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Mercury 135HP Optimax Low Voltage

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Angelo321

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A few months back I posted an issue with one of my 135 Opti's have low voltage. After crawling out from the aftermath of Irma, I'm finally getting back to troubleshooting the low voltage issue. Below is the data I've collected so far.

Boat has two, 2003 135 HP Opti's, three battery system, one for each motor and a center battery that can tie in all the batteries, isolate starboard and port from each other and tie in either the starboard or port engine to the center battery.
Batte
Original issue was low voltage on the starboard engine while running, ~ 11.7v at the gauge.

Voltage data collected on 11/10/18
Both engines off, battery switches on for each motor, center switch selected to "All"
Volts all three batteries - 12.1
Starboard engine running at idle, all switches selected "on" or "all"
Starboard battery volts - 11.95v
Center battery - 11.95v
Port battery - 11.95v
Gauge at console - 11.8v

Shut engine off, starboard battery on, center off and port battery off
Again starboard engine running
Starboard battery - 11.80v
Center battery - 12.1v
Port battery - 12.1
Starboard gauge - 11.7v
Starboard Alternator voltage - 11.72v
Slave solenoid - 11.72v

Shut starboard engine off, selected battery switches to "on" or "all"
Port engine running at idle speed
console gauge - 12.5
Starboard battery - 12.8v
Center - 12.8v
Port 12.8v
Alternator - 13.7

Port engine at 1000 rpm
Port gauge - 14.0v
Alternator volts - 14.31v

Starboard engine running at 1000 rpm
Starboard gauge - 11.9v
Alternator volts - 11.93v

sorry for long explanation. Any suggestions would be appreciated.
Angelo321
 
Not charging. Look at the voltage regulator/ rectifier. You might swap them to see if the problem follows to the other motor.

Jeff
 
Not charging. Look at the voltage regulator/ rectifier.
Click to expand...
It dont have one..it has alternator like a automobile. Check the alternator bracket and block grounds Check the alternator fuse and fuse holder.The earlier ones are welded together and non repairable. Make sure you have 12v switching on/off from purple at alternator. Also motor must be idling above 1000rpm foryou to measure any output correctly
 
Jeff, thanks for the reply, but these motors have an alternator so the voltage regulator/rectifier is integral to the alternator, therefore the alternator will need to be replaced or rebuilt.
 
Thank you sir for the response, I very much appreciate it. Unforetunately, I don't have my boat here at home so I'll have to perform more diagnostics next week. When I did check last week. The alternator bracket and block grounds appear to be good. I'm not sure where the fuses are (not on the wiring diagram), but I traced the red wire coming from the alternator and there is a clear heat shrink with what appears to be a link with 100 stamped on it. I did check the voltage downstream and it was the same as at the alternator 11.72v. I don't understand what you mean about 12v switching on/off from the purpe wire at the alternator. I see the purple wire on the wiring diagram, do I check for voltage when engine is on and off. If this helps, the voltage at the gauges were reading about 12v when I was on a plane. Typically it was 14 or more. This is what led me to this issue. I hope this helps. Again thanks for your help.
 
When you start engine the purple wire that plugs into alternator "excites it" or say turns it on. Check that it(purple wire) has 12v when key is on and 0v when off. Also do not switch batteries when running as this can spike the diodes in alternator, and make sure the battery switches are "make before break" to prevent this.
 
Thanks again, I understand about switching the batteries while the engine is running, but it could happen. Will corrosion on the battery terminals affect the voltage?
 
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