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Old 03-29-2008, 06:23 AM   #5
2bucks
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Join Date: Oct 2007
Posts: 698
RE: 125 amp alternator

Having been down that road myself I have to agree that the single belt will not be satisfactory. It will run fine when you put it on and load it for a minute. It will seem to be just perfect until that morning when you get up and pull the anchor after 2 days on the hook. The batteries will be down and the alternator will try to charge them back up.

Even though you would be happy with 100 amps the alternator will try to put out 125 or whatever it's max amps is. The belt will squeal for a while while it overheats and eventually breaks. If you have a spare you will now be bobbing out in the middle somewhere replacing the belt so the water pump will turn again and not overheat the engine. If you don't have a spare then you'll get to meet the tow boat fellow.

Now the other thought might be to tighten up the belt so tight it can't slip. This puts so much pressure on the water pump bearings and the alternator bearings that they wear out prematurely. Maybe you're lucky enough to have a system where only the alternator is running on the belt and you'll only damage the bearings in it and could still drive home without a charging system. But you'll still be spending time replacing belts and not have a reliable system.

Ideally you want an alternator that gives you the rated output safely and without added maintenance. About 70 amps is the maximum for a single belt. The car manufacturers don't double belt high amperage alternators because they look "cool". They do it for reliability. I think most boaters agree that a breakdown on the water, even if you can fix it yourself, is not part of the cruising experience you look forward to.

Just my thoughts,
Ken Buck
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