# 15HP Mercury alternator question



## aeviaanah (Oct 23, 2011)

I am waiting on my new Mercury 15hp outboard to come in. The specs show it has a 12amp (138 watt) alternator output. Just curious what is needed to get this thing to charge my batteries. How does this work? Does the motor hook straight up to battery?

My plan was to use a car battery for starting since I have a pull start for emergencies. I thought I may be able to use car battery for bilge pumps as well. 

I will go out and buy a deep cycle solely for the trolling motor. After a bit I can upgrade the other battery to deep cycle as well.

Can the alternator charge both batteries at once? Roughly how long will it take to charge a battery off this motor?


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## Captain Ahab (Oct 23, 2011)

Just like your car - hook the battery up and you will be fine  


You really should get a proper Marine Grade Starting / Cranking battery for the engine and a Marine grade deep cycle for your other electronics


You are gonna drop all that coin on a new motor - spend the money and get the correct batteries and charger 


Was the alternator standard when you ordered your motor?


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## aeviaanah (Oct 23, 2011)

Captain Ahab said:


> Just like your car - hook the battery up and you will be fine
> 
> 
> You really should get a proper Marine Grade Starting / Cranking battery for the engine and a Marine grade deep cycle for your other electronics
> ...


I dropped all the coin i got! Still got to get other stuff too... I will be getting a marine grade deep cycle. Just for now I thought I could use this old car battery for cranking. Since I have the alternator could I get away with one deep cycle for the whole boat (for starting and electronics)? Its a small 12' boat.

Mercury outboards are optionally equipped with alternators starting at 4 hp - 6 hp. At 8 hp and up the alternator is standard.


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## Captain Ahab (Oct 24, 2011)

Get the deep cycle for the electronics and use the car batt. to crank the engine


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## aeviaanah (Oct 24, 2011)

Captain Ahab said:


> Get the deep cycle for the electronics and use the car batt. to crank the engine


K thanks for all your help!


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## FuzzyGrub (Oct 29, 2011)

For such a small boat, I'd just get the next size larger deep cycle than you already plan. More reserve amps. Keep the weight down from having two batteries. Just about any DC will have more than enough cranking amps for that size motor. Don't count on the few amps to keep your battery charged though. Always put the charger on it when the day is over.


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## aeviaanah (Oct 31, 2011)

FuzzyGrub said:


> For such a small boat, I'd just get the next size larger deep cycle than you already plan. More reserve amps. Keep the weight down from having two batteries. Just about any DC will have more than enough cranking amps for that size motor. Don't count on the few amps to keep your battery charged though. Always put the charger on it when the day is over.


Alright I will do, thanks for the help!


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## nomowork (Oct 31, 2011)

I have a 15hp pull start only Honda that has a 14v charging circuit. It just attaches across the positive and negative feed off of the battery where I mount the trolling motor. I use a very small car battery that I picked up at Wally World. It has enough capacity to run the trolling motor, fish finder and nav lights.

BTW, that same battery is also used for a backup starting battery for my other 40hp Mercury.


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## aeviaanah (Nov 1, 2011)

nomowork said:


> I have a 15hp pull start only Honda that has a 14v charging circuit. It just attaches across the positive and negative feed off of the battery where I mount the trolling motor. I use a very small car battery that I picked up at Wally World. It has enough capacity to run the trolling motor, fish finder and nav lights.
> 
> BTW, that same battery is also used for a backup starting battery for my other 40hp Mercury.


Interesting. At first I will be using the small battery with everything to see how it performs. When i get the trolling motor I may upgrade to a deep cycle.


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