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Determine mAh

Discussion in 'Electronic Design' started by Andy K, Nov 11, 2013.

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  1. Andy K

    Andy K Guest

    Is there a way to determine if a camera battery that ouputs 7.4 V really has a 1900 mAh rating instead of a 1000 mAh ?

  2. Andy K

    Andy K Guest

    Is the 7.7 Wh on the battery Watts/hr ?

    How would the rated load be applied ?

    I have a Sunwa YX-360TR but it does not have that feature.

  3. I doubt if there is an accurate non-destructive method.

    You can however measure the charge transfer, Q in a number of ways. integrating I*t=Q

    1) power the camera using a very large capacitor charged externally from the battery, Monitor the charging current with a 100R in series and measure time to fully charge.

    2) Use a tiny shunt resistor and scope the current pulse ( harder)

    3) Measure the charge voltage on the battery remaining after each photo and lens adjustment. You may be able to extrapolate a very flat curve to estimate the current state of charge for that chemistry using the OEM specs. from 100 to 10%

    You can also measure the quality of the battery by it's ESR which rises with with reduced capacity and rapidly near end of life. If you are looking for statistical data, it may be a good metric for SOC using historical data.
  4. miso

    miso Guest

    You need to know the "official" termination voltage of the battery pack.
    That is, 7.4V is a nominal fully charged pack, but what is the voltage
    when it is considered discharged. For NiMH and nicad, 1V per cell is a
    fair estimate. Some people take them down to 0.9V per cell.

    Your 7.4V pack COULD be 6 cells. Usually it is 1.2V per cell, but it all
    depends on how things are rounded. So pull the expected load current out
    of the fully charged pack and see how long it takes to reach 6V under
    load.. If you pulled 1000ma for one hour and 54 minutes, the pack would
    be 1900mAh.

    It helps to know the load current used by the battery manufacturer in
    their datasheet. That is, to verify a datasheet specification, you need
    to know the exact test conditions. [You don't know the number of fucking
    idiots that call manufacturers complaining parts don't work to spec, but
    don't test them as stated in the datasheet.]

    Needless to say, you will need to use an electronic load. There are
    plenty of circuits floating around the internet on how to do this. For a
    battery test, the electronic load design is basically a DC circuit, so
    it isn't all that hard to build. [Transient load testing is difficult.]
    For battery capacity testing on the cheap, it can be done with analog
    alarm clocks for timers. I've seen battery capacity testing projects
    that look like bomb factories.

    Some people have used the current limit in a bench power supply to do
    capacity testing. I don't like the technique, but it should be written
    up on the internet somewhere. [Note that battery might lift the supply
    voltage since regulation expects current sourcing, not sinking.]

    Another scheme is to use a power supply "under" the battery voltage.
    That is, the positive output of the power supply goes to the ground of
    the battery. You use a resistive load going from the positive pin of the
    battery to the negative output of the power supply. The idea is to make
    the change in voltage across the battery be small percentage wise so it
    looks like a current source. [Obviously Ohms law is used to pick the
    resistor.] If the supply was 20V, that mean the voltage across the
    resistor varied from 27.4V to 26V, with a median voltage of 26.7V. That
    implies the error in the current is +/- 0.7V/26.7V or 2.6%. All
    presuming I made no math errors. Be sure to check the power rating on
    the resistor.
  5. Guest

  6. Guest

    No, it's 7.7 watts * hours. One watt for 7.7 hours or 7.7 watts for 1
    hour. In reality, your battery is something else. Reality matters.
    If you want to test the batter to the manufacturer's specifications,
    than you test the way the manufacturer specifies.
    What feature?
  7. Phil Allison

    Phil Allison Guest

    "miso" = moron

    ** Hardy matters at all.

    One the cell voltage drops below 1.1V it then drops rapidly to 1.0V or 0.9V.

    Digital cameras auto shut off at about 1.1V per cell anyhow - and INCREASE
    the current draw as the terminal voltage falls.

    ** Horse poo.

    A 10W resistor of 6.8 ohms will do fine.

    Monitor the actual current and plot it against time every 10 minutes.

    Use the simple average.

    .... Phil
  8. Guest

    10 ohms??? Are you outta your mind, that would be almost 0.8A. Just about every battery, regardless of technology, specs the capacity, C, at load current of 0.1C. He needs to load it with 1900 mAH/10=190 mA. For 7.4V terminal voltage, which as Miso stated is realy 6x 1.2=7.2V, he needs 7.2V/0.19A= 37.89473684 ohms! That's 36-39 ohm nominal resistance to you. Then Prating=0.19 x 7.2= 1.368W = 5W nominal to you.
  9. Phil Allison

    Phil Allison Guest

    ** My post says 6.8 ohms at 10Watts.
    ** You must certainly be.
    ** Horrors...........

    Just about every battery, regardless of technology, specs the capacity, C,
    at load current of 0.1C.

    ** So fucking what ?

    NiCd and NiMH cells can easily do a 1 hour discharge with barely any loss of

    Plus a digital camera draws at least that much.
    ** Your totally mad opinion.

    Bet anything a bullshitter like you has NEVER tested a NiCd or NiMH cell or
    pack in you whole life.

    ** ROTFLMAO !!!!!!!!!!!!!!

    Wot a pedantic IDIOT !!!!!!!!!

    **** off - you fucking, tenth wit MORON

    .... Phil
  10. Guest

    On Monday, November 11, 2013 8:40:37 PM UTC-5, Phil Allison wrote:

    Your subhuman intelligence is coming through. Care to explain how he's going to verify the rated capacity if he discharges the battery at an inordinately high discharge rate at which the apparent capacity is significantly less???? Like probably 50% less at your dumb suggestion.
  11. Bill Bowden

    Bill Bowden Guest

    I did it once using the camera as a load. The camera had a 'slide show' mode that continuously displayed pictures on the memory card. I think the camera drew about 600mA and the show lasted about 2 hours, so the battery capacity was around 1200mAH.

  12. mpm

    mpm Guest


    You would think the 1900 would last a lot longer. If you have both varieties, just time them in actual use.

    The mAh rating is a guide, but becomes much more meaningful when you know the discharge, recharge and temperate curves for the battery chemistry. Youcould rig up a discharge test while monitoring cell voltage, amperage and temperature and then test/compare each battery.

    For a lead-acid battery, Google Peukert's Law.
    It won't hold perfectly true for a different battery chemistry, but it may give you some rough ideas about how to approach the problem. If both batteries are the same basic chemistry, (Li-ion, for example) I'm wondering out loud whether you could just weigh each battery - and assume the energy-to-weight ratios for both camera batteries are at least in the same ballpark.
  13. Andy K

    Andy K Guest

    Keep your day job.
  14. Andy K

    Andy K Guest

    Thanks for the positive responses.

    My question was because someone is selling Vivitar batteries at 1900 Mah.

    Vivitar's own site has no such battery. Only a 1000 Mah battery.

    I can see another company making a higher capacity battery, but why is Vivitar's name on it? :)
  15. Guest

    That's because 9 is next to 0 on the qwerty and it's a typo in the ad. They probably mean 1000mAH .
  16. miso

    miso Guest

    Horse shit yourself.

    When you measure a spec, you do it accurately. You sound like the kind
    of fucking idiot that calls up manufacturers and tells them the part
    doesn't meet spec when in reality it is your own stupidity.
  17. mike

    mike Guest

    It's amazing the amount of useless posturing you get from such a simple

    Why not start with the problem you're trying to solve?

    The answer to the question you asked is that you read the label or the spec
    that you're sure matches the instance of battery that you have.
    If the RATING is not on the label, there's not much you can do to determine
    the RATING.

    If you want to determine the ACTUAL capacity of the battery you're holding
    in your hand, you just load it with the test current you want and
    discharge it to the terminal voltage you want and see how long it takes.

    But the devil is in the details.
    If 7.4V is the voltage RATING it's probably a two-cell lithium.
    If 7.4V is the MEASURED voltage, could be anything.
    While the battery technology doesn't really matter when you multiply
    the current and time, it might affect the test parameters.

    I've done considerable automated battery testing. I've got a box full
    of laptop batteries that still have most of their RATED capacity when tested
    at low current, but won't boot the laptop at all.
    mAh is not always the problem.
    High ESR is often the issue for high-current applications.

    What are you going to do with the answer? Acquiring info that doesn't
    change your future is wasted effort.

    Which gets us right back to determining the problem you're trying to
    solve that will make your future better.
  18. Phil Allison

    Phil Allison Guest

    "miso" = moron
    ** Go **** you mother - ASSHOLE
    ** But that is NOT the case here with the OP's question.

    YOU are just another nut case, autistic, pedantic

    FUCKING IDIOT that causes all the trouble on earth.

    FOAD and take all the other trolls with you.
  19. miso

    miso Guest

    I don't recall the OP asking "Is there some fucking stupid way to
    measure battery capacity." If the OP stated it that way, I would have
    simply waited for you to answer the question.
  20. miso

    miso Guest

    That makes a lot of sense. Sometimes they put in higher capacity
    batteries as chemistry progresses, but a pack the same physical size
    probably wouldn't have a nearly 2x improvement. A typo is much more likely.
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