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Old 06-19-2012, 03:00 PM   #11
bshanafelt
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City: Port Orchard, WA
Vessel Name: Isobel K
Vessel Model: 37' Custom Pilothouse
Join Date: Oct 2007
Posts: 426
There is no question that bigger is better when talking alternators and DC charging systems. The heat issue ends up being the biggest enemy of the solid state parts as well as bearings etc on the alternator.

Using a large frame unit, then de-rating it via a smart regulator will ensure a long life for your system. Always use temp sensors on both the alternator and battery bank.

My boat came with a stock 60A small frame and when I asked it to try and charge a house bank around 500Amps, it simply could not do the job.

I then upgraded to a small frame on steroids 120A unit coupled with a smart regulator, which did an adequate job, but got REALLY hot.

Since my motor has a serpentine belt, it was a fairly simple matter to fit a large frame 200A unit, which charges my now very large 1350AH bank quite nicely. I have de-rated the alternator to 160A so it never runs at the max design in any circumstance.


If you have room and pulley/belt ability, just get a truck alternator - Ebay has lots of choices Leece/Nev 160-200A units are around $200.


It is always easier on the entire system to use less charging than you have available.
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