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Old 03-02-2016, 10:22   #1
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Join Date: Mar 2013
Location: Merritt Island, FL USA
Boat: 1980 Cal 39 Mk II Type 3
Posts: 28
Crazy Tachometer

Our 1980 Cal 39 has a Perkins 4-108 with a Balmar 9115 dual output alternator and Teleflex diesel alternator type tachometer.

When I first start the engine, the tach doesn't register for about 2 minutes. (Mechanics have told me this is normal with the type of alternator we have.) Then it goes up to whatever rpm the engine is running at and with the exception noted below it has always worked perfectly. It has done this since we bought the boat 3-1/2 years ago.

While I was warming up the engine yesterday, idling at 700 rpm, and the tach giving a normal reading, the tach suddenly jumped to 2800. The engine, however, was still running at the same speed.

This happened once before about a month ago, lasted about 5 minutes, and then the tach went back to normal. This time, no matter how I adjust the engine speed the tach remains pegged between 2800 and 3200.

We have checked and cleaned all the electrical connections on the back of the tach. And we have found and changed a 10 amp fuse that may be part of the alternator-tach circuit. The fuse looked OK, but we changed it out anyway.

We still can't get the tack to read lower than 2800 rpm.

Any ideas?

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Old 07-02-2016, 17:26   #2
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Join Date: Jul 2008
Location: Fort Lauderdale Florida
Boat: Northstar 1500, 35', Siren
Posts: 303
Re: Crazy Tachometer

I would start by checking/cleaning ground connections, block included. Next, if possible, connect a different tach (I have original 3" that I replaced with a 4"), this lets you know tach/alternator. If tach, replace or depending on type, dip switch or potentiometer (rotary) rpm fine adjust, you might try to operate dips (noting 1/0 code) or rotate screw noting original position in an attempt to "clean" contacts (need non-contact or mechanical tach to re-calibrate) salt air takes its toll. Others may have a more savvy approach....

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Old 07-02-2016, 18:59   #3
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Join Date: Dec 2010
Location: W Carib
Boat: Wildcat 35, Hobie 33
Posts: 6,061
Re: Crazy Tachometer

Could be related to the regulator. Do you have a spare to swap in or the ability to go back to internal regulalor?
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Old 03-04-2016, 06:38   #4
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Join Date: Jan 2011
Boat: Conser 47
Posts: 61
Re: Crazy Tachometer

I have a Volvo MD2040 with a 60 amp alternator and the tach started jumping around and then goes to zero and the alarm comes on. Occasionally it will jump up even higher than engine rpm. The belt is good and therefore the engine is cooling properly. Also there is no output from the alternator. My other engine is charging properly?

Alternator had been running properly for several days cruising. It happened after starting the engine with batteries at 11.8. While running the alternator to charge my wife also used the inventor putting a strain on the electrical system.

Is this a bad alternator caused by over stressing it?

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Old 03-04-2016, 12:46   #5
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Join Date: Apr 2004
Location: Southern Maine
Boat: Prairie 36 Coastal Cruiser
Posts: 582
Re: Crazy Tachometer

Don't overlook the possibility of interference. My tachs go wacky when I turn on the 12V florescent ER lights.
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Old 03-04-2016, 13:20   #6
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Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 5,428
Re: Crazy Tachometer

If it ain't at the alternator end, then it's either the wiring (rare) or the connecvtions at the OTHER end.

Check the tach. Depending on what tach you have, use Google to find out how to check it out. All manufacturers have calibration and checkout troubleshooting guides.

Good luck.
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
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Old 06-04-2016, 05:28   #7
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Boat: Conser 47
Posts: 61
Re: Crazy Tachometer

Suddenly the alternator worked fine today. Looking at the wiring. I suspect a bad ground neutral connection.

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