is my alternator big enough for this?

[trevor.resar]

I own a 1995 Sea Ray Sea Rayder, powered by a 90HP Mercury Sport Jet. I am trying to wire a small 400 watt amp into the boat to power a 10" Subwoofer for my audio system. Before I jump into this, will the alternator on this particular boat be able to keep the battery charged with this kind of set up?

 

[Silvertip]

Re: is my alternator big enough for this?

If the alternator is the same as on a 90 HP outboard, I believe it is a 18 amp unit. The question is not so much will the alternator handle it as much as will the battery handle it. The battery is more than likely a rather smallish starting battery so you are down on power on two of the three categories right from the git-go. Battery size, battery type, and alternator capacity determine whether this will be an acceptable situation. The starting battery will not likely last long. Look at it this way. If the amp drew 20 amps to be conservative, and you ran it for an hour (provided the battery lasted that long) you would need to run the boat wide open for over an hour to charge the battery reasonably close to full charge. Now -- does that sound like a winning situation?

 

[Boatist]

Re: is my alternator big enough for this?

400 watts at 12 volts will draw 33.3 amps if the amp is 100 percent effiicent. So with a 18 amp alternator the battery will have to supply the extra 15 amps. How long can your battery supply 15 amps before it goes dead.

Of course the amp only draws 400 watts at full power but then again the amp is only about 70 percent efficent.

For me I see no need for a amp over 10 watts on a boat unless your trying to destroy the peace and quite of other boaters enjoying the day. At least the noise will not last long and if your lucky one of the quite boaters might tow you in.

Another factor is your alternator will only put out full power at about 3000 rpms or more and most outboard alternators will over heat and burn up if run in that mode for long.

Have fun while it last.

 

[trevor.resar]

Re: is my alternator big enough for this?

Wow, who would have thought such rude comments would come from your "opinions"

But thanks for the info on the question I asked. Looks like my alternator may be a little small for this application.

 

[bruceb58]

Re: is my alternator big enough for this?

You could measure the current tha amp is drawing at your normal listening level to get a better idea. Doubt you would draw more than 10 amps on average. You can do the math after that. If you run your amp for 2 hours you will draw down the battery by 20 amps. I would suggest having a second deep discharge battery for this though or have your main battery be a deep discharge battery. A deep discharge battery will have no problem starting an outboard.