brad101010

Hey there all i wanted to find out some info from somone. I have a 1978 280z and i plan on installing a stereo system. I beleave I will need to upgrade my alt. to handel the additional pawer draw on my battery. I have considered going to a 2 battery system for this application, but i am not sure how to do all that, can someone point me in the right dirrection. I have also considered installing an cap. for the stereo system so the power can be drawen from that, instead of the battery. Can somone please share there thoughts with what i can in mind and please help me.

BoulderZ

Some thoughts, that probably aren't too well organized:

For the easiest to find and install alternator upgrade, there's this guy:
http://www.zspecialties.com/cat_chargingstarting-1.htm
Bolts right on, even has a warranty. Couldn't be easier. But that is $200 to $250.

There are some other options that people on here have used that are cheaper but require more effort in fit and wiring, etc. In any case, if you're planning a stereo upgrade, you definitely want a higher-capacity alternator and a capacitor. The original S30 alternators produce enough power at or around idle to run the motor, some lights, and the little 2x4.5" am/fm original radio, and that's about it. So it doesn't take many modern add-ons to outclass it.

If you have sufficient alternator capacity, then you don't need two batteries. In theory, your car and/or stereo should never be running off of the battery. The battery should act as a reservoir between drives and only be used during starting. After that, the alternator should have enough power to run the motor, recharge the battery from the cranking/starting, and run any lights, accessories, etc. How big an alternator is necessary depends on the total worst-case consistent demand of the car, lights, stereo, and whatever else is added. Add enough stuff, and you end up needing expensive, crazy equipment like custom-built high-capacity alternators, or two alternators.

However, big stereos of course can have brief spells of really high demand that no alternator(s) could possibly meet. Times like high volume, with an amp, and subwoofer(s), with a heavy bass section in a song. These demand spikes are quite brief, but not small. Unfortunately, deep-cycling or high frequency cycling a typical lead-acid car battery drastically shortens it's life. So, you definitely should go with a capacitor, as you mentioned. That'll supply those brief spikes and spare your battery. Not doing that will give you the headlights-pulse-with-the-bass effect that says to to the world, "I did a poor job building my car".

One final "what if". The two-battery set-ups are for car stereo show type conditions, where the motor isn't running (i.e. no alternator to supply power, so the batteries have to do it). So if you're doing stereo shows, or maybe you're the designated music guy at pick-up basketball games or something, then that's the only case where you might need two batteries. In that kind of situation I'd recommend marine-use batteries or others designed for both high CCA engine-starting loads as well as deep-cycling.

I think there was a really good article in Sport Z about this a few issues ago. If you're interested, you may want to check out their site, www.sportzmagazine.com or maybe email them to ask what issue it was in (if you don't already have it).

good luck,
Dave

brad101010

thanks for the help, it does point me in the right dirrection, i will go to the website and see what they have to offer. If i have ony other question i will post them here, you have been a great help

NismoPick

I bought a 78 Amp 1 wire GM alternator from AutoZone for $70, & modified the bracket. Works fine.

brad101010

I don't suppose you happen to know the part number on that alt do you?

NismoPick

Negatory, but when I was talking w/ them, they said there are only 2 or 3 GM alternators that they sell, and only one 1 wire alts. They needed a car model to look it up in their comp, so I said it was for an 85 Camaro. When you see the alternator, it should have the same thin top bracket, but the bottom one will be several inches wide. That's the one I sawsall'd to fit the Z bracket. You will only be able to bolt it up to the front bottom Z bracket.

You also won't need to hook up the Z's alternator check light wire.