rectifier problem .
Alternator coils testing
Set multimeter to ohms , test measurements between all three yellow wires and then all yellow wires to earth .
Stator coil resistance
122 , 0.1 ~ 1.0 ohms
123 , 0.2 ~ 0.4
3 X tests between yellow coil wires
Then test yellow wires to earth
use body of stator or black yellow wire
Need a new Alternator Stator try on Ebay UK here
see more Aprilia RS 125 posts here
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