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Thread: MEP-804A 24V Alternator no output and RPM Dropouts While Running

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    Private mrosalik's Avatar
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    Default MEP-804A 24V Alternator no output and RPM Dropouts While Running

    Hi folks, new here but have been running an 804A on a 20-mile Off-Shore lighthouse restoration job. Our donated 804A alternator has given up the ghost. Been using two 12V chargers to keep batteries up but need alternator. hopefully these photos help identify what brand this is.

    Searches for what is printed on a tag on it have come up with nothing so far.20190629_111043.jpg20190629_111054.jpg20190629_111104.jpg

    Second issue is random RPM drop-outs or a slowing down. Seems to be when very lightly loaded. Do these have some sort of semi-sophisticated speed control tied to the frequencysetpoint?

    Thanks for any help.

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    From Army TM 9 - 6 1 1 5 - 6 4 3 - 1 0. TMs for 804A here: https://www.steelsoldiers.com/showth...n-the-MEP-804A

    Battery Charging Alternator:
    Manufacturer Hitachi
    Model LR220-24
    Rating 20 amps at 24 VDC
    Protective Fuse 30 amps

    $82 to $103 from a variety of suppliers: Search on model number.
    Last edited by Zed254; 07-09-2019 at 12:56.

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    Private mrosalik's Avatar
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    Thank you so much.

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    I'm curious: is your project at Stannard Rock, MI?

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    Private mrosalik's Avatar
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    No. White Shoal. Stannard Rock is even farther from inhabited land than we are. There are uninhabited islands within 10 miles of us.

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    That's us! This generator is our main workhorse until a serious set of solar and big 220V inverter can be installed.

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    Quote Originally Posted by mrosalik View Post
    Hi folks, new here but have been running an 804A on a 20-mile Off-Shore lighthouse restoration job. Our donated 804A alternator has given up the ghost. Been using two 12V chargers to keep batteries up but need alternator. hopefully these photos help identify what brand this is.

    Searches for what is printed on a tag on it have come up with nothing so far.20190629_111043.jpg20190629_111054.jpg20190629_111104.jpg

    Second issue is random RPM drop-outs or a slowing down. Seems to be when very lightly loaded. Do these have some sort of semi-sophisticated speed control tied to the frequencysetpoint?

    Please define Random RPM dropout. Will the engine just slow down and jump right back up? Or slow down and then pick slowly back up? Or slow down and stay at the lower RPM?

    What do you consider "semi-sophisticated speed control tied to the frequency set point?" This is a precise Power gen set. It has a Magnetic Pickup, (Speed sensor) Governor Control Unit, (GCU) and Electric actuator, (EA). They all control speed, (RPM=HERTZ).

    Need the answer to the first question, to judge how to help your problem..

    Thanks for any help.
    .

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    Private mrosalik's Avatar
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    The engine sounds like it studders and or loses power. The frequency meter will drop way back and or pin to the left under 50 Hz. Sometimes it is a very brief "burble" with quick recovery. Other times several seconds prompting me to want to shut it down.

    It sounds like it slows down very briefly and picks back up fast. Other times it seems like it may even stall lasting several seconds.

    I found a loose terminal on the 20a alternator Positive terminal. It needed almost one turn to tighten. I'm wondering if that damaged the alternator. The misbehaving is much less since I put two battery chargers on it bringing that voltage back up. When I last went out the batteries were barely 11V each and the starter solenoid only clicked.

    The terminals were badly corroded so I fixed that and charged the two batteries with a back up generator. After getting it running I found the alternator was not putting out. It did come back briefly at 28V but only a few minutes. The starting battery meter was in the green then dead.

    With the now increased battery voltage and less "events" is why I'm assuming that the Frequency/RPM control may be electronic versus purely mechanical like the 6-71N in the boat.

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    Suggestion, just take it [alternator] to a alternator shop get it checked out and or fixed as required, easy to put back on and you know it is good to go either way, it pass's check and or it gets repaired .. mac/mc

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