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Thread: Troubleshooting Denso Alternator

  1. #1

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    Default Troubleshooting Denso Alternator

    I have a Colt with an 0290D2 engine. After starting the engine last week the amp meter showed a positive charge for about 5 seconds and then dropped to zero. I took the alternator to a shop and they said it was working fine. I reinstalled it and started the engine again and still no charge. I connected alligator clip to the top post on the alternator and to a volt meter with the other lead going to the negative post of the battery and it showed no charge. Did I check it the right way? Also with the engine running the fuel gauges showed the correct level until I turned on the landing light at which time both the gauges dropped to zero fuel level. I cycled the master switch off and then back on and the fuel gauges returned to normal. If I turned on anything with less draw than the landing lights the fuel gauges showed normal. What kind of hint is this?

    Thanks
    Bob

    PS I checked the ground from the alternator back to the battery and it showed continuity.

  2. #2
    Steve Pierce's Avatar
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    Default Re: alternator question

    Lots of previous threads on charging issues and troubleshooting them. You sure it is an alternator and not a generator? Which one? Should be a 337 on the install. Need more information to help you. Also the amp meter will show a charge for a sort period and then go to zero.

  3. #3

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    Default Re: alternator question

    thanks Steve. Yes, it is a Denso alt. I have never seen the meter drop instantly like it did. I have seen it slowly work it's way back to O

  4. #4
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    Default Re: alternator question

    Pretty simple alternator, internally regulated. Small wire has 12 volts to energize the field, big wire should show 13 plus volts when charging.

  5. #5

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    Default Re: alternator question

    thanks. when I tested it on the plane I got zero voltage at the big wire after it was bench tested and was told that it was fine

  6. #6
    Steve Pierce's Avatar
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    Default Re: alternator question

    Quote Originally Posted by pipercolt View Post
    thanks. when I tested it on the plane I got zero voltage at the big wire after it was bench tested and was told that it was fine
    That wire goes straight to the bus and battery so zero voltage doesn't sound right.

  7. #7

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    Default Re: alternator question

    When you turn on the master (engine not running) does the amp gauge go negative? If so then it is likely working when it displays 0 amps while running.

    Tim

  8. #8

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    Default Re: alternator question

    I hate to admit this Steve but I was thinking about it tonight and I had my meter on DC voltage not AC. oops

  9. #9
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    Default Re: alternator question

    I think the Denso has a built in rectifier so its output is DC.
    "Progress is our most important problem"

  10. #10
    Steve Pierce's Avatar
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    Default Re: alternator question

    Yes, should be DC.

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