Ammeter V Voltmeter

Discussion in 'Electrical Systems' started by Poida, Nov 23, 2006.

  1. marshmat
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    marshmat Senior Member

    For recharging, same integral... cumbersome and not ideal for the everyday boater, but this is how we calibrate those power curves in the first place for the lithium polymer packs.

    Current is not an indicator of battery condition, not until you start to draw so much that you completely drain it. To use voltage as an indicator of charge level, you need (as Greg describes) the power curves for your pack. And you need a meter that is calibrated accordingly- a standard voltmeter won't do the job, the difference in voltage between full and dead is very, very small.
     
  2. longliner45
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    longliner45 Senior Member

    the reason I asked ,is because on night I was sinking ,,I looked at my amp gauge and it droped to 50 amps,,I knew I was running all pumps ,,before this it read 200,,,,I watched as it draind down to 50,,so I always thought that it measured stored amps....longliner
     
  3. luckettg
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    luckettg Junior Member

    Matt,
    How similar are the lithium polymer packs to lead/acid batteries? I usually see a couple of volts difference from charged to discharged in the low dwell batteries I use on sail boats. I usually put a known load on a battery and watch the current flow and voltage for indications as to its condition, and when in doubt, I haul them over to the local supply house to be tested on a battery tester. Oh, the other indicator before that is the way a charger acts when hooked to the battery and how long it takes the battery to recharge (if ever).
    Greg Luckett
     
  4. Ike
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    Ike Senior Member

    Voltage tells you the condition of the battery, whether it is fully charged or not and can tell you the condition of individual cells if you have the right monitoring equipment. A hygrometer will tell you this too but only on a wet battery. That won't work on a sealed battery.

    An amp meter tells you how much draw there is on the battery, in other words what load you are putting on the battery. This tells you at what RATE the battery is being discharged.

    In reverse, when charging a battery an amp meter will tell you the RATE at which a battery is being recharged, but not the state of the battery. A voltmeter tells you that.

    Frankly I would have both, come to think of it , I do have both!
     
  5. marshmat
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    marshmat Senior Member

    Greg,
    The test you describe in post #18 is pretty much the same as what we do to test the LiPo cells, except we'll run the voltmeter and ammeter to a computer and plot the discharge curve as we do it. Then, battery voltage (ideally between 3.6 V to 4 V) can be used (via that curve) to find the energy left. Similar to what a commerical meter for your lead-acids would do. But in general, integrating the energy flow has proven easier and more reliable when on the run.
    I would advise everyone to not try to home-build lithium based batteries unless you know what you are doing. These are an order of magnitude more powerful than lead-acids, but require careful monitoring. If you drop the voltage too low, metallic lithium crystals grow across the electrodes and permanently short-circuit the pack. Cross the terminals, and instead of a spark you get a 3,000 degree arc of nitrogen-oxygen plasma. Leave them crossed and the cell will either vent hydrofluoric acid gas (if you're lucky) or explode (if you're not lucky). When you see these in commercial devices like cellphones, they have sophisticated fail-safe control circuitry attached to keep them happy. Not for the amateur.
     
  6. StianM
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    StianM Senior Member

    Set up a voltmeter with voltemter switch witch allow you to mashure betwen L1-L2, L1-L3, L2-L3, L1-Earth, L2-Earth and L3-Earth.

    It will make you able to mashure diference betwen pase-pase and if your voltage betwen pase-earth is less than pase/root off 3 then it's a indication on isolation faliure on that phase.

    I would say they are equaly inportant, but if I had to chose I would take the voltmenter.
     
  7. hartley
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    hartley Junior Member

    For Heavens sake .refer to post number 4 and fit both,plus a few lights and anything else that takes your fancy,itwill only cost a few dollars ,and i am quite sure you will be able to figure it all out !!!!Yea verily i say unto you !!!
    Ok i've had a few sherbets pls forgive ......cheers now
     
  8. marshmat
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    marshmat Senior Member

    Right on Hartley, I wouldn't even think about installing batteries without both types of meters....
    Stian, we're talking here about batteries- that's DC. Not three-phase AC as you seem to suggest in post #21. I can think of absolutely no reason to have 3-phase on a pleasure craft unless you have diesel-electric power and a really, really large hotel load.
     

  9. StianM
    Joined: May 2006
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    StianM Senior Member

    It don't make voltmeter less important if it's a dc system.

    A voltage drop that inticate insulation faliure s more critical on a dc system, low voltage dc is even worse to eat up metal on your hull then AC.

    I would sugest to also find a isolation guard for it.

    On exspresion is that it's posible to save utill you become poor.

    Spend money and save money by avoiding truble in the future.
     
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