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Ammeter Safety?

Discussion in 'Intermediate CJ-5/6/7/8' started by dane71, Oct 13, 2019.

  1. Apr 3, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

    Medford Mass USA
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    Vacuum gauge.
     
  2. Apr 3, 2020
    sterlclan

    sterlclan Member

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    Oil pressure
     
  3. Apr 3, 2020
    Jeff Bromberger

    Jeff Bromberger Quarantined in the Garage 2020 Sponsor 2019 Sponsor

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    Ported or Manifold? Which is more useful?
     
  4. Apr 3, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

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    Manifold. You want to see the vacuum at idle. Ported vacuum is only useful for device control.
     
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  5. Apr 4, 2020
    SleepyJeeper

    SleepyJeeper New Member

    Michigan
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    I was actually worried about the ammeter as well. On my Renegade II it has a special 40-0-40 ammeter with a stock 35 amp motorola alternator. I was reading through the instructions on the painless wiring harness kit and it said a minimum of 60-0-60.
     
  6. Apr 4, 2020
    givemethewillys

    givemethewillys Sponsor

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    What's the point of an ammeter? Every one I've ever seen just chills in the vertical position. Is it supposed to indicate something?
     
  7. Apr 4, 2020
    wheelsontheroof

    wheelsontheroof New Member 2020 Sponsor

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    an ammeter tells the rate of charge or discharge of the battery . it can also indicate an abnormal discharge such as a short circuit. under normal operating conditions it should indicate just a hair to the right. in a situation where you are using more current than the generator can provide you can use it to manage electrical loads so as not to discharge the battery. alternators are so efficient that you wont have to worry. an example would be high beams on , heater on high and wipers on. if ammeter showed discharge with engine at modest speed you might dim headlights or put heater on low until ammeter reads to right of center
     
  8. Apr 5, 2020
    givemethewillys

    givemethewillys Sponsor

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    That makes sense, I guess that was necessary when generators put out 20 amps. Not much of a problem with my 12si alternator swap
     
  9. Apr 6, 2020
    dane71

    dane71 Member 2019 Sponsor

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    Yeah I can barely get mine to move, i guess its a good thing but not too exciting.
     
  10. Apr 9, 2020
    Sierra Bum

    Sierra Bum Member

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    Simply put, an ammeter measures current flowing through a circuit. It's wired in series. In this case the charging circuit. They are antiquated for a modern system with a higher output alternator. It does not make sense to run 6 or 4 or 2 awg wire to and from the dash, or wire in a shunt, just to monitor charging current. A volt meter with an alternator warning light is safer, provides better info and is much easier and simpler. Problems occur when people introduce components/accessories that use or generate more current than the system is designed for without upgrading the wiring, connections fuses, etc.
     
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  11. Apr 9, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

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    If you had a voltmeter, you would not see much under normal conditions either. With the engine off, you would see something like the battery potential which is 12.6V for a lead-acid battery. You may see a little more, because the charging system tends to pack the battery full of electrons, and with no load the indicated voltage will be a little higher than the chemical potential of the cells.

    When running, the battery acts like a current sink or source. Starting drains off a bunch of amps, and the indicated voltage drops in response. The alternator immediately senses this drop in potential and works to boost the alternator output voltage to its set point (ca 13.5-14V). The battery is now sinking a lot of current, and it takes a lot of current to bring the voltage up to the set point. The alternator sends more and more current to its field windings, making more output until the alternator brings the voltage back to the set point. As the sink is filled, it takes less and less current to maintain the set point, as the battery comes up to fully charged. The internal resistance of the battery limits how much current you can stuff into that whomping big sink at once. It's this internal resistance that causes heat in the battery if your alternator tries to charge the battery too fast, indicated by over-voltage.

    Your voltmeter would hang at its normal charging voltage ca 13.5-14V during normal usage. Not exciting, but you are looking at the same signal that the alternator uses to determine charge current.
     
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  12. Apr 9, 2020
    duffer

    duffer Rodent Power 2019 Sponsor

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    Awwww Where's the sense of adventure when that amp meter for the 150 amp alternator shorts out under the dash-------- Your own on-board welder. Personally, I always liked amp meters more than voltage meters as it was a little easier for me to see what was happening. That was ok with 37 amp versions but by the time they got to 63 amps I swapped gauges.
     
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  13. Apr 9, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    When you start the engine you should see it move some and then drop off as it recharges the battery....normally it won't take long.
     
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  14. Apr 16, 2020
    kenb

    kenb Member

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    Early on in this thread there was discussion of a fusable link between the battery and the ammeter. What exactly is that? I am wiring a Jeep with an alternator and an ammeter on the dash. It works but I suspect I should put some kind of safety device on that wire.
     
  15. Apr 16, 2020
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    A fuseable link is simply a length of smaller guage wire, normally 2 wire sizes smaller, than the wire it's protecting. What size that wire would be depends on what alternator you're using.

    Proper link wire will have a flame proof insulation.
     
  16. Apr 16, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

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    My apologies Howard; I would not contradict you but I think this is important. My understanding is that the fusible link formula is "add 4." Use a 14 ga fusible link to protect a 10 ga wire, etc. It's purpose is to protect the Jeep from the battery if something catastrophic happens, like a wreck. It's the final line of defense against a car fire. I agree that the insulation is flame-proof, with the intention that the link won't set anything afire if it actually fuses. Whether the wire material is different or not, I don't know.
     
  17. Apr 16, 2020
    kenb

    kenb Member

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    OK thanks for the info. I honestly don't know what alternator I have. My M38A1 was converted to 12v and converted to an alternator. I think it will indicate over 30 amps of charge initially after a start.
     
  18. Apr 16, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

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    Go by wire size. Protect the wire from the battery.
     
  19. Apr 16, 2020
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

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    So for 30 amps book value for the alt-battery wire would be 12 gauge, mostly I think you'll see 10 gauge wires though. Wire comes in even sized numbers- 6 - 8 - 10 - 12 - 14 - 16 with the higher numbers indicating smaller wire.
    You need about 6" of two actual sizes (or 4 numbers) smaller so you want a 14 Gu. piece of wire with some fire proof sleaving over it.

    Splice it into the big wire near the alternator with really good quality crimp butt connectors, or even solder it if you're capable.
     

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