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Technical Alternator question...

Discussion in 'The Hokey Ass Message Board' started by 1stGrumpy, Aug 16, 2022.

  1. I put a 63 amp 10SI 3 wire alternator on my '56 fairlane a year ago and all was well but now I am in the process of finally hooking up the a/c portion of a VA heat, cool and defrost unit and am wondering if that 63 amps is going to be enough. Now I know the smartest way would be by putting a 100 amp alternator in but the current alternator is only a year old and doesn't need replacing. Plus I hate spending money when it ain't nessesary! The only thing electrical that I am adding is the a/c compressor. As I said in the beginning, the 63 amp handled the lights, radio, heater/defroster and electric cooling fan just fine. 90 percent of my driving is daylight driving and according to my calculations the draw will be between 53 and 87 amps.
    Now I know that I will most likely regret this next question but.... what do the experts say?
     
  2. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 2,556

    wheeltramp brian
    Member

    I would use at least a 100 amp but on customers cars I install a 140 amp powermaster and a 4 GA charge wire.my 2 cents
     
    lothiandon1940 and 1stGrumpy like this.
  3. dalesnyder
    Joined: Feb 6, 2008
    Posts: 609

    dalesnyder
    Member

    Oems started using 100 amp alts because of the high loads that the electric cooling fans used. If you are keeping the mechanical fan , your current alt should be fine..
     
    olscrounger and seb fontana like this.
  4. Thank you
     

  5. Electric
     
  6. I have an 80 amp in my Buick. Handles the AC, the off topic fuel management with no problems.
    Give it a try. What is to lose? If it is enough, great. If not, THEN change it out.

    Ben
     
  7. sdluck
    Joined: Sep 19, 2006
    Posts: 3,186

    sdluck
    Member

    Hook up amp meter, Turn everything on including the lights, electric fan and read the amp draw make sure everything is warmed up and see what reserve you have now both @ idle and @ 2000. D40.o you have electronic Ignition ? With out more info what does VA suggest , 140 I bet ?
     
    Last edited: Aug 16, 2022
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  8. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    the majority of rear wheel drive GM vehicles ran 63 amp alternators up to around 1980 when even the non luxery cars started having power everything .
    I've got to go with the concept of run it and see what it does. It's a 15 minute project to swap alternators on most rigs that have them where you can see and reach them. Meaning once you start driving it on a regular basis and if it doesn't keep up, then upgrade.
    Now if if you happen to have a daily driver rig that all the sudden needs an alternator and that one just happens to be the right one, fair is fair..
     
  9. jaracer
    Joined: Oct 4, 2008
    Posts: 2,419

    jaracer
    Member

    In 56 if that car had dealer installed A/C it would have had a 25 or 30 amp generator at best. Unless you have some accessory on the car that over 30 amps, I think you are good to go. A lot of AC equipped cars in the 70's had less than 50 amp alternators. I think the first 100 amp alternator I saw was on a 77 Dodge with the police package.
     
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  10. That's what I'm leaning towards, ain't got nothing to lose except a few minutes...
     
    Hemi Joel and firstinsteele like this.
  11. Of course, VA is selling 140's!
     
  12. Joe H
    Joined: Feb 10, 2008
    Posts: 1,525

    Joe H
    Member

    I run one of the small diameter alternators with A/C, it works OK, the battery is always charged, and the amp gauge is always in the middle. It might be a 50 amp unit.
     
    1stGrumpy likes this.
  13. A 63 amp alternator will be skimpy. Taking a rough estimate of your continuous loads, you've got about 15 amps in lighting, another 8 for the radio (assuming no external amplifiers), 10 for the heat/defrost/AC fan, another 10 amps for the ignition, and another 10 for electric wipers if converted. That's 53 amps, and doesn't include the cooling fan. You're already treading on very thin ice IMO, adding another 10 amps for the AC compressor clutch will max out the output without the fan. Granted, this is a worst-case but could result in not getting home if driving on a hot, sweltering, rainy night. It's also not good for the alternator to run them for extended periods at max output.

    Time for an upgrade....
     
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  14. mike in tucson
    Joined: Aug 11, 2005
    Posts: 520

    mike in tucson
    Member
    from Tucson

    Dont forget that the inrush current when an electric fan kicks on is
    sometimes around 80 amps or so, regardless of what the steady
    running current is listed as.
     
    1stGrumpy likes this.
  15. You can generally discount the inrush current as the battery will absorb that, although it can cause the alternator to increase the charge rate.

    One thing you can do to help is increase the wire size from the alternator to the main harness, and from the battery to the harness. Voltage drop will measurably increase current draw on motors, adding to the problem.
     
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  16. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,802

    jimmy six
    ALLIANCE MEMBER

    Grump….I added AC to my 56 a year ago on my Y Block. . I used the VA brackets (very pleased with them) which has the Alternator on top. I already had a Power Master 100 amp installed which kept the i-did-it light. The compressor was a Sanden and the AC-heater unit was an electronic controlled Old Air Products.
    With unit AC on high fan, headlights on high beam, radio on, and brake lights on, the total load was 33 amps. The only thing I didn’t have on was the Newport Electric wipers. All readings were taken by a Fluke clamp-on DC meter.
    I have never ran the AC above medium and it’s mostly on low which freezes us out. We rarely use the car at night but I have a few times with the AC on coming home from a car gathering.
    The factory 56 Ford with AC had a 40 generator instead of the standard 30 amp.
    My only concern would be electric engine fans which I do not have and I believe you do.

    PS: I’m still using the stock wiring which is a #10 wire from the Gen, now alt, connected to the “bat” wire on the regulator (no longer used and in the Power Master instructions) to the light switch, to the ignition switch, to the starter solenoid, finally to the battery. Since a #10 AWG is good for 30 continuous amps and during the day with the AC on I’m under 20 I see no problem.
     
    Last edited: Aug 16, 2022
    Truckdoctor Andy and 1stGrumpy like this.
  17. Maybe think about it this way. 65 amp single wire alternators was pretty much standard on GMs into the '80s. adding the AC is going to add a blower fan and an electric clutch. The clutch is going to draw in the neighborhood of 3-4 amps. Even without AC unit blower motors were pretty much standard until "trad" hot rods became all the craze. ;)

    Hope this helps you decide.
     
    1stGrumpy likes this.
  18. Thanks to all for the input. I am going to leave the 63 amp on for now and see what it does.
     
  19. Truck64
    Joined: Oct 18, 2015
    Posts: 5,325

    Truck64
    Member
    from Ioway

    Measure the voltage drop across the cables and ground connections under load. If there is corrosion, or loose connections, undersized, or old cables it will cripple any alternator no matter how big. Clean and tight is super important with electrical stuff.
     
  20. Good man.

    Ben
     
  21. spanners
    Joined: Feb 24, 2009
    Posts: 2,074

    spanners
    Member

    The chances of having all the electrical doodads on at the same time is minimal. Go with what you've got.
     
  22. Well, here's a little update...
    I got everything back together and checked to see how that 63 amp alternator was holding up, with just the electric fan running it was putting about 12.15 volts to the battery at idle and with the a/c and electric fan on it was well below 12 volts. I ordered a 140 amp alternator this afternoon!
     
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  23. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 2,556

    wheeltramp brian
    Member

    Just remember to make the charge wire the right size. I would probably run 4 gauge from my alternator to the battery that's about 2 ft away. Usually they come with a chart Inside the Box
     
  24. I would say the same thing except he's running an electric fan, that will push it over the edge. Get an 80 or 100 amp 3 wire and keep the 63 amp for something else with less accessories.

    I'm always late to the party. 140 should do it (but it's kinda overkill). Even with a 63a alt and electric fan on you should have over 13v (and the amps are more important) at the battery when running, something is wrong.
     
    Last edited: Aug 30, 2022
  25. I would also recommend to anyone who want to do some light electrical testing to invest in an amp clamp. You can use them to check things like a starter amp draw, charging amps, AC amp draw and you can use it as a regular meter also. There's a bunch of different brands and prices out there, just make sure you get one that goes up to the amps your wanting to use it for and that it measures DC on amps and volts.



    [​IMG]
     
  26. I couldn’t agree more! I have one like that at work and it’s invaluable. It gets used every day, I’d be lost without it.
     
  27. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,802

    jimmy six
    ALLIANCE MEMBER

    You will notice the Fluke show also has an ohmmeter scale selection and AC & DC voltage selections along with AC & DC amps. The leads go in at the bottom.

    Fluke makes high quality instruments and this single unit is excellent for guys wanting to do electrical checks of any kind on their cars or home.

    Many years ago getting DC current reading was much harder. Fluke made this a lot easier.
     

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