voltage problems, alternator upgrade?

[sunnygrill]

I have a 1977 mercury outboard 115 hp L6 and I just put in a pretty powerful stereo system. I took it out to the lake and the first day I had not really a problem but the second day the marine optima had enough. I dont think the motor is supplying enough juice to the battery, so what can I do to solve my problem? Thanks.

 

[Scali]

Re: voltage problems, alternator upgrade?

maybe a bigger battery, youve got to be carefull because not all Mercs hve voltage regulators { @ least mine doesnt 1994 40 } .<br />I was checking my voltage output just yesterday & it's 17.5 volts @ idle.<br />That may not be good for a stereo, guess you'd just end up with a blown fuse though maybe ..

 

[Chris1956]

Re: voltage problems, alternator upgrade?

Sunny, That motor has an unregulated ~6 Amp charging system. The battery load will generally keep the voltage under 14V. I would check to make sure the battery is being charged by the motor. The easy way to do this is to put a DC voltmeter on the battery, note the voltage and then start the motor. If the voltage rises as the rpm rises, it is charging.

 

[briannh1234]

Re: voltage problems, alternator upgrade?

I think it's really a 12 amp charging system. But if your running a big stero off it and the motor is not charging the battery enough then you need a new source of power.<br /><br />I would recommend that when you are not using your boat that you get a smart charger and plug it in. Optima batteries are real picky about their chargers - look for one that claims to be optima compatable.

 

[sunnygrill]

Re: voltage problems, alternator upgrade?

briannh1234, what kind of other power source?

 

[sunnygrill]

Re: voltage problems, alternator upgrade?

chris, I'll check that but when the battery would get really low I would turn off the radio for a while and the battery did charge but with the stereo on it just drains the battery. Now I have a second battery for back up, but what can I do to to illiminate this problem? What would you do?Thanks.

 

[Chris1956]

Re: voltage problems, alternator upgrade?

Sunny, If the charging system plus the battery cannot supply the stereo, there are only three things you can do. One is to get a generator, which is impractical. Two - don't listen to the stereo, also impractical. Three - use a battery isolator and associated wiring such that your stereo and other accessories run off their own deep cycle battery. Have the motor starting battery only start and run the motor.<br /><br />Let me say this. I would really look into the amperage draw of your stereo. Even a 15 Amp draw by a stereo (which is a lot) shouldn't affect a charged battery, if you are listening to the stereo on a day boating trip. if you anchor overnight and burn lights also, that is a different story.

 

[briannh1234]

Re: voltage problems, alternator upgrade?

Sunny -<br /><br />For your other source of power I would suggest using a smart charger before you go out boating. This will store the power you will need in the battery. The problem with the smart charger is you need a place to plug it in when the boat is not being used. I keep my boat on my trailer so it's not a big deal for me. But if you keep your boat in the water you may want to look into one with the word "Marine" on it as well as "Optima".<br /><br />Most boat charging systems will not completely recharge the battery on a short run. You will need to run the motor for hours to truly recharge the battery.