Battery load test results

Discussion in 'Maintenance Bay' started by Morgan3820, Nov 12, 2018.

  1. Morgan3820

    Morgan3820 Cleared for Takeoff

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    Using a Foxwell BT705 battery load tester on my Concorde RG-35. The logbooks do not show when it was installed, so I have no idea as to the age of the battery. The voltage was 12.5, which I found a chart that says that is equivalent to 80% charged. The CCA measured at 290 vs. the rated 390.
    Is this good? 75% of rated?
     
  2. NoHeat

    NoHeat En-Route

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  3. Bell206

    Bell206 Line Up and Wait

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    I've never had any luck trying to compare aircraft capacity checks with "battery load tests."
     
    Last edited: Nov 13, 2018
  4. Morgan3820

    Morgan3820 Cleared for Takeoff

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    Looking at the Concord criteria, I am due for a new battery, surprise.
     
    Bill Watson likes this.
  5. 455 Bravo Uniform

    455 Bravo Uniform Pattern Altitude

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    Email the company, they’ll tell you the mfg date. Mine was 9 years old and still weakly cranking the engine when I replaced it. I emailed the company just out of curiosity and they got back with me within the week.
     
  6. bnt83

    bnt83 Final Approach

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    Aircraft batteries are capacity tested, usually by top charging then discharging at a constant 1C (ex: 29 amp hour battery would be discharged at 29 amps) until reaching minimum voltage, timing how long it stays above minimum voltage. I think they are typically considered bad if less than 75% capacity remains.

    Anyone can make a makeshift battery capacity tester, just get a 12 VDC to 110VAC converter, an ammeter, and hook up a load that draws 1C from the battery, time how long it stays above minimum voltage measured with a volt meter. Probably not as easy or accurate as $2k aircraft battery capacity tester but will get you in the ballpark. (Note: must have the battery manufacturer's manual for specific specifications).
     
    Last edited: Nov 13, 2018
  7. Bill Watson

    Bill Watson Pattern Altitude

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    If it’s 12.5V, 4 hours after a full charge, that battery needs replacement. The capacity test confirms it.

    I noted in the doc that if a new battery tests at 12.5, don’t install until capacity tested. If it has sat around at 12.5, that will kill it over time anyway.


    Sent from my iPad using Tapatalk Pro
     
  8. Bell206

    Bell206 Line Up and Wait

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    While it might still not meet OEM values, the only way to confirm is by a capacity check. The load check you did is not the same thing. Making a DIY cap tester like above gets you close.
     
    Last edited: Nov 13, 2018
  9. Dan Thomas

    Dan Thomas En-Route

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    It needs to be a load that stays at 1C. As voltage drops across a constant resistance, so will the current, reducing it below 1C and fudging the time in the battery's favor. Not very accurate.
     
  10. Dan Thomas

    Dan Thomas En-Route

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    Capacity check, not capacitance. Big difference.
     
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  11. Dr. O

    Dr. O Pattern Altitude

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    The way the engines crank is my tester. Mine needs replacement. The way I can tell is the cranking is more peppy on the first engine than the second. When it was newer that made no difference.
     
  12. flyingbrit

    flyingbrit Pre-Flight

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    I've never liked the idea of an annual capacity test as it involves a deep cycle and is therefore destructive and will shorten the life of the battery. I expect Gill and Concord don't mind this though...
     
  13. Checkout_my_Six

    Checkout_my_Six Final Approach

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    I don't do them.....I believe the drain is to stressful and produces too much wear and tear. I'd rather monitor the "quality" of starting and operation of the battery. When weak I'll replace it.....With a properly charging system your battery should last 5-7 years. I've had no issues getting 6-7 years with either a Gill or Concorde.