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Old 04-20-2011
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Tach and alternator intermittent problem

While motoring away from an anchorage this weekend, I noticed the tachometer drop to “0” for a few seconds and then back up to speed. My chartplotter shows voltage and it would drop from 14v to 12.4v when the tach would drop. It’s like the alternator was cutting off for a few seconds and then back on. It did this about 10 times in 15 minutes and stopped for the rest of the day. I checked for any loose connections and could not find any.
I have a couple of questions about this:
If an alternator is going out can they act like this?
What other checks should I do?
Should the system be charging at 14v with the batteries almost fully charged or is that too high? The batteries were at 12.7v with no load when I checked with a meter.
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Old 04-20-2011
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Eletronic tach/alernator problems


Almost all electronic tachs work on the output of the alternator. The is a seperate terminal on most tachs that is designated for this purpose. If the output stops for any reason, which could be many, the tach stops working.

If you are a bit mechanical and have a tester, you could check the output of the tach independant of your electronics, although you say the voltage was fluctuating down while the tach was not working.

I recomend taking the alternator and the voltage reguator to a good service shop and have them tested as a unit. Some alternators have an internal regulator, and they do fail from heat and vibration. A bit of internt research may help you determine what type your particular alt. has. When removing, make sure you make a good diagram of all wire connections and tape and tag the ends of all wires.

Good Luck
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Old 04-20-2011
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I am pretty sure the tach output from alt. is ac if so use ac on meter.IMHO that is before regulator.marc
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