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LIFE batteries charging question

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  • LIFE batteries charging question

    In a weak moment a few months ago I purchased a used Pilot RC Yak 54, 30% scale with a 55cc DLE engine. This is my first gas powered plane. I just had to try it, and hope to very soon.

    The two batteries for the receiver and one for the ignition are all LIFE, 2 cell packs. The original ignition battery would take no charge at all so I replaced it. This new one will charge up to 3.6 Volts per cell and quickly drop back to 3.3V per cell after a few minutes of engine running. So it starts out at 7.2 Volts total and then levels off at 6.6 Volts total. Apparently this is normal.

    The 2, 2 cell batteries for the receiver however will not take a proper balance charge. Each battery charging to 3.6V in one cell and only 3.4V in the other for a disappointing total of only 7.0 volts. These two batteries however after some use will also return back to 3.3 Volts per cell. So this part is normal behaviour. How long they will last at this level though, has yet to be determined.

    So my question is: Should I be concerned that I can't put a good balance charge into these two receiver batteries? Is this balance charging problem a sign these batteries are failing? Even though one of the batteries is there for redundancy what if they both failed at the same time?

    Thank you for your reply, anyone who has experience with LIFE batteries.

  • #2
    Either battery failing can bring down the RX system if there is no automatic isolation (as provided with the Spektrum "PowerSafe" high current buss RXs or the "SmartFly" regulator systems with dual battery inputs)
    This applies regardless of type of battery. A dead cell in one pack will discharge the other if there is no automatic isolation.

    You may be using the wrong voltage for the DLE ignition if not using a regulator. Unless they changed since I got mine the ignition wants 5.0v. Best is regulated, second best is a 4 cell NiCd. I do know that some engines are now using ignitions that can take (or want) 2 cell LiPo, as my Evolution 33cc wants the LiPo.

    LiFe has a really flat discharge curve. Its not far from full to 3.3v/cell and then stays there a long time, followed by a rapid loss of voltage when they are depleted. (don't let them get in that last part of the curve) There is very little % of capacity difference between 3.4v/cell and 3.6v/cell.

    You also need to verify with a second charger or a good meter to see if the charger is out of calibration.
    FF gliders and rubber power since 1966, CL 1970-1990, RC since 1975.

    current planes from 1/2 oz to 22 lbs

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    • #3
      Thanks for your reply fhhuber. My receiver is a Spektrum AR9110-X with connections for battery one and battery two. I will have to read the literature more to find out how the redundancy works. I know that the whole receiver and servo system will run with just one battery turned on.

      You may be right about the Life battery voltage being a little too high. I just read the manual and DLE recommends voltage 4.8 to 6 volts. This plane is about 7 years old and has had numerous flights I am told. It was built by a reputable builder and the quality is good so I never questioned it until now.

      The Life battery power curve is what has me worried because it's not as easy to monitor as a Lipo which we are all familiar with. I may just replace those two batteries, they're not expensive, it's just another delay before the first flight.

      Good suggestion to double check the voltage readings I'm getting. A higher quality voltmeter may tell a different tale.

      I appreciate your input. You have got me thinking!

      Cheers, Bluebird

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      • #4
        Generally a cell will not simply refuse to come up to full charge , but still give decent capacity. Its usually a charger issue.

        You can make an adapter and charge each cell separately as if it was a 1 cell pack. With both cells charged by the same single cell portion of the charger you can compare apple to apple. The balance section or the meter may be out of calibration. If its just the meter you note the error amount and use a separate balancer until you can get a different charger or get it calibrated.
        FF gliders and rubber power since 1966, CL 1970-1990, RC since 1975.

        current planes from 1/2 oz to 22 lbs

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        • #5
          Ok that's a good thought fhhuber. If I could make an adapter to allow charging each cell separately that would make sense.

          The charger I have is a higher end HiTec multi , which has been working well on Lipo's and seems to work well on the new LIFE battery I bought. I'm honestly not sure how to make the adapter you refer to so I think for now I'm going to put some kind of load test on each battery and if they hold up well and don't break down rapidly I'll consider them good to go.

          Before I do that though, after charging I will check with a high quality meter as per your suggestion, looking for errors in the equipment I've been using.

          I think for the cost of a couple of new batteries VS the risk of loosing my airplane, new batteries make the most sense at this point if I have any doubts after doing further checks.

          Thanks gain for your input. Cheers! Bluebird

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