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  1. #1

    Default honda bf8ah alternator output

    Good morning everyone, can anyone out there tell me what the alternator should read on a multimeter when my bf8ah motor is running at approx 1/2 speed ? Thanks in advance for any input !

  2. #2
    Join Date
    Apr 2018
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    Default Re: honda bf8ah alternator output

    There are no specs in the manual other than individual components resistance charts. I would just say that if the battery voltage is more than 12v then it's charging. This is a very low output system and will not compensate for large current draws.

  3. #3
    Join Date
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    Default Re: honda bf8ah alternator output

    I don't have that particular manual but I seem to remember that there were two amp ratings offered for the charging coil. Something like 6amp or 12amp. The lower was intended for battery replenishment only while the higher was for a small auxiliary load like radio and depth sounder or running lights.

    A fully charged, wet cell, automotive type storage battery is designed for 12.6v. Or, 2.1v per cell to look at it accumulativly.

    So, knowing that, the voltage to keep it in that "state" would need to be higher. This is typically regulated from anywhere above 13.5v to a maximum of 14.2v.
    Any reading below 13.2v usually suggests a low charge condition while anything above 14.9v is considered an overcharging condition.
    Last edited by jgmo; 03-20-2020 at 10:16 AM.

  4. #4

    Default Re: honda bf8ah alternator output

    Quote Originally Posted by jgmo View Post
    I don't have that particular manual but I seem to remember that there were two amp ratings offered for the charging coil. Something like 6amp or 12amp. The lower was intended for battery replenishment only while the higher was for a small auxiliary load like radio and depth sounder or running lights.

    A fully charged, wet cell, automotive type storage battery is designed for 12.6v. Or, 2.1v per cell to look at it accumulativly.

    So, knowing that, the voltage to keep it in that "state" would need to be higher. This is typically regulated from anywhere above 13.5v to a maximum of 14.2v.
    Any reading below 13.2v usually suggests a low charge condition while anything above 14.9v is considered an overcharging condition.
    Thanks for the info but what i am wanting to know is what would the normal voltage reading be
    on a multimeter, coming out of the dc receptacle on the motor when it is running at approx 2,000 rpms ? I am getting a reading 03 to .05 & that doesn't seem right to me.

  5. #5
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    Default Re: honda bf8ah alternator output

    I may be wrong but I'm not sure that it will charge if it's not hooked up to a battery. Because, the system won't be grounded properly through the meter probes.

    If you don't have the battery harness to plug into the receptacle, you can rig jumper wires to temporarily hook up a battery to check to see if it's charging.

    Just be VERY careful not to reverse the polarity as that would probably damage the regulator.

    At the battery posts, it should read above 13.2v at idle and below 14.4v at 2000 rpm. If it's in that "range" I would say it's working properly.

  6. #6

    Default Re: honda bf8ah alternator output

    That's helpful info but shouldn't you get some sort of reading at the receptacle when it is unplugged that would tell you if it is putting out any juice ? I have a feeling that the rectifier may be fried because it has come disconnected from the motor when running,on more than one occasion but i don't know how to check it with a multimeter. When revving the motor up when it's connected the reading at the battery stays at 12.49 & doesn't move.

  7. #7
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    Default Re: honda bf8ah alternator output

    I do not know how to accurately test the rectifier.

    It's clear that your system isn't charging but that doesn't necessarily mean that the regulator/rectifier is bad.

    The good news is that it can likely only be one of three things:
    1.The regulator/rectifier
    2. The charge coil.
    3. The wiring and connections between the components.

    If you can verify that the charge coil isn't open or shorted and if the wires and connectors are good then you can be reasonably confident that the problem is with the regulator/rectifier.

    I don't have the specifications for your charge coil but I will look for something that you can use. However, if you want check the coil for being open or shorted to ground, there should be two gray wires coming from under the flywheel that you can probe with an ohmmeter.

    Also probing those same gray wires using your multimeter set to the alternating voltage (AC volts) scale, you should be able to read AC volts, with the engine running, that should increase with engine rpm.

    Good luck.

  8. #8

    Default Re: honda bf8ah alternator output

    Thanks for the information,i'll see what i can find out with the multimeter & let you know what i find out as soon as i can !

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