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Technical Alternator confusion...

Discussion in 'The Hokey Ass Message Board' started by 19blockhead72, Mar 16, 2021.

  1. 19blockhead72
    Joined: Feb 17, 2012
    Posts: 204

    19blockhead72
    Member

    Screenshot_20210316-183209_Chrome.jpg So I'm beside myself here. Bought this alternator to give myself some room under the hood of my roadster with gm style wiring harness. I did not wire the car bought it the way it is. So plugged it in and charged fine but ended up with a dead battery a few hours later when it was off. So I have battery to the main post, all the time hot (battery) to the top blade and switched to the bottom. When I unplug the top blade plug (hot) I don't have a drain. Obviously this alternator is different than what was it. What do I need to do to make this on work properly? Thanks
     
  2. The internal diode has probably gone bad so it is back feeding and draining the battery. I went through 4 "new" alternators before I got one that worked last summer that did the exact same thing. You can get an alternator that works (easier said than done these days)or put the diode inline.
     
  3. Doublepumper
    Joined: Jun 26, 2016
    Posts: 951

    Doublepumper
    Member

    Hmmm....externally regulated?
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 48,327

    squirrel
    Member

    search the tractor forums (that's what the alternator is for, you know), maybe you'll find a wiring diagram similar to this

    wiring-diagram-denso-alternator-four-wire-best-of-a.gif

    and note that it is NOT wired like a GM alternator. You need to switch the sense wire, you can't leave it connected all the time.

    (this diagram may or may not work with your alternator)
     
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  5. 19blockhead72
    Joined: Feb 17, 2012
    Posts: 204

    19blockhead72
    Member

    It's supposed to be internal....
     
  6. 19blockhead72
    Joined: Feb 17, 2012
    Posts: 204

    19blockhead72
    Member

     
  7. Doublepumper
    Joined: Jun 26, 2016
    Posts: 951

    Doublepumper
    Member

    Interesting. Learned something.
     
  8. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,831

    Mr48chev
    ALLIANCE MEMBER

  9. brading
    Joined: Sep 9, 2019
    Posts: 382

    brading
    Member

    On " squirrel's " diagram the switched live and the ignition light wires after the fuse box go the terminal on the ignition switch that has power when the ignition switch is turn on. The Denso alt is internally regulated.
     
  10. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 281

    Fabulous50's
    Member
    from Maine

    The only wire which should be hot all the time is the bigger "batt" wire. The others are for excitation. Squirrel's post shows that.
     
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  11. Jack E/NJ
    Joined: Mar 5, 2011
    Posts: 646

    Jack E/NJ
    Member
    from NJ

    Agreed. Actually the switched sensor terminal also seems to be a good idea with the 10si & 12si units. Some regulators seem to leak more than a few mAs thru this terminal even though it senses the voltage OK. Jack E/NJ
     
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  12. 37 caddy
    Joined: Mar 4, 2010
    Posts: 388

    37 caddy
    Member
    from PEI Canada

    I had a similar problem on my 37 when i started using it,we had to rewire the car,it is still the 6 volt pos ground.I used a "tractor" regulator from a early ford 8N,it showed a charge at the guage but the battery kept going dead,it turns out the charge was going nowhere,changed the wiring a bit and all was well,that could be yor problem,juice is moving but not in the right place? Harvey
     
  13. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 281

    Fabulous50's
    Member
    from Maine

    I always run the sense wire to a switched source on a 3 wire alt like the Denso or GM Si units. You can even share the same fuse as used for the dash idiot light. 16159959261465587038889894180315.jpg

    EDIT: Some guys just run the sense wire to the BATT terminal which I have seen drain the battery from internal leakage of the regulator.
     
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  14. squirrel
    Joined: Sep 23, 2004
    Posts: 48,327

    squirrel
    Member

    Interesting. Have you ever measured the voltage drop in the circuit that feeds the sense wire, when you do it this way?
     
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  15. Jack E/NJ
    Joined: Mar 5, 2011
    Posts: 646

    Jack E/NJ
    Member
    from NJ

    Fab50>>>EDIT: Some guys just run the sense wire to the BATT terminal which I have seen drain the battery from internal leakage of the regulator. >>>

    This sensor leakage is most important. Some SI regulators have been as much as 100mA. Over 2 AHr per day. Voltage drop varies depending on length of switch wire, fuse resistance, & switch resistance. Mine's less than 0.1volt the way Fab50's diagram goes measured at the batt terminal vs measured at sense connection near the idiot light engine off. Jack E/NJ
     
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  16. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 281

    Fabulous50's
    Member
    from Maine

    I haven't measured drop. However it all goes back to load on the circuit. I never use actual ignition switches for any load in any car I have built or wires for someone else. I relay everything either under the dash and/or under the hood. So generally speaking I'd use a relay just for the sense wire which would be very close to the battery.

    For what worth, my preference is Bosch alternators and I have had good results with their Bosch internal brush/regulator assembly and if there is some type of odd setup with excessive voltage drop I use an aftermarket regulator with a voltage adjustment. I shoot for 13.5 volts at the battery. I have found that to be best for battery longevity. Even though it is technically slightly undercharg.
     
    olscrounger likes this.
  17. Wonder what is wrong with my parts store rebuilt one wire GM alternator !
    Still running after nine years and 20,000 + miles. Amp/charge indicator bypassed and use a volt meter. Did I do something wrong for this to still be working?

    Ben
     
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  18. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 281

    Fabulous50's
    Member
    from Maine

    No, nothing wrong.

    Some of them just end up with a draw through the sense wire. That is all we are discussing.
     
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 48,327

    squirrel
    Member

    Interesting....GM built millions of cars with 10SI alternators, as far as I know none of them had the sense wire going to switched power, and they mostly all worked fine.
     
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  20. Jack E/NJ
    Joined: Mar 5, 2011
    Posts: 646

    Jack E/NJ
    Member
    from NJ

    Yep. They don't build them like they used to any more. 8^) Jack E/NJ
     
  21. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 281

    Fabulous50's
    Member
    from Maine

    You dont need to switch the sense wire. The point was that it provides some insurance if the regulator has excessive leakage current which some of the rebuilt with Chinese parts do/will.

    The Bosch units I like dont have a sense wire and are effectively connecting it directly to the BATT terminal.
     

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