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Old 04-19-2011, 03:10 PM   #1
phishown's Avatar
Join Date: Aug 2010
Posts: 17
Help with tach issues???

When I purchased the boat the tachs did not work and was told the previous owner just replaced the alternator with a 100 amp alternator and put an external smart regulator *SAR 12 for the batteries. *I notice that *there is no R terminal on the back of the new alternator and the tach wire was unplugged because of this. *I had an R terminal installed on the alternator so I could hook my tachs back up with no luck in running the tachs. *I am only getting 2 volts out of the R terminal along with 2 volts at the back of the tachs. * I took the alternator back to shop today and they tested everything and all was fine and they stated I should be getting a constant 7 volts out of the R terminal. *The tach only moves slightly when reved up. *Could the smart regulator be shutting the alternator down because the batteries are full? I am usually pretty good with 12 volts....I even had a mechanic look at everything last night with no luck. *Any ideas?

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Old 04-19-2011, 08:03 PM   #2
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City: Saltspring Island
Country: BC, canada
Vessel Name: Retreat
Vessel Model: C&L 44
Join Date: Nov 2007
Posts: 1,668
RE: Help with tach issues???


Exactly the problem that I have, with a smart reg on the port side and a dumb one on the Starboard side, I only get tach on port if the reg stops putting amps into the batteries. this usually only happens near the end of a voyage, after 2 or 3 hours running. I have become adept at guessing when both engines are at the same rpm, from the harmonics, so I really only need one operating tach. Single engine would be more of a test. So far I am 11 years with this situation and I haven't needed to do anything about it.

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Old 04-20-2011, 05:14 AM   #3
phishown's Avatar
Join Date: Aug 2010
Posts: 17
RE: Help with tach issues???

I will try the microwave trick.....thanks for your help it definately sounds like the smart regulator is to blame. *

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Old 04-20-2011, 07:09 AM   #4
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City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 8,460
RE: Help with tach issues???

I have been battling the same issues with my port tach. When the ammeter load is up, the tach works better...sometimes spot on, sometimes 300 RPM slow. I was planning to replace that alternator with a 100A Balmar with smart regulator, but maybe that won't fix my problem. Does anyone know why this happens? Is there a reliable fix?
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