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Wanting to add a battery charging circuit to manual "pull start" F25LMHC

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  • Wanting to add a battery charging circuit to manual "pull start" F25LMHC

    Hello, I have a wood boat I just finished up and installed a new 2020 F25 manual "pull" start engine. I would like to add a battery and some electronics like a fish finder and nav lights. The owners manual says it has a 16amp alternator. I've located the rectifier/regulator but am unsure where to wire the battery leads and fuse block. It seems this should be straight forward but I can't find any info on the matter. Is there an installation kit required? There doesn't appear anywhere connect 12ga wiring.

  • #2
    Parts catalog shows you what is needed. https://www.boats.net/catalog/yamaha...tional-parts-2

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    • #3
      Great thanks for the quick reply! This appears to be what I need. I have located the rectifier and the harness that connects to it so hopefully all I need is half of what is in the manual. Is there a location I can download a pdf of the entire parts catalog?

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      • #4
        Boats.net I would think

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        • #5
          So I've looked under the cowl and found the rectifier/regulator and where the ground connects. I cannot find what the hot wire connects to. I have found a solid green wire that is capped and a wire that is green with an orange stripe. There is also a red wire that looks dead ended too. I haven't found anything else obvious that the harness connect too. Thanks.

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          • #6
            Need a photo of your rectifier/regulator. Mostly the bottom part.

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            • #7
              That reg/rect supplied on the manual/pull start engine from factory only runs the fuel injection system, you will need to buy/install a new rect from Yamaha, it is a different part number but looks the same visually, you will need to look up the part number for the reg/rect on the same year model F25 but it has to be a factory electric start model, that reg/rect is the one you need to run battery charging on the manual/pull start version.

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              • #8
                Thanks for the replies. I was hoping the reg/rect was the same. I see the difference in the part number now that I looked again, I missed the -XX difference. So I also checked out the electric starter kit. It also come with the reg/rect I need. Is it safe to assume the electric start kit will also charge a battery? If that’s the case that would give me the most bang for the buck.

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                • #9
                  I am trying to do the same. I have a 2019 Yamaha F25 SMHC, which is the manual start. I would like to be able to charge my battery from the engine.
                  I do not want to add the electric start kit though. What parts would I need to order?

                  Would it just be?
                  6FM-81960-10-00 (Rectifier and Regulator ASSY)


                  Also has anyone tried this and how well does it charge the battery?
                  I have a 35AH battery, and my electronics draws about max 3 amps, and I plan to be on the water a max of 8 hours.


                  Thanks!

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                  • #10
                    What RPM do you plan on running the motor over that 8 hrs?

                    small motors do not put out many amps when running at idle.

                    but 8 X 3 = 24 so your battery should handle 3 amps for 8 hours since it is a 35AH

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                    • #11
                      I will be running between 5-8mph, which should be around 2500-3500 RPM. I did not want to draw my battery down too far.

                      Yamaha advertises the alternator putting out 16 A at wide open throttle, but I was not sure what the output would look like at 3000 RPM. I was thinking it would be around 10 amps, but not sure how much of that goes back to the engine.

                      I appreciate the help!

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                      • #12
                        Seems to me it would be the parts that Yamaha says that are needed. Just what the parts catalog sez.

                        4 amps at 1000 RPM. 16 amps at more or less mid RPM.

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                        • #13
                          Thank you. I looked a little harder in the service manual and saw the rectifier/regulator is different, and has an extra working port on the bottom.
                          4amps at 1000 RPM will work great. I will post how much current makes it to the battery once I get it installed.

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                          • #14
                            that 4 stroke puts out more amps than I thought it would

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                            • #15
                              Originally posted by 99yam40 View Post
                              that 4 stroke puts out more amps than I thought it would
                              Surprised me too. I guess Yam recognizes the need for more electrical power and has upped the gaame.

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