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Old 22-06-2018, 02:57   #1
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Join Date: May 2017
Location: NE Florida
Boat: Cape Dory 28
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Good basic Alternator for MD7A

Hello, I'm looking for some ideas and thoughts on replacing my alternator.

I'd prefer to keep it simple, without excess external controls, but I'd like to do better than the standard 35 amp stock model. Something in the 50-65 range perhaps ? It does need to have a send for my tachometer.

Something that is not in the $500+ range too please.

Appreciate the help ! Thanks !
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Old 22-06-2018, 03:26   #2
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Location: Grand Manan,N.B.,Canada N44.40 W66.50
Boat: Mascot 28 pilothouse motorsailer 28ft
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Re: Good basic Alternator for MD7A

I bought (2) rebuilt original style 60A for< $120 ea.
I keep one aboard well wrapped in plastic as a spare.

My personal experience & humble opinions-feel free to ignore both
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Old 22-06-2018, 13:01   #3

Join Date: Apr 2006
Posts: 15,129
Re: Good basic Alternator for MD7A

I would suggest a process requiring some paper and pencil. First off, what are your engine rpms? At idle, at typical cruising speed, and at "battle speed"?

Ideally you want an alternator that fits your engine spaces (sometimes there's not much room) AND:
Puts out some charging power at idle
Puts out good charging power, full rating, at cruising speed
Won't burn out from the rpm at maximum engine speeds
And that's all based on the ratio of the alternator pulley to the engine pulley, which will determine how many shaft rpm the alternator is turning at. Sometimes the stock alternator pulleys just don't work out right, and you need to drop a fast hundred bucks at a machine shop to get one that is right for you. That can literally cut your charging time in half.
Some alternators can be rated as nearly zero output until 2000rpm, and burning out if they run over 10,000 rpm, giving you a 1:5 rpm range if you accept "zero" output at idle. Others may put out rated power at 2000 rpm (allowing you to match up the pulley and get full power at idle) and tolerate 17,000 rpm all day long. So, you've got full charging power at pretty much any engine speed.
It can be a nuisance to run the numbers back and forth and try to find an alternator that really fits (physically too) but *well* worth the effort, considering the payback.
The Delco CS130D Type 100 is one good example of a robust and reasonably priced alternator.
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