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OT Camera battery question. Why 3 contacts?

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  • OT Camera battery question. Why 3 contacts?

    The batteries for my Canon SD300 digital camera died after about 3 years of use. One was the original Canon and the other a Lenmar that cost about 1/4 a real Canon replacement, but worked just fine.

    Can someone explain why they have 3 contacts (in layman's terms). I thought dc stuff was pretty straightforward: ya got a "plus" and ya got a "minus" or do we need a third contact to be PC?

    Doug

  • #2
    Ask Evan he's a technobuff Alistair
    Please excuse my typing as I have a form of parkinsons disease

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    • #3
      this is just a guess...
      (how's that for an opener?)

      3 'contacts' for DC usually imply a split +/- power supply..
      that means 0V (GND), +V, -V.

      this is usually done at the board (chip) level so I'd exclude
      that from the battery. all thats left is some kind of "info"
      contact -- perhaps a reference for the camera to measure
      the battery level without putting additional drain on it.

      i say this because, usually, (mine included), the battery
      charger also has 3 contacts. i'd put my money on
      it being a 'reference' or measurement terminal.

      am interested to hear the real answer...

      -Tony

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      • #4
        yes, i use a canon myself and one of the terminals is for the camera battery life meter and when cahrging it tells the charger the battery status.

        Dave
        If it does'nt fit, hit it.
        https://ddmetalproducts.co.uk
        http://www.davekearley.co.uk

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        • #5
          Can be two separate cells, they might run them in series or parallel but the third wire can be a way of monitoring each individual cell, I think thats what their doing on my li-po's .

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          • #6
            The third contact is usually a thermistor or a semiconductor temp sensor in NiCd and NiMH packs. In li-ion and lipos it may be a data line like I2C for communicating with the board in the battery pack.

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            • #7
              Yep, temperature sensor.

              I2C requires 2 wires. There is a one wire standard though.
              Free software for calculating bolt circles and similar: Click Here

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              • #8
                The third contact in lithium batteries is for sensing of the charge rate, etc.. If it is a lithium battery it needs special attention during charging. If incorrectly charged it can burst into flames or explode. It can happen even with the correct charger if the battery is bad or damaged.

                Is yours a lithium battery?
                It's only ink and paper

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                • #9
                  Originally posted by Carld
                  The third contact in lithium batteries is for sensing of the charge rate, etc.. If it is a lithium battery it needs special attention during charging. If incorrectly charged it can burst into flames or explode. It can happen even with the correct charger if the battery is bad or damaged.

                  Is yours a lithium battery?
                  Yes, these are lithium-ion. So the third contact is actually a connection to some electronic component within the battery, rather than a + or - terminal?

                  Doug

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                  • #10
                    The third wire is for sucking money out of your pocket.

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                    • #11
                      Originally posted by john hobdeclipe
                      The third wire is for sucking money out of your pocket.
                      Certainly true if you go with a Canon replacement @ $40. The Lenmars weren't too bad @ $10 off amazon.com. I saw no difference in performance or life between the two brands. ymmv.

                      Doug

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                      • #12
                        like everything else, the minute you throw something away, that's when you need it.
                        i have a similar Canon camera, with i think the same batteries. for about 6 months one was laying in the center console in my car with the covers off, and my wife just cleaned the car out and threw the battery away. if i still had it i'd post a photo. anyway, yes, the third wire went to some small electronics inside the battery case. in cell phones the third contact is a thermistor to sense temperature. i'm guessing it's the same for these.

                        andy b.
                        The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

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                        • #13
                          Like many have said above it is for a temperature sensor. Lithium batteries are extremely temperature sensitive, both while charging and actually before charging. If the battery is to cold the charger should not charge the battery until it warms up. If you try to charge a cold lithium ion battery without protection in the charger it will be damaged and/or destroyed, sometimes violently This was the explanation I was given by the battery system engineers for the radio batteries I use a lot.

                          Robin
                          Robin

                          Happily working on my second million Gave up on the first

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                          • #14
                            Some of the lithium packs have a connection to several points in the battery to sense if sections of the battery are charging faster than others.

                            The lithium battery can be a very dangerous item if mishandled or damaged. Because of the charge/discharge conditions of model airplanes the lithium batteries are dangerous and have to be handled with caution. They are charged/discharged in a metal box or some method to contain a fire or explosion if something goes wrong.
                            Last edited by Carld; 05-17-2008, 12:59 PM.
                            It's only ink and paper

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                            • #15
                              Finally something I have some solid info on. The last 5 years I have been working with Large Li packs. up to 2 KW :-) single modules
                              Almost for certain it for a temperature sensor. As other have stated most Li based pack have this sensor for the charge circuit to monitor temp for under and over temp. If the pack is Ni based its used for Dt/dt or some other charge termination technique.

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