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Alternator Issue

Discussion in 'Early CJ5 and CJ6 Tech' started by Steve's 70-5, Oct 21, 2021.

  1. Oct 21, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

    Louisville, Ky
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    I put a 12s, single wire alternator on my Jeep. The hand-held for my EFI I can show battery voltage. I took the Jeep cluster out and put a Speed-Hut cluster in. While I had the Jeep cluster in, the hand-held was showing 12.5 volts while driving. Since I have put the Speed Hut cluster in the voltage showing is 11.5. This number stays the same no matter what the engine RPM is, from idle to 2500 plus.

    The alternator is wired

    There is a heavy gauge wire from the stud on the back of the alternator to the starter.

    There is a wire from the stud on the back on the alternator to the ignition switch.

    The plug on the side of the alternator, the red wire loops to the stud on the back of the alternator.

    The plug on the the side of the alternator, the white wire goes to the amp light in the cluster, I put a diode in this wire.

    Since I changed to the Speed Hut cluster, the white wire has been capped off at the cluster

    What could the issue be on the change of voltage?
     
  2. Oct 21, 2021
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

    Tantallon, Nova...
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    First off a single wire alternator is just that- single wire. One connection to the battery or solenoid & that's it.

    Second, get a hand held multi meter & use it to check the battery voltage at a fast idle. Let us know hat the reading is.

    Got a link to the instrument cluster you're using?
     
  3. Oct 21, 2021
    blevisay

    blevisay Oh Noooooooooooooooo! Staff Member

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    12.5 with the old cluster tells me it wasn’t charging.
     
  4. Oct 21, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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  5. Oct 21, 2021
    dnb5853

    dnb5853 Member 2021 Sponsor

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    I used this same gauge cluster on my resto-mod. I used a 4 wire 12SI alternator. I have a matching Speedhut volt meter; 12+ volts stationary & 14+ volts while running.
    The volt meter is NOT part of the speedometer cluster; just the check engine warning light.
    Speedhut took my request to bring both wires for the check engine light out of the cluster so I could use both wires for the check engine circuit (white wire from alternator).
    Since our old Jeeps don't have a check engine supply wire coming from an ECU, you have to improvise with the electronic cluster.
    With the cluster wired this way, the check engine light ONLY indicates a lack of charge; nothing else. This indicator is so high in the cluster, it's tough to see from the drivers seat due to the bezel.
     
    Last edited: Oct 21, 2021
  6. Oct 22, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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    I have a stand alone 12 volt meter mounted under the dash. I just used the power plug from the cluster to power the 12 volt gauge. The 12 volt gauge I have has a warning light in it. Do not remember what the back of the gauge is. Can I run the white wire to it?
     
  7. Oct 22, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Yes, the one-wire alternator eliminates the need for any connections to that plug. One wire, from the alternator output stud to the battery (typically a solenoid post). If you add a second wire, it's no longer a one wire. Seems pointless to spend the extra money for a one-wire and then wire it up essentially the same as a conventional 3-wire would be. Semantics.

    Depending on the internal circuitry of the "one-wire" alternator, your second wire may show an accurate charging voltage. Why not measure? Measure, measure, measure! Compare your battery voltage to the white wire voltage at idle and above. If they are the same, you can use it. However, on a "one-wire" alternator, it is intended for an alternator light, not a voltmeter.

    Also, why is this in off-topic? The thread is clearly topical.
     
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  8. Oct 22, 2021
    dnb5853

    dnb5853 Member 2021 Sponsor

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    The power plug (small black & white wire loom) from the Speedhut cluster gauge is for lighting only of additional gauges. These can be daisy chained together.
    Your 12V meter should have a dedicated terminal for a battery connection. While it's probably grounded though the dash, it's a good idea to have a dedicated ground here as well.
    Get out the wiring diagrams for each of the gauges and vehicle. Have a good understanding of what everything is and how it interfaces with the rest of the circuit(s).
     
  9. Oct 22, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Expanding on this some, normally your voltmeter is connected in some way to the ignition switch. Thus when the key is on, the voltmeter reports the voltage of the battery without the engine running. This should be close to 12 volts. IMO you don't need to be fancy with this - for my J20 I connect the voltmeter (converted from an ammeter) to the same trace on the cluster that comes from the ignition switch and supplies the gauges and indicator lights. Does not need to be fancy - the voltage drop from the battery to the dash will be small, and the voltmeter probably is not accurate enough to show the difference.

    When the key is on and the engine is not running, the alternator GROUNDS that white wire. Thus your alternator light, connected from the ignition to this white wire lights up, indicating no charging. When the alternator start charging, the white wire goes to (should go to) whatever the charging voltage is. Thus the ignition and the white wire are both at charging voltage, no current flows, and the light goes out.

    With a voltmeter and a "one wire" alternator, the alternator light does not tell you much more than reading the gauge does. The voltmeter should stay at something around 13.5 to 14 volts while running. 12 is too low (not charging), 15 or 16 is too high (too much charging). Unless you want an extra indicator light on the dash that comes on when the alternator is not charging, I suggest you leave off the plug or tape off the wire. And do like everybody else, connect the voltmeter to the ignition switch (anywhere convenient) and ground.

    Suggest the mods move this from off-topic to the EarlyCJ-5 forum.
     
    Last edited: Oct 22, 2021
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  10. Oct 22, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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    My volt meter has 3 wires going to the plug, this plug is daisy chained to/from the other gauges. Call Speed Hut and they said the gauge is only will monitor voltage of the battery, not charging voltage.
     
    Last edited: Oct 22, 2021
  11. Oct 22, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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    Check voltage on the Jeep

    Battery, Jeep not running 12.67V

    Jeep at idle
    Battery, Jeep running12.14V

    Jeep running, headlights on 12.07V at battery, 12.06 V at stud on back of alternator

    Jeep running, headlights and heater blower on, 12.02 V at battery, 11.99 at back of alternator

    With Jeep engine revved, voltage at alternator did not increase.

    Going to pull alternator tomorrow and have it tested
     
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  12. Oct 22, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    They don't know what they are talking about. The voltage across the battery is the charging voltage. There is only one voltage for the whole Jeep: the voltage across the battery. The battery voltage is the sum of the electrochemical potential plus the charging current times the internal resistance of the battery.

    Get your multimeter and check the voltage across the battery while the engine is running. Check the voltage across the battery with the engine stopped. (Never mind - looks like you did that and posted while I was replying.) The difference in voltage is the charge current from the alternator times the battery resistance. V=IR, Ohm's law.

    Even at idle, the alternator should maintain a voltage above 12 volts, typically 13.5 to 14 volts. Notice that no one has posted to contradict this.
     
    Last edited: Oct 22, 2021
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  13. Oct 22, 2021
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    When the car is running the battery voltage is at charging voltage...(I see Tim beat me to it)
     
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  14. Oct 22, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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    Like I said, going to have the alternator tested tomorrow to see what it is doing.

    This type of electric is not my strong suit
     
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  15. Oct 24, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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    Had the alternator tested, tested out OK. Put it back on, only installed one wire from alternator to the solenoid/battery voltage stayed the same when the engine was revved. I know I bought a high amp alternator, with what little draw that is on the electric system, only the EFI system and a fuel pump, I am wondering (if the alternator can read the power needs of the vehicle) sees no need to produce high voltage.
     
  16. Oct 24, 2021
    dnb5853

    dnb5853 Member 2021 Sponsor

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    Everything you've said indicates a bad alternator.
    Check it with your own VOM. The battery should read 12V (or just higher) while not running. It should jump to about 14V once started, regardless of current demand.
    You should be able to turn on the headlights and see a fluctuation in the volt meter as the alternator compensates for the load.
     
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  17. Oct 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Yep. The alternator measures the voltage across the battery, and increases its current output until that's something like 14V. That's how it works.

    The battery has an internal resistance. When you apply a charging current across it, that resistance makes a voltage. Ohm's law, voltage equals current times resistance, V=IR. The regulator regulates voltage across the battery - that's all it does. Voltage regulator. It looks at the voltage across the battery and increases the current until the voltage matches its internal set point.

    Nothing more - it does nothing as human as you are suggesting. Simple voltage feedback. Voltage too low, increase the current until it's ok. Voltage too high, reduce the current until it's ok.
     
    Last edited: Oct 24, 2021
  18. Oct 25, 2021
    Fireball

    Fireball Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Just to double check, you have it connected to the same post on the soleniod as the postitive battery cable?
     
  19. Oct 25, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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    I had to check, on the same post.
     
  20. Oct 25, 2021
    Steve's 70-5

    Steve's 70-5 Active Member 2020 Sponsor

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    Was thinking about this.
    Do alternators have different rotations. I do not remember where I got the number for the alternator or what vehicle it is for. It is a Delco.

    Need vehicle or part number of alternator that is being used on a oddfire v-6. Needs to be single wire. At this point 10si or 12si. Want to get this issue resolved.
     
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