Force 120 hp Alternator Amp Output

[tmecca]

I'm planning on installing the new Blue Sea Systems automatic battery charging relay system to manage the charging of the starting and house batteries on my boat. Their instruction manual specifies the wire sizes and fusing required, but to select the right ones I need to know the amp output of the engine's alternator. Can anyone help me with that? And, of course, any advice on the do's and don'ts of doing this right. I intend to install their auto relay and battery switch system (their PN 7649).

 

[pnwboat]

Re: Force 120 hp Alternator Amp Output

Depending on which stator you have it's either 9 amps or 16 amps output.

 

[tmecca]

Re: Force 120 hp Alternator Amp Output

Thanks, that really helps. One more question is what wire sizes to use from the batteries to the battery switch. It seems that the right size depends on length of the runs and the amp draw of the starter. The one way distance to switch is less than 4 feet. Down't know starter's amp draw, or tolerance to voltage drop...3%?? Can anyone help...would 4 AWG wires be good enough?

 

[pnwboat]

Re: Force 120 hp Alternator Amp Output

I know that automotive starters can pull in the neighbor hood of about 200 - 250 amps max. A lot of the battery cables I see are 6 gauge. Using that as a general guideline and the chart below, I would venture to say that 4 gauge will probably work fine. But that's just my opinion.

 

[tmecca]

Re: Force 120 hp Alternator Amp Output

Thanks, a nice no nonsense chart.