Yamaha 90 overcharging problem

[Once Bitten]

Problem: Overcharging<br />Motor: 1993 Yamaha 90 TLRR<br />Symptoms: Yamaha multi-gauge reads up to 16.2vdc and begins to flash.<br /> Trimming up or down lowers voltage reading, then it slowly<br /> climbs back up while running. <br />What's been done:<br /> Verified actual voltage across battery versus gauge reading <br /> while underway using external voltmeter. Meter readings match.<br /> Switched to #2 battery(deep cycle) and confirmed same problem.<br /> Verified proper battery water levels.<br /> Replaced voltage regulator/rectifier. Same results.<br /> Ohmed out both regulator/rectifiers per service manual. Both<br /> measure ok.<br /> Disconnect #2 battery to confirm no wiring issues.<br /> Verified 0 ohms resistance from regulator/rectifier ground to<br /> battery ground.<br /> Generated inline harness to monitor regulator/rectifier voltages <br /> during normal operation. Four wires involved: black = gnd, <br /> red = voltage(dc), green & green/white = charging coil(voltage ac).<br /> Test results with engine running: <br /> Red = 15.2vdc creeping up(matches gauge)<br /> Green & green/white = 11.2vac<br /> Trim up slightly<br /> Red = 13.6vdc and creeps back up(matches gauge)<br /> Green & green/white = 15.8vac and creeps back down<br /> Switched to #2 battery and confirmed same behavior.<br /> <br />This is a long standing problem previously resolved by replacing batteries<br /> with partially discharged batteries.

 

[rodbolt]

Re: Yamaha 90 overcharging problem

about all it can be now is a bad battery or a defective regulator, its designed to shunt excess voltage to ground, make sure the regulator ground is good. the specs for the lighting coil are not published in the service manual so I cant help you on that. but the regulator shunts the current to ground when excess voltage is sensed in the regulator.

 

[reelfly]

Re: Yamaha 90 overcharging problem

Did you ever find the solution? I have a 2004 90 with seemingly the same problem. Mine overcharges to almost 17 volts when there's no load on the alternator. With a load on it it drops to normal then creeps back up once the load is removed. I have tried replacing the regulator without improvement. I have also checked battery connections and engine grounds for voltage drops and all are good. Well I hope you still are in contact with this forum and have an answer for me. Thank You