Join Date: Feb 2011
Location: San Francisco Bay area
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Re: m25 alternator question
Yes the internal temp compensation is a factor as well and a poorly suited alt for charging a deeply cycled bank.. Those alts, usually Valeo on Volvo's or Hitachi's on Yanmar's were never meant to charge large banks. As a way to keep them from burning up during the warranty period some genius decided they could drop the voltage as the alt temp increased to reduce the output... Yep, it works but is not at all optimal for a cruisng sailboat but neither are the jokes of charging circuits on many sailboat aux engines.. There are piles of non-temp compensating alts out there that put out 14.2V - 14.6V and of course you can always go with a smart regulator too...
The OP's alt does not have internal temp compensation though and many of them were factory set for 14.2V - 14.4V though some with the ammeter circuit were actually set for 15.0V...
Possibly those alternators are automotive-sourced, and on a car the assumption that the alternator is at a similar temperature to the battery (unless you have the battery in the trunk) is a reasonable one. Probably not so much on a boat....
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