Correct size 12 volt battery for a 9.9 Yamaha 4 - stroke electric start outboard.

[fredrussell]

According to Yamaha their 9.9 has an alternator

View attachment 149986

Apols, I assumed OP’s one was the older model that I had. I think mine was a 2005 model or thereabouts- no alternator on that one. Just the usual charging coil Angus refers to.

 

[Rum_Pirate]

Apols, I assumed OP’s one was the older model that I had. I think mine was a 2005 model or thereabouts- no alternator on that one. Just the usual charging coil Angus refers to.

My 9.9 (the one referred to in the OP) outboard is a May 2011 manufactured model.

 

[Chiara’s slave]

Smaller outboards don’t have alternators - they have a charging circuit based around a fairly simple coil setup on the stator plate.

My 1992 motor on my F27 did. My current 15hp honda does. A 2016 motor.

 

[AngusMcDoon]

Apols, I assumed OP’s one was the older model that I had. I think mine was a 2005 model or thereabouts- no alternator on that one. Just the usual charging coil Angus refers to.

A charging coil is a magneto which is an alternator using technically correct language. Given that the Yamaha 9.9 is still only produces 6 Amps, the same as my 2000 year model, it doesn't look like they have changed the technology and moved to what in common language is now called an alternator with a field coil instead of permanent magnets. It looks like they have just changed their marketing description, and are pedantically and technically correct in doing so.

 

[QBhoy]

That must be pretty ancient, I’ve owned Mercury outboards on acRIB from the early 80s, they had alternators. How on earth does it work without? Had a previous owner just removed it?

I’d be almost certain that they probably didn’t. It would have been a stator with an AC to DC rectifier system.

 

[Chiara’s slave]

I’d be almost certain that they probably didn’t. It would have been a stator with an AC to DC rectifier system.

It might be worth me showing you a photo under the covers.

 

[Refueler]

EVERY Outboard I have and I have some old ones !! Even the old dog Soviet ones ... ALL require a Rectifier to convert the AC produced into DC for charging any battery. The only job that any can do without such 'black box' is to power low power 12v lighting.

I've even dug out my old Evinrude / Johnson Outboard Workshop Manual for 1973 - 1990 2hp to 40hp ..... it states clearly for all that have power take off for charging etc - must use a rectifier to correct AC to DC .......

My Johnson 5HP FastTwin actually has a factory label on the case depicting AC power at the plug in point.

 

[fredrussell]

A charging coil is a magneto which is an alternator using technically correct language. Given that the Yamaha 9.9 is still only produces 6 Amps, the same as my 2000 year model, it doesn't look like they have changed the technology and moved to what in common language is now called an alternator with a field coil instead of permanent magnets. It looks like they have just changed their marketing description, and are pedantically and technically correct in doing so.

Yes, I think I may be confusing the issue here by thinking of an alternator as a separate generating device driven by a belt from engine. I’m fairly certain that the workshop manual from my early 2000’s Yam 9.9 didn’t mention an alternator, but that, as Angus suggests, what Yamaha at that time described as a charging circuit (or words to that effect) actually was (technically) an alternator.

Chiara, I would be interested in seeing a pic of the alternator on your OB, I’ve only owned sub 10hp outboards - just curious really.