A question about alts.

[Janus]

I'm new to this site and this board so let me tell you briefly about my system and my car.

i have an '88 Beretta GT (2.8L V-6), almost completely stock except for the audio system. I bought this car about a month or so ago because i needed a car (i'm starting college and need some way of getting there) and it seemed fairly reliable and it was in my budget (i'm a poor student).......

Anyway, I'm running mostly old equipment. I have the stock 6x9's running in the back, 2 JL audio subs in a box in my trunk, a yamaha amp that i have no idea as to the power of (instead of showing the usual 600W or 300W or whatever, it just says 35W x 4 / 70W x 2. My guess is that it's not really that powerful.) and i i have two 100W max. 30W nominal Pioneer 4" speakers in the dash. Oh yeah, my head unit is a Pioneer DEH-205 single disk CD-player.... it's old. Everything except the 4" in the dash were in the car when i bought it.

Now that we have that explained, let me get to my question.

The car had a 100A alt. installed before i bought it. Everything that i understand tells me that this should provide more than enough power for my meager system, but when i turn the volume up past 18 (the volume controls go from 1-30) and even lower on really bass intensive songs, the lights begin to dim to the beat. My battery is at about half charge, i'm guessing that this might be the problem? Am i right?

Also i remember reading somewhere that there was some sort of calculation you could do to figure out how much extra power your alt. had that you could use for accessories (systems, security, anything that is a post-production add-on to the electrical sys.). Does anyone know what this is?

Ok, thank you to anyone who actually read this, and an anticipated thank you to anyone who can help me out here.

Janus.

Click to read more...

 

[blackgeltabs 5,000+ posts]

Are they dimming to a heavy extent?? Cause with a new 100a alt you should have plent of power with tons to spare. You battery maybe the first problem, if its old and has been used through most of the cars life then yes it might be time to get another one. Even a rather cheap one should do the job just fine. Also you probably get a refubished alt, and sometimes they are not built right id suggest haveing check the output of the alternator to make sure its up to snuff. Let know how it goes, it mustbe one of the things I said becasue a 300 watt amp WILL not draw that kinda current from the electrical system.

Also welcome to fourm its good to have you here, I hope you learn a lot from us. There is a good group of guys here that are very knowledgeable.

 

[Janus]

Thanks for the help. I was pretty sure that i was correct in believing that the battery was the culprit. i wanted a second opinion though. i understand electricity, and electronics fairly well (i would never consider myself an "expert") but automotives and sound systems are fairly new territory to me.

I am still curious however to figure out how much extra electricity i have to work with for any additions that i want to make. i plan on hooking up fog lamps, I would also like to get a second amp for the speakers.

Mostly it's driving me crazy that i know i saw a website on car audio systems and it explained how to figure out how much power you still have left to work with (EX: alternator puts out X amps. Car uses Y amps for it's operation. This leaves you with Z amps left to work with). I know not everything on the internet is true, but it makes enough logical sense that there should be a formula to that effect.

Ok, thanks again for the help.

Janus

 

[maylar 10+ year member]

100 amp alt should be fine for that. Something else is wrong. I'm betting that you'll see your lights dim just by turning on your heater or rear window drfogger. If so, then the electrical system isn't up to factory specs. Either a battery or new alternator is in your future.