charging system

[Taube]

I have a 78 merc 175 and want to be able to upgrade my stereo system with a couple subs. I know i'll need a 2nd battery, but what is the deal with my charging system on engine? upgrade? ive seen the add on alternator that is belted to the wheel on top but don't want to lose power. I have a 79 eluder how do i wire the terd for two batteries and keep it charged on the water

[Taube]

I have a 78 merc 175 and want to be able to upgrade my stereo system with a couple subs. I know i'll need a 2nd battery, but what is the deal with my charging system on engine? upgrade? ive seen the add on alternator that is belted to the wheel on top but don't want to lose power. I have a 79 eluder how do i wire the terd for two batteries and keep it charged on the water

[supergenius74]

I know exactly what you are going through, and I believe that 78 has a 12amp system which isn't nearly enough for a good amp and subs, my buddy has an I/0 and upgraded his alternator to a hi-po 100 amp one just to run a descent system, anyways we tried the dual battery set-up and that helps but the bottom line is you need more charging power and I don't think that after-market one will even work on your motor, I thought it was for newer 2.5L engines. I think the best solution for a big stereo is 2 deep cycle batteries wired all together, then add one of those 30 dollar in-boat chargers that always is wired to the system, when you are finished boating just plug it in and it will slow charge the whole system all the time keeping it full, the two-battery setup helps if you want to park the boat for hours and crank up the tunes, we ran this on a bayliner with 2 12 rockford subs and 2 large amps all day long and still had enough juice to start up and drive back. But the older outboard engines only made enough amps to keep themsevles running, not enough to compensate for huge current draws. Hope this helps. shane