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Alternator - Turning it On & Off ?

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  • Gin Kii
    replied
    Originally posted by Aaron View Post

    I’m genuinely curious to know if you’d even see the difference on the dyno.
    I seriously doubt an on water difference will be reailsed, love the chasing the last HP though but doubt it will come with a dumb alternator.

    Modern day smart alternators can turn on an off ... just sayin.
    Last edited by Gin Kii; 04-07-20, 06:26 PM.

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  • Aaron
    replied
    I’ll stand by the cutting out the pies being a a real performance gain versus fucking with the alternator coming on or off.

    If you can dyno it just run it up without the alternator being driven. Log the current draw from the battery of running the motor and boat systems.
    The alternator will be about 70% efficient and the belt drive about 90% efficient.

    That means for every Watt of electrical load you’re “robbing” around 1.6W of power from the crankshaft - that’s using very “average” and generic efficiency figures.

    I’m genuinely curious to know if you’d even see the difference on the dyno.

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  • MWP
    replied
    Originally posted by Do the safety dance. View Post
    Is the ignition and fuel system gonna handle the drop in voltage?
    Yup, no worries there.
    He's also built himself a water-brake dyno, so we can tune for all that easily.

    Originally posted by Aaron View Post
    Surely unless the thing is piloted by a jockey already having the driver lay off the pies for a bit would be more effective than chasing 1hp of electrical load?

    Yes, quite possibly.

    Originally posted by Roy928tt View Post
    Sound observation ^^ I used to see it in Dirt Circuit, silly people spending stupid amounts on HP when they would have been better off reducing the weight of their vehicle.
    It's all CF and alloy.
    Apparently it'll be pretty much the lightest boat in the class.
    Last edited by MWP; 04-07-20, 02:58 PM.

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  • Roy928tt
    replied
    Sound observation ^^ I used to see it in Dirt Circuit, silly people spending stupid amounts on HP when they would have been better off reducing the weight of their vehicle.

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  • Aaron
    replied
    Surely unless the thing is piloted by a jockey already having the driver lay off the pies for a bit would be more effective than chasing 1hp of electrical load?

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  • aerobrick
    replied
    ^ good point - make sure the tuning is done at ~12.6v battery voltage and not 14.2v alternator voltage.

    Sounds like something that will introduce a lot of gotchas.

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  • Do the safety dance.
    replied
    Is the ignition and fuel system gonna handle the drop in voltage?

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  • Gin Kii
    replied
    Originally posted by 36 View Post
    It's doable - plenty of cars do it these days - BiTurbo Rangers for instance. You probably don't want an alternator that big but might be able to work out what the widget is that makes it work.
    Sounds like a dumb alternator has already been purchased and buying a smart one is not on the cards.

    Will a dumb one cope with being switched on and off ?

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  • 36
    replied
    It's doable - plenty of cars do it these days - BiTurbo Rangers for instance. You probably don't want an alternator that big but might be able to work out what the widget is that makes it work.

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  • MWP
    replied
    It's hydroplane racing. These things: https://www.youtube.com/watch?v=JWL-rmWNdy0
    So on the throttle 80% of the time I guess?

    Turning the Alt off wont be a problem. I'll have spare ECU outputs that can deal with that.

    My main concern is if turning it on & will cause voltage spikes, prematurely kill the alt, etc.

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  • 36
    replied
    Basic solution is to put a push button switch on the steering wheel to disconnect the alternator- relies on the driver being sensible with it. Will of course trigger the ignition light, so if it chucks a fan belt at the same time you don't get warning that the water pump has stopped..

    All depends on the inputs - if the races are short enough, take your 2-3kg of alternator and put in a bigger battery and change/charge battery between runs.

    How much time does a boat spend at full throttle? Is there "traction" style issues, during which its a good time to use excess power to charge the battery?

    Personally, I prefer to have a charging system. Saves a lot of headaches.

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  • Roy928tt
    replied
    No, always use a charging system. Otherwise at the end of the day the battery is going doughy the thing is reluctant to start and there isn't enough juice for the ignition system and fuel pump it breaks down at revs and you might as well throw the day away.

    I suppose a micro switch to turn the alternator off at full throttle will do it.

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  • BigJonWB
    replied
    Maybe a better result would be a higher capacity lithium battery and no on board charging.

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  • MWP
    replied
    It's just a standard IG/L/S Toyota (Denso i guess) alternator.
    He's already bought a new alternator, and milled up a nice ally bracket for it. I doubt he'll want to change type now.

    There is a very short cable distance from alt to battery, so i was going to wire sense straight to the alt's batt lug.

    Originally posted by BigJonWB View Post
    How long are the races? Does it even need to charge the battery?
    I'm not sure actually, but it's running quite a small battery.
    Last edited by MWP; 03-07-20, 05:01 PM.

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  • Gin Kii
    replied
    Similar to how an ECU switches a smart alternator on and off ?

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