1980/81 Mercury Outboard Charging Battery?

[Sunset Cruise]

I bought a pontoon a year ago with a 1980/1981 50 HP electric start outboard. (Serial # 5832737) This years project involves installing navigation/anchor lights, battery #2 and a battery switch- nothing else was drawing on the battery other than starting up. When preparing to install the battery switch I noticed the battery cables to the motor were not colored positive or negative so just to be safe I did some research (on this forum) to verify the motor wouldn’t run if the battery was connected wrong. Went down to the boat today to check the battery charging as one method to be sure and the readings (12.4 before starting, 12.04 at idle and revved up) prompted more questions. The boat’s battery has been connected this way for more than a year without issue.

My questions:
1) is it even possible for this motor to run with the battery cables reversed?

2) If the cables are connected properly, do the voltage readings lead you to believe I have a bad diode or other problem with the charging system?

Thanks in advance for your help.

 

[Chris1956]

The engine has an alternator driven ignition system. This ignition system is isolated from the battery, so the motor will run without a battery, or with one hooked up backwards. However, the starter should crank backwards, if the battery is hooked up wrong.

That motor should have a full wave rectifier which converts the AC power from the stator to DC to charge the battery. I suspect yours is not working. The rectifiers will easily be damaged if the battery is disconnected with the engine running or is connections are intermittent.

So if the starter turns in the correct direction, the battery is likely hooked up properly.

 

[Sunset Cruise]

Thanks Chris,

Update: went back out to the boat this morning (still in the water) and measured the following:
12.22V before starting
12.10 at idle
12.18 at medium rev (no tach)
12.18 after the motor was shut off (ran about 5 minutes in total)

(I've heard this motor essential charges the battery at a trickle charge rate?)

I plan to go out on the lake this afternoon and give it a good run and measure the voltage again.

 

[GA_Boater]

Welcome aboard.

When you measure the battery voltage, are you putting the leads on the posts or the cables? You can get different results depend how you measure.

First thing I would do is clean the battery posts, battery connections and where the cables are connected to the motor. Do both positive and negative.

The battery is not charging. The rectifier should make about 14.5 to 15.5 volts at a fast idle if it has no regulator, still close to 14 or a little more with a regulator.

 

[Yate1s]

I have a new Mercury 4HP 4-stroke Sailpower outboard that has a built in alternator/charger liteblue.

 

[Sunset Cruise]

Closing the loop on this thread, installed the new rectifier yesterday and now charging at 15.3 volts. Fairly straightforward job, the cowling removal/installation took as much time as replacing the rectifier. Always appreciate this forum and those willing to help others.