Alternator cut off switch
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Alternator cut off switch

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    Retired Air Force Master Sergeant's Avatar
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    Default Alternator cut off switch

    Are there any worthy gains to be had by fitting a cut out switch to the alternator, de-energizing it to remove the load during a race?

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    Spiral out MikeF's Avatar
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    Quote Originally Posted by Master Sergeant View Post
    Are there any worthy gains to be had by fitting a cut out switch to the alternator, de-energizing it to remove the load during a race?
    Not really.......The mechanical act of turning the pulley/armature is still there....which is where most of the load comes from.

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    Senior Member wagspe208's Avatar
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    NOT if you have an MSD or similar system. You will give up HP by losing voltage.
    Wags

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    Senior Member SoldHondaBoughtHondo's Avatar
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    So making amps is free? I guess you have never hooked jumper cables to a dead battery from a running engine and heard it drag rpm down? Used to be rule of thumb was alt. took about 5hp to run
    depending on how much work you re asking it to do. V-belt uses more hp than serp. belt. Starting a race with a fully charged battery
    helps. Running an ignition on anything less than full charge voltage might cause a problem. The only performance gain would only be at wot.
    The first problem you will run into is how to turn an alternator off at wot. Going to need some kind of throttle switch to control a relay that will cover the max output of the alt. I'm going to take a wild guess and say any performance gains would be somewhere in the minuscule category.
    I'm thinking best results would be found with using a serp. belt, smaller crank/larger alt. pulley OR an alt with output rating just high enough to cover system load.......although i think your time might be better spent making sure your tune is spot on.....or maybe going on a diet. lol

    Or just buy a 16 volt battery and special charger, ditch that evil power sucking alternator and pulleys and belt.....just make sure you remember to charge it between races
    Last edited by SoldHondaBoughtHondo; 08-05-2012 at 08:24 AM.
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    steelcomp was here
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    Quote Originally Posted by SoldHondaBoughtHondo View Post
    So making amps is free? I guess you have never hooked jumper cables to a dead battery from a running engine and heard it drag rpm down? Used to be rule of thumb was alt. took about 5hp to run
    depending on how much work you re asking it to do. V-belt uses more hp than serp. belt. Starting a race with a fully charged battery
    helps. Running an ignition on anything less than full charge voltage might cause a problem. The only performance gain would only be at wot.
    The first problem you will run into is how to turn an alternator off at wot. Going to need some kind of throttle switch to control a relay that will cover the max output of the alt. I'm going to take a wild guess and say any performance gains would be somewhere in the minuscule category.
    I'm thinking best results would be found with using a serp. belt, smaller crank/larger alt. pulley OR an alt with output rating just high enough to cover system load.......although i think your time might be better spent making sure your tune is spot on.....or maybe going on a diet. lol

    Or just buy a 16 volt battery and special charger, ditch that evil power sucking alternator and pulleys and belt.....just make sure you remember to charge it between races
    I'm pretty sure all you have to do is kill the 12v supply to the alt., not worry about it's max output. Simple toggle switch could do that before a pass, or micro switch on the carb, or rpm window switch in the igntion if you have one. Really no load on the voltage going into the alternator.
    Everything else, I agree with.
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    Resident Ford Nut Sleeper CP's Avatar
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    Quote Originally Posted by MikeF View Post
    Not really.......The mechanical act of turning the pulley/armature is still there....which is where most of the load comes from.
    Oh I don't think so. Have you ever had an alternator spun up and tested? when they aren't charging they just spin freely when you stop spinning them. When they are charging and you stop spinning them they can damn near lock up and stop spinning.


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    I've been running one for years. I haven't seen a performance disadvantage yet. Mine is a standard GM 100 amp that is spun 1:1 with the engine. Have never had a dead bateery. Total MSD igntion.

    Tim

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    Senior Member wagspe208's Avatar
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    Right... same old dead horse... let's keep beating it.
    "start a race with a fully charged battery" Define that. How many volts? How many years old is the "fully charged battery?" How many rounds have you run that day on said "fully charged battery?" Do you have an electric fuel pump? Any other loads other than ignition?
    Sure, put in a 16v battery.
    Fuck it. Keep beating.
    If you are running a PE boat, you should just charge the battery before you leave the house.. or 6 second cove class. All will be fine.
    Wags

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    Quote Originally Posted by wagspe208 View Post
    Right... same old dead horse... let's keep beating it.
    "start a race with a fully charged battery" Define that. How many volts? How many years old is the "fully charged battery?" How many rounds have you run that day on said "fully charged battery?" Do you have an electric fuel pump? Any other loads other than ignition?
    Sure, put in a 16v battery.
    Fuck it. Keep beating.
    If you are running a PE boat, you should just charge the battery before you leave the house.. or 6 second cove class. All will be fine.
    Wags
    Dang, Wags...not racing this weekend? Little grumpy?
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    Member gijoel's Avatar
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    Seems like it might be worth trying. Keep the switch on up until you run a pass so the battery is fully charged. Then you could test your results with and without.

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    When I took my alternator in to have it disassembled, I ask the Alternator guy about how much power an alternator uses. This is what he told me. He said his alternator tester uses a three horsepower electric motor to drive the alternators and that it will handle all sizes of alternators except the very largest used on some new cars. I think that is somewhere around 150 - 200 amps.

    In his opinion, using the alternator is a plus factor because your ignition is based on the voltage supplied to it and multiplied. The alternator puts out 14 volts as compared to the 11.5 to 12.5 volts from a battery and when the ignition takes its power along with an electric fuel pump and gauges, there is a large difference in the voltage to the spark plugs.

    Keep in mind the 3 horsepower electric motor tester is more than enough to handle most alternators we normally run. When the alternator has charged the battery, it essentially shuts down on its own and uses virtually-0- power.
    I plan to keep my alternator.

  14. #12
    Senior Member SoldHondaBoughtHondo's Avatar
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    Quote Originally Posted by steelcomp View Post
    I'm pretty sure all you have to do is kill the 12v supply to the alt., not worry about it's max output. Simple toggle switch could do that before a pass, or micro switch on the carb, or rpm window switch in the igntion if you have one. Really no load on the voltage going into the alternator.
    Everything else, I agree with.
    Brown trigger wire on a gm alt? Going to have a hard time turning mine off....i don't have that wire
    Trigger wire just kicks alt on




    Quote Originally Posted by River Rat 005 View Post
    I've been running one for years. I haven't seen a performance disadvantage yet. Mine is a standard GM 100 amp that is spun 1:1 with the engine. Have never had a dead bateery. Total MSD igntion.
    Tim
    Might have had an almost dead and never knew it. Ye old 100 amp alt. turns into discharge without sufficient rpm to do any work.


    Humpty grumpty.
    "Fully charged' in my little world anyway, would indicate a battery that has been charged to the point where it no longer accept an appreciable amount of current. All the work that the alternator does and the power it consumes is limited to whatever load the rest of the electrical system puts on it.

    100 amp alt will consume the same hp as a 50 amp if the battery is fully charged and the rest of the system only uses 20 amps.
    A 100 amp alternator achieves that rating at something like 3000 engine rpm overdriven 300%.....Same alt driven @ 1:1 might take 9000 rpm to make that rating.
    Bigger alt pulley and 100 amp alt. might be good for a few hp as long as the battery is full....run that puppy 1:1...make a couple passes through the channel with the tunes bumping hard...back out on the lake for a hard run and now the alt gets to replace all the current that was used when the system was using more than alt output.....and it's probably using more hp to do it....

    Any which way it is set up i can't see it involving more than 10 hp....whatever hp a 100 amp might use to charge a dead battery and maintain system voltage....i can't see it using more than 10.....race application, fully charged battery...might be worth 2 hp....20% of that might be v-belt drag..i bet serp. belt is half that.

    And yep, i run over sized alt pulley on my deal and i need to make best use of every hp i make...cause it's not that many
    But the only reason that pulley is on there is because it's the easiest way to keep the belt on past 6500.....Actually..now that i think of it..i might have already tested the alt/no alt theory...been doing some testing.....best rpm so far was 6750....and the belt was still on after that run....been running 6600- 6700..except for with them muffs that rex sells...thing wouldn't even spin 6k

    Cheater way is to just run the belt loose...belt that is tight enough will be when you can't turn alt. pulley by hand....Alt output is limited and so is the power it can suck....or spend the 250 and buy a 16 volt...it will keep system voltage up till it's almost dead...long past cranking motor over.

    Years ago i built a 750 honda chopper.....10 'C' sized ni-cads stuffed in frame tube for the battery...kick start...ran discharge below 1100 rpm 1300 with headlight on..points ignition, nothing else electrical...brake light on rear brake only...never had a problem as long as i avoided cruising state street...save 8lbs...confused a lot of people
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    Distinguished Member David 519's Avatar
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    Quote Originally Posted by Master Sergeant View Post
    Are there any worthy gains to be had by fitting a cut out switch to the alternator, de-energizing it to remove the load during a race?
    Tim, you'll get as many opinions as there are people that post. Yes, the alternator "drag" uses HP, but not enough that you'd measure it even on a track (at least in a boat). However, if you're running a MSD and a bunch of other electrical stuff, you'll defintely lose HP if your system voltage drops low enough. IMHO, an alternator is a "must have" with a MSD style igniton.
    On the flip side, if you run a mag (the prefered ignition of REAL racing engines ), mechanical fuel pump & gauges, there's no reason to even have an alternator in the boat...
    Quote Originally Posted by gn7 View Post
    ....... David 519 is 100% correct........

    Quote Originally Posted by fuelinmyveins82 View Post
    .....I think people forget that racing is supposed to fun. Losing shouldn't be discouraging it should motivate you work on your pile to make it faster.....

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    Spiral out MikeF's Avatar
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    Quote Originally Posted by Sleeper CP View Post
    Oh I don't think so. Have you ever had an alternator spun up and tested? when they aren't charging they just spin freely when you stop spinning them. When they are charging and you stop spinning them they can damn near lock up and stop spinning.


    S CP
    Sooooo, Are you providing voltage/amps to a coil on a race boat........MS's boat.

    Or are you providing voltage/amps to your blender, a/c unit, navigation/depth finder screen, gps unit, radar boom, cooling fan, TV, refrigerator and raw water pump on your race boat.

    Lets talk LOADS here.

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