Anyone know anything about alternator? - SailNet Community
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post #1 of 15 Old 10-26-2008 Thread Starter
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Anyone know anything about alternator?

I'm trying to figure out how long it will take my 50amp alternator to recharge by batteries.

I've got 220 amp house battery, say it's down to 50%, how long do I need to run the engine to fully recharge?

Are there formulas for this sort of thing???

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post #2 of 15 Old 10-26-2008
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Do you have an externally regulated three stage charger, or the stock internal regulator? That factor alone will make all the difference in the world.

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post #3 of 15 Old 10-26-2008 Thread Starter
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Just the stock internal regulator.

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post #4 of 15 Old 10-26-2008
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Figure that the battery bank will accept pretty much maximum amperage until it hits the 85% charge level...so from 110 amp-hours to 190 amp-hours or 1.6 hours... as the charge level increases from that point... the charge acceptance rate will drop... so it may take another eight-to-ten hours or so to get up to 100% as a rough guess...so you're looking at about 10-12 hours over all.

However, since you only have the internal regulator, you'll probably start frying the batteries after hour three or four, since it won't drop the voltage and amperage the way an intelligent three-stage charger would.

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post #5 of 15 Old 10-26-2008
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How do you know its down? What are you using?
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If you have a voltmeter, you can roughly estimate this... a fully charged 12 VDC system is about 12.6-12.7 volts... at 50% it'll be about 12.1-12.2 VDC... at 0% it'll be 11.6 VDC or so.
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How do you know its down? What are you using?

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post #7 of 15 Old 10-26-2008 Thread Starter
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Figure that the battery bank will accept pretty much maximum amperage until it hits the 85% charge level...so from 110 amp-hours to 190 amp-hours or 1.6 hours... as the charge level increases from that point... the charge acceptance rate will drop... so it may take another eight-to-ten hours or so to get up to 100% as a rough guess...so you're looking at about 10-12 hours over all.

However, since you only have the internal regulator, you'll probably start frying the batteries after hour three or four, since it won't drop the voltage and amperage the way an intelligent three-stage charger would.
So,

Does a 50amp alternator put out 50 amps/hour? Is that how they are measured? 10-12 hours! Wow, one night of fun and then there's hell to pay.

Is an internal regulator that bad that it would severely overcharge a battery?

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post #8 of 15 Old 10-26-2008 Thread Starter
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I don't know it's down. I'm just setting up, and installed 2 6v batteries in series as the house bank. I'm just thinking of how this will play out. I hate motoring. Yet I don't have any other means of recharging.

I also set up the BlueSea ACR thanks to the tips from you guys. I don't yet have any way to easily tell the state of my batteries, other than the volt-meter test.

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post #9 of 15 Old 10-26-2008
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Of course, the actual output of the alternator really depends on the engine RPMs... if the engine is going too slowly, it won't put out the rated amperage.

Ideally, you'd have a three-stage external regulator on the alternator, and some alternate form of charging—either solar or wind. If you keep the boat in a slip, you'd probably want to have a shore power setup and a good three-stage AC-powered battery charger.

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Last edited by sailingdog; 10-26-2008 at 07:56 PM.
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post #10 of 15 Old 10-26-2008
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Best way is just to run engine and monitor results

Best way is just to run engine and monitor results.
I had 5 (12 volt , 525 total amps or so) batteries aboard.
Only had a 35 amp alternator. It worked fine to recharge.
Run for an hour and check results.
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