battery/stereo questions - new amp

so i'm getting things together for my stereo upgrade and had a few more questions

i bought an infinity 7540a amplifier. it's rated at 111-watt x 4 channel at 4-ohms rms and is cea rated. what i'm concerned with is that in the specs, it says it draws a max current of 80amps. that's a lot! i've only got 2 batteries, and one is going to be isolated with a combiner so really it's just a backup. so with that said, i really only have one battery for all my accessories. since most of our listening is with the boat off just floating around hanging out, i'm concerned that even at normal listening volumes i'm not going to have a lot of battery life. do you think i'll be okay? i mean an hour+ to me is considered exceptable, but if i had to start the boat every half an hour that would be a drag. what do you guys think? do you think i'll be okay?

here's what i'm planning

infinity 7540a
(2) polk mmc650's (rated at 80-watts continues) --> 2 channels of 7540
(1) JL 10W1v2 10" sub (rated 150-watts) --> 2 channels bridged of 7540
(2) polk DB1000 tweeters (rated 60-watts continues) --> either deck power (kenwood kdc-mp4028 55-watts x4), or in parallel to mmc650's.

which way would you go with the tweeters? would you use deck power? one thing to consider is i can turn off the amp in the head unit, which i would think would give me more runtime, but if i hang them off the head unit, i'll have to have it on. i just want what sounds best. what do you think?

do you guys think i'm going to get an hour of listening time with that setup? i'm switching out the stock battery 1 for a new optima blue top to match battery 2. then i'm going to have them install the yandina c100 for me as well.

i wish i had room for another battery, but the reality is, i don't. so do you think i'm on the right track? any suggestions, recommendations? do you think that will sound good? do you think i'll be able to get an hour+ with this setup?

the other thing is, my alternator is a 60amp, should i worry about that?

car toys, who is going to do the install, is telling me not to worry about it. i maybe am over-thinking it a bit, but i want it to sound good, work well, sound great at low volumes, and run for at least an hour with the boat off.

one last thing i couldn't get a straight answer on is that the amp has two 30 amp fuses on it. car toys is telling me that that means it theoretically can't draw more than 60-amps, while infinity is telling me that the fuses are to protect the output of the amp, not the input.

please advise-

(Message edited by brucemac on February 02, 2006)

(Message edited by brucemac on February 02, 2006)

Bruce wrote:
"one last thing i couldn't get a straight answer on is that the amp has two 30 amp fuses on it. car toys is telling me that that means it theoretically can't draw more than 60-amps, while infinity is telling me that the fuses are to protect the output of the amp, not the input. "


Fuses are one of the most mis-understood devices in wiring.....

Fuses rarely protect the piece of equipment that they are associated with. The fuse is generally to protect the wiring and/or to keep the piece of equipment from starting a fire should somethng go wrong in the equipment.

One reason that fuses will not protect the equipment is that if the fuse is big enough to avoid "nuisance trips" then it reacts way too slowly to prevent circuit damage.

The rating of the fuse is what it will carry indefinately. The fuse will carry much more current for a short period of time.

For example, from the data sheet for a 30 amp, "LittelFuse": will carry 150% (45 amps) for approximately 10 seconds, or 200% (60 amps) for 1 second, or 600% (180 amps) for a half a second.

The fuse will tend to average the current over a few seconds, which works well for amplifiers because you rarely have maximum volume continuously.

If thats the only amp your running im sure youll get an hour out of it. We sit sometimes for 2-3 running 1 out of three amps (the towers @ 800 watts rms) not all the way up though and dont have any problems. The max current will not be seen as youll most likely hear distortion prior to max amplifier output and theoretically would never draw that much. It does depend somewhat on the type and size of your batteries though.

Rod

so with that said, there's no way that this amp could draw more than 60 amps for more than a minute, which in a real world situation means that at "normal" listening volumes it would probably operate at 1/2 to 2/3rds of that (30-45 amps) at a bad guestimate maybe? if not even less? combine that with the fact that aside from the sub, my speakers are fairly effecient this should all work fine and acheiving an hour with a blue top deep cycle should be doable???

bob, after my upgrade, both batteries will be the optima blue top deep cycles

what do you guys think of the configuration? should i run the tweeters off the head unit? or off the same channel as the mmc650's?

(Message edited by brucemac on February 02, 2006)

any advice on the tweeters?