Alternator Amperage I/O

Discussion in 'Boating Discussion' started by willit float, Feb 12, 2019.

  1. willit float

    willit float Member

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    Well I've replaced nearly all of the other mechanical components on my engine just to be sure everything is new and nice. Now I'm looking at the alternator, it works fine now, does not make any noise and charges everything showing good positive amperage on the dash gauge. All this aside the alternator is part # 1100576 rated at 42 AMPS.

    The engine has a 40 amp circuit breaker, other things being ran are bait pump-centrifugal 10 amp, bilge pump 8 amp, bilge blower 6amp, misc standard newer model radio, gps-fish finder, lights and auto helm system that is all electric.

    This boat was equipped and has been running on the 42 amp alternator for years. I have taken out some of the older electronics and replaced with newer less draw equipment thus reducing the running loads. For lighting I intend to eventually switch over to LED as on the bait tank light.

    QUESTION: looking on line I'm seeing replacement alternators as high as 200 amp for this marinized application.
    I was planning on either rebuilding my current alternator or going max of 63 AMP replacement. I've heard that going with larger amperage alternators than really needed could cause other issues and I'm not wanting to go full pooch on this rig.

    Ideas ?

    Thanks
     
    Last edited: Feb 12, 2019
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  2. MYNomad

    MYNomad Heading South

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    An important part of the equation is your battery configuration. Think of the battery as a reservoir -- and you probably/should have two reservoirs (each composed of one or more batteries). One of the reservoirs usually called the starting bank, is reserved for starting the engines and the other, called the house bank, is for running everything else.

    Particularly for starting, the current flow will be way higher than your alternator can provide (especially since the engine isn't running at that time, it is cranking at only a few hundred rpm, not nearly enough to produce any significant current), so all of that electricity comes out of the starter bank. Similarly, even when the engine is running and the alternator is producing its max output, it may be that the house demands temporarily exceed the current produced. This could be the case, for example, when your bilge pumps go on, if the current they consume, added to the current everything else is consuming, exceeds what the alternator can put out. In either case, your reservoir starts to empty (just as real life reservoirs empty during the summer). So long as it doesn't get too low (lead acid batteries get damaged by going below 50%), the fact that the battery is being depleted isn't a problem. The key in sizing your alternator is to make sure that it is big enough to provide, over time, the average demand placed upon the batteries.

    In thinking about your alternator's capacity, it is also important to realize that it produces max amps only at "high" rpm. At idle speeds, it will be considerably lower. So, in considering whether your alternator produces enough electricity to cover average electrical demands, it is important to consider how you use the boat. If you idle a lot (or worse, stop the engines a lot), you will need a larger amperage than if you run the engines at high rpm most of the time.

    The best way to know this is to install a fancy state of charge / battery monitoring system. This will tell you everything you want to know about how low your batteries get, how fast they are charging, how long they will last under current circumstances, etc. Armed with that information, you can either adjust your electrical consumption, or add a larger alternator (etc.).

    But, to keep it simple, if your batteries tend to be fully charged after a day of boating, you can infer that your alternator is sufficient, at least for the use pattern that day.

    One last thought -- the only problem I am aware of that could result from a larger alternator is that it will burn fan belts faster. If your water pump is on the same belt, that is not a good thing, but routine inspection / maintenance (and listening for belt squeals) should protect you against that.
     
  3. jasper hickman

    jasper hickman Well-Known "Member"

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    Also the larger output alternator will require more power to turn, you’ll loose HP with a 200amp alternator.

    I would think if you have been running a 43amp unit for years without issues a new 63 amp unit would be about perfect.
     
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  4. MATTANZA

    MATTANZA old man of the sea, in training.

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    if it works , don't "fix" it. 200 amps is almost 5 times what you have now 63amps would be almost 50% upgrade. my outboard puts out 65amps, and I have all kinds of lights, pumps, stereo/amp etc. I have 3 batteries, 2 house , and 1 start. it's all works fine.
     
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  5. willit float

    willit float Member

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    Thanks for the good info. I am going to take it off inspect the screens and possibly tear it down to check it out. I like the idea of less drag on the HP to will wither stick with this one rebuilt or get the 63 amp. At the present time the batteries seem to be holding up fine.
    Should I run with both batteries or "all" on my selector switch or alternate between the batteries for recharging purposes ?
     
  6. MYNomad

    MYNomad Heading South

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    IMO, that should not be a significant consideration since 200 amps at 13.8 volts is less than 4 horse power (746 watts = 1 hp), so even with inefficiency of the alternator, it will consume only 6 horsepower, and that is MAX, meaning max rated rpm and max battery demand -- if your batteries do not NEED the excess amperage the alternator won't produce it and the horsepower loss will be correspondingly less.
     
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  7. jasper hickman

    jasper hickman Well-Known "Member"

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    One would also need to consider the amount of physical room available on the engine. The 200amp alternater will have a bigger frame as well.
     
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  8. willit float

    willit float Member

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    I decided to tear down the original US made Delco and rebuild it. The inside had some surface rust on the rotor blades and the screens had paint build up on them. I gave a clean and acid bath to take the screens back to clean bare metal. Not wanting to paint them again I opted to parkerize the screens instead and they turned out great. Have not positively identified as the 10 or 12SI nor amperage yet. The case is stamped 42 amp but it may have been upgraded prior to higher. I might pick up a kit but so far everything inside might be in good shape tho I’m not sure about reusing the condenser.
     
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  9. willit float

    willit float Member

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    Yep, there is no room. I even got a .5” shorter belt to move it away from the side of the engine compartment. When I rebuild the dog house I plan to sleek it down for tighter fit.
     
  10. willit float

    willit float Member

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    I found some info online that said the lower amperage 10SI would produce as much or more charge amps at an idle and low rpms as the higher rated alternator in the same single wire series. Not sure if factual but I’ve read reviews also about the cheap new import alternators so I’m holding on to this one.
     
  11. SD2600

    SD2600 Member

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    Any pics before and after if your teardown?
     
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  12. MYNomad

    MYNomad Heading South

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    That could well be, but I am skeptical (if you have a link, I would be very curious to check it out). The way an alternator works, you need a magnet spinning in a coil. To increase the current produced, either the coil has to get bigger, or it has to spin faster, and that relationship is pretty linear. Through gearing, it is possible to spin the coil as fast at idle speeds as at much higher rpm, but then it is spinning REALLY fast at high RPM -- and producing a lot more current, perhaps 5 times as much; So who is going to produce an alternator that produces 200 amps (or whatever) at idle, and 1,000 amps at max rpm, but market it as a 200 amp alternator? Heat dissipation becomes an issue, but the point remains: it is a mechanical necessity that the alternator will have the capacity to produce proportionately more current at higher rpms. One "solution" could be a variable speed transmission, but I can't imagine anyone putting that on a car/boat alternator (unless it's being built for the federal government on a cost plus basis). Beyond that, someone would need radically new technology. Like cold fusion (remember that?).
     
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  13. willit float

    willit float Member

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    I did a quick check for the link showing the potential for the 10/12SI lower amperage alternators to produce as much or more than the larger high amperage same series alternators at an idle or low speed-rpm and did not find the exact link but did find some info that supports not over installing.
    My findings are that as long as the battery bank and electronic demand is met to keep the batteries- alternator cycling to peak that the lower amperage alternator will be better for my need. Smaller pully, turns the rotor faster, less drain on HP draw, less belt wear. The rating on alternators in one sample that I read online show they are capable of producing their max rating at 6000 alt rpm. In my case I will probably not be cruising around at anything over 3000 rpm so that is a non issue as I would not be utilizing the full potential of the larger amp alternators but would still be paying for the idea of more amperage in belts, fuel and etc.

    https://www.windcheckmagazine.com/article/keeping_up_a_charge_the_basics_of_your_boat_s_alternator/
     
    Last edited: Feb 16, 2019
  14. willit float

    willit float Member

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    Yes, it was butt ugly on the outside. The rotor blade tips had some rust on them which could not have been a good thing. Everything else seemed to check out OK. I did clean and remove the paint clogging the spark screens that was likely put on in the last rebuild or something. The screens were prepped and hot dipped in a Parkerize solution to get the black coating that should help with rust prevention. I'll be watching it close to monitor the effectiveness of it.

    IMG_7509.JPG IMG_7510.JPG IMG_7511.JPG IMG_7512.JPG IMG_7513.JPG
     
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  15. SD2600

    SD2600 Member

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    Looks great...
     
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  16. mischief1

    mischief1 Member

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    Check out this Company they have some great electrical products and best of all cool Tech Tips.

    arcomarine.com/
     
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  17. willit float

    willit float Member

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    So after all that BS, I got the alternator tested prior to installing and the internal regulator is dodgy. So instead of throwing any money at it decided to go with a new 105 amp and even found a genuine Delco as the imports had me on the fence.
    This explains why sometimes the battery was not full charged some of the electronics would drop out..well at least potentially. HA.!
     
  18. MYNomad

    MYNomad Heading South

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    If you have a gas boat, make sure your new alternator is the marine (spark proof) version.
     
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  19. willit float

    willit float Member

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    Yes, for sure it’s a direct marine replacement.
     
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  20. willit float

    willit float Member

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    The old 42 amp just needed either the voltage regulator re energized or replaced but being 42 amps I figured to go ahead and upgrade even tho the new one will use more hp and fuel to run it. Probably have to improve other things in the loop.
     

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