High Output Alternators.......Thoughts?

[Roadster-Boy]

Hi All --

I'm tired of my blinkers blinking once every 5 seconds when I'm turning, and my headlights dimming when I slow down. One of the vendors offers a 125 amp alternator that puts an end to these deficiencies, but what else will it do? Is 125 amps overkill? Is there an inherent overload danger in running that much amperage? Their product description says we shouldn't believe the rumors that high output alternators can ruin the electrical system. True?

Thanks in advance!

Geoff

[ttyR2]

125A is huge and total overkill for something like a Roadster. I would suspect you have wiring and switch issues at play, not an undersized alternator.

[nissantoy]

Unless you are supporting a lot of stereo equipment / driving lights ect. A gm alt @ 75/80 amps is ok,. but what ever you use by pass the amp meter or it will fry

nissantoy

[Roadster-Boy]

Thanks, Jeremy -- No wiring or switch issues. I don't think my problem is uncommon for a 35 amp alternator, which I think is what was used originally. The blinkers are slow at low rpms, and the headlights will dim slightly, but the car operates fine. My first SRL311 (25 years ago) did the same thing and that had the 35 amp alt, too. I'm just wondering how high I can go with amperage before there's a problem.

Nissantoy -- I once heard that an early 80s Ford Courier alt was a straight swap. I bought one and the thing had 3 ears instead of 2. Is there a high(er) output alternator out there that is truly a straight swap with no modifications?

Geoff

[nissantoy]

check past posts for gm 1 wire alt change and converting to right side of engine to get away from exhaust heat

nissantoy

[spl310]

Nissantoy -- I once heard that an early 80s Ford Courier alt was a straight swap. I bought one and the thing had 3 ears instead of 2. Is there a high(er) output alternator out there that is truly a straight swap with no modifications?

Geoff

3 ears sounds like it was a swap in for an early car.

[Nissanman]

Their product description says we shouldn't believe the rumors that high output alternators can ruin the electrical system.

Be very, very careful here!
A high output alternator is really only a consideration if, like others have said, you are contemplating fitting an accessory requiring a heap of power.
In that case, you should provide the new power feed independent of the Roadster wiring.

Power feed compressed.jpg

Then you should protect the factory Roadster wiring from a possible overload by fitting a maxi-fuse at the alternator output post.

Narva Maxi-Fuse and Fusible Links.jpg

If the original Alternator is a 35A say then the original wiring is probably dimensioned for a similar current.
Unless you protect the wiring by limiting the current draw with a 35A fuse, the possibility exists for the original wiring to draw, under a fault condition, the full output of the new alternator.
EXIT ORIGINAL WIRING IN A FLASH
Furthermore, the Ammeter is designed to measure current draw from the battery [DISCHARGE or "-" indication] and current flow into the Battery [CHARGE or "+" indication].
This is so the driver can determine if the Charging System is performing correctly.
The Ammeter therefore only shows the amount of current and the direction of that current in respect to the Battery.
The only time the Ammeter shows the TOTAL current draw from the Battery is when the IGN is ON and the engine is NOT RUNNING i.e. alternator not charging.
So, a more powerful alternator WILL ruin the original electrical system IF that system is not adequately protected.
The Factory did not utilize any protection for the wiring, so even with a stock system, it would benefit from this protection.
Initially, I would have the Charging System diagnosed to see if the Voltage Regulator is allowing the Alternator to produce the necessary power at idle/low speeds.
The Alternator also needs to be above a critical speed before it produces an output but this is usually only a couple of hundred RPMs.

[dbrick]

Agree with Nissanman. I have a GM one wire alternator, 100 amp IIRC, on the drivers side, it's a bolt in, no modifications. It feeds direct to the battery. I found the biggest weak link on the later roadsters is the starter harness. Most are in sad shape and simply don't pass the current, causing volt drop and problems. All power for the car passes through it. Check it thorougly and either repair or upgrade it, or relocate the junction up away from the starter. I plan to move the junction up onto the fender with a jumper down to the starter.

[ttyR2]

How about one of those Subaru Justy alternators that some people use? I think they are a lot smaller than the GM alternator and readily available from a junk yard.

[Roadster-Boy]

Thanks, Jeremy -- I see there are a number of posts regarding this alternator. Anyone know what the output of the Justy alternator is?

Geoff

[ppeters914]

Output about 55A, however, I've only heard it used on SR20 swaps to replace the physically bigger SR20 alternator.

The L-motor folks upgrade the stock 35A to the later 50A-80A alts found on 280Z/ZX and 240SX, and 1992-95 Saturns. I've been wondering if those will fit the R16/U20 as easily.

That said, the Chevy alt, while a bit bigger, is a no-brainer.

[dbrick]

I'm with Pete on the Chevy, no mods to the brackets and works well. Heard to see inthe photo, but the pulley on the GM alternator is rather large, keeps the RPM down.

[Daryl Smith]

I have to agree with Nissanman, Pete, dbrick, etc.
IMHO, 100+ amps is way overkill and extra weight you don't need. Unless you are adding A/C, Heated seats, drink cooler, huge stereo, etc, etc,... a 55 -60 amp alternator is more than enough. That is almost double what your electrical system was designed to handle, so whatever you decide to install, make sure you fuse it adequately to protect your harness.

The new alternator should take care of your slow blinker and help with the headlights. If you really want to improve your headlights tho, you might want to rewire them so the switch only turns on a relay to turn the lights on.....

There is a good thread here somewhere about headlight rewiring, conversion or something......

[ttyR2]

The GM alternator looks like a small trash can compared to the stock unit, hence my comment about the Justy alternator

[Roadster-Boy]

Dave -- Can you provide me with all the numbers on the 100 amp 1-wire GM alternator I will need to hunt one down? I went into the PMWIKI Tech Section: Alternator Alternatives, but couldn't find anything on it.

Thanks!