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.
Great Harbor Cay, Bahamas
---In amelyachtowners@..., <svgarulfo@...> wrote :
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?
Amel 54 #122
Union Island, St Vincent & the Grenadines