Join Date: Jan 2003
Location: Maine Coast
Thanked 205 Times in 154 Posts
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Re: m25 alternator question
While they are 50% discharged or so, measure the voltage output of your alternator (should be 14.4 or above for flooded or AGM batteries) and measure the amperage output as well. That should give you a much better estimate of how well your alternator and regulator are working.
That would be very misleading at 50% DOD for that alt if he was looking for 14.4V at 50% DOD.. It will be in bulk and having a tough enough time just getting to 13.6V let alone 14.4V... It should not hit absorption voltage until the bank is around 80% SOC but with voltage drop typical of these factory wiring systems it may not come up to absorption at the batteries until the high 90's when the current really starts to drop off..
The best test to know the regulator voltage set point is when the bank is full. This is when it is "limiting" the voltage and with little current flowing you won't have the voltage drops you will at higher amperages.
Test your regulators set point with the bank full and measure it directly at the B+ terminal on the back of the alt. This will tell you the alternators voltage limiting or absorption voltage set point.
Here's an example of the typical piss poor factory wiring we see on some marine engines and the voltage drops associated with it..
-Maine Sail / CS-36T
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