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Thread: Generator overheating

  1. #1
    Join Date
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    Deerfield, NH
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    Default Generator overheating

    1950 Chris Craft Utility converted to 12 volt components this past winter and Spring. What could cause the generator to heat up and melt some wiring? The guy who rewired it said the cause could be a bad cell in the battery (new battery) or bad ground. Hmmm. Prior to the meltdown, the boat started fine. No sign of battery failure. I had no clue if there was a problem with the charging circuit.

    In any case, it was odd how it happened. My mechanic friend was over trying to get the engine to accelerate to full throttle, which he did (apparently the carb jet was in the wrong place (hmmm, nobody I know touched it. (Do those move during running?). We ran it up to full throttle with good smooth acceleration a few times. However, during this process at the high end of acceleration it would suddenly pop out of gear. So the next thing was to check the linkage. He wanted to check how it would run if he separated the linkage so he could put it into gear manually without using the shifter. He wasn't so successful at that so he reconnected the linkage, and when we tried again the battery seemed suddently dead (clicking noise). Wasn't the generator supposed to be working charging the battery? Then we smelled the melting wire, and the generator and and can on its side were blazing hot!

    I presumed the generator was working before this. The engine always cranked into action everytime I turned the key. We've put only about 4-5 hours on the 12-volt components and battery running the boat at low RPMs (up to 750 because above that it got sporadic, for unknown reasons). Yes, the bilge ran quite a bit over the past 4 weeks of rain. But enough to run the battery down, with us running the boat for an hour or so every couple of days?

    The next day, I hooked up another battery and the starter jumped into action. So the starter didn't get damaged, but now I don't know how to check the condition of the generator other than taking it off and sending it back to the guy who rebuilt it.

  2. #2
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    Default Re: Generator overheating

    If you have a multimeter you can check your generator quite simply by checking the voltage at the battery terminals with the engine not running, then check it with the engine running. It should read around 12.6V before starting and closer to 14V when running.
    Last edited by Stiletto; 09-09-2022 at 07:28 PM.
    There is nothing quite as permanent as a good temporary repair.

  3. #3
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    Default Re: Generator overheating

    " 1950 Chris Craft Utility converted to 12 volt components"

    Was it 24 V previously ?
    For sure you know 12 V doubles the amps vs 24 V for the same power.
    Did the guy rewired with double section wires everywhere ?

    By "Generator", you mean Alternator right ?
    Last edited by Rapelapente; 09-10-2022 at 03:28 AM.
    Gerard.
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  4. #4
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    Default Re: Generator overheating

    Great! Will check.

  5. #5
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    Default Re: Generator overheating

    Thanks for the reply, It was 6v originally.

  6. #6
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    Queens, NY
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    Default Re: Generator overheating

    sounds like perhaps the field windings in the generator were not swapped 6V for 12V ??

    that would probably run hotter and eventually burn up, if the only thing changed was the voltage regulator.
    i wonder if the rebuilder was aware of your plan for voltage conversion ?

    some additional reading for tractor applications, but same idea:
    https://www.yesterdaystractors.com/c...mall&th=351437

  7. #7
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    Default Re: Generator overheating

    6v field windings are a heavier gauge, I'm not sure that would cause this problem. It sounds to me like he may have had a regulator issue, or a short (closed) circuit somewhere. It seems entirely possible the "mechanic" working on the boat had nothing to do with the problem.
    Usually generators that melt down are caused by the cut-out relay sticking closed while the engine is not running causing the generator to think it is a motor and try to turn. Of course it cannot rotate the engine and if not caught quickly it will definitely let all the smoke out of that unit and out of the battery... i.e. battery will be dead, and the generator will be cooked.
    Always glance at your amp gauge when the engine is shut down and note whether or not there is a draw before you walk away from it. A stuck cut-out rely will bury the amp gauge.

    Another, different issue is field windings (whatever gauge) cannot take full armature voltage for very long, if the regulator sticks allowing full armature voltage to the fields that can also "burn up" a generator and soon boil out a battery. I have tested unregulated 12v generators on the bench and seen a 100 volt spike which can survive no problem for a second or two.

  8. #8
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    Default Re: Generator overheating

    Where is the regulator on the generator? The little "tin can" on the side? That was hotter than hell. BTW, I recharged the battery and it measured at about 12.6V. When I re connected the generator, I didn't even have time to measure the voltage again (hoping for 14V) because that "tin can" was increasing significantly in temp.

  9. #9
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    Default Re: Generator overheating

    Just buy a 12v. generator.

  10. #10
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    Default Re: Generator overheating

    My take--simples first. Battery cable(s) were old.They can look good but be shot inside.
    This caused resistance and melted the cable. But before it melted completely, resistance (load) shot way up generating the heat you recorded.

    Kevin
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  11. #11
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    Default Re: Generator overheating

    I don't think this is a battery cable resistance issue. If that were the case then I think the heat would not be from the voltage regulator, but from the cables or the battery terminals. A voltage regulator will get hot when it steps down the voltage. If the input voltage is too much higher than the output limit it can definitely overheat. Is it possible that you still have a 6V regulator on your now-12v generator? If that's the case then yes - it could get very hot very quickly.
    - Chris

    Any single boat project will always expand to encompass the set of all possible boat projects.

    Life is short. Go boating now!

  12. #12
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    Default Re: Generator overheating

    if you ran a 6V generator with the original 6V windings inside, but a new 12V regulator, it would probably charge the battery fine (at high enough rpm, not so well near idle rpm)
    but it would get hot !

    i would for sure collect some data with a multimeter and again ask your rebuilder friend what was replaced in the generator

  13. #13
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    Default Re: Generator overheating

    Jeebus, just buy a 12v generator. Not that hard to get nor expensive. Chris had them from the early 50s onward.

  14. #14
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    Default Re: Generator overheating

    I’m thinking it sounds like a regulator issue too.
    ….About the reverse gear popping into neutral, how much force does it take to put it in gear (forward)?

  15. #15
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    Default Re: Generator overheating

    Quote Originally Posted by nedL View Post
    I’m thinking it sounds like a regulator issue too.
    On a generator, part of the regulator (or possibly the "can" on the side) is actually a cut off that disconnects the generator when the engine is not turning. Of it shorts (the contacts get welded) the generator turns into a DC motor and tries to turn the engine. If not fused, that will melt a wire.

    Edit: I see Canoeyawl beat be to it
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