Re: 308 Alternator
From: Douglas Anderson (
Date: Thu, 29 Jul 2021 10:10:33 -0700 (PDT)


The evil sisters of electrical problems are: Miss Opens, Miss Shorts, and Miss Grounds.

Oh – and if you ever do short out a wire while working on your project . . . NEVER pull the wire to stop the process.




From: Ferrari < [at]> On Behalf Of Rick Moseley
Sent: Thursday, July 29, 2021 8:10 AM
To: DOUG <dnt [at]>
Cc: The FerrariList <ferrari [at]>
Subject: Re: [Ferrari] 308 Alternator


Rob, Yes, no problem.


You want your alternator to put out more than 12v to charge your battery.

As for the amperage, your circuits and devices will only draw what they need.

You can get into trouble two ways:

1) A dead short will pull the full amount your alternator will offer, until the wire burns up.  The burn will be faster and more dramatic.   As always, try to avoid dead shorts. 

2) Generally the the higher the output of your alternator, the faster it needs to spin to get to full output.  So, the output at idle on a high amp alternator is less than than the output at idle of a low amp alternator. **


That is why on the older cars with upgraded alternators that still have incandescent headlights you see a dimming or yellowing of the beam at idle and as soon as you start moving again you get a nice bright white beam.  In your case the amperage is not significantly different to cause an issue.


**For those saying but, but, but....   Yes, there are high output alternators that give full power even at idle...  but they are usually MUCH more expensive.  You find these 200 to 500 amp alternators in things like Ambulances that need to have full power for lots of devices at idle.  The problem is, they don't like to be spun at high RPM. The better of these have a planetary coupling that will kick in and let the alternator run at a slower speed as the engine moves to higher RPM.   The higher the RPM, the higher the Hz, the harder to rectify.  The lesser quality devices just start playing with the waveform to keep the voltage and amperage in check.  Waveform...  Keep in mind, all alternators generate AC and are either internally or externally rectified to DC.  In some industrial applications they run two alternators in parallel.   This allows them to shut one off at idle and the other off at high RPM to keep from having to play with the waveform or having a failure with a planetary...


Side note:  When we were running TransAM and GT-1, we always ran the alternator off a pulley on the differential/3rd member/pumpkin input.   The fresh battery would run the car in the pits and on the starting grid.  The spin speed of the alternator saw less drastic RPM changes than on the front of the motor.  More reliable that way and since it was post geared there was less parasitic drain on the motor and you could keep full power to the ignition box coming out of a long turn as the rear end would still be running higher rpm even if the motor had dropped to idle.  Secondary effect was putting another heavy device at the rear of the car, down low, near the centerline to help offset the weight of the engine for setup balance.   The battery was in the back so the charge line was shorter too.  Tertiary effect was the alternator ran in a much cooler environment than sitting right behind a radiator belching out BTUs.   Quaternary effect was the rules let us cool the alternator... but not the rear end.  Since one was bolted to the other.... well, it was a cheat, but a legal one.




On Wednesday, July 28, 2021, 8:42:48 PM PDT, Robert Garven <rgarven [at]> wrote:





I found a really nice rebuilt alternator but it's 14v 65 amps. I know that's more than the factory rated one. Will this cause any damage to my electrical system or will it actually charge the battery better? That was hard to get off. I was smart enough last time I serviced the car to reverse the bolt holding the alternator to its bracket so you don't have to remove the dipstick tube, but still with the alternator heat shield in place it barely had enough room to slip off! 

It's been a while since I did a major service and I'm amazed at how some of the prices and availability have changed!






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