Quick Alternator Question

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lazza
lazza Solar Expert Posts: 336 ✭✭✭
in Off Grid Solar & Battery Systems #1
Imagine the following scenario:

A 50A alternator of a motorboat connected to a pair of 12V batteries, connected in turn to an inverter and subsequently 230V equipment.

My question is: If, say, the consumption is 1kW in total at a given time (with the motor running), will the alternator:
  1. try to provide ALL of the power to the inverter..
  2. or will the system take some from the alternator and some from the battery?

If the 1st answer is correct, we could have a big problem of overloading the alternator if i'm not mistaken?

Thanks
Larry
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #2
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    Re: Quick Alternator Question

    The answer is # 2 with a couple caveats. It's doubtful that the alternator put's out 50 amps at all rpm's, so to know what your replacing can be difficult. Depending on how the Ignition is wired your still feeding enough power to keep the motor running. If those are the same batteries you start the motor with you don't run them down.

    For instance, if you have electronic controls most will not work below 10.5 v. If you dropped a big draw on the batteries you might not have throttle control or shifting ability, again, depends on how it's wired.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
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    Re: Quick Alternator Question

    Blackcherry is correct re the alternator not putting out full power at all RPM's. It must indeed be reved up to get full output.
    Also, assuming the alternator will indeed output 50 amps @ 12 volts, 50X12 = 600 watts. Your load is 1000 watts. Thus assuming you have the revs up, all the alternator output will be going to the load, + another 400 watts will be draining from your battery. The alternator will get hot, but as long as the revs are up, it's cooling fan should prevent damage. The above calculations by the way, ignore the extra power losses that will be happening with the inverter etc, for simplicity of explanation. In reality the 1000 watts could end up being perhaps a 1200 watt load on the system, resulting in 600 watts load on the battery, not the 400 watts first mentioned.
    Unfortunately we can't get something for nothing when it comes to electricity :cry:
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  • 65DegN
    65DegN Solar Expert Posts: 109 ✭✭
    #4
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    Re: Quick Alternator Question

    Seems to me that the power will be drawn from the source with the highest voltage. If your generator was capable of several KW I suspect that practically all the power would be drawn from the generator. If the generator is smaller I suspect it will supply the load until it's output voltage drops, from loading, to equal the battery voltatge. At that point they would load share.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
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    Re: Quick Alternator Question
    65DegN wrote: »
    Seems to me that the power will be drawn from the source with the highest voltage. If your generator was capable of several KW I suspect that practically all the power would be drawn from the generator. If the generator is smaller I suspect it will supply the load until it's output voltage drops, from loading, to equal the battery voltage. At that point they would load share.

    Exactly! But now I have to add extra words so the form will accept my intended single word comment: Exactly!
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