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Alternator - How to ID output

Discussion in 'Early CJ5 and CJ6 Tech' started by Warloch, Apr 19, 2011.

  1. Warloch

    Warloch Did you say Flattie??? Staff Member

    Guys - lots of discussion on Alternators lately and the 1 vs 3 wire setups. One thing I would like to see how other folk ID the output of the alternators. I have some known outputs and others that I have been 'told' what they are, and still other I have no clue.

    How do you test - if you can on your own - and ID the output of the alternators? For the most part I have taken them down to the parts store, but my 'good' one has changed hands and I am not sure I trust the answers I am getting.
     
    Warloch, Apr 19, 2011
    #1
  2. EricM

    EricM Active Member

    I have not done it, but I think you would need to put a load on the alternator and measure the output. Maybe using one of these as a load:

    http://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html

    or you could also simulate the load with a winch, and watch the amp meter output. To measure the amps, you'd need a voltmeter with one of those inductive clamps that measures amps. The voltmeters at HF measure AC but not DC current. Here's one that will measure up to 400A DC:

    http://www.sears.com/shc/s/p_10153_12605_03482369000P
     
    Last edited: Apr 19, 2011
    EricM, Apr 19, 2011
    #2
  3. w3srl

    w3srl All-around swell dude Staff Member

    Not sure how you would test only the output of an alternator, even with a load bank like that. Even the instructions that came with my load bank (very similar to the one posted) only mention a pass/fail test of the alternator, rather than a quantitative test. If you had a 90-amp alernator you'd need to find a way to pull all 90 amps at the same time while watching the positive cable with a clamp-on ammeter.

    BTW, I'm not sure I'd want to be standing next to the battery while doing this! :shock:
     
    w3srl, Apr 19, 2011
    #3
  4. EricM

    EricM Active Member

    I would think that if the load was large enough, you'd max out the output of the alternator. If you were measuring the output with an inductive clamp you should see the number of amps being put out by the alternator peak at a certain value, and go no higher.
     
    EricM, Apr 19, 2011
    #4
  5. dnb71R2

    dnb71R2 SuperDave 2023 Sponsor

    My local friendly starter & alternator shop checked mine after I had it serviced (off the Jeep). My Delco 12si (conversion) is actually putting out its rated 90+ amps. I watched him hook it up and saw the meter give the amp readout.
    I don't know how this could be done at home, without a big DVM capable of high current capability.
     
    dnb71R2, Apr 19, 2011
    #5
  6. nickmil

    nickmil In mothballs.

    To really test the full output you need a true load tester. Parts houses, at least around here, don't do a full load test. They just check to see if it is putting out, not true total output. You could install it in a vehicle and find someone with a load tester like an old VAT-40 or similar or take it to someone who rebuilds starters and alternators as they should have a load test bench.
     
    nickmil, Apr 19, 2011
    #6
  7. Pack Rat

    Pack Rat Old Timer

    Another way to test, there's a D shaped hole on the back of the alternator case which lines up with a tang on the regulator. Using a small screwdriver or something similar ground that tang to the case which full fields the alt and will give you maximum output. You will of course need an ammeter to check the output. An AVR is the quickest/easiest on vehicle way though which, BTW, is just a carbon pile.
     
    Last edited: Apr 19, 2011
    Pack Rat, Apr 19, 2011
    #7
  8. Patrick

    Patrick Super Moderator Staff Member

    I use one of these.

    [​IMG]
     
    Patrick, Apr 19, 2011
    #8
  9. jpflat2a

    jpflat2a what's that noise?

    mine is stamped into the case by the Delco number: 63A
     
    jpflat2a, Apr 19, 2011
    #9
  10. curtcanada

    curtcanada L, L, and the POH!

    Warloch,
    I've taken alternators to AutoZone for testing, but never payed much attention to the process. I would assume they put a load to it while testing...and it should be free of charge?! The question is, will they offer up the results?!

    I'm going to be replacing mine with the engine rebuild (225 oddfire Dauntless V-6). I'm not running anything heavy (like an electric winch); but, I'm entertaining the idea of a dual battery system. I'll need to start researching this on ECJ5.
     
    curtcanada, Apr 19, 2011
    #10
  11. Warloch

    Warloch Did you say Flattie??? Staff Member

    What really brought this to light for me was my contemplation of swapping out the Alt in my rig now that I have the winch. It is a single wire and 'supposed to be' 63A. I used the winch some and have since had a hard time getting it to kick into charge mode and it does not seem to put out enough amps.

    It checked 'OK' with the new folks.

    I have another 100 A Alt that I know was working fine before (checked by the old guy last fall) and he stated it looked pretty new (fit with what I was told when I got the motor). It's been sitting on the shelf. According to the new folks - since they know I was thinking of going to a higher output Alt - 'it's suddenly NOT OK' by them...

    I was hoping someone would have a good solution as I think my only other possibility is another shop in town to see what they say. That and I had all my alts organized so I knew what was what and where... Then someone 'helped' me organize some things on the shelves and I am not sure which is which in a couple cases.

    Jim - where is the stamp on yours (just curious to see if I am looking at the same place)? Does it give a 10 vs 12si indication anywhere?
     
    Warloch, Apr 19, 2011
    #11
  12. EricM

    EricM Active Member

    Taken from :
    http://www.madelectrical.com/electricaltech/delcoremy.shtml

    A 10si has a metal fan, and ribbed case:

    [​IMG]

    A 12 si has a plastic enclosed fan, and a smooth case:

    [​IMG]

    If the alternator has been rebuilt, you can't be 100% sure the case stamping is accurate based on this excerpt:

     
    EricM, Apr 19, 2011
    #12
  13. Pack Rat

    Pack Rat Old Timer

    There's two possible places for the amp output stamped into the front case half-

    [​IMG]

    [​IMG]
     
    Pack Rat, Apr 19, 2011
    #13
  14. jpflat2a

    jpflat2a what's that noise?

    jpflat2a, Apr 19, 2011
    #14
  15. nickmil

    nickmil In mothballs.

    You've gotta be careful about the stamped in numbers unless buying a non reman alternator. The rebuilders don't care what's stamped on the case when rebuilding. I've seen plenty remans with the wrong rating stamped on the case. I have a 94 amp with 37 stamped on the case and I've seen em go the other way too
    Posted via Mobile Device
     
    nickmil, Apr 19, 2011
    #15
  16. Pack Rat

    Pack Rat Old Timer

    R) :iagree: I was going to mention that, more so because of guys like me who start messing around and changing things :).
     
    Pack Rat, Apr 19, 2011
    #16
  17. Warloch

    Warloch Did you say Flattie??? Staff Member

    Yay - so far you guys are confirming that I have no way to know for sure what I have unless I get them tested... :)

    I know the 1 100A unit I have looks like a 10SI and it's probably a crap shoot on the 4 that I have picked up over time.
     
    Warloch, Apr 19, 2011
    #17
  18. Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    The only way you can tell for sure is to tear it apart. The resistance of the rotor and the resistance of each leg of the stator. Years ago I pretty much knew what amperage to resistance was but I have long forgotten. If you put a 63 amp rotor into a 100 amp stator, you will have a max of 63 amp output. The rebuilders only make sure the stator wiring is good then install a good rotor of measured resistance which their table/chart tells them the rated amp output.
     
    Walt Couch, Apr 19, 2011
    #18