What size alternator do I need?

I'm going to upgrade my alternator. I don't know its current size or age, but she's been around a while. Last year it barely keep up and this year it looks like it just won't get the job done. So, what size do I need?

I don't have a "kicking" sound system, and I never will. I do have a simple radio and four speakers that gets occasional use. I don't really run anything additional during the day. At night I have the navigation lights and occasional use of a million candle watt power spotlight. So I obviously don't need a 200 amp alternator, but do I need more than a 55?

This seems to be a common replacement type from DB Electrical: http://www.dbelectrical.com/p-3611-1...8-amn0002.aspx

This seems to be a possible one wire option (and it's 63 amp versus 55): http://www.dbelectrical.com/p-10903-...70-others.aspx

The three wire application doesn't bother me, so I'm not needing simplicity in installation.

Thoughts? Suggestions?

And here's an option from eBay. 105 amp for less than DB Electrical's 55?

http://www.ebay.com/itm/NEW-105-Amp-...83505d&vxp=mtr

Here is the one I have. http://www.dbelectrical.com/p-3609-n...e-adr0334.aspx

the 51 amp alt. should be fine. All PCM 351W came with them... They keep up just fine. That is 14 volts * 51 amp = 714 watts. Each Nav light is only a few watts, the dash light are even smaller...

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Originally Posted by beat taco

Here is the one I have. http://www.dbelectrical.com/p-3609-n...e-adr0334.aspx

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I would go with this one if you are looking in that range and that company. Sure you don't have a kicking stereo, but you never know. For $10 more, why even have to worry about it? Get the bigger one and don't worry.

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Originally Posted by beat taco

Here is the one I have. http://www.dbelectrical.com/p-3609-n...e-adr0334.aspx

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This is the alternator I'm using. It is the same 10si that's in your eBay link. For my needs it's just fine and I'm quite happy with it. I only replaced mine because I had to rev above 2000 RPM to start the old 50 amp charging. Much cheaper than a new factory alternator and twice the power.

Sold. Thanks for the DB link. I'd prefer to buy from them, but I couldn't find anything there other than the smaller 51 and 63 AMP versions. 105 will be plenty I'm sure.

Sounds like you've made a decision, but to be honest, theres not any info that would make answering your original question possible. Im sure a 105A alt will be fine, but the decision needs to take into account the average continuous of your stereo and other loads, the total battery Ah and hoe you use the boat/stereo. Just keep in mind though, even a 105A alt is not going to do well to recharge depleted batteries. Asking an alt to recharge batteries should not be confused with an alternator that "doesnt keep up".