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Alternators 101 - Hopefully everything you ever wanted to know.


With halogen headlamps and high power stereo amplifiers & Subs getting popular, I’m guessing there are many people out there with alternators that are just not keeping up in the old Mustangs, resulting in flat batteries. So I have some questions, and I hope the answers will be useful to all.

With city driving at 30-35mph (50km/h) the alternator is doing fairly low RPM and thus not providing much current (faster = more current). So with the stereo blasting or the lights on it’s a flat battery in the morning. So what is the answer?

A)   To install a larger Alternator does the regulator also need to be up-rated? Are some regulators better than others?

B)   A smaller alternator pulley may be a solution, but what is the max safe RPM for an alternator?   

C)   What is the benefit of a single wire alternator? My understanding is they don’t generate anything at low RPM?

D)   I believe the 66 originally came with a 38Amp alternator (mine is now a 60A) what size is typical for a modern family car as they have more electronics and better headlights.

E)   Maintenance? – this I can answer – Clean those battery, ground, alternator and starter cable connections – at both ends of the cable!!! and even consider larger cables between the battery, starter and alternator. In a 12 VDC system even a small amount of oil, dirt or corrosion costs a lot of power.

So answers to the above please….. Thanks.

I would recomend you use an electronic regulator only for reliability purposes. The old style Ford regulators with contact points work well but upgrade. A single wire system does away with all that. All alternators' charge rate is low with low RPMs and after a certain high RPM, you get no additional current, that's part of what a regulator does. That's why on high reving engines, a larger pulley is installed on the alternator. I've seen a couple of setups that use an additional battery. If you do this, install a battery isolator. Another trick is to use a truck alternator. The low riders perfected that for their hydraulics.

You will always need to put on a new voltage regulator when you change alternators.  The 0ld 40 amps are adequate for Mustangs like mine with an
AM radio, but if you have a power draining stereo, you need to step up to the 60 amp.  Not sure about the pulley though.  Sure, it will spin the alternator faster, but not sure how much more benefit you will get.  The VR keeps the current to the battery steady after idling speed. 


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