Alternator upgrade help

[CC Sparky]

New to PN, and looking for some tech help on upgrading the alternator in my 04 SANLE. I installed the 100amp upgraded alternator and replaced the cables to larger guage, and still the voltmeter drops everytime I blast the stereo. Now I am looking at a 220amp upgrade, does anyone have any experience in this arena??

[Chexi]

Golf cart batteries and a shore charger for your audio completely isolated from you audio. If you must charge your audio batteries with your alternator, use an isolator - combiner.

[surroundsound64]

What kind of power are you trying to push? If you've got a kickin stereo and pushing it hard you may need a big capacitor to help in order to not see a big voltage drop.

[CC Sparky]

The boat came with a perko, and I changed out the batteries to optima blue tops. I have 3 JL Audio amps totaling about 2200watts, which are supposed to have a regulated power supply, eliminating the need for a capacitor.
When I charge the batteries at home the system seems to work Ok at first, then out on the lake, as the day wears on the voltmeter starts dropping and the alarm sounds.
I have been looking into a 220amp alternator, and I want to make sure this is really the problem. The 100amp alternator I installed made things better, but still cant keep up with the demand.

[Chexi]

(A) 220 amp alternator is wicked expensive, and you need to upgrade your electical system if you go that route.
(B) You are better off isolating your audio power needs from your starting battery by using 2 (or more) banks of 6v golf cart batteries (hooked up in series within a 2 battery bank to get 12v, but each bank (if you go more than 1) hooked up in parallel to maintain 12v). Then, shore charge with a proper deep cycle charger the golf cart batteries. These should work fine for your demands and not risk your starting power. If you feel you absolutely must run your audio off the alternator, then you can hook up an isolator combiner that will not charge the second battery unless the first battery is fully charged, so you at least won't be charging 2 batteries and running the audio. Whether or not you can use golf cart batteries in that system is a little beyond my knowledge. My dealer warned me about charging deep cycle batteries with an alternator... basically that I would be cooking them, and the bigger the alternator, the more cooking I would be doing.

[CC Sparky]

You are right about that alternator being expensive, to the tune of about $400. I am a little confused about the isolater.. does the perko not do the same thing, for example charging one battery(whichever is selected) then the other? That is how I understood it to work.
I have the amps all running on one battery, and the other for starting, the problem is we do a lot of idling to and from our ski spot and at idle the stereo cant be turned up. BTW good point about charging deep cycles I hadnt given that much thought.

[Chexi]

Hmm... if you are using a Perko and running in the 1 position (i.e., charging only your starting battery), then you are not running your audio off the alternator presently. This means that your problem is the blue top you have dedicated to your audio doesn't have enough amp hours. A pair of decent 6v golf cart batteries will give you way more. Google them and checkout the relative specs.

The isolator/combiner I am talking about is the Blue Sea version that has a Perko like switch (not identical) and also an isolator/combiner relay that will automatically allow you to charge both batteries when the main battery is between a certain range of voltages. It's a pretty slick hands-free system. It does allow manual combining if you ever needed it to start.

[TX-Foilhead]

Chexi is right on the batteries, you've got 2 blue tops and no charging with the way the switch is set. So basically you've only got about 120 amp hours and those JL amps are sucking them down harder as the voltage drops. Set the switch to both unless you're sitting and I bet you'll have no problems.

The other thing that caught my eye was a $400 alternator being 'wicked expensive'. That price sounds way low, be sure you a marine alternator, you don't want to turn your boat into a bomb.

[Chexi]

^ Agreed. Don't set your boat up as the bomb...

A 100 amp marine alternator kit is almost $400. A 240 amp marine alternator (presumably the balmar) should be quite a bit more, like around $3,000. That's not counting the wiring upgrade you would need to do. Nevertheless, you do not need to do this.

[wake_fun]

Set the switch to both unless you're sitting and I bet you'll have no problems.

That's what I do. Charge up your batteries to make sure they're good and fully charged, then keep the Perko switch set to "BOTH" all day long, unless you park and listen to music. When you park set it to #2. When you go back out set it back to "BOTH".
Try that first before spending anymore money!

[CC Sparky]

Sounds good, I will try running the perko on both, and sitting on only one battery. The alternator I found was from DB Electrical, and it was $395, and claims to be marine grade. Who knows, Hopefully I dont need to worry about replacing the alternator.
Thanks everyone!