Marine Alternators and charging systems

[kinematics]

Hi,

I need to pick a alternator for my 1976 General with a OMC electric shift outdrive and 1966 Ford 289 engine. I'm converting the engine to fuel injection and will be making my own wiring harness. I've spent considerable time reading about marine alternators and charging circuits but still overwhelmed with all the different options. I'm favoring a Delco 10si 3 wire alternator, but don't have enough information to make a decision on power output needs or compatibility with my mounting brackets. Due to the lack of a charge controller and mnimal electricity need, I feel a 60-70 watt output would be ideal. I'm concerned having a 100+ watt output alternator without a charge controller will decrease the life of my battery due to overcharging. In addition, I can not find a answer if any of the alternators I've looked at will work with my mounting brackets. I suspect my brackets are designed to be used with any alternator but not sure. I've attached a photo of a very similar bracket setup. Am I over analysing, should I have other concerns?

 

[Silvertip]

Re: Marine Alternators and charging systems

You don't have a "charge controller" -- you MUST have a "voltage regulator". Alternators are specified in AMP OUTPUT, not watt output. 60 - 70 watts is hardly enough to light a few light bulbs. You should be looking at 60 amp or higher alternators. Alternators typically have internal regulators so there is no need to have an external regulator. The alternator you have may be sufficient.

 

[UncleWillie]

Re: Marine Alternators and charging systems

The rating of the Source(Alternator) is only an indication of what it is CAPABLE of delivering,
NOT what it will force on the load. More is Better!
You can plug you DC Cell phone charger into the boat and it will NOT pump 100+ AMPS into the phone.

Much like your house has 200 AMP (48,000 Watt) Service;
Your Clock Radio does not go up in smoke when you plug it in.

 

[kinematics]

Re: Marine Alternators and charging systems

Silvertip - thank you for clarifying alternator rating units, I really should have caught that mistake in my original post.

I've noticed most the modern alternators are internally regulated although my original prestolite was external.

Unclewillie - I'm aware a electronic device will only draw the necessary current. My concern is in regard to over charging the battery. My understanding is the battery can explode if unable to vent during over charging. I understand explosions are rare but I would feel much better if I understood all the determining factors.

Does anyone have experience with the Ford mounting brackets? Is it a universal mount?

 

[Nickypoo]

Re: Marine Alternators and charging systems

If the voltage regulator is functioning properly, a high output alternator won't overcharge your battery. They self regulate their output according to the system voltage.

If the voltage regulator on any alternator is bad it could fry your battery and electrical system.

Batteries release hydrogen gas if they are overcharged. This won't automatically blow up, much like gas fumes in your boat won't spontaneously combust. There needs to be an ignition source too. The amount of hydrogen gas produced also depends on to what extent they are overcharged.

Internally regulated alternators are far superior to externally regulated.

Ford's alternator form factor hasn't really changed much. I know it was pretty much the same from the 80's through the 90's. The one in your picture looks a lot like a 90's era form factor, but it could differ in dimensions and pully offset. You could probably take that one to a junkyard and compare it to automotive versions, although you would need a marine style. Just so you know what to order. Generally your alternator will have a case style you should know that determines its mounting tabs, dimensions, etc.

 

[UncleWillie]

Re: Marine Alternators and charging systems

Unclewillie - I'm aware a electronic device will only draw the necessary current. My concern is in regard to over charging the battery...

If the voltage regulator is functioning properly, a high output alternator won't overcharge your battery. They self regulate their output according to the system voltage...

A battery is just like any other electrical load. It will only draw what it needs.
Unless the battery is extremely discharged, charging currents of more than ~30 amps will be seen for only a very short time.
Once the Battery Voltage reaches the Alternator voltage, The Battery starts Absorption Charging. Details Here.
As the battery reaches full charge it will eventually draw less than 2 amps from the charging system. (Alternator or AC Charger)
It will make little difference to the battery if the alternator is a 65 amp or a 100+ amp model.
The battery will not be charging at 100 amps.

 

[kinematics]

Re: Marine Alternators and charging systems

Thank you both for the information, I feel much more comfortable with how the system works.

I'm hoping someone has input on the quality of the different marine alternators. The Delco alternators caught my attention but concerned with the 1 year warranty. What are some of the experiences you guys have had with alternators in the past? Thanks!

 

[Silvertip]

Re: Marine Alternators and charging systems

Keep an alternator dry and have adequate engine compartment ventilation and you will not have alternator trouble any more or any less than you would have with the unit installed in your car or truck. Buy a quality unit and you will have quality service life if treated accordingly.