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post #10 of Old 09-16-2009
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Originally Posted by simple72 View Post
I sail a 1984 Tartan 3000 sloop. I'm currently living aboard and fine tuning her for a big cruise.

Here's my issue.
The boat is equipped with a 50amp Motorola alternator and two new group 27 wet batteries.

The batteries are discharged and reading about 12.10 volts with no load.
When I run the engine at about 2000rpms I get about 12.9 volts with the guest battery selector on Both. I get about 13.2 volts with the selector on battery 1 or 2.

According to Don Casey's book this voltage is inadequate for charging.

I'm getting 13.8 volts at the alternator. The alternator output wire joins the harness and travels back to the cockpit engine panel. When I read the voltage there it's 13.2.

I've tested the output wire for resistance and got a zero reading.

Does anyone have any idea why I'm not getting enough voltage? Is my alternator shot??? Should I install an new and larger alt output wire???

Please help!!!!
You cannot tell anything by using the Ohm function. I can already see you have high resistance by your voltage readings. Anything more than .3 to .5 volt drop is high resistance. You have either dirty terminals or corrosion somewhere and the only way to find it is by doing a voltage drop test.

You must use the voltmeter function and do a voltage drop test of the circuit. Just do a search on how to do voltage drop testing, youtube has some good videos on that subject.

13.8v is the minimum acceptable voltage for an alternator. Acceptable Alternator voltage output will range from 13.8 to approximately 14.8 volts. While your output is on the lowside it is still in the acceptable range.
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