Cooling problem solved now what's wrong with my tach? - Page 2 - SailNet Community
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post #11 of 15 Old 02-03-2014
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Re: Cooling problem solved now what's wrong with my tach?

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Originally Posted by MarkSF View Post
My boat came with a blown alternator, and then I blew the diodes on the replacement by turning off at the key before stopping the engine. In both cases, the tachometer would not work. As Faster says, you really need to check that you have a healthy charging voltage - 14V or more.

If not, either the alternator is faulty, or it is not getting the excite voltage via the ignition switch.

Mark,

I would love to know exactly how that alternator was wired so that turning off the key disconnected it from the load? Turning off the key has zero effect on most alternators. The only time it would, could be if a PO improperly wired something... Most factory alts are either key on excite or self sensed. With key on excite turning the ignition key off just turns off the regulator and the alt shuts down. With self sense excite it keeps on working even with the key off and unless the key also turned off the battery switch or other funky home brew configuration then the alts keeps running.

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post #12 of 15 Old 02-03-2014
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Re: Cooling problem solved now what's wrong with my tach?

The boat was wired with excite via the ignition key. So yes, I just disconnected the excite. Some alternator expert told me that disconnecting the excite while an alternator is putting out a good output is not good practice. Most of the time, it might be OK, but occasionally, not so. I think generally most of us avoid bad practice on principle.

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post #13 of 15 Old 02-04-2014 Thread Starter
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Re: Cooling problem solved now what's wrong with my tach?

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T... Don't think you ever confirmed whether or not you were actually charging?
No, that was one step I missed due to a misplaced multimeter which I have now replaced with a new one. I'll be back up there for the Saturday race (brrr) and will check that out as well though there seems to be plenty of battery for starting the engine.
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post #14 of 15 Old 02-21-2014
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Re: Cooling problem solved now what's wrong with my tach?

Could you possibly reverse the original fix (replaced sender, etc.) and see if the tach problem still exists? If not, your answer could be in the incompatible or defective replacement parts.
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post #15 of 15 Old 02-21-2014
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Re: Cooling problem solved now what's wrong with my tach?

If you have a "one wire" alternator, where the sense lead is tied back to the output (usually at the starter lead) then you may also have to blip the engine to get the alternator to turn on, and the tach won't read until then. Blip can mean 2x-3x cruising speed for 5-10 seconds.
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