Yamaha 90 overcharging problem

[Once Bitten]

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

This is a long standing problem previously resolved by replacing batteries
with partially discharged batteries.

[boats.net]

You might try to test the grounds. With a jumper wire ground the reg. and bracket that reg. is mounted on to the battery cable ground terminal on engine. Look for any loose or broken ground wires on engine. With a set of jumper cables jump from battery neg. post and engine ground and then do the same test with positive cable. Check for battery voltage at reg. with engine not running, the reg. has to read battery voltage in order to regulate the charge rate.

[CharlieK1988]

The answer is a voltage con*****er. I use a FlexCharge NC25A-12 It's made for solar collectors and outboard motors. Perfect for unregulated charging circuits. Cost is $95.00 at www.solerseller.com

If you don't want to go that route you can buy a DC to DC regulator from Jameco. It only handles 30 watts (2.1 amps), but you can use it for your instruments (tach fishfinder GPS ect) and at least avoid blowing them out. It puts out 12 volts with an input of 9 to 18 volts. Works great.

[NoNameDk]

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

This is a long standing problem previously resolved by replacing batteries
with partially discharged batteries.

Hi, I have the exact same problem on my 2stroke 140hp 1987 engine.
What was your final conclusion? thx in advance, Br Nicolai