Rectifier / Regulator


The regulator/rectifier is a very standard part found on many motorcycles.  It takes a 3-phase AC input and converts it to a charging voltage of nominally 13.8 VDC.

If you are seeing diagnostic trouble codes in K-Scan like P0563 (System voltage too high) testing the rectifier/regulator would be prudent.

I have been experimenting with an aftermarket OTK M261 MOSFET rectifier/regulator after an original equipment (OE) unit failed in one of my bikes.   MOSFET rectifier/regulators exhibit some theoretical benefits including more efficient, cooler operation and a more constant output voltage.  Although it seems to be working fine, the output voltage is a bit higher than I would like to see (so can not yet recommend it).  It seems to make a constant 15.0 volts DC regardless of rpm.   OTK's specification sheet says 14.5 +/- 0.3 VDC.  It exhibits a very small AC content (as measured with a true-RMS meter) of about 0.4V.  Conversely, the OE thyristor-based rectifier/regulators are more variable with rpm - approximately 12.6 to 13.1 VDC, with a higher AC reading of around 1.5 volts.

Rectifier/Regulator Testing

Twelve separate measurements must be made using a multimeter (preferably one with a Diode Test function).

Red (+) multimeter lead to positive rectifier/regulator terminal.  No diode present on any of the 3 AC inputs.

Black (-) multimeter lead to positive rectifier/regulator terminal.  Diode present on each of the 3 AC inputs.

Red (+) multimeter lead to negative rectifier/regulator.  Diode present on each of the 3 AC inputs.

Black (-) multimeter lead to negative  rectifier/regulator.  No diode present on any of the 3 AC inputs.

If your meter does not have a diode test function, look for continuity (diode) and open circuit (no diode).

This test does not guarantee a good rectifier/regulator, but failing the test requires replacement. 

Pin functions for OE regulator

Filter Capacitor (Early Models)

The filter capacitor is mounted behind the number plate.  It is closely related to the rectifier/regulator because there is no battery in the system.

The output of the rectifier/regulator is pulsating DC.  In most vehicles' electrical systems, a lead-acid battery smooths these pulsations into a low-ripple DC output.  Because the TR280i has no battery, the capacitor is necessary.  I measured its capacitance at approximately 23,000 uF.  A proper replacement capacitor would be rated to withstand sufficient ripple current (which makes these capacitors fairly large physically).  The capacitor weighs 162 grams.

On bikes with the Easy-Start system, the filter capacitor is smaller (10,000 uF) and mounted inside the Easy-Start box.  Furthermore, this capacitor is only connected to the rectifier/regulator when the fan is energized via the chassis relay.   

12V bus, good rectifier/regulator @ idle, fan off

Small SLA battery next to filter capacitor