What size alternator should I use for dual battery hookup

[Hollis]

I have an A/B switch behind my 460, What size alternator is recommended when the switch is set to both A and B battery's?
Would it matter if one is a deep cell?

[mister460]

Bigger alternators are always better but a stock type should work just fine. It'll just take a little more time to charge them. Maintaining a charge while running doesn't take a whole lot of output usually.

[Havasu Hangin']

I agree with mister289... http://www.planetsmilies.com/smilies/happy/happy06.gif
However, remember that an additional battery is an additional load (ESR) on the alternator, so I would say that stock alternators (55 amps or so) should only be switched on "both" when necessary. That poor little alt will strain to charge both...especially if your "deep cell" is deep in the cycle...
Most stereo guys (hard on charging systems) with dual batteries will use 90+ amp alternators...
http://www.planetsmilies.com/smilies/happy/happy25.gif

[mister460]

I.........hate........you........guys! http://free.***boat.net/ubb/wink.gif J/K

[DOHARA]

I have a question, My boat was rigged with only a single battery when I bought it. I installed dual batts. and switch. When I put the selector on both and run it and then I shut it off it usually pops the main breaker. When it's on either a or b it won't pop it. Only thing I can think of is to put a higher amp rating breaker in cause the original isn't high enough to handle dual batt set up. What do you think?
DANO

[mister460]

Does everything work fine after you reset the breaker? Probably just cause the alternator is puttin out more for both batteries when you throw the switch. Try a slow blow breaker.

[Havasu Hangin']

Originally posted by DOHARA:
...When I put the selector on both and run it and then I shut it off it usually pops the main breaker.
Well, Dano...I'm by no means an expert...but if I had to guess...
Your alt may be charging at a higher level to keep up with the dual batteries...somehow, you have a surge between the key being shut off and the alt quitting.
Or the breaker may be tired...either way, the breaker is made to protect your boat from a short, so a little larger probably won't hurt...what size is in there now?
If you go with a slightly larger breaker...I am not liable for what happens... http://www.planetsmilies.com/smilies/happy/happy06.gif
As I mentioned earlier, if you run your batteries down, running on two batteries is tough on the alt. Also, the batteries tend to equalize themselves, so instead of one charged and one spent, you may end up with two half-charged.
An isolator will keep both batteries separated, and the alt will charge the one that's lower first...
http://www.planetsmilies.com/smilies/happy/happy25.gif

[Havasu Hangin']

I like mister289's answers...to the point...no ramblings...
http://www.planetsmilies.com/smilies/happy/happy25.gif
[This message has been edited by Havasu Hangin' (edited April 17, 2002).]

[Hollis]

Thanks guys, where can I find the isolater?

[Havasu Hangin']

Originally posted by Hollis:
Thanks guys, where can I find the isolater?
Pep Boys has em for around $20, or you get a marine isolator at stores like West Marine or Boat/US (http://www.boatus-store.com/browse/item.asp?CFSR=1&IID=17001) for around $50-$70.
http://www.planetsmilies.com/smilies/happy/happy25.gif
[This message has been edited by Havasu Hangin' (edited April 17, 2002).]

[BOATDRINKS]

Originally posted by Hollis:
Thanks guys, where can I find the isolater?
Your best bet is to get a "Smart Solenoid" made by SURE power industries. Get the model 1315 its a complete no Brainer
and will do all the work for you. Its a solid piece made by a Quality marine electronics firm. Trust me, it will be the best piece of electronics you'll buy for your boat.
Just My .02
Boatdrinks

[lilrick]

hay Boatdrink! wontcha' tell me more about this little whiz-bang 1315,sounds cool!

[Hollis]

http://www.surepower.com/isolators.html

[DOHARA]

THANKS GUYS!!!! I figured that was it but a second opinion is always good. The boat was originaly with one batt. and probably has a small amp breaker. I will put in higher amp breaker and see if it stops. I have never had the batts die even when rockin out for hours with radio on.
THANKS AGAIN........
DANO