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post #7 of Old 07-15-2013 Thread Starter
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Re: m25 alternator question

Originally Posted by Maine Sail View Post

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..
Voltage Drop From Factory Alternator Wiring - YouTube
This is also good to know. For the most part I charge by solar. I have two 30 watt panels that will put out 2 amps or so for part of the day. My solar regulator will stop at 14.1 ish. What should the battery volts read when it is full or close as I understand volts is not a 100% guarantee. I will test may alternator after I fill the batteries and discharge them a bit. I will use a battery charger when I am at a dock next to top it up and be confident it is toped up.

Last edited by SSBN506; 07-15-2013 at 02:41 PM.
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