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  1. #1
    Join Date
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    Default More Yamaha outboard nonsense

    Up to my eyes in bits from my own 4hp, a pal turned up this morning with a Malta (3.5). He wants an outboard to charge a battery. I'm happy to swap the motors, if his cannot be modified and mine can.

    Does anyone know?
    Grow old disgracefully, it's more fun

  2. #2
    VicS is offline Registered User
    Location : Home: Kent. Boat: Chichester
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    Default Re: More Yamaha outboard nonsense

    It depends on whether they have lighting coils fitted, if not then it'll cost an arm and a leg to fit them even if they can be. If they are fitted then all you need is a rectifier but again it'll cost a stupid amount to fit the official part but it is almost certainly possible to do something cheaply with a Maplins part or parts. (Just a bridge rectifier probably)

    The electrical output from many small outboards can be pretty minimal though.

  3. #3
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    Default Re: More Yamaha outboard nonsense

    I don't know about the lighting coils, how would I recognise them? I don't have a workshop manual for either engine.

    And another, is it possible to get fine pitch props for either engine?
    Grow old disgracefully, it's more fun

  4. #4
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    Default Re: More Yamaha outboard nonsense

    If it has a lighting coil there will be a 2-pin output socket somewhere. If so, you will probably need a rectifier to charge a battery as the outputs are usually AC rather than DC.

    As Vic says, the output is pretty meagre and you will need a lot of engine hours to put more than a few amperehours back.

    I set up one on an Evinrude 9.9 many years ago & was very disappointed in the output produced. It just about kept the battery going for a week's summer cruising with no electronic stuff beside the occasional use of an echo sounder, VHF on receive, a small tiller pilot & a fluorescent light.
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  5. #5
    Join Date
    Jun 2002
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    Default Re: More Yamaha outboard nonsense

    Consider using a solar panel also, the plus outboard charge should give u enough
    for electronics, vhf, small chart plotter, depthsounder

  6. #6
    Billjratt's Avatar
    Billjratt is offline Registered User
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    Default Re: More Yamaha outboard nonsense

    Funnily enough, that's why they don't call it a charging coil or alternator. You can wind one on an old transformer core, as I did years ago, but you only get one (electrical)cycle per flywheel rev, lose through the bridge rectifier, and end up with not-a-lot, unless the engine is screaming. Best just to connect a bulb on top of th motor, then folks will see you at night. (Unless there is room under the flywheel for multiple coils in parallel, each rectified, like a proper alternator))
    Left hand down a bit.

  7. #7
    Billjratt's Avatar
    Billjratt is offline Registered User
    Location : Firth of Clyde
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    Default Re: More Yamaha outboard nonsense

    Forgot to add - if you're successful with the charging ploy, you probably won't have much in the way of power left to drive the boat....
    Left hand down a bit.

  8. Default Re: More Yamaha outboard nonsense

    Here's one for the more mathematically/electrically inclined.

    I have a Yamaha 9.9hp 4-stroke electric start as our main engine. I want to be able to continue to charge the starter battery as needed and then via an A/B switch, trickle charge the house batteries.

    The Yamaha ignition system is AC with a rectifier, not an alternator. There is no regulator. The battery leads from then engine outputs 13 amps DC at 13.5 volts, thus producing 175 watts. This being the case, I want to make sure I don't over-cook the house battery bank with 13a when only a 2a float charge is required.

    As silly as it may sound, I'm toying with the idea of simply connecting a 150 watt, 240v inverter to the 13 amp 13.5v engine output to run my 240v shore-power battery trickle charger. In essence, I would be using the 240v inverter as a regulator between the engine and the batteries.

    My shore power charger 240v mains supply specs:
    Charging at:
    2a draws 0.16a off the mains,
    4a draws 0.26a
    8a draws 0.51a
    16a draws 1.04a

    As long as I set it to only a 2a charge, a 150w inverter should be more than enough. Indeed, an 8a charge would only require 122 watts.

    My question is; while motoring, would I be able to do a 2a trickle charge from the 240v mains charger (which requires 38.4 watts) using a 150w 12v inverter which supplies the 240v?

    I'm sure I'm missing something obvious here, or my math is wrong, but if it works, it would enable a more stable charging environment for the house batteries.

    The mains charger automatically adjusts its output to maintain the proper charge and gives a nice digital readout of amps, volts and percentage of charge. Also it would be nice to leave everything connected when we simply want to re-plug into shore power again.

  9. #9
    Join Date
    Sep 2008
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    Default Re: More Yamaha outboard nonsense

    The Yamaha has an alternator - thats the gadget that produces alternating current. If the said alternator is controlled to produce no more than 13.5 volts you wont fry your battery bank - the alternator on a conventional diesel is usually regulated to float at 13.7 volts or thereabouts once the batteries are charged. The battery voltage by that timne has risen to 13.7 otr just below so no current flows.

    If there really is no control on the output of the Yamaha alternator, then the voltage could simply continue to rise above 13.5 and you would have a problem. Check with Yamaha.

    If you have any doubts about what I say above, take your voltmeter and put it across the battery terminals of your car with the engine running and after the battery has become fully charged. Lights etc off. You will see a voltage in the 13s

  10. Default Re: More Yamaha outboard nonsense

    The "alternator" on the Yamaha 9.9 is actually made up of a couple of coils under the flywheel that generate AC into a rectifier assembly when a magnet in the flywheel passes by. A pretty blunt instrument indeed. You would have to get into the motor's guts to find a way to reduce the charge voltage.

    The problem is that I can't merely reduce the maximum output voltage, as that will also cut output at lower RPM's. What happens is that when the batteries are getting near full charge, the voltage starts creeping upwards, and can reach 16 or 17 volts, which is hard on the house battery.

    I have to constantly monitor charging voltage and when it gets above 14.7 volts, I have to turn on the cabin lights, etc. to get the voltage lower. That's really not satisfactory. As I mentioned, my owners manual recommends buying an optional regulator from my Yamaha dealer for just this situation, but no dealer globally seems to be aware of it's existence.

    The cables from the engine to the battery are used for both supplying power to the starter, and then to provide charging to the batteries. I need to limit the charge voltage to 14.7 volts, and whatever rectifier/regulator is built into the motor doesn't do that.

    I tried asking Yamaha, since they vaguely mention the existence of such an animal in the literature that came with the motor. After going in circles between the company, and the numerous dealers they referred me to, nobody has a clue. I have found some regulators designed for solar panels, but they don't take into account supplying heavy (100 amps!) current back to the starter motor.

    Thus is my predicament when it comes to safely charging the house (other than using a separate on-deck generator, or going totally solar).

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