[Amel Yacht Owners] Re: Isolated alternators


Sv Garulfo
 

Thanks Bill, 

The original alternator and the replacement are both of the same type: case grounded. I’ll work towards isolating the alternator ext rnal case from the engine block. 

As an owner of an SM, could you indicate what type is typically fitted there?

As an aside, am I right in thinking the solenoid on the negative circuit connects the engine block to the negative terminal of the starter battery only during the start procedure and not all the time the engine is running?

Also, I’d like to understand the advantage of the floating negative in the amel design. It seems to go against the litterature I know of, that tends to indicate the bonding should be connected to the negative battery terminal (if I’m not mistaken). Is it to do with the presence of both 12V and 24V circuits?

Thanks

Thomas
GARULFO
Amel 54 #122
Union Island, St Vincent & the Grenadines 


On Fri, 19 Jan 2018 at 16:58, greatketch@... [amelyachtowners] <amelyachtowners@...> wrote:
 

Thomas,


There are two significantly different types of alternators, depending on where the how the return circuit to the battery negative is made.
Tter
In a "case grounded" alternator there is usually an attachment on the alternator for the battery Positive wire ONLY.  The connection back to the battery Negative is through the alternator external case, and then through the engine block.  This will not work on an Amel because the engine block is not continuously connected to the battery negative. These are the common alternators used on automobiles.  

Occasionally, this type of "case grounded" alternator has a connection for a battery negative cable on it.  The way to check if your alternator is "case grounded" is to look for continuity between the Negative terminal on the alternator and the the alternator's external case. If the alternator is "case grounded" it will show near zero ohms on this path.  It is not suitable for an Amel UNLESS the case is electrically isolated from the engine block with the plastic inserts.  Putting one of these on an Amel without the isolation parts will make a continuous direct connection between the bonding system (connected to the engine) and the battery negative (connected to the alternator case).  This eliminates the "floating negative" that the Amel was designed with.  It would put all the underwater parts of the boat at risk for stray current corrosion.

The other type of alternator with an "isolated ground" has connections for both battery Positive and battery Negative on the alternator.  This is the best type of alternator, and hopefully the one you have.  On this type of alternator, if you test the resistance between the Negative terminal and the case you will see an open circuit--no connection.  If you have this type of alternator, it can be installed safely without the plastic isolation parts since it is already electrically isolated from its mount to the engine.

Bill Kinney
SM160, Harmonie
Great Harbor Cay, Bahamas




greatketch@...
 


Thomas,

I can not tell you what was "typically" fitted on an SM because our alternator in not original.

You are correct about the function of the ground relay on the engine, hence the requirement for all the sensors to be two wire style instead of grounding to the engine block.

You are also correct, the Amel floating ground is unusual on FRP boats, but not at all unique. It has nothing to do with having both 12 and 24 volt systems onboard.  Floating grounds are standard on metal hulled boats, especially aluminum hulls, for example. 

Even very knowledgable people will have passionate arguments about the pros and cons of a floating ground. It should be obvious to anyone that either system can work well.  My old boat had it's negative and bond connected together. It had no significant issues and it was 40 years old.  

Some types of corrosion are eliminated by one system, and some types by the other.  Some types of maintenance issues show up on one, and not the other.

The KEY is to be sure that you understand which system you have, and make sure you understand what is needed to keep it as it was designed.  Mixing and matching have to potential to set up stray currents that cause serious problems.

Bill Kinney
SM160, Harmonie
Great Harbor Cay, Bahamas


---In amelyachtowners@..., <svgarulfo@...> wrote :

Thanks Bill, 

The original alternator and the replacement are both of the same type: case grounded. I’ll work towards isolating the alternator ext rnal case from the engine block. 

As an owner of an SM, could you indicate what type is typically fitted there?

As an aside, am I right in thinking the solenoid on the negative circuit connects the engine block to the negative terminal of the starter battery only during the start procedure and not all the time the engine is running?

Also, I’d like to understand the advantage of the floating negative in the amel design. It seems to go against the litterature I know of, that tends to indicate the bonding should be connected to the negative battery terminal (if I’m not mistaken). Is it to do with the presence of both 12V and 24V circuits?

Thanks

Thomas
GARULFO
Amel 54 #122
Union Island, St Vincent & the Grenadines