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Infant Mortality battery tester

Discussion in 'Electronic Design' started by JaBrIoL, Feb 20, 2004.

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  1. JaBrIoL

    JaBrIoL Guest

    All,

    Here is another interesting project,
    I am to build a infant mortality battery tester.

    the tester is to be designed to a 110amp load

    for a 12 volt 16amp battery (the battery is actually capable of
    putting out 110amps for 16 seconds)

    Hence after a 6 second with a load attached, the battery should
    recover and measure 9.6 volts.

    running the numbers I came with

    resistor= .109 at 1.32KW

    Yes I know, why not lay a bare wire over the darn thing..?
    crude simple and effective which may cause personal injury burns, etc,
    blah,blah lawsuit. I think I will go with a test fixture. So far It
    has become difficult to locate a manufacturer for this type of
    resistor.

    I've been throwing around other... a resistor in a can of mineral oil
    etc.. (the ole dummyload)

    any ideas or suggestions?
     
  2. Tim Wescott

    Tim Wescott Guest

    Use resistance wire and make up your own resistor, suitably shielded. You
    shouldn't have to mess with immersing it unless you want to. Pay attention
    to the resistance change of the wire as it heats up (immersion would help
    here), and design your mechanical arrangement accordingly.

    If you need a precise current then switch in a number of individual segments
    in parallel, or use the wire to absorb the first 700-800 watts and a (well
    heatsunk!) transistor load to control the current.
     
  3. CFoley1064

    CFoley1064 Guest

    From: (JaBrIoL)
    Most resistor manufacturers will do a custom job for you -- but you won't like
    the price ;-)

    How about just getting 18 ea. 2 ohm, 100 watt resistors and paralleling them on
    busbar under a perforated metal cowl? These are $4.49 ea. from Marlin P.
    Jones. Spend $80 USD plus shipping and be done with it. That's .11 ohms at
    1.8 kW.

    http://www.mpja.com/productview.asp?product=7122+RS

    Good luck
    Chris
     
  4. Mjolinor

    Mjolinor Guest

    Buy a commercial lead acid battery tester or two and nick the resistance
    element out of them.
     
  5. Tim Wescott

    Tim Wescott Guest

    -- snip --
    And you can switch some or all of them to control your current in 6 amp
    increments.
     
  6. Ben Bradley

    Ben Bradley Guest

    http://elecdesign.com/Articles/Index.cfm?ArticleID=2144
     

  7. If this were up to me I would take a large plastic bucket, such as a 40 lb.
    laundry detergent bucket, and fill it with water. 12V is quite low and even
    with highly salty (like ocean water) water the current flow through water
    will be very small compared to the 110A or whatnot. It will also be quite
    safe to play with at 12V.

    Once filled with water I would go here:

    http://www.mogami.com/e/cad/wire-gauge.html

    And find out what the resistance of some different wires are. I would
    probably use something like 18 AWG copper wire for this job. From the
    calculator we see the DC resistance is 20.9mOhm per meter. So you want
    109mOhm, so about 109/20.9 = 5.2 meters. I would get this length of
    uninsulated or plain magnet wire and place this inside the plastic bucket of
    water. I would make sure to make good connections on the ends with
    something like 2 AWG wire leading to the battery terminals so that all the
    18AWG wire is fully immersed in the water.

    Voila. 0.109 Ohm resistor at 1.32kW. Cost may be nothing out of pocket if
    you have this stuff laying around. If I wanted to store it for any length
    of time I would make sure to include a lid for the bucket as well as putting
    something in the water like antifreeze to make sure algae and other
    biologics don't grow out of control in the water.
     
  8. Jerry G.

    Jerry G. Guest

    If you want something calibrated and engineered for you that is safe, buy a
    commercial high power battery tester. All the automotive places that do auto
    electrics will have these. They are not extremely expensive for what goes
    in to them. The ones that I have seen have a variable loading on them, and
    you can measure the point at which the battery starts to go down. You can
    then determine an exact measurement of the battery condition that would be
    repeatable, and accurate. The very high end ones use an actual variable type
    resistor assy that is properly rated. It works through a bridged loading
    with the amp and volt meters. This affair gives a very concise reading.

    If you want to mess around, you can start by using nichrome heating element
    wire to make your resistors. Use many in parallel to take up the load, and
    to also be able to have low resistance with more mass, thus giving better
    stability. Remember, as this heats up, its resistance will also change, thus
    not making the readings linear. The commercial units are worked out to
    compensate for this.

    --

    Greetings,

    Jerry Greenberg GLG Technologies GLG
    =========================================
    WebPage http://www.zoom-one.com
    Electronics http://www.zoom-one.com/electron.htm
    =========================================


    All,

    Here is another interesting project,
    I am to build a infant mortality battery tester.

    the tester is to be designed to a 110amp load

    for a 12 volt 16amp battery (the battery is actually capable of
    putting out 110amps for 16 seconds)

    Hence after a 6 second with a load attached, the battery should
    recover and measure 9.6 volts.

    running the numbers I came with

    resistor= .109 at 1.32KW

    Yes I know, why not lay a bare wire over the darn thing..?
    crude simple and effective which may cause personal injury burns, etc,
    blah,blah lawsuit. I think I will go with a test fixture. So far It
    has become difficult to locate a manufacturer for this type of
    resistor.

    I've been throwing around other... a resistor in a can of mineral oil
    etc.. (the ole dummyload)

    any ideas or suggestions?
     
  9. Robert Baer

    Robert Baer Guest

    I take it that what you mean by "a 12 volt 16amp battery" is that it
    has a 16 Amp-Hour rating.
    Therefore, a 110 amp load is *abusive*; look at the quote from
    Interstate Batteries!
    The spec from Interstate Batteries is: "If the battery can sustain a
    load equal to 2 times the Amp-Hour capacity, holding a voltage of at
    least 10.5 volts for 5 seconds, then the battery should be considered
    structurally sound." NOTE: the voltage mentioned is read *during* the
    load time.

    Some testing procedures for heavy duty automotive and/or marine
    batteries (type not specified in the literature) mentions a 300 amp load
    for 15 seconds, but that clearly is not commensurate with your
    application or battery type/design.
    Looking at a lot of literature, i find that the 10.5V specification as
    being the most realistic; i suggest that you modify that 9.6V limit and
    also the reading method.
    A battery that cannot recover to full voltage is either not good or
    has been subjected to an abusive load, which can shorten its life
    expectancy at minimum, or create internal damage.

    If the battery is useable, then the current will be constant for the
    purposes of the test, and if it is bad, then it does not matter that the
    voltage and current drops a lot.
    I have tested over a hundred reject batteries, some were useable for
    non-medical purposes (they were from motorized wheel chairs and
    scooters) as-found, and some were recoverable for non-medical purposes.

    **
    There are automotive car battery load testers, and some of them are
    portable.
    They include a voltmeter, a resistive load in the region of interest,
    and heavy duty leads with heavy duty clips.
    That load resistor and its enclosure can be very useful for making of
    a suitable tester.
    Harbor Freight or other "discounter" (read: seller of Chinese made
    stuff) has such an item that is not too expensive for either casual or
    serious use.
     
  10. Robert Baer

    Robert Baer Guest

  11. .

    . Guest

    I saw a construction article in either Radio Electronics or Popular
    Electronics during the 1980s for a battery tester capable of loading a car
    battery. I received these magazines starting in 1982. They used a specific
    length of 1/2 inch steel strapping that was wound around dowels on a wooden
    base. The article can be found at the library if anyone is interested.

    Ken
     
  12. BFoelsch

    BFoelsch Guest

    Resistors in the rating area you describe are used in the electric power
    industry.

    I don't know if they still make them, but as of my last association with
    them the Square D Company made several lines of resistors for similar use,
    crane and hoist speed control and braking, etc. One model was known as the
    PX resistor and were of nichrome on ceramic construction. and quite low in
    cost. If that product line still exists I am sure they could provide
    something suitable. Post-Glover is another manufacturer of industrial power
    resistors.
     
  13. We manufacture a unit which draws up to 450 amps out of 12V automotive
    batteries for around the time you require. Our load is about a stainless
    steel bar, roughly 1200 mm long, 20 mm x 5 mm cross section. Its easy to
    slide a contact (such as a heavy duty battery clip) along the bar to get the
    current you need.

    Stainless steel has a pretty high temperature coefficient, but the exact
    current does not matter to us - and I suspect the current does not have to
    be precise for your application.

    For high duty cycle use, we use a small computer type cooling fan to move
    some air over the bar. At only 110 amps, you shouldn't have nearly so much
    trouble with heat.

    The battery voltage will drop under load, so you might want less resistance
    than you calculate using 12V and Ohms Law.

    Your test spec looks unusual to me. Even a half dead battery will recover
    to above 9.6 volts when you remove the load, unless it has an internal open
    circuit. The standard Battery Council International load test for Starting
    Batteries is to draw 0.5 of rated Cold Cranking Amps for 15 seconds - the
    voltage should remain above 9.6 volts while the load is applied. Test
    temperature 18 degrees F.

    Roger
     
  14. JaBrIoL

    JaBrIoL Guest


    We have one. However Hawker Genesis, belives that many of the reading
    from their
    lead battery might be erroneous. these batteries lead-accid are not in
    the sense lead acid batteries, they are more like Lead asorb by tin
    batteries.

    the test I described, is recommended by them.
     
  15. JaBrIoL

    JaBrIoL Guest

    Thanks, the 110 amp load I got.. was from Hawker Genesis. they belive
    if I went over 15 seconds, it would be abusive to their batteries.

    interesting however, they would want me to do a voltage read after the
    load test. If the battery recover to 9.6 volts, they consider it a
    good battery.

    I Like your suggestion though, I consider it a bit more safe.
     
  16. JaBrIoL

    JaBrIoL Guest

    Your test spec looks unusual to me. Even a half dead battery will
    recover

    that is the purpose of the test.. hence looking for infant mortality
    of the batteries in quextion. It seem that ther manufacturer does not
    confide mich in many battery testers. I am assuming that they have
    high turn over rate of failed batteries, that when is returned, by
    their standards is good. This creates a logistical problem, I intended
    to avoid on my end.
     
  17. Robert Baer

    Robert Baer Guest

    I suggest that you view my response and quote from Interstate.
    A load of 100 amps *is* abusive on those poor little batteries, and
    the spec is a higher voltage *during* load.
     
  18. Robert Baer

    Robert Baer Guest

    A 100 amp load can *create* "infant mortality" of the batteries due to
    excessive internal heating created by the massive current.
    Might as well put a #0000 silver busbar wire across the terminals and
    let the battery melt or explode.
    If a battery melts or explodes in those conditions, then it *WAS*
    good; if not, it was (and is) bad.
    Sort of like the joke about testing fuses.
     
  19. JaBrIoL

    JaBrIoL Guest

    Oh I know... hence my comment on the original post about laying a bare
    wire across.

    however the manufacturer claims that it can hold 110amp load for 15
    seconds.
    16 seconds would be abusive. figure that one out. I think I might go
    a differnt route all together.
     
  20. JaBrIoL

    JaBrIoL Guest

    got a website? distributors in the states?
     
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