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Thread: Ignition battery

  1. #11
    Senior Member ceslaw's Avatar
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    Default Re: Ignition battery

    Interesting

    I look forward to what you learn

  2. #12
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    Default Re: Ignition battery

    I have a similar problem. I replaced my battery with a brand new PowerSonic battery. During run up when checking the emergency ignition function the voltage would drop to well below 12 volts in about ten seconds. The engine continues to run, but the significant drop in voltage was concerning and I am not sure how long it will run.

    It seems like the circuit has an additional load or short when the emg switch is turned on.

  3. #13
    Senior Member Andy's Avatar
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    Default Re: Ignition battery

    Quote Originally Posted by stautz View Post
    It seems like the circuit has an additional load or short when the emg switch is turned on.
    The only load on the battery when the emergency ignition is on should be the LED and the ignition module itself. The switch disconnects the battery from the charging source and connects it to the ignition module.

    My test data show battery discharge current of 1.2 A at start of a 30 minute discharge test and 1.5 A at the end of test. The increase in current as battery voltage drops appears to be consistent with the use of a linear voltage regulator in the ignition module.

    If a new battery that has a full charge won't hold voltage during a normal emergency ignition test then the problem is likely that the new battery is no good. This is why I have decided to test and replace on condition rather than on calendar date.

    Here is a sample of battery voltage plots for a the battery that has been in my FX-3 since it was built early in 2020. These are all preflight ignition tests not the extended 30 minute discharge test:

    ign tst plots.png
    Last edited by Andy; 09-29-2021 at 10:00 AM.

  4. #14
    Senior Member ceslaw's Avatar
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    Default Re: Ignition battery

    Andy:

    EXCELLENT information. It is great seeing data to back up a theory.

    Would the take away be to test for ten seconds, confirm it is holding voltage, than end the test? Is ten seconds an appropriate length? Based on fairly consistent results over time with your data, it would seem to be the case.

    Presumably only testing for ten seconds would have virtually no effect on total capacity of batter in a true emergency.

    Knowing that replacement batteries can be bad (as was the case on one I replaced at the annual condition inspection), this would indeed seem to be a better approach than annual replacements.

    Chuck

  5. #15
    Senior Member Andy's Avatar
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    Default Re: Ignition battery

    Quote Originally Posted by ceslaw View Post

    Would the take away be to test for ten seconds, confirm it is holding voltage, than end the test? Is ten seconds an appropriate length? Based on fairly consistent results over time with your data, it would seem to be the case.
    I think the 10 second discharge test gives a reasonable indication of battery condition but it's not as good as a 30 minute discharge test. As I said in an earlier post I'm concerned about the emergency battery unregulated charging current. I'm going to hold off on doing another 30 minute test until I have a charge current limiter installed.

    Since you are taking an interest in the topic here are the voltage and current plots for my most recent 30 minute in-flight discharge test:
    Attached Images Attached Images

  6. #16
    Senior Member ceslaw's Avatar
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    Default Re: Ignition battery

    Quote Originally Posted by Andy View Post
    I think the 10 second discharge test gives a reasonable indication of battery condition but it's not as good as a 30 minute discharge test. As I said in an earlier post I'm concerned about the emergency battery unregulated charging current. I'm going to hold off on doing another 30 minute test until I have a charge current limiter installed.

    Since you are taking an interest in the topic here are the voltage and current plots for my most recent 30 minute in-flight discharge test:
    Perhaps one could treat that back up battery like an ELT battery by way of comparison. In other words, if an emergency occurs and it is used for an extended period, consider replacement. If no emergency occurs, test it for 10 seconds and use it indefinitely as long as it passes the run up check. The need to rely upon it in an emergency should be extremely rare, so it should last a long time based on your data.

    You noted substantial current draw to recharge it after a deep discharge. If it is only tested for 10 seconds on the run up I assume it would charge at only a few hundred milliamps and high current flow would be the rare exception following an emergency.

    I'm just trying to come up with protocols that I can follow going forward consistent with data you have acquired. Thanks for posting.

  7. #17
    Senior Member Andy's Avatar
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    Default Re: Ignition battery

    Quote Originally Posted by ceslaw View Post

    You noted substantial current draw to recharge it after a deep discharge. If it is only tested for 10 seconds on the run up I assume it would charge at only a few hundred milliamps and high current flow would be the rare exception following an emergency.
    I don't have a family of plots for charging current after a 10 second test but, in a quick check, I found that 0.9 A peak seems to be typical. Charge current exceeded 0.3 C for 7 seconds in one example. I doubt that this would be damaging but I'd prefer to keep charge current under 0.3 C (0.6 A).

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