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73 240Z alternator upgrade advice needed


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As it stands, my car's got two 6x9" speakers in the rear. It will be receiving two more 3.5" speakers and a 12" subwoofer powered by a 400W mono amp.

The headlights dim and the turn signal hangs when when I let off the gas already, so I'm assuming I'll need significantly more power to drive a beefed up audio system. My question is, how many more amps of power should I be shooting for? Getting a direct bolt in alternator is not as easy as it seems when looking for lots of amps. I don't really know what to expect, and I'd think that a 280ZX-T alternator SHOULD be sufficient as it's designed to power far more electronic equipment than mine, but I'm not sure how a massive sub system will affect things (especially since I like my music loud). I want to keep costs down as much as possible, but I need the setup to be reliable. I can't see myself adding any more electronics than that, so my concern is primarily to ensure adequate power for that setup at a reasonable price.

 

Will the 280ZX turbo alternator suffice? If not, how many amps should I seek?

Edited by nthiogen
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JeffP's Extreme280ZXT webpage on Anglefire, check the alternator page.

 

Got one that will drive it all at IDLE, and properly regulate to the highest speeds.

 

Amperage is a function of size---turns and diameter of the alternator, as well as Diode Capacity of the rectifier bridge used.

 

You would think a ZX is a big upgrade, and it is, but not for audio systems with big transient loads. Get some big capacitors!

 

And put your lights on a relay setup (they have a plug and play for 240's)---they will be a lot brighter going locally to a direct ground, instead of back through the steering column switch/master ground point!

 

For your winkers, get a solid state flasher relay...they don't care about bulbs burnt out, using LED's, etc...

 

Good Luck! Alternators aren't what they are cracked up to be! :angry:

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  • 3 weeks later...

Thanks for the advice Tony D, sorry for not responding earlier. My car's been getting 14 MPG highway and 10 or so in the city, so electronics are on the back burner for now. Just ordered some Z-therapy SU's. Nice dent in the wallet, but I figure they should be more than worth it.

 

What's this about capacitors and relays? I know nothing about electronics/ignition in a car. It's the one arcane field of car stuff that I have absolutely no insight in. I probably know as much or less than the layman.

 

I have to be honest, even though JeffP's setup was built from expensive trial and error, buying a 200amp alternator seems... unnecessarily expensive powerful. My I35 most definitely did not have a 200amp alternator, and it powered a 10-inch sub as well as all the other power options it came with (of which there were plenty, which I'm sure you already know).

 

I leaning more towards rebuilding a junkyard alternator off a modern car and adapting that. I see cars with subs hanging from the headliner that definitely haven't had their alternators replaced and they do just fine.

 

I don't want to sound like I'm blowing off your advice, especially because you clearly know what you're talking about. I was just hoping for a solution that was less pricey and fancy.

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  • 1 month later...

Stiffening capcitors used in car audio systems help reduce the "holes" in the voltage supply to the amplifier(s) caused by the transient peaks that is in music. The largest cause for these transient peaks is the bass in music, it draws the largest current when compared to higher frequencies. Stiffening caps should not be used in place of a good charging system, just to augment one.

 

I have a Delco CS130 style alternator on my 240Z (L28E) Mine is built to put out 160 amps max, but the stock units are designed for between 100 and 120 amps, and have good low RPM (some would call this "idle") charge abilities. Mine, since it's built beyond factory specs needs an engine idle RPM of about 900 to be at a charge level I like. I can turn idle down to about 800 and it still charges, just barely. A stock CS130 alternator should have no problems with an engine idle of about 700 RPM, depending on the pulleys you have. My crank pulley is the tiny one found on early 240Zs IIR it's about 5" in diameter. I have a small alternator pulley to get the shaft RPM up. I was going to install a larger 280ZX crank pulley, but it turned out to be cracked, so I didn't and have just left the high idle.

 

A few pictures of mine:

58756_10150246978375051_651865050_14621311_4046120_n.jpg

 

57929_10150246978650051_651865050_14621323_34951_n.jpg

 

Link to more info: http://www.ontariozcar.com/forum/showthread.php?64-Six_Shooter-s-money-pit-time-vampire&p=2289#post2289

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Dont think you will need a 100+ amp alternator for just a 400 watt mono amp and a head unit. Optima Yellow Top Battery ($200), 280zx alternator upgrade ($100) and a Capacitor and you should be fine.

This cap is a little overkill at 10 farad, but if you decide to add another amp for your 6x9s and 6.5" speakers, it should be more then enough.

 

http://cgi.ebay.com/ROCKFORD-FOSGATE-RFC10HB-10-FARAD-HYBRID-CAPACITOR-CAP-/390337061609?pt=LH_DefaultDomain_0&hash=item5ae1e6e2e9

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Dont think you will need a 100+ amp alternator for just a 400 watt mono amp and a head unit. Optima Yellow Top Battery ($200), 280zx alternator upgrade ($100) and a Capacitor and you should be fine.

This cap is a little overkill at 10 farad, but if you decide to add another amp for your 6x9s and 6.5" speakers, it should be more then enough.

 

http://cgi.ebay.com/ROCKFORD-FOSGATE-RFC10HB-10-FARAD-HYBRID-CAPACITOR-CAP-/390337061609?pt=LH_DefaultDomain_0&hash=item5ae1e6e2e9

 

400W = 63amps peak, using 50% efficiency for the amp (Even Class D aren't as efficient at peak power as the manufacturers would like you to believe).

 

So 100A alternator with the tunes cranked will leave about 37 amps to run the car, and the rest of the audio system. That's the deck, lights, EFI/ignition, heater fan, electric cooling fans (if equipped), etc. With the poor headlights the S30 comes with, any little bit helps.

 

Now, this is peak current draw of the one amplifier, and average current draw will be less, but I would not run a system like this with a 65A 280ZX alternator.

 

A Cap should only be used to supplement a proper, good working charging system, it should not be used as a band aid for a lesser charging system. A stiffening cap's job is to have an instant burst of energy available at the amplifier, to bridge the time that it takes for the alternator and the wire between to provide the necessary current.

 

I would also recommend a red top Optima battery as the starting battery, not yellow. The Red top is designed as a starting battery that will discharge and recharge quickly. Yellow tops are a deep cycle battery that are better suited for systems or uses where there will be extended key off time to run something electrical. I have seen many yellow top battery live a short life, being used as a starting battery, where a red top in the same application has lasted much longer.

 

I have used Red top batteries since about '96 or so, in all of my vehicles, except my Dakota, which I just haven't had time to swap my "extra" Red Top in.

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  • 2 months later...

Sorry for the extremely late reply y'all. I appreciate the info and links. For now I'll have to focus on the essentials, as my ignition system is in need of an overhaul. I'm planning on doing a write-up for it as well, so hopefully I'll have a little something useful to contribute to the forum.

 

I think that about 80-90amps should be plenty for me. I'm planning on putting LEDs in the interior and side markers to help relieve some strain on the electrical system, and I am staying carbureted and fan clutch'd so I won't have to worry about high current draw.

 

Thanks for the tip on the Red Tops, Six. I'll definitely be keeping that in mind when I start redoing the charging system.

 

And good look on the link, wrcbonk.

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