Recommended Alternator Amp Output

Discussion in 'Sparky's corner' started by Dan Gerber, Oct 30, 2019.

  1. Dan Gerber

    Dan Gerber Platinum Level Contributor

    I'm upgrading my Skylark with a pretty strong BBB. While I'm at it, I plan to replace replace my non-stock (i.e., from a late 70's Oldsmobile), internally regulated alternator because it's getting a little noisy and, at a measured 85 Amp output, may not meet my needs when I add a self-learning throttle body EFI.

    I will most likely purchase a stock-appearing, internally regulated Powermaster 12si style alternator.

    My electrical loads currently come from:
    Convertible top
    Power windows
    Relatively small aftermarket sound system
    Halogen headlights
    HEI ignition (Dave's small body)

    Additional planned loads:
    MSD spark box (maybe)

    I'm thinking that the 75/90/100A (idle/cruise/top end) version will be more than adequate.

    Thoughts? Comments?

    Thanks in advance for your responses.
  2. TrunkMonkey

    TrunkMonkey Well-Known Member

    I am very happy with the high amp, externally regulated (OEM Delco housing 3 wire style) alternator from Quality Power.

    I stuffed a nailhead in my '64 lark, convertable, original alt was fine, but later I added 2x4 EFI, and then added dual SPAL fans that eat about 100 amps on startup and about 50 amps at load.

    My original alternator was not able to hold up, and I tried an 80 amp alternator (built up from OEM) but it was not able to keep up in high idle traffic.

    I now have the 135 amp alt with the smaller diameter pully, and it puts out 85 amps at idle (550 RPM) and 130 at moderate speeds.
    (My fan controller failed, so I wired the fans 100% on all the time for a few weeks, drove a week to and from Cruisin' the Coast, Florida to Mississippi and back and battery meter was dead on 14.7 the entire time.

    Hope that helps.

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