86' Johnson GT150 Charging Voltage Question

[mak747]

I have a 1986 Johnson GT-150 outboard with the 35 amp alternator. Lately I have noticed that my volt meter has started reading up to 15.5 volts while at WOT. The sonar unit I have displays the supply voltage and it too shows ~15.5 volts while at WOT. When at idle the voltage reading is ~12.5 and it steadily increases as I accelerate. In the past I only remember the max reading to be ~13.5 volt max. Could this be caused by the starting battery going bad or is it most likely the rectifier/regulator going out. Even after running the electronics all day the battery seems to easily start the motor, just not sure if this charging voltage seems excessive. Thanks in advance for any comments/recommendations.

 

[Barnacle_Bill]

Re: 86' Johnson GT150 Charging Voltage Question

Check all your battery connections. They must be clean and tight. If all good have the battery load tested.

 

[metriccrescentwrench]

Re: 86' Johnson GT150 Charging Voltage Question

Keep an eye on battery voltage when the engine is off and you're running some electronics and maybe a livewell pump, etc. My bet is that it's dropping off more now than it used to, indicating a weakened battery. But also check all the battery connections.

By the way, how old is the battery? Have you checked the water levels?

 

[mak747]

Re: 86' Johnson GT150 Charging Voltage Question

Water levels are good. Battery is ~2.5 years old. I do run several electronic devices and a live well for extended periods of time between making short runs with the outboard between fishing spots. I will double check all of the connections and make sure they are clean and tight. Will also take the battery to have it load tested. I have an onboard 3 bank charger and am very conscientious about plugging it in as soon as I get home from the lake to try and prolong battery life. When I take it for a load test should I unplug the charger for a while to dissipate surface charge or does it really matter?

 

[boobie]

Re: 86' Johnson GT150 Charging Voltage Question

A GOOD load tester will normally take care of the surface charge.