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Testing 12V Generator Output, 58 CJ5?

Discussion in 'Early CJ5 and CJ6 Tech' started by skratch, Dec 10, 2017.

  1. Dec 10, 2017
    skratch

    skratch Banned

    bernardo, nm
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    Dec 9, 2016
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    My generator on a F134 seems to be just barely charging. The wiring has been changed to 12v. With nothing but the elec. fuel pump running the battery condition gauge shows just under normal. When I turn the heater on the gauge drops to 10v. Would this cause the battery to be undercharging.
    Question is do I need some special type of tester to check it or is this normal ?

    Thanks for any info !
     
  2. Dec 10, 2017
    Karl Childers

    Karl Childers Member

    Taos New Mexico
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    It may be the Voltage regulator or if the battery has been disconnected you may need to polarize the generator which is a simple procedure of jumping two terminals on the regulator momentarily. It's been a few years since I've had a truck with a generator in it but I'm sure some one will come along shortly with that information.
     
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  3. Dec 10, 2017
    baldjosh

    baldjosh Member

    pacific north west
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    use a volt meter to confirm, a guage is super iffy on accuracy.
     
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  4. Dec 10, 2017
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    At what rpm is this happening? At idle generators generally don't charge, just FYI in case you didn't know that.
     
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  5. Dec 10, 2017
    Karl Childers

    Karl Childers Member

    Taos New Mexico
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    To polarize the genny momentarily jump the battery terminal to the field terminal. Once polarized if all else is good your generator will produce 12- 14 volts above idle.
     
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  6. Dec 10, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Try with a fully charged battery, be sure your battery is not the issue. Make sure battery connections are good at both ends.
    Voltage drop should be minimal, even without the generator input.

    FSM has test procedures for generators and voltage regulators.
     
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  7. Dec 10, 2017
    skratch

    skratch Banned

    bernardo, nm
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    Thanks to all ! When I first bought the Jeep it had an old " for sale" battery in it. I put a new one in, it ran OK for a while but drained, running off the battery I guess. I tried the polarize thing but not sure I got it right but it hasn't drained the battery so far.

    Glenn, it occurs at all RPM.
     
  8. Dec 10, 2017
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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  9. Dec 11, 2017
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Do you have the proper size belt? Are you sure it's not slipping?
     
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  10. Dec 11, 2017
    skratch

    skratch Banned

    bernardo, nm
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    Belt and tension OK.
     
  11. Dec 11, 2017
    skratch

    skratch Banned

    bernardo, nm
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    Thanks Karl, would that be the + battery terminal to the field terminal on the genny ? How long to jump ? Should the engine be running ?
    Thanks for your help !
     
  12. Dec 11, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Only a momentary flash, engine off.
    Proper connections depend on which make of generator/regulator you have. ('A' or 'B' type.)

    According to Walt, Prestolite you should flash the 'Field." Delco you should flash "Armature."
     
    Last edited: Dec 11, 2017
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  13. Dec 12, 2017
    skratch

    skratch Banned

    bernardo, nm
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    Thanks to all ,with all the help and info provided I think I've found the solution.
    John,,,,,
     
  14. Dec 13, 2017
    Karl Childers

    Karl Childers Member

    Taos New Mexico
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    Glad to hear that, Enjoy your Jeep!
     
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  15. Dec 13, 2017
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Let us know the results, what it took to fix it. :coffee::)
     
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  16. Dec 20, 2017
    skratch

    skratch Banned

    bernardo, nm
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    Thanks Glenn, I finally got a meter, best I can tell the genny may not be working up to par, I've read that if the 12v redo and the v regulator isn't matched it might be the problem, it looks to be an old one, 1958 WILLYS, has the instruction to polarize the generator on it.

    Sorry for all the questions, when it comes to automotive elec. I'm lost.

    I'll try to figure out how to test the regulator but it seems the batt isn't charging. When I start the engine the volt gauge shows a drop, I think because of the elec. fuel pump. If I turn on the heater the gauge drops down quite a bit, to 10v. After running the engine with only the fuel pump running the battery all to soon needs recharging, it's a new batt. Ignition running only off batt . ?

    Thanks for any ideas. I really appreciate the help from all the members !
     
  17. Dec 21, 2017
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Questions? We all love questions, and I don't think one has ever been asked that someone didn't know the answer to. Yours is definitely running off of the battery, no doubt about that.
     
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  18. Dec 21, 2017
    Karl Childers

    Karl Childers Member

    Taos New Mexico
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    Bring it up to Taos, I'll give you a hand. If you can't do that make sure all your grounds are clean and tight on bare metal. Check all conections and don't trust crimp connectors even if they appear to be good. Properly soldered connections are your friend. I'm not one to just throw parts at a problem but a regulator is cheap and will eliminate that aspect of it one way or the other. Be sure to polarize it. Do you have a wiring schematic? It would be worth having one and tracing all the wires in the charging circuit down to make sure they are correct. Previous owners can make real messes of wiring on a vehicle. Be systematic in your trouble shooting and trace each circuit back to its source one at a time, don't jump place to place, be methodical. Some years back there were good books on automotive wiring that covered the sort of technology our vehicles use, see if you can find a copy.

    If all this turns up short in the charging dept. process of elimination will be leaning in the direction of the generator itself. If you have an old timer in your area that works on them have him thoroughly test it for you.
     
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  19. Dec 21, 2017
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    x2.

    And don't go nuts with replacing stuff (yet). It could be as simple as a stuck/worn brush, dirty commutator, or a loose wire.
     
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  20. Dec 21, 2017
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    Whack the regulator with a BFH & see it it starts charging.
     
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