dead battery on outboard

pistonhonda · Aug 18, 2014

Took the boat out this weekend and the battery died while sitting with radio going and using pump airing up floats, finally got someone to jump me off and took off down the river but i noticed that the meter gauge was showing that the battery was draining as we were driving close to 10 volts when we reached the dock. while we were trying to start the motor I used the good battery to start the engine on my boat and planned to switch batteries but as soon i disconnected the good battery it would die. I didnt know if that is a sign like a car that the stator is bad or if outboards just wont run without a battery? Hooked the battery up to the battery tender that night and let it charge over night, the next morning the charge showed the battery was not full but i took it to advance to get a test done and it tested good but showed about 75% charge. Checked it myself with a multimeter and it read 12.18vdc started the engine got it up 25-3000rpm and no change but it stayed steady at 12.18vdc with radio going. After pricing stator I figured i would get more info before buy something. wanted to see if you guys thought it was a bad battery or stator. The battery is alittle over a year old and the motor is a 2003 Yamaha F75 carbed engine. thanks

scrowexj · Aug 18, 2014

I would guess stator. But try battery first. But if you swap stators I would put a higher output on it. So you could run more stuff and not have to worry about it again. And a stator is not gonna charge as fast like an alt. Either. I'm pretty sure they are to practically just hold the charge maybe charge a Little but it's not gonna do much. Someone correct me if I'm wrong

pistonhonda · Aug 18, 2014

the motor holds the battery at 12.18vdc with the radio going and set at 2500-3000rpm. I just expected to see around 13vdc with the motor running. thanks

JRowe · Aug 19, 2014

I've got the same motor and just had to replace the R&R (regulator and rectifier). They are known to go bad on these motors and have been through 3-4 updates.

You can check to see if the stator or R&R is good/bad w a multimeter. Btw you will need a 1/4" drive 10mm wobble socket for the inside bolt.

Little bit of copy paste from info I researched...

I would take a voltmeter and test the voltage at the battery when it will start for you. Say its 12.4 with the engine off. Once its running it should rise.....usually between 13 and 14.4 volts depending on engine speed.

If your voltage does not rise, it is not charging. If thats the case, the easiest thing for you to check (with no specialized tools), is the voltage regulator/rectifier. It is located behind the air silencer on the front of the engine. Remove the air box, and look for a little rectangular metal box (app 2" x 3") with wires coming out of it. It will have cooling fins built into it. It is held in by two 10mm bolts. Remove it from the power head. Check to see if the epoxy on the backside of it is melted or charred. If it is, thats at least one of your charging problems. Replace that and re-test.

The lighting coils(AC charging source under the flywheel) are part of the stator on that engine. They are not really a known failed part. The reg/rectifier on those mid hp 4-stroke ranges is though. They just get hot, and self destruct.

You have a rectifier/regulator system. In almost all cases that is the problem. There are only two parts to your charging system the stator which is a series of coils under the flywheel and the rectifier/regulator.
Disconnect the battery.

To test the stator you will need an ohm meter. Set it to the 1 scale.
Disconnect the stator harness from the rectifier in the front of the engine.
Test from each of the green wires from the stator. Mark each green wire #1,2,3.
Test from #1 to #2 then from #1 to #3 then from #2 to #3 the reading should be .2 to .8 ohms. If not the stator is bad.
If the stator checks bad then the rectifier is probably OK but to check it check the green wires on the rectifier side of the harness; Put your meter to the 10 scale, put the red lead on the red wire of the rectifier then the black meter lead to each of the green wires one at a time, you should read 100-300 ohms. Now put the meter's black lead to the red wire and the red meter to each of the green wires and you should not get a reading.

These resistance tests should tell you if the problem is the stator or the rectifier/regulator.

Buy the yamaha part not a cheaper aftermarket one.

67F81960-12